Scientific Output

Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.

Below, you can either scroll through the complete list of our annually published material, search for a specific author or term via the free text search, or use the interactive keyword cloud to get to know our research strengths. You can also review the publication record of every Materials Chain member via his or her personal member’s page.

Interactive keyword cloud:

adsorption  aluminum  anisotropy  atomic force microscopy  atoms  calculations  carbon  carbon dioxide  catalysis  catalysts  chemistry  coatings  computer simulation  copper  crystal structure  deformation  density functional theory  deposition  diffusion  elasticity  electrodes  electrons  finite element method  gold  grain boundaries  high resolution transmission electron microscopy  hydrogen  liquids  manganese  mass spectrometry  mechanical properties  metabolism  metal nanoparticles  metals  microstructure  molecular dynamics  nanocrystals  nanoparticles  nickel  optimization  oxidation  oxygen  particle size  plasticity  polymers  probes  scanning electron microscopy  silicon  silver  single crystals  substrates  surface properties  synthesis (chemical)  temperature  thermodynamics  thin films  titanium  transmission electron microscopy  x ray diffraction  x ray photoelectron spectroscopy 
- or -

Free text search:

  • 2020 • 310 Overcoming the Limitations of Transient Photovoltage Measurements for Studying Recombination in Organic Solar Cells
    Azzouzi, M. and Calado, P. and Telford, A.M. and Eisner, F. and Hou, X. and Kirchartz, T. and Barnes, P.R.F. and Nelson, J.
    Solar RRL 4 (2020)
    Transient photovoltage (TPV) measurements are frequently used to study recombination processes in thin-film solar cells by probing the decay of a small optically induced voltage perturbation to infer the charge carrier dynamics of devices at open circuit. However, the validity of this method to probe organic semiconductors has recently come into doubt due to large discrepancies in the reported carrier lifetime values for the same systems and the reporting of unrealistic reaction order values. Herein, the validity of TPV to extract reliable charge carrier lifetimes in thin-film solar cells is explored through the use of time-dependent drift-diffusion simulations and measurements. It is found that in low-mobility materials, TPV serves primarily as a probe of charge carrier redistribution in the bulk rather than bulk recombination dynamics and that the extracted time constant is highly mobility dependent. To address this shortcoming, transient photocharge, a new technique to measure the charge carrier density during photovoltage decay, is introduced and applied to study the recombination dynamics in a series of (fullerene and nonfullerene) organic solar cell systems. It is shown that using this technique the charge carrier recombination lifetime in the active layer is more accurately determined. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/solr.201900581
  • 2020 • 309 Electronic structure based design of thin film metallic glasses with superior fracture toughness
    Evertz, S. and Kirchlechner, I. and Soler, R. and Kirchlechner, C. and Kontis, P. and Bednarcik, J. and Gault, B. and Dehm, G. and Raabe, D. and Schneider, J.M.
    Materials and Design 186 (2020)
    High fracture toughness is crucial for the application of metallic glasses as structural materials to avoid catastrophic failure of the material in a brittle manner. One fingerprint for fracture toughness in metallic glasses is the fraction of hybridized bonds, which is affected by alloying Pd57.4Al23.5Y7.8M11.3 with M = Fe, Ni, Co, Cu, Os, Ir, Pt, and Au. It is shown that experimental fracture toughness data is correlated to the fraction of hybridized bonds which scale with the localized bonds at the Fermi level. Thus, the localized bonds at the Fermi level are utilized quantitatively as a measure for fracture toughness. Based on ab initio calculations, the minimum fraction of hybridized bonds was identified for Pd57.4Al23.5Y7.8Ni11.3. According to the ansatz that the crystal orbital overlap population at the Fermi level scales with fracture toughness, for Pd57.4Al23.5Y7.8Ni11.3 a value of around 95 ± 20 MPa·m0.5 is predicted quantitatively for the first time. Consistent with this prediction, in micro-mechanical beam bending experiments Pd57.4Al23.5Y7.8Ni11.3 thin films show pronounced plasticity and absence of crack growth. © 2018 The Authors
    view abstractdoi: 10.1016/j.matdes.2019.108327
  • 2020 • 308 Cellulose Nanocrystal-Templated Tin Dioxide Thin Films for Gas Sensing
    Ivanova, A. and Frka-Petesic, B. and Paul, A. and Wagner, T. and Jumabekov, A.N. and Vilk, Y. and Weber, J. and Schmedt Auf Der Günne, J. and Vignolini, S. and Tiemann, M. and Fattakhova-Rohlfing, D. and Bein, T.
    ACS Applied Materials and Interfaces 12 12639-12647 (2020)
    Porous tin dioxide is an important low-cost semiconductor applied in electronics, gas sensors, and biosensors. Here, we present a versatile template-assisted synthesis of nanostructured tin dioxide thin films using cellulose nanocrystals (CNCs). We demonstrate that the structural features of CNC-templated tin dioxide films strongly depend on the precursor composition. The precursor properties were studied by using low-temperature nuclear magnetic resonance spectroscopy of tin tetrachloride in solution. We demonstrate that it is possible to optimize the precursor conditions to obtain homogeneous precursor mixtures and therefore highly porous thin films with pore dimensions in the range of 10-20 nm (ABET = 46-64 m2 g-1, measured on powder). Finally, by exploiting the high surface area of the material, we developed a resistive gas sensor based on CNC-templated tin dioxide. The sensor shows high sensitivity to carbon monoxide (CO) in ppm concentrations and low cross-sensitivity to humidity. Most importantly, the sensing kinetics are remarkably fast; both the response to the analyte gas and the signal decay after gas exposure occur within a few seconds, faster than in standard SnO2-based CO sensors. This is attributed to the high gas accessibility of the very thin porous film. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsami.9b11891
  • 2020 • 307 From Precursor Chemistry to Gas Sensors: Plasma-Enhanced Atomic Layer Deposition Process Engineering for Zinc Oxide Layers from a Nonpyrophoric Zinc Precursor for Gas Barrier and Sensor Applications
    Mai, L. and Mitschker, F. and Bock, C. and Niesen, A. and Ciftyurek, E. and Rogalla, D. and Mickler, J. and Erig, M. and Li, Z. and Awakowicz, P. and Schierbaum, K. and Devi, A.
    Small 16 (2020)
    The identification of bis-3-(N,N-dimethylamino)propyl zinc ([Zn(DMP)2], BDMPZ) as a safe and potential alternative to the highly pyrophoric diethyl zinc (DEZ) as atomic layer deposition (ALD) precursor for ZnO thin films is reported. Owing to the intramolecular stabilization, BDMPZ is a thermally stable, volatile, nonpyrophoric solid compound, however, it possesses a high reactivity due to the presence of Zn-C and Zn-N bonds in this complex. Employing this precursor, a new oxygen plasma enhanced (PE)ALD process in the deposition temperature range of 60 and 160 °C is developed. The resulting ZnO thin films are uniform, smooth, stoichiometric, and highly transparent. The deposition on polyethylene terephthalate (PET) at 60 °C results in dense and compact ZnO layers for a thickness as low as 7.5 nm with encouraging oxygen transmission rates (OTR) compared to the bare PET substrates. As a representative application of the ZnO layers, the gas sensing properties are investigated. A high response toward NO2 is observed without cross-sensitivities against NH3 and CO. Thus, the new PEALD process employing BDMPZ has the potential to be a safe substitute to the commonly used DEZ processes. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.201907506
  • 2020 • 306 Laser-induced surface relief nanocrowns as a manifestation of nanoscale Rayleigh-Plateau hydrodynamic instability
    Pavlov, D.V. and Gurbatov, S.O. and Kudryashov, S.I. and Gurevich, E.L. and Kuchmizhak, A.A.
    Applied Surface Science 511 (2020)
    Nanoscale hydrodynamic instability of ring-like molten rims around ablative microholes produced in nanometer-thick silver and gold films by tightly focused nanosecond (ns) laser pulses was experimentally explored in terms of laser pulse energy and film thickness. These parametric dependencies of basic instability characteristics - order and period of the resulting nanocrowns - were analyzed, revealing its apparently Rayleigh-Plateau character, as compared to much less consistent possible van der Waals and impact origins. Along with fundamental importance, these findings will put forward ns pulsed laser ablation as an alternative facile inexpensive table-top approach to study such hydrodynamic instabilities developing at ns temporal and nanometer spatial scales as well as to produce unique plasmon-active hierarchical surface morphologies applicable for chemo- and biosensing. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2020.145463
  • 2020 • 305 Ultra-fast measurement circuit for transient space charge limited current in organic semiconductor thin films
    Rojek, K. and Schmechel, R. and Benson, N.
    Measurement Science and Technology 31 (2020)
    The charge carrier mobility is a crucial parameter determining the device performance for numerous different semiconductor applications. Consequently, an accurate measurement of this quantity is crucial. For this purpose, the transient space charge limited current (SCLC) method is commonly applied and is preferable over, for example, Hall or field effect measurements, as the analyzed current direction is in line with typical device architectures. For the transient SCLC method, a voltage step is applied and the transit time of injected charge carriers is determined using displacement currents. Consequently, the difficulty of this method is the use of an adequate RC time constant for the sample charging, as it needs to be much shorter than the transit time. This parameter generally limits the application of transient SCLC strongly, in terms of obtainable charge carrier mobility or minimum required film thickness. Here, we demonstrate a measurement circuit with a low RC time constant, which works in a wide current range (1 ϵA-0.5 A) and thus allows for significant flexibility in terms of minimum film thickness or detectable charge carrier mobility. The circuit is fast enough to measure, for example, charge carrier mobilities of up to 10-4 cm2 Vs-1 for a 76 nm thick 4,4',4"-Tris[phenyl(m-tolyl)amino]triphenylamine (MTDATA) layer, without using limited bridge circuitry. For this purpose, a capacitor coupled fast transistor switch generates a voltage step to avoid voltage oscillations and a fast operational amplifier is used for amplification of the voltage over a variable measurement resistor. We demonstrate the circuit working principle by measuring benchmarked MTDATA diodes and discuss its range of application. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6501/ab3b2d
  • 2020 • 304 Silicon Oxide Barrier Films Deposited on Polycarbonate Substrates in Pulsed Plasmas
    Shafaei, S. and Yang, L. and Rudolph, M. and Awakowicz, P.
    Plasma Chemistry and Plasma Processing 40 607-623 (2020)
    For many applications of polycarbonate (PC) from packaging to micro-electronics improved barrier properties are necessary. In this contribution, silica thin films were deposited from hexamethyldisiloxane/oxygen (HMDSO/O2) on polycarbonate substrate in three step plasma processes by combining a microwave (MW) surface wave discharge of 2.45 GHz with an optional radio-frequency (RF) bias of 13.56 MHz. The influence of interlayer thickness, HMDSO flow and oxygen to HMDSO ratio on barrier performance for three step-coating processes was investigated. The morphology and surface properties of the coated surface of PC were studied by atomic force microscopy (AFM). The surface topography showed a silica particles distribution on the PC substrate with relatively smooth surface roughness. AFM-QNM provides more insight into the surface morphology and stiffness. The results identify the coating structure for PC film coated with and without bias. High barrier improvement of the deposited films on PC substrates was obtained after plasma silicon coating process with a barrier improvement factor up to 337. It was found that the deposition process is optimal for food packaging applications by using combined MW-RF PECVD technology. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
    view abstractdoi: 10.1007/s11090-019-10049-y
  • 2020 • 303 LPBF-M manufactured Zr-based bulk metallic glasses coated with magnetron sputtered ZrN films
    Tillmann, W. and Fehr, A. and Wegner, J. and Stangier, D. and Kleszczynski, S. and Witt, G.
    Surface and Coatings Technology 386 (2020)
    The fabrication of Zr-based bulk metallic glasses (BMGs) by means of laser powder bed fusion of metals (LPBF-M) is recently emerging. This production route allows to widely overcome current geometrical restrictions of casting routes while maintaining the amorphous character, which is decisive for the unique mechanical properties, for instance. However, the roughness of the LPBF-M fabricated BMGs is still a challenging property, impeding the application of near-net shaped thin films that modify BMG surfaces, e.g. with respect to wear resistance. Zr59.3Cu28.8Al10.4Nb1.5 (at.%) substrates were manufactured by means of LPBFM, applying various exposure strategies, including laser remelting of the last solidified layer to influence the surface topography. Furthermore, BMG substrates were post-treated by grinding and polishing. Thus, varying degrees of crystallinity as well as surface roughness states were generated to analyze the effect of these characteristics on the microstructural properties of additionally applied magnetron sputtered ZrN films. Substrates that were fabricated with higher energy densities during LPBF-M exhibited (101)-Zr as well as (013)- and (110)-CuZr2 phases, which were accompanied by a decreased surface roughness. It was shown that all films had a crystalline structure on amorphous and partly crystalline BMG surfaces. A decreased surface roughness of the BMG substrates could be directly correlated with a higher hardness and a better adhesion of the ZrN film. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2020.125463
  • 2020 • 302 Effects of acetylene flow rate and bias voltage on the structural and tribo-mechanical properties of sputtered a-C:H films
    Tillmann, W. and Ulitzka, H. and Lopes Dias, N.F. and Stangier, D. and Thomann, C.A. and Moldenhauer, H. and Debus, J.
    Thin Solid Films 693 (2020)
    The properties of sputtered a-C:H films are significantly influenced by the C2H2 flow rate and bias voltage. A suitable Design of Experiments allows to consider their effects on the mechanical and tribological properties. The a-C:H films are deposited by varying the C2H2 flow rate from 5.9 to 34.1 sccm and the bias voltage from −83 to −197 V, following the Central Composite Design. In Raman scattering studies, the presence of C[sbnd]H bands with increasing C2H2 flow rate is identified. Additionally, a decrease of the I(D)/I(G) ratio is observed with increasing C2H2 flow rate. Both observations indicate the formation of sp³-hybridized C[sbnd]H bonds. In contrast, a low C2H2 flow rate and a high bias voltage result in a higher I(D)/I(G) ratio and a lower intensity of the C[sbnd]H stretching bands, indicating a lower amount of C[sbnd]H bonds. The mechanical properties are also considerably influenced by these parameters. A higher C2H2 proportion results in a lower hardness and elastic modulus, which are related to a higher H content. However, a higher bias voltage increases the hardness and elastic modulus due to densification mechanisms, which increase the degree of distortion of the a-C:H films. Consequently, a low C2H2 flow rate and a high bias voltage ensure a high hardness of up to ~24 GPa due to a lower amount of C[sbnd]H bonds and a higher degree of distortion. In tribometer tests, most a-C:H films exhibit a low coefficient of friction against steel, ranging from 0.23 to 0.25. All a-C:H films are marked by a deformative wear, indicating a high resistance against abrasive wear when sliding against steel. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2019.137691
  • 2020 • 301 TiAlN-Beschichtungen mittels hoch-energetischer Kathodenzerstäubung: Eine Studie zur Auswirkung von Eigenspannungen auf die Leistungsfähigkeit von TiAlN-Dünnschichtsystemen
    Tillmann, W. and Stangier, D. and Grisales, D.
    Vakuum in Forschung und Praxis 32 26-32 (2020)
    TiAlN-coatings by means of high-energy sputtering. According to current knowledge, high-energy plasmas represent a promising tribological property profile for nitride hard material coatings and their applications. However, the increased ionization rate results in a high level of residual compressive stresses in TiAlN thin films (σTiAlN ∼ –6000 MPa), which can negatively influence the adhesion between substrate and coating and thus can lead to delamination and damage. In this context, the presented investigations prove that a hybrid process consisting of the synchronous use of direct current (DC) and high power pulse sputtering (HiPIMS) can be used to reduce the residual stress state in the coating. This allows to combine the advantages of both technologies and thus to qualify TiAlN thin films for an extended range of applications as tribological coatings for heat treated tool steels. © 2020, Wiley-VCH Verlag. All rights reserved.
    view abstractdoi: 10.1002/vipr.202000737
  • 2020 • 300 Influence of the bias-voltage, the argon pressure and the heating power on the structure and the tribological properties of HiPIMS sputtered MoSx films
    Tillmann, W. and Wittig, A. and Stangier, D. and Moldenhauer, H. and Thomann, C.-A. and Debus, J. and Aurich, D. and Bruemmer, A.
    Surface and Coatings Technology 385 (2020)
    Understanding the growth process and its correlation to the structure of MoSx thin films is essential to control the friction behavior. Nevertheless, structural changes related to kinetic and thermal processes occurring during the deposition are not yet fully understood within the context of MoSx sputtered thin films. Therefore, MoSx films were synthesized by HiPIMS (High Power Impulse Magnetron Sputtering) technique using the one factor at a time method. By systematically changing the bias-voltage (0 to −200 V), the argon pressure (200 mPa to 600 mPa) or the heating power (0 to 3000 W) the interaction between the deposition parameters and their impact on the structure and the tribological properties was analyzed.The results show significant differences regarding the influence of kinetic and thermal effects. The investigation of the crystallographic orientation by XRD measurements reveals that a high kinetic energy induced by a high bias-voltage favors the growth of the (100) edge plane. A deposition process with a low deposition temperature and thus a low deposition rate leads to a more pronounced (002) basal plane due to the lower surface energy of the (002) surface. A high kinetic energy is also related to a densification of the morphology and a decrease in the sulfur content, which results in a thicker tribofilm and thus a lower wear and friction. Films deposited with a high heating power on the other show a low friction, but at the same time a columnar microstructure and high wear. Thus, the structure affects the amount of generated wear particles during the sliding, but more important is the ability of keeping them in the contact area during the tribo-tests. © 2020
    view abstractdoi: 10.1016/j.surfcoat.2020.125358
  • 2019 • 299 Developments in pre- and post-treatment of thin films and their influences on surface topography and coating adhesion strength of cutting tools
    Bathe, T. and Biermann, D.
    Production Engineering 13 751-759 (2019)
    Due to the increased requirements on machining of metallic and non-metallic materials, the pre- and post-treatment of hard thin films has been an important topic in several researches in the past decade. The main improvement in tool properties by a reduction of surface inhomogeneities is reached by an additional mechanical or chemical treatment before and/or after the coating process. Especially the cleaning before coating has to be considered to reduce the amount of debris of the pre-treatment which may negatively effect surface quality after the coating process. The mainly used processes of mechanical treatment to enhance surface topography before and after coating are several machining processes such as abrasive jet machining or drag finishing. This paper introduces a novel process for the pre- and post-treatment of coated cutting tools by elastically bonded diamond grinding wheels. Both the removal rate of surface inhomogeneities, the influence of surface topography before and after coating and the influence of the initial tool surfaces regarding coating adhesion strength were investigated to underline the potential of this pre- and post-treatment. Additionally, a new method for characterizing and describing the number of coating defects and proportion area of coating defects per mm 2 is presented. © 2019, German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-019-00921-3
  • 2019 • 298 Role of gallium and yttrium dopants on the stability and performance of solution processed indium oxide thin-film transistors
    Jaehnike, F. and Pham, D.V. and Bock, C. and Kunze, U.
    Journal of Materials Chemistry C 7 7627-7635 (2019)
    We study the effect of gallium and yttrium doping on both the electrical performance and the stability of indium based metal-oxide thin-film transistors (MOTFTs) at varied concentrations. As the Ga (Y) content in the In1.0GaxOy (In1.0YxOy) channel material was increased to x = 0.1 the mobility of the MOTFTs degrades by a factor of 4. Thereby the temperature stress stability is clearly enhanced by increasing doping concentration: the onset voltage shift is reduced by a factor of 3 for both In1.0Ga0.1Oy and In1.0Y0.1Oy films compared to that in indium-oxide TFTs. Also the stability during negative bias stress (NBS) is improved since the strong oxygen binders Ga and Y prevent the desorption of oxygen at the surface. In contrast, the onset voltage shift during positive bias stress (PBS) of doped metal oxide TFTs is higher ΔVon = 12 V for InGaO (100:10) TFTs and ΔVon = 15 V for InYO ((100:10) TFTs) compared to that of intrinsic indium oxide TFTs (ΔVon = 6 V), which could be attributed to the generation of flat trap states at the dielectric/semiconductor interface. Doping with Ga and Y significantly enhances the temperature and NBS stability of TFTs and simultaneously degrades the performance. © 2019 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8tc06270f
  • 2019 • 297 Functionalizing plasmonic nanoparticles through adding a shell to improve electronic properties of c-Si thin-film solar cells
    Jalali, M. and Jalali, T. and Nadgaran, H. and Erni, D.
    Journal of the Optical Society of America B: Optical Physics 36 101-107 (2019)
    Embedding plasmonic nanoparticles (p-NPs) inside the solar cell’s active layer is capable of enhancing active layer optical absorption; however, such inclusion has some detrimental effects on the electronic properties of the solar cells. In addition, p-NPs are highly catalytic, their presence enables other non-radiative decay channels besides generation of electron–hole pairs, and the electrons usually get absorbed by these p-NPs. This results in the unfavorable fact that the potential enhancement in the carrier generation rate and the generated current is no longer in line with the enhancement in the optical absorption. In this paper, we propose to functionalize p-NPs by adding a dielectric or semiconductor shell, to passivate the p-NP without deteriorating scattering and/or plasmonic effects. Ag@SiO 2 and Ag@TiO 2 core–shell p-NPs have been intensely studied using extensive computational electromagnetic simulations to model the spectral response of the active layer’s optical absorption as well as electronic properties as a function of both shell composition and thickness. It is shown that a 5 nm TiO 2 shell is apt to optically passivate the p-NP without any reduction in optical absorption, while improving the short circuit current density (J sc ) of the thin-film solar cell by 33.3%. © 2018 Optical Society of America.
    view abstractdoi: 10.1364/JOSAB.36.000101
  • 2019 • 296 Highly Compact TiO 2 Films by Spray Pyrolysis and Application in Perovskite Solar Cells
    Möllmann, A. and Gedamu, D. and Vivo, P. and Frohnhoven, R. and Stadler, D. and Fischer, T. and Ka, I. and Steinhorst, M. and Nechache, R. and Rosei, F. and Cloutier, S.G. and Kirchartz, T. and Mathur, S.
    Advanced Engineering Materials 21 (2019)
    Transparent and pinhole free hole-blocking layers such as TiO 2 grown at low temperatures and by scalable processes are necessary to reduce production costs and thus enabling commercialization of perovskite solar cells. Here, the authors compare the transport properties of TiO 2 compact layers grown by spray pyrolysis from commonly used titanium diisopropoxide bisacetylacetonate ([Ti(OPr i ) 2 (acac) 2 ]) precursor to films grown by spray pyrolysis of TiCl 4 . Spray pyrolysis provides insights into the interdependence of precursor chemistry and electron transport properties of TiO 2 films and their influence on the performance of the perovskite solar cells. X-ray diffraction and X-ray photoelectron spectroscopy data confirm the chemical and structural composition of the obtained films. Thin film deposition at lower temperature (150 °C) are conducted using TiCl 4 to evaluate the influence of crystal growth and topography by scanning electron microscopy and atomic force microscopy as well as thickness (profilometry) and transmittance (UV/Vis spectroscopy) on the power conversion efficiency of perovskite solar cells. TiO 2 compact layers grown from TiCl 4 enhance the power conversion efficiency by acting as superior electron transfer medium and by reducing hysteresis behavior, when compared to films grown using titanium diisopropoxide bisacetylacetonate. UV/Vis spectroscopy and external quantum efficiency studies reveal the correlation of transmittance on the power conversion efficiency. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.201801196
  • 2019 • 295 Resonant Raman scattering characterization of thermally annealed HiPIMS deposited MoSx coatings
    Moldenhauer, H. and Wittig, A. and Kokalj, D. and Stangier, D. and Brümmer, A. and Tillmann, W. and Debus, J.
    Surface and Coatings Technology 377 (2019)
    Raman spectroscopy is used to investigate the structural and tribological properties of HiPIMS sputtered MoSx thin films which were post-growth-annealed at different temperatures. The Raman scattering combined with X-ray diffraction determines a reduction in the residual strain within the MoSx layers with increasing annealing temperature. In the high-temperature annealed coatings a Raman signature at 40 cm−1 emerges, which results from a strengthening of the inter-layer van-der-Waals interaction. This observation indicates that the thermally annealed MoSx thin films become more resistant against shear forces, which is manifested in an increase of the coefficient of friction measured with a ball-on-disc tribometer. The coefficient of friction moreover decreases with lowering the sulfur/molybdenum ratio which, in turn, depends on the substrate and annealing temperatures. Furthermore, a Raman forbidden mode may be exploited to detect stacking faults within the sputtered coatings. Its observation is realized through resonant excitation of an MoS2 exciton at about 633 nm. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2019.124891
  • 2019 • 294 Influence of Ag on antibacterial performance, microstructure and phase transformation of NiTi shape memory alloy coatings
    Momeni, S. and Tillmann, W.
    Vacuum 164 242-245 (2019)
    Shape memory binary NiTi and ternary NiTiAg coatings were deposited by means of magnetron sputtering technique. The results show how simultaneous sputtering of Ag can affect the microstructure, phase transformation behavior and antibacterial properties of NiTi coatings. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.vacuum.2019.02.051
  • 2019 • 293 Role of elemental intermixing at the In 2 S 3 /CIGSe heterojunction deposited using reactive RF magnetron sputtering
    Soni, P. and Raghuwanshi, M. and Wuerz, R. and Berghoff, B. and Knoch, J. and Raabe, D. and Cojocaru-Mirédin, O.
    Solar Energy Materials and Solar Cells 195 367-375 (2019)
    In the present work, sputtered In 2 S 3 buffer layers are deposited on Cu(In,Ga)Se 2 absorbers with no or minimal sputter damage. Buffer deposition at slower sputter rates (0.22 Å/s) with H 2 S as a reactive gas improved the interface quality and uniformity. We obtained crystalline In 2 S 3 films at room temperature with the deposition parameters used in this work. Elemental intermixing effect at the In 2 S 3 /CIGSe heterointerface at different annealing temperatures was mapped in 3-dimensions using atom probe tomography (APT). APT results revealed the induced sputter damage during buffer layer deposition, and the effect of diffusion and segregation of elements at the heterointerface. Knowledge of elemental redistribution at the buffer-absorber heterointerface can help better understand the relation of the chemical intermixing with electrical performance of the cell. X-ray photoelectron spectroscopy (XPS) reveal accelerated Cu + doping of the In 2 S 3 buffer at 225 °C. Cu-depletion on CIGSe surface up to a few nanometers improves the cell performance. However, at higher annealing temperature of 275 °C, CuIn 5 S 8 and Cu(In x Ga 1-x ) 5 Se 8 phases are formed which is detrimental for cell performance. Na diffusing from the CIGSe absorber segregates at the In 2 S 3 /CIGSe heterojunction. This actively suppresses the formation of charged antisites defects, lowering the recombination in the space charged region. Cu-depletion at CIGSe surface, Cu and Na diffusion in In 2 S 3 and passivation of interfacial defect states by Na, giving an efficiency of 13.84% (14.83% with CdS-reference) for sputtered In 2 S 3 buffer layers. Consequently, this work elucidates the chemistry of buried hetero-interfaces and their significance to improve the electrical performance of solar cells. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.solmat.2019.03.026
  • 2019 • 292 Validation of a Terminally Amino Functionalized Tetra-Alkyl Sn(IV) Precursor in Metal–Organic Chemical Vapor Deposition of SnO2 Thin Films: Study of Film Growth Characteristics, Optical, and Electrical Properties
    Zanders, D. and Ciftyurek, E. and Hoppe, C. and de los Arcos, T. and Kostka, A. and Rogalla, D. and Grundmeier, G. and Schierbaum, K.D. and Devi, A.
    Advanced Materials Interfaces 6 (2019)
    Tin(IV) oxide is a promising semiconductor material with leading-edge properties toward chemical sensing and other applications. For the growth of its thin films, metal–organic chemical vapor deposition (MOCVD) routes are advantageous due to their excellent scalability and potential to tune processing temperatures by careful choice of the reactants. Herein, a new and highly efficient MOCVD process for the deposition of tin(IV) oxide thin films employing a terminally amino alkyl substituted tin(IV) tetra-alkyl compound is reported for the first time. The liquid precursor, tetrakis-[3-(N,N-dimethylamino)propyl] tin(IV), [Sn(DMP)4], is thermally characterized in terms of stability and vapor pressure, yielding highly pure, polycrystalline tin(IV) oxide thin films with tunable structural and morphological features in the presence of oxygen. Detailed X-ray photoelectron spectroscopy (XPS) analysis reveals the presence of oxygen vacancies and high amounts of chemisorbed oxygen species. Based on these promising features, the MOCVD process is optimized toward downscaling the thickness of tin(IV) oxide films from 25 to 50 nm to study the impact of incipient surface morphological changes occurring after initial thin-film formation on the electrical properties as investigated by van der Pauw (vdP) resistivity measurements. Optical bandgaps of thin films with varying thicknesses are estimated using ultraviolet–visible (UV–vis) spectroscopy. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/admi.201801540
  • 2018 • 291 Antibacterial Efficacy of Sacrifical Anode Thin Films Combining Silver with Platinum Group Elements within a Bacteria-Containing Human Plasma Clot
    Abuayyash, A. and Ziegler, N. and Gessmann, J. and Sengstock, C. and Schildhauer, T.A. and Ludwig, Al. and Köller, M.
    Advanced Engineering Materials 20 (2018)
    Silver (Ag) dots arrays (64 and 400 dots per mm2) are fabricated on a continuous platinum (Pt), palladium (Pd), or iridium (Ir) thin film (sacrifical anode systems for Ag) and for comparison on titanium (Ti) film (non-sacrifical anode system for Ag) by sputter deposition and photolithographic patterning. The samples are embedded within a tissue-like plasma clot matrix containing Staphylococcus aureus (S. aureus), cultivated for 24 h. Bacterial growth is analyzed by fluorescence microscopy. Among platinum group sacrifical anode elements and a dense Ag sample, only the high Ag ion releasing Ag–Ir system is able to inhibit the bacterial growth within the adjacent plasma clot matrix. This study demonstrates that the antibacterial efficiency of Ag coatings is reduced under tissue-like conditions. However, the new sacrificial anode based Ag–Ir system can overcome this limitation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.201700493
  • 2018 • 290 Electron transport in Bi2Se3 ultra thin films
    Bauer, S. and Bernhart, A.M. and Bobisch, C.A.
    Applied Surface Science 432 140-146 (2018)
    We studied the electronic transport properties of a 4 QL thin Bi2Se3 film in the hybridized phase on Si(111) by scanning tunneling potentiometry. When a transverse voltage is applied, the film exhibits a homogeneous electric field on the nm scale. In addition, thermovoltage signals with lateral nm variations are found which result from sample heating by the transverse current. The thermovoltage signals are directly correlated to morphological structures on the surface, i.e. step edges, and indicate a lateral variation of the local density of states at the Bi2Se3 surface. No discernible voltage drops appear at the surface so that the whole film serves as a current carrying medium and scattering at surface defects is less important. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.03.229
  • 2018 • 289 Electron transport in Bi 2 Se 3 ultra thin films
    Bauer, S. and Bernhart, A.M. and Bobisch, C.A.
    Applied Surface Science 432 140-146 (2018)
    We studied the electronic transport properties of a 4 QL thin Bi 2 Se 3 film in the hybridized phase on Si(111) by scanning tunneling potentiometry. When a transverse voltage is applied, the film exhibits a homogeneous electric field on the nm scale. In addition, thermovoltage signals with lateral nm variations are found which result from sample heating by the transverse current. The thermovoltage signals are directly correlated to morphological structures on the surface, i.e. step edges, and indicate a lateral variation of the local density of states at the Bi 2 Se 3 surface. No discernible voltage drops appear at the surface so that the whole film serves as a current carrying medium and scattering at surface defects is less important. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.03.229
  • 2018 • 288 Low-temperature MOCVD deposition of Bi2Te3 thin films using Et2BiTeEt as single source precursor
    Bendt, G. and Gassa, S. and Rieger, F. and Jooss, C. and Schulz, S.
    Journal of Crystal Growth 490 77-83 (2018)
    Et2BiTeEt was used as single source precursor for the deposition of Bi2Te3 thin films on Si(1 0 0) substrates by metal organic chemical vapor deposition (MOCVD) at very low substrate temperatures. Stoichiometric and crystalline Bi2Te3 films were grown at 230 °C, which is approximately 100 °C lower compared to conventional MOCVD processes using one metal organic precursors for each element. The Bi2Te3 films were characterized using scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. The elemental composition of the films, which was determined by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, was found to be strongly dependent of the substrate temperature. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.jcrysgro.2018.03.021
  • 2018 • 287 An N-Heterocyclic Carbene Based Silver Precursor for Plasma-Enhanced Spatial Atomic Layer Deposition of Silver Thin Films at Atmospheric Pressure
    Boysen, N. and Hasselmann, T. and Karle, S. and Rogalla, D. and Theirich, D. and Winter, M. and Riedl, T. and Devi, A.
    Angewandte Chemie - International Edition 57 16224-16227 (2018)
    A new N-heterocyclic carbene (NHC)-based silver amide compound, 1,3-di-tert-butyl-imidazolin-2-ylidene silver(I) 1,1,1-trimethyl-N-(trimethylsilyl)silanaminide [(NHC)Ag(hmds)] was synthesized and analyzed by single-crystal X-ray diffraction, 1H and 13C NMR spectroscopy, as well as EI mass spectrometry, and subsequently evaluated for its thermal characteristics. This new halogen- and phosphine-free Ag atomic layer deposition (ALD) precursor was tested successfully for silver thin film growth in atmospheric pressure plasma enhanced spatial (APP-ALD). High-purity conductive Ag thin films with a low sheet resistance of 0.9 Ω/sq (resistivity: 10−5 Ωcm) were deposited at 100 °C and characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, optical transmittance, and Rutherford back-scattering techniques. The carbene-based Ag precursor and the new APP-ALD process are significant developments in the field of precursor chemistry as well as metal ALD processing. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201808586
  • 2018 • 286 Femtosecond laser crystallization of amorphous titanium oxide thin films
    Hoppius, J.S. and Bialuschewski, D. and Mathur, S. and Ostendorf, A. and Gurevich, E.L.
    Applied Physics Letters 113 (2018)
    In this paper, we demonstrate experimentally that crystalline phases appear in amorphous titanium oxide upon processing with ultrafast laser pulses. Amorphous titanium thin films were produced by plasma-enhanced chemical vapor deposition and exposed to femtosecond laser pulses. Formation of a rutile phase was confirmed by X-ray diffraction, Raman measurements, and electron backscattering diffraction. A range of processing parameters for the crystallization is reported, and possible background mechanisms are discussed. © 2018 Author(s).
    view abstractdoi: 10.1063/1.5027899
  • 2018 • 285 Electron-Blocking and Oxygen Evolution Catalyst Layers by Plasma-Enhanced Atomic Layer Deposition of Nickel Oxide
    Hufnagel, A.G. and Henß, A.-K. and Hoffmann, R. and Zeman, O.E.O. and Häringer, S. and Fattakhova-Rohlfing, D. and Bein, T.
    Advanced Materials Interfaces 5 (2018)
    A plasma-enhanced atomic layer deposition (ALD) process is presented, capable of producing thin conformal films of nickel(II) oxide (NiO) on various substrates. Nickelocene (NiCp2) is used as an inexpensive metal precursor with oxygen plasma as the oxidant. The film growth rate saturates with both nickel precursor and plasma exposure. An ALD window is observed between 225 and 275 °C. Linear growth is achieved at 250 °C with a growth rate of 0.042 nm per cycle. The thickness is highly uniform and the surface roughness is below 1 nm rms for 52 nm thick films on Si(100). Substrates with aspect ratios up to 1:10 can be processed. As-deposited, the films consist of polycrystalline, cubic NiO, and are transparent over the entire visible range with an optical bandgap of 3.7 eV. The films consist of stoichiometric NiO and contain ≈1% of carbon impurities. Two promising applications of these films are showcased in renewable energy conversion and storage devices: The films are pinhole-free and exhibit excellent electron blocking capabilities, making them potential hole-selective contact layers in solar cells. Also, high electrocatalytic activity of ultrathin NiO films is demonstrated for the alkaline oxygen evolution reaction, especially in electrolytes containing Fe3+. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/admi.201701531
  • 2018 • 284 An in situ XPS study of L-cysteine co-adsorbed with water on polycrystalline copper and gold
    Jürgensen, A. and Raschke, H. and Esser, N. and Hergenröder, R.
    Applied Surface Science 435 870-879 (2018)
    The interactions of biomolecules with metal surfaces are important because an adsorbed layer of such molecules introduces complex reactive functionality to the substrate. However, studying these interactions is challenging: they usually take place in an aqueous environment, and the structure of the first few monolayers on the surface is of particular interest, as these layers determine most interfacial properties. Ideally, this requires surface sensitive analysis methods that are operated under ambient conditions, for example ambient pressure x-ray photoelectron spectroscopy (AP-XPS). This paper focuses on an AP-XPS study of the interaction of water vapour and l-Cysteine on polycrystalline copper and gold surfaces. Thin films of l-Cysteine were characterized with XPS in UHV and in a water vapour atmosphere (P ≤ 1 mbar): the structure of the adsorbed l-Cysteine layer depended on substrate material and deposition method, and exposure of the surface to water vapour led to the formation of hydrogen bonds between H2O molecules and the COO− and NH2 groups of adsorbed l-Cysteine zwitterions and neutral molecules, respectively. This study also proved that it is possible to investigate monolayers of biomolecules in a gas atmosphere with AP-XPS using a conventional laboratory Al-Kα x-ray source. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.11.150
  • 2018 • 283 How Contact Layers Control Shunting Losses from Pinholes in Thin-Film Solar Cells
    Kaienburg, P. and Hartnagel, P. and Pieters, B.E. and Yu, J. and Grabowski, D. and Liu, Z. and Haddad, J. and Rau, U. and Kirchartz, T.
    Journal of Physical Chemistry C 122 27263-27272 (2018)
    An absorber layer that does not fully cover the substrate is a common issue for thin-film solar cells such as perovskites. However, models that describe the impact of pinholes on solar cell performance are scarce. Here, we demonstrate that certain combinations of contact layers suppress the negative impact of pinholes better than others. The absence of the absorber at a pinhole gives way to a direct electrical contact between the two semiconducting electron and hole transport layers. The key to understand how pinholes impact the solar cell performance is the resulting nonlinear diodelike behavior of the current across the interface between these two layers (commonly referred to as a shunt current). Based on experimentally obtained data that mimic the current-voltage characteristics across these interfaces, we develop a simple model to predict pinhole-induced solar cell performance deterioration. We investigate typical contact layer combinations such as TiO 2 /spiro-OMeTAD, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/phenyl-C 61 -butyric acid methyl ester, and TiO 2 /poly(3-hexylthiophene). Our results directly apply to perovskite and other emerging inorganic thin-film solar cells, and the methodology is transferable to CIGS and CdTe. We find substantial differences between five commonly applied contact layer combinations and conclude that it is not sufficient to optimize the contact layers of any real-world thin-film solar cell only with regard to the applied absorber. Instead, in the context of laboratory and industrial fabrication, the tolerance against pinholes (i.e., the mitigation of shunt losses via existing pinholes) needs to be considered as an additional, important objective. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b09400
  • 2018 • 282 A Versatile Thin-Film Deposition Method for Multidimensional Semiconducting Bismuth Halides
    Khazaee, M. and Sardashti, K. and Sun, J.-P. and Zhou, H. and Clegg, C. and Hill, I.G. and Jones, J.L. and Lupascu, D.C. and Mitzi, D.B.
    Chemistry of Materials 30 3538-3544 (2018)
    Despite the significant progress in fabricating hybrid organic-inorganic lead halide perovskite solar cells, their toxicity and low stability remain as major drawbacks, thereby hindering large-scale commercialization. Given the isoelectronic nature of lead(II) and bismuth(III) ions, potentially stable and nontoxic alternatives for efficient light absorption in thin-film photovoltaic (PV) devices may be found among bismuth-based halide semiconductors. However, high-quality polycrystalline films of many of these systems have not been demonstrated. Here we present a versatile and facile two-step coevaporation approach to fabricate A3Bi2I9 (A = Cs, Rb) and AgBi2I7 polycrystalline films with smooth, pinhole-free morphology and average grain size of >200 nm. The process involves an initial two-source evaporation step (involving CsI, RbI or AgI, and BiI3 sources), followed by an annealing step under BiI3 vapor. The structural, optical, and electrical characteristics of the resulting thin films are studied by X-ray diffraction, optical spectroscopy, X-ray/UV photoelectron spectroscopy, and scanning electron microscopy. Copyright © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.8b01341
  • 2018 • 281 Water film thickness imaging based on time-multiplexed near-infrared absorption
    Lubnow, M. and Jeffries, J.B. and Dreier, T. and Schulz, C.
    Optics Express 26 20902-20912 (2018)
    We demonstrate the imaging of the thickness of liquid water thin films in the 100–1500 µm range at a constant temperature by monitoring the pixel-by-pixel ratio of absorbance at two near-infrared (NIR) wavelengths near 1400 nm detected with a fast framing InGaAs focal-plane array camera. Experiments were performed in reflection mode with films of pure water and water/ethanol mixtures supported on opaque surfaces using two illumination–detection configurations. One scheme uses specular reflection of incident and reflected linearly polarized diode-laser light at Brewster’s angle, which enables detection of signal light that has twice traversed the liquid film with negligible interference from unwanted partial reflections of the incoming beams at the front surface interfaces (air/window and window/water for films constrained by a cover plate or air/water for free-standing films). The second configuration located the detection camera perpendicular above the surface where the detected light was transmitted through the sample and diffusely scattered from the support surface. Imaging measurements of film thickness using both configurations were successfully demonstrated. Time-resolved measurements capture the dynamics of flowing water films or waves generated by droplet impingement. © 2018 Optical Society of America
    view abstractdoi: 10.1364/OE.26.020902
  • 2018 • 280 Water assisted atomic layer deposition of yttrium oxide using tris(N,N0-diisopropyl-2-dimethylamido-guanidinato) yttrium(III): Process development, film characterization and functional properties†
    Mai, L. and Boysen, N. and Subaşı, E. and De Los Arcos, T. and Rogalla, D. and Grundmeier, G. and Bock, C. and Lu, H.-L. and Devi, A.
    RSC Advances 8 4987-4994 (2018)
    We report a new atomic layer deposition (ALD) process for yttrium oxide (Y2O3) thin films using tris(N,N0-diisopropyl-2-dimethylamido-guanidinato) yttrium(III) [Y(DPDMG)3] which possesses an optimal reactivity towards water that enabled the growth of high quality thin films. Saturative behavior of the precursor and a constant growth rate of 1.1 Å per cycle confirm the characteristic self-limiting ALD growth in a temperature range from 175 C to 250 C. The polycrystalline films in the cubic phase are uniform and smooth with a root mean squared (RMS) roughness of 0.55 nm, while the O/Y ratio of 2.0 reveal oxygen rich layers with low carbon contaminations of around 2 at%. Optical properties determined via UV/Vis measurements revealed the direct optical band gap of 5.56 eV. The valuable intrinsic properties such as a high dielectric constant make Y2O3 a promising candidate in microelectronic applications. Thus the electrical characteristics of the ALD grown layers embedded in a metal insulator semiconductor (MIS) capacitor structure were determined which resulted in a dielectric permittivity of 11, low leakage current density (z107 A cm2 at 2 MV cm1) and high electrical breakdown fields (4.0–7.5 MV cm1). These promising results demonstrate the potential of the new and simple Y2O3 ALD process for gate oxide applications. © The Royal Society of Chemistry 2018.
    view abstractdoi: 10.1039/c7ra13417g
  • 2018 • 279 Atomic Layer Deposition of Molybdenum and Tungsten Oxide Thin Films Using Heteroleptic Imido-Amidinato Precursors: Process Development, Film Characterization, and Gas Sensing Properties
    Mattinen, M. and Wree, J.-L. and Stegmann, N. and Ciftyurek, E. and Achhab, M.E. and King, P.J. and Mizohata, K. and Räisänen, J. and Schierbaum, K.D. and Devi, A. and Ritala, M. and Leskelä, M.
    Chemistry of Materials 30 8690-8701 (2018)
    Heteroleptic bis(tert-butylimido)bis(N,N′-diisopropylacetamidinato) compounds of molybdenum and tungsten are introduced as precursors for atomic layer deposition of tungsten and molybdenum oxide thin films using ozone as the oxygen source. Both precursors have similar thermal properties but exhibit different growth behaviors. With the molybdenum precursor, high growth rates up to 2 Å/cycle at 300 °C and extremely uniform films are obtained, although the surface reactions are not completely saturative. The corresponding tungsten precursor enables saturative film growth with a lower growth rate of 0.45 Å/cycle at 300 °C. Highly pure films of both metal oxides are deposited, and their phase as well as stoichiometry can be tuned by changing the deposition conditions. The WOx films crystallize as γ-WO3 at 300 °C and above, whereas the films deposited at lower temperatures are amorphous. Molybdenum oxide can be deposited as either amorphous (≤250 °C), crystalline suboxide (275 °C), a mixture of suboxide and α-MoO3 (300 °C), or pure α-MoO3 (≥325 °C) films. MoOx films are further characterized by synchrotron photoemission spectroscopy and temperature-dependent resistivity measurements. A suboxide MoOx film deposited at 275 °C is demonstrated to serve as an efficient hydrogen gas sensor at a low operating temperature of 120 °C. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.8b04129
  • 2018 • 278 Simultaneous measurement of thermal conductivity and diffusivity of an undoped Al0.33Ga0.67As thin film epitaxially grown on a heavily Zn doped GaAs using spectrally-resolved modulated photothermal infrared radiometry
    Pawlak, M. and Pal, S. and Scholz, S. and Ludwig, Ar. and Wieck, A.D.
    Thermochimica Acta 662 69-74 (2018)
    In this paper, we propose a method for measuring thermal and infrared properties of infrared transparent and semi-transparent thin film. We have investigated an undoped Al0.33Ga0.67As thin film epitaxially grown on a heavily Zn doped GaAs substrate using spectrally-resolved modulated photothermal infrared radiometry (SR-PTR). We perform supplementary measurements in order to determine values of layer thickness and infrared absorption coefficient and estimate successively values of the thermal conductivity and diffusivity of the Al0.33Ga0.67As thin layer, using the SR-PTR method. The obtained values of the thermal conductivity and diffusivity of the Al0.33Ga0.67As thin layer demonstrate that PTR method can be used for the thermal characterization of infrared transparent layers deposited on a highly infrared absorbing substrate. Supplementary Fourier Transform Infrared (FTIR) Spectroscopy measurements yield information only about the thickness of the Al0.33Ga0.67As layer. The results demonstrate that the SR-PTR method is a very good method for characterizing the thermal, geometrical and infrared properties of infrared-transparent thin film samples. However, some of the layer properties should be known a priori. It is worth emphasizing that the spectrally resolved measurements increase the reliability in estimating parameters of the thin layer by introducing additional channels of information. Finally, we conclude that the SR-PTR method combines features of infrared spectroscopic and calorimetric methods. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.tca.2018.02.009
  • 2018 • 277 The Role of Excitation Energy in Photobrightening and Photodegradation of Halide Perovskite Thin Films
    Quitsch, W.-A. and Dequilettes, D.W. and Pfingsten, O. and Schmitz, A. and Ognjanovic, S. and Jariwala, S. and Koch, S. and Winterer, M. and Ginger, D.S. and Bacher, G.
    Journal of Physical Chemistry Letters 9 2062-2069 (2018)
    We study the impact of excitation energy on the photostability of methylammonium lead triiodide (CH3NH3PbI3 or MAPI) perovskite thin films. Light soaking leads to a transient increase of the photoluminescence efficiency at excitation wavelengths longer than 520 nm, whereas light-induced degradation occurs when exciting the films with wavelengths shorter than 520 nm. X-ray diffraction and extinction measurements reveal the light-induced decomposition of CH3NH3PbI3 to lead iodide (PbI2) for the high-energy excitation regime. We propose a model explaining the energy dependence of the photostability that involves the photoexcitation of residual PbI2 species in the perovskite triggering the decomposition of CH3NH3PbI3. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpclett.8b00212
  • 2018 • 276 Low intrinsic c-axis thermal conductivity in PVD grown epitaxial Sb2Te3 films
    Rieger, F. and Kaiser, K. and Bendt, G. and Roddatis, V. and Thiessen, P. and Schulz, S. and Jooss, C.
    Journal of Applied Physics 123 (2018)
    Accurate determination and comprehensive understanding of the intrinsic c-axis thermal conductivity κc of thermoelectric layered Sb2Te3 is of high importance for the development of strategies to optimize the figure of merit in thin film devices via heterostructures and defect engineering. We present here high precision measurements of κc of epitaxial Sb2Te3 thin films on Al2O3 substrates grown by physical vapor deposition in the temperature range of 100 K to 300 K. The Kapitza resistances of the involved interfaces have been determined and subtracted from the film data, allowing access to the intrinsic thermal conductivity of single crystalline Sb2Te3. At room temperature, we obtain κc = 1.9 W/m K, being much smaller than the in-plane thermal conductivity of κab = 5 W/m K and even lower than the thermal conductivity of nano crystalline films of κnc ≈ 2.0-2.6 W/m K published by Park et al. [Nanoscale Res. Lett. 9, 96 (2014)]. High crystallinity and very low defect concentration of the films were confirmed by x-ray diffraction and high resolution transmission electron microscopy. Our data reveal that the phonon mean free path lmfpT is not limited by defect scattering and is of intrinsic nature, i.e., due to phonon-phonon scattering similar to other soft van der Waals type bonded layered systems. © 2018 Author(s).
    view abstractdoi: 10.1063/1.5025491
  • 2018 • 275 Correlative transmission Kikuchi diffraction and atom probe tomography study of Cu(In,Ga)Se2 grain boundaries
    Schwarz, T. and Stechmann, G. and Gault, B. and Cojocaru-Mirédin, O. and Wuerz, R. and Raabe, D.
    Progress in Photovoltaics: Research and Applications 26 196-204 (2018)
    We combined transmission Kikuchi diffraction and atom probe tomography techniques to investigate the relationship between the structure and chemistry of grain boundaries in Cu(In,Ga)Se2 thin films. Kikuchi patterns with the tetragonal structure of Cu(In,Ga)Se2 were simulated to emphasize the pseudosymmetry issue in this material system and, hence, the orientation determination ambiguity in case of indexing with a cubic zinc-blende structure. We compared these patterns with experimental data. We detect an elemental redistribution at random high-angle grain boundaries but no chemical fluctuations at Σ3 twin boundaries. The atom probe tomography analyses reveal Cu depletion as well as In and Se enrichment at random grain boundaries and, at some random grain boundaries, a slight Ga depletion. This In on Cu scenario is accompanied by cosegregation of Na and K originating from the soda-lime glass substrate. The amount of impurity segregation does vary not only from one grain boundary to another but also along an individual grain boundary. Hence, our results suggest that the degree of passivation of detrimental, nonradiative recombination centers does differ not only between Σ3 twin boundaries and random grain boundaries but also within the same random grain boundary. Copyright © 2017 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/pip.2966
  • 2018 • 274 Fracture toughness of Mo2BC thin films: Intrinsic toughness versus system toughening
    Soler, R. and Gleich, S. and Kirchlechner, C. and Scheu, C. and Schneider, J.M. and Dehm, G.
    Materials and Design 154 20-27 (2018)
    The fracture behaviour and microstructure evolution of sputtered Mo2BC films as a function of their deposition temperature is studied. Bipolar pulsed direct current magnetron sputtering was used to deposit Mo2BC thin films onto Si (100) wafers at substrate temperatures ranging from 380 to 630 °C. Microstructural characterization by transmission electron microscopy revealed that increasing the deposition temperature induces larger and more elongated grains, and a higher degree of crystallinity, transitioning from a partially amorphous to a fully crystalline film. The intrinsic fracture toughness of the Mo2BC films was studied by focussed ion beam milled micro-cantilever bending tests. A mild dependency of the intrinsic fracture toughness on the substrate deposition temperature was found. Fractograph analysis showed that the fracture behaviour was dominated by intergranular fracture or by fracture within the amorphous regions. Additionally, nanoindentation based fracture toughness measurements were used to probe the fracture behaviour of the Mo2BC/Si system, where residual stresses define the ‘apparent’ fracture toughness of the system. Depending on the substrate deposition temperature either compressive or tensile residual stresses developed in the films. This causes a relative change in the system toughness by up to one order of magnitude. The fracture experiments clearly reveal that notched cantilevers provide intrinsic toughness values of a material, while nanoindentation probes the toughness of the entire coating-substrate system. The combination of both techniques provides valuable design information for enhancing fracture resistance of Mo2BC films. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.matdes.2018.05.015
  • 2018 • 273 Deformation of Mesoporous Titania Nanostructures in Contact with D2O Vapor
    Song, L. and Rawolle, M. and Hohn, N. and Gutmann, J.S. and Frielinghaus, H. and Müller-Buschbaum, P.
    Small 14 (2018)
    For many applications, mesoporous titania nanostructures are exposed to water or need to be backfilled via infiltration with an aqueous solution, which can cause deformations of the nanostructure by capillary forces. In this work, the degree of deformation caused by water infiltration in two types of mesoporous, nanostructured titania films exposed to water vapor is compared. The different types of nanostructured titania films are prepared via a polymer template assisted sol–gel synthesis in conjunction with a polymer-template removal at high-temperatures under ambient conditions versus nitrogen atmosphere. Information about surface and inner morphology is extracted by scanning electron microscopy and grazing incidence small-angle neutron scattering (GISANS) measurements, respectively. Furthermore, complementary information on thin film composition and porosity are probed via X-ray reflectivity. The backfilling induced deformation of near surface structures and structures inside the mesoporous titania films is determined by GISANS before and after D2O infiltration. The respective atmosphere used for template removal influences the details of the titania nanostructure and strongly impacts the degree of water induced deformation. Drying of the films shows reversibility of the deformation. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/smll.201801461
  • 2018 • 272 Tribo-mechanical properties of CrC/a-C thin films sequentially deposited by HiPIMS and mfMS
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D.
    Surface and Coatings Technology 335 173-180 (2018)
    A sequence of high power impulse magnetron sputtering (HiPIMS) and mid-frequency magnetron sputtering (mfMS) was carried out to deposit a chromium carbide (CrC) interlayer and an amorphous carbon (a-C) top layer. The deposition of the interlayer by HiPIMS results in a higher adhesion strength and hence affects the properties of the a-C layer. The mechanical and tribological properties of a group of CrC/a-C films consisting of CrC with growing C content are investigated. In this context, single CrC and CrC/a-C films were systematically analyzed in order to evaluate the influence of the CrC interlayer on the properties of CrC/a-C. A higher amount of C changes the morphology of CrC films from a columnar to fully dense microstructure. The hardness decreases from 13.8 to 12.3 GPa with a growing C content, but the H/E- and H3/E2-ratios increase to 0.073 and 0.068 GPa, respectively. In contrast to the CrC interlayers, the CrC/a-C film systems are marked by a higher hardness of up to 19.8 GPa. The H/E- and H3/E2-ratios are also significantly higher with values of 0.090 and 0.155 GPa when compared to the CrC single films. The CrC layers exhibit the best adhesion class HF1 in Rockwell tests and a maximum critical load Lc3 of 41 N in scratch tests. The adhesion strength of CrC/a-C is strongly affected by the CrC interlayers; as generally similar failure mechanisms are observed for both film systems. The friction behavior of the CrC/a-C films is only influenced by the a-C top layer. The high adhesion strength of CrC prevents delamination failures when tribologically loading CrC/a-C films. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.12.035
  • 2018 • 271 Effect of Hf on the microstructure, mechanical properties, and oxidation behavior of sputtered CrAlN films
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D.
    Vacuum 154 208-213 (2018)
    Al-rich CrAlN films with a varying Hf content between 0 and 11.6 at.-% were synthetized by dc magnetron sputtering. The structural changes in the morphology and topography caused by Hf were evaluated by scanning electron microscopy. In addition, the phase composition of the Hf-alloyed CrAlN films was determined utilizing X-ray diffraction. The hardness and indentation modulus were determined using nanoindentation. In order to evaluate the effect of Hf on the oxidation behavior, the films were tempered in ambient air at 800 °C and subsequently analyzed. The incorporation of Hf leads to a morphological change from a fully-dense structure with small columns to a structure with more pronounced columns, which are visible as larger column tops on the surface. The Al-rich CrAlHfN films consist of the Wurtzite structure of AlN. A hardness decrease from 22.2 to 18.6 GPa is observed with an increasing Hf content and ascribed to the structural changes. When exposed to higher temperatures, the Hf-alloyed CrAlN films form an oxide layer, whose thickness is affected by the Hf content. An improved oxidation resistance is already achieved by a small amount of 2.0 at.-% of Hf. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.vacuum.2018.05.015
  • 2018 • 270 Effect of Pt and Au current collector in LiMn2O4 thin film for micro-batteries
    Trócoli, R. and Dushina, A. and Borhani-Haghighi, S. and Ludwig, Al. and La Mantia, F.
    Nanotechnology 29 (2018)
    The crystal orientation and morphology of sputtered LiMn2O4 thin films is strongly affected by the current collector. By substituting Pt with Au, it is possible to observe in the x-ray diffraction pattern of LiMn2O4 a change in the preferential orientation of the grains from (111) to (400). In addition, LiMn2O4 thin films deposited on Au show a higher porosity than films deposited on Pt. These structural differences cause an improvement in the electrochemical performances of the thin films deposited on Au, with up to 50% more specific charge. Aqueous cells using thin film based on LiMn2O4 sputtered on Au or Pt as the cathode electrode present a similar retention of specific charge, delivering 85% and 100%, respectively, of the initial values after 100 cycles. The critical role of the nature of the substrate used in the morphology and electrochemical behaviour observed could permit the exploration of similar effects for other lithium intercalation electrodes. © 2017 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/aa9e33
  • 2017 • 269 Weak ferromagnetism and short range polar order in NaMnF3 thin films
    KC, A. and Borisov, P. and Shvartsman, V.V. and Lederman, D.
    Applied Physics Letters 110 (2017)
    The orthorhombically distorted perovskite NaMnF3 has been predicted to become ferroelectric if an a = c distortion of the bulk Pnma structure is imposed. In order to test this prediction, NaMnF3 thin films were grown on SrTiO3 (001) single crystal substrates via molecular beam epitaxy. The best films were smooth and single phase with four different twin domains. In-plane magnetization measurements revealed the presence of antiferromagnetic ordering with weak ferromagnetism below the Néel temperature TN = 66 K. For the dielectric studies, NaMnF3 films were grown on a 30 nm SrRuO3 (001) layer used as a bottom electrode grown via pulsed laser deposition. The complex permittivity as a function of frequency indicated a strong Debye-like relaxation contribution characterized by a distribution of relaxation times. A power-law divergence of the characteristic relaxation time revealed an order-disorder phase transition at 8 K. The slow relaxation dynamics indicated the formation of super-dipoles (superparaelectric moments) that extend over several unit cells, similar to polar nanoregions of relaxor ferroelectrics. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4977421
  • 2017 • 268 Electron transport in stepped Bi2Se3 thin films
    Bauer, S. and Bobisch, C.A.
    Journal of Physics Condensed Matter 29 (2017)
    We analyse the electron transport in a 16 quintuple layer thick stepped Bi2Se3 film grown on Si(1 1 1) by means of scanning tunnelling potentiometry (STP) and multi-point probe measurements. Scanning tunnelling microscopy images reveal that the local structure of the Bi2Se3 film is dominated by terrace steps and domain boundaries. From a microscopic study on the nm scale by STP, we find a mostly linear gradient of the voltage on the Bi2Se3 terraces which is interrupted by voltage drops at the position of the domain boundaries. The voltage drops indicate that the domain boundaries are scatterers for the electron transport. Macroscopic resistance measurements (2PP and in-line 4PP measurement) on the μm scale support the microscopic results. An additional rotational square 4PP measurement shows an electrical anisotropy of the sheet conductance parallel and perpendicular to the Bi2Se3 steps of about 10%. This is a result of the anisotropic step distribution at the stepped Bi2Se3 surface while domain boundaries are distributed isotropically. The determined value of the conductivity of the Bi2Se3 steps of about 1000 S cm-1 verifies the value of an earlier STP study. © 2017 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/aa7a3c
  • 2017 • 267 Film forming properties of silicon nanoparticles on SixNy coated substrates during excimer laser annealing
    Caninenberg, M. and Kiesler, D. and Benson, N. and Schmechel, R.
    Optics and Laser Technology 90 33-39 (2017)
    In this article we investigate the film forming properties of excimer laser annealed silicon nanoparticles on non-silicon substrates. In contrast to their film forming properties on oxide free silicon substrates, the nanoparticle thin film tends to dewet and form a porous µ-structure on the silicon nitrite covered glass model substrates considered for our investigation. This is quantified using a SEM study in conjunction with image processing software, in order to evaluate the µ-structure size and inter µ-structure distance in dependence of the laser energy density. To generalize our results, the film forming process is described using a COMSOL Multiphysics ® fluid dynamics model, which solves the Navier Stokes equation for incompressible Newtonian fluids. To account for the porous nanoparticle thin film structure in the simulation, an effective medium approach is used by applying a conservative level set one phase method to our mesh. This effort allows us to predict the Si melt film formation ranging from a porous Si µ-structure to a compact 100% density Si thin film in dependence of the substrate / thin film interaction, as well as the laser energy used for the nanoparticle processing. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.optlastec.2016.11.010
  • 2017 • 266 High-throughput heterodyne thermoreflectance: Application to thermal conductivity measurements of a Fe-Si-Ge thin film alloy library
    D'Acremont, Q. and Pernot, G. and Rampnoux, J.-M. and Furlan, A. and Lacroix, D. and Ludwig, Al. and Dilhaire, S.
    Review of Scientific Instruments 88 (2017)
    A High-Throughput Time-Domain ThermoReflectance (HT-TDTR) technique was developed to perform fast thermal conductivity measurements with minimum user actions required. This new setup is based on a heterodyne picosecond thermoreflectance system. The use of two different laser oscillators has been proven to reduce the acquisition time by two orders of magnitude and avoid the experimental artefacts usually induced by moving the elements present in TDTR systems. An amplitude modulation associated to a lock-in detection scheme is included to maintain a high sensitivity to thermal properties. We demonstrate the capabilities of the HT-TDTR setup to perform high-throughput thermal analysis by mapping thermal conductivity and interface resistances of a ternary thin film silicide library FexSiyGe100-x-y (20<x,y<80) deposited by wedge-type multi-layer method on a 100 mm diameter sapphire wafer offering more than 300 analysis areas of different ternary alloy compositions. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4986469
  • 2017 • 265 Effects of incident N atom kinetic energy on TiN/TiN(001) film growth dynamics: A molecular dynamics investigation
    Edström, D. and Sangiovanni, D.G. and Hultman, L. and Petrov, I. and Greene, J.E. and Chirita, V.
    Journal of Applied Physics 121 (2017)
    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200 K, a temperature within the optimal range for epitaxial TiN growth, with an incident N-to-Ti flux ratio of four, are carried out using incident N energies EN = 2 and 10 eV and incident Ti energy ETi = 2 eV. To further highlight the effect of EN, we grow a bilayer film with EN = 2 eV initially and then switch to EN = 10 eV. As-deposited layers are analyzed as a function of composition, island-size distribution, island-edge orientation, and vacancy formation. Results show that growth with EN = 2 eV results in films that are globally overstoichiometric with islands bounded by N-terminated polar 110 edges, whereas films grown with EN = 10 eV are flatter and closer to stoichiometric. However, EN = 10 eV layers exhibit local N deficiency leading to the formation of isolated 111-oriented islands. Films grown by changing the incident energy from 2 to 10 eV during growth are more compact than those grown entirely with EN = 2 eV and exhibit greatly reduced concentrations of upper-layer adatoms, admolecules, and small clusters. Islands with 110 edges formed during growth with EN = 2 eV transform to islands with 100 edges as EN is switched to 10 eV. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4972963
  • 2017 • 264 Surface micro-patterning as a promising platform towards novel polyamide thin-film composite membranes of superior performance
    ElSherbiny, I.M.A. and Khalil, A.S.G. and Ulbricht, M.
    Journal of Membrane Science 529 11-22 (2017)
    Novel and efficient micro-patterned polyamide (PA) thin-film composite (TFC) membranes are successfully fabricated. Polyethersulfone support membranes are micro-patterned using two microfabrication methods, combined processes of vapor- and non-solvent-induced phase separation micro-molding, as well as micro-imprinting lithography. PA layer is successfully adapted on the developed micro-patterned supports and the impact on the membrane performance as a result of the difference in micro-patterning resolution is explored. The patterned PA TFC membranes exhibit superior water permeability, ~2–2.4 times compared to the flat PA TFC membranes, without sacrificing the membrane selectivity. This is mainly due to the distinguishable enhancement in membrane active surface area (~40–70%) and the increasing of the surface roughness upon micro-patterning. Furthermore, the concentration polarization analysis using different membrane orientations, with patterned grooves “parallel” and “perpendicular” to the direction of feed flow, and various feed concentrations is carried out. The results explicit the merits of implementing the micro-patterned TFC membranes in producing specific surface-induced mixing effects, which are found to reduce the concentration polarization, even at a high feed concentration. Moreover, the fidelity of the micro-patterning methods used in this work is comprehensively studied and different mechanisms for membrane surface patterning are proposed. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2017.01.046
  • 2017 • 263 Combinatorial study of Fe-Co-V hard magnetic thin films
    Fackler, S.W. and Alexandrakis, V. and König, D. and Kusne, A.G. and Gao, T. and Kramer, M.J. and Stasak, D. and Lopez, K. and Zayac, B. and Mehta, A. and Ludwig, Al. and Takeuchi, I.
    Science and Technology of Advanced Materials 18 231-238 (2017)
    Thin film libraries of Fe-Co-V were fabricated by combinatorial sputtering to study magnetic and structural properties over wide ranges of composition and thickness by high-throughput methods: synchrotron X-ray diffraction, magnetometry, composition, and thickness were measured across the Fe-Co-V libraries. In-plane magnetic hysteresis loops were shown to have a coercive field of 23.9 kA m–1 (300 G) and magnetization of 1000 kA m–1. The out-of-plane direction revealed enhanced coercive fields of 207 kA m–1 (2.6 kG) which was attributed to the shape anisotropy of column grains observed with electron microscopy. Angular dependence of the switching field showed that the magnetization reversal mechanism is governed by 180° domain wall pinning. In the thickness-dependent combinatorial study, co-sputtered composition spreads had a thickness ranging from 50 to 500 nm and (Fe70Co30)100-xVx compositions of x = 2–80. Comparison of high-throughput magneto-optical Kerr effect and traditional vibrating sample magnetometer measurements show agreement of trends in coercive fields across large composition and thickness regions. © 2017 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis.
    view abstractdoi: 10.1080/14686996.2017.1287520
  • 2017 • 262 Diffusion across the glass transition in silicate melts: Systematic correlations, new experimental data for Sr and Ba in calcium-aluminosilicate glasses and general mechanisms of ionic transport
    Fanara, S. and Sengupta, P. and Becker, H.-W. and Rogalla, D. and Chakraborty, S.
    Journal of Non-Crystalline Solids 455 6-16 (2017)
    Viscosity and diffusivity of silicate melts and glasses are related to each other through relaxation timescales. The systematic is explored based on published data. Diffusion coefficients for Sr and Ba were measured in calcium aluminosilicate glasses at conditions near the glass/supercooled liquid boundary in temperature – time space making use of thin film technology and Rutherford Backscattering Spectroscopy (RBS) to measure concentration profiles on nanoscales. These data extend the range of published diffusion coefficients and combined with the systematic noted above allow the nature of change of diffusion coefficients across the glass transition region to be studied. Activation energies for diffusion in the glassy state (~ 360 kJ/mol) are higher than in the molten liquid (~ 213 kJ/mol). A defect based model of glass transition derived by Ojovan and coworkers, where attainment of a percolation threshold of configuron-type defects accounts for the glass – liquid transition, can explain the observed diffusion behaviour. Data treatment using this model yields a defect formation enthalpy of ~ 146 kJ/mol and a migration enthalpy of ~ 213 kJ/mol. The results of this study provide generalized expressions for the prediction of diffusion coefficients of cations in silicate melts for any composition at any temperature. © 2016
    view abstractdoi: 10.1016/j.jnoncrysol.2016.10.013
  • 2017 • 261 Thin SnOx films for surface plasmon resonance enhanced ellipsometric gas sensing (SPREE)
    Fischer, D. and Hertwig, A. and Beck, U. and Lohse, V. and Negendank, D. and Kormunda, M. and Esser, N.
    Beilstein Journal of Nanotechnology 8 522-529 (2017)
    Background: Gas sensors are very important in several fields like gas monitoring, safety and environmental applications. In this approach, a new gas sensing concept is investigated which combines the powerful adsorption probability of metal oxide conductive sensors (MOS) with an optical ellipsometric readout. This concept shows promising results to solve the problems of cross sensitivity of the MOS concept.Results: Undoped tin oxide (SnOx) and iron doped tin oxide (Fe:SnOx) thin add-on films were prepared by magnetron sputtering on the top of the actual surface plasmon resonance (SPR) sensing gold layer. The films were tested for their sensitivity to several gas species in the surface plasmon resonance enhanced (SPREE) gas measurement. It was found that the undoped tin oxide (SnOx) shows higher sensitivities to propane (C3H8) then to carbon monoxide (CO). By using Fe:SnOx, this relation is inverted. This behavior was explained by a change of the amount of binding sites for CO in the layer due to this iron doping. For hydrogen (H2) no such relation was found but the sensing ability was identical for both layer materials. This observation was related to a different sensing mechanism for H2 which is driven by the diffusion into the layer instead of adsorption on the surface. Conclusion: The gas sensing selectivity can be enhanced by tuning the properties of the thin film overcoating. A relation of the binding sites in the doped and undoped SnOx films and the gas sensing abilities for CO and C3H8 was found. This could open the path for optimized gas sensing devices with different coated SPREE sensors. © 2017 Fischer et al.; licensee Beilstein-Institut.
    view abstractdoi: 10.3762/bjnano.8.56
  • 2017 • 260 Influence of Substrate Temperature and Film Thickness on Thermal, Electrical, and Structural Properties of HPPMS and DC Magnetron Sputtered Ge Thin Films
    Furlan, A. and Grochla, D. and D'Acremont, Q. and Pernot, G. and Dilhaire, S. and Ludwig, Al.
    Advanced Engineering Materials (2017)
    Ge was deposited as thickness gradient films at temperatures up to 800°C by direct current (DC) and high power pulsed magnetron sputtering (HPPMS). Structural characterization shows increased crystallization with increasing substrate temperature and film thickness. Thermal conductivity was measured by a novel high-throughput time-domain thermo-reflectance method. Thermo-electrical properties correlate to the degree of crystallization. Conductivities increase with increasing substrate temperature up to 500°C. For higher temperatures the trend reverses. A room temperature deposited/annealed film displays smaller crystallites (10nm) and lower thermal conductivity (5Wm-1K-1) compared to 25Wm-1K-1 for hot DC deposition. Compared to DC, HPPMS films show higher thermal conductivities up to 45Wm-1K-1. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201600854
  • 2017 • 259 New amidinate complexes of indium(III): Promising CVD precursors for transparent and conductive In2O3 thin films
    Gebhard, M. and Hellwig, M. and Kroll, A. and Rogalla, D. and Winter, M. and Mallick, B. and Ludwig, Ar. and Wiesing, M. and Wieck, A.D. and Grundmeier, G. and Devi, A.
    Dalton Transactions 46 10220-10231 (2017)
    For the first time, synthesis of two new amidinate-ligand comprising heteroleptic indium complexes, namely [InCl(amd)2] (1) and [InMe(amd)2] (2), via salt-metathesis and their detailed characterization is reported. For comparison, the earlier reported homoleptic tris-amidinate [In(amd)3] (3) was also synthesized and analyzed in detail especially with respect to the thermal properties and molecular crystal structure analysis which are reported here for the first time. From nuclear magnetic resonance spectroscopy (NMR) and single-crystal X-ray diffraction (XRD), all three compounds were found to be monomeric with C2 (compound 1 and 2) and C3 symmetry (compound 3). Both halide-free compounds 2 and 3 were evaluated regarding their thermal properties using temperature-dependent 1H-NMR, thermogravimetric analysis (TGA) and iso-TGA, revealing suitable volatility and thermal stability for their application as potential precursors for chemical vapor phase thin film deposition methods. Indeed, metalorganic chemical vapor deposition (MOCVD) experiments over a broad temperature range (400 °C-700 °C) revealed the suitability of these two compounds to fabricate In2O3 thin films in the presence of oxygen on Si, thermally grown SiO2 and fused silica substrates. The as-deposited thin films were characterized in terms of their crystallinity via X-ray diffraction (XRD), morphology by scanning electron microscopy (SEM) and composition through complementary techniques such as Rutherford-backscattering spectrometry (RBS) in combination with nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS). From UV/Vis spectroscopy, the deposited In2O3 thin films on fused silica substrates were found to be highly transparent (T > 95% at 560 nm, compound 3). In addition, Hall measurements revealed high charge carrier densities of 1.8 × 1020 cm-3 (2) and 6.5 × 1019 cm-3 (3) with a Hall-mobility of 48 cm2 V-1 s-1 (2) and 74 cm2 V-1 s-1 (3) for the respective thin films, rendering the obtained thin films applicable as a transparent conducting oxide that could be suitable for optoelectronic applications. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7dt01280b
  • 2017 • 258 Stability, phase separation and oxidation of a supersaturated nanocrystalline Cu-33 at.% Cr thin film alloy
    Harzer, T.P. and Dehm, G.
    Thin Solid Films 623 48-58 (2017)
    A binary nanocrystalline Cu67Cr33 thin film alloy consisting of columnar grains was synthesized via co-evaporation of the constituent elements under non-equilibrium ultra-high vacuum conditions using molecular beam epitaxy. In the as-deposited state, the alloy film is a supersaturated solid solution with a single-phase body-centered cubic structure. In order to study the thermal stability of the microstructure and phase separation behavior towards the two phase equilibrium structure, isothermal annealing experiments in a temperature range of 150 °C – 500 °C were conducted inside a transmission electron microscope and compared to data obtained by X-ray diffraction under protective N2 atmosphere. It is shown that the single-phase nature of the alloy film is maintained for annealing temperatures of ≤ 300 °C, whereas heat treatment at temperatures of ≥ 400 °C results in the formation of a second phase, i.e. the equilibrium face-centered cubic phase of Cu. Phase separation proceeds predominantly by a spinodal-type decomposition process but a simultaneous diffusion of Cr along the columnar grain boundaries to the surface of the alloy film is observed as well. Temperature dependent diffusion coefficients for volume and grain boundary diffusion along with the activation energy for volume diffusion of Cr within the crystal lattice of the alloy film in a temperature range between 400 °C – 500 °C are determined from analytical in situ transmission electron microscopy experiments. Moreover, grain boundary diffusion of Cr leads to the growth of an external Cr-rich oxide scale. It is found that the growth kinetics of this oxide scale exhibits a transition from a linear to a nearly parabolic growth rate. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2016.12.048
  • 2017 • 257 Microstructural evolution and solid state dewetting of epitaxial Al thin films on sapphire (α-Al2O3)
    Hieke, S.W. and Breitbach, B. and Dehm, G. and Scheu, C.
    Acta Materialia 133 356-366 (2017)
    Solid state dewetting can be used for targeted patterning, but also causes degradation or failure of thin film devices. In this work the temperature-induced changes of a tetracrystalline model system with inhibited surface diffusion are studied. This is accomplished by growing Al thin films by molecular beam epitaxy on single crystalline (0001) oriented sapphire substrates. The as-deposited Al films form two orientation relationships (OR I and OR II) both subdivided in two twin-related growth variants leading to a tetracrystalline microstructure. Two processes evolve during annealing at 600 °C. Grain growth and texture evolution towards OR II occur in addition to the formation of drum-like voids in the Al film covered by a thin membrane. The surface oxide suppresses Al surface diffusion and in contrast to classical solid state dewetting interface and grain boundary diffusion dominate. High energy grain boundaries were identified as initial points of the void formation. © 2017 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2017.05.026
  • 2017 • 256 Influence of organic surface chemistry on the nucleation of plasma deposited SiOx films
    Hoppe, C. and Mitschker, F. and Giner, I. and De los Arcos, T. and Awakowicz, P. and Grundmeier, G.
    Journal of Physics D: Applied Physics 50 (2017)
    doi: 10.1088/1361-6463/aa69e5
  • 2017 • 255 Synthesis and evaluation of new copper ketoiminate precursors for a facile and additive-free solution-based approach to nanoscale copper oxide thin films
    Karle, Sarah and Rogalla, Detlef and Ludwig, Arne and Becker, Hans-Werner and Wieck, Andreas Dirk and Grafen, Markus and Ostendorf, Andreas and Devi, Anjana
    Dalton Transactions 46 2670--2679 (2017)
    Novel copper ketoiminate compounds were synthesized and for the first time applied for additive-free solution-based deposition of nanoscale copper oxide thin films. The two closely related compounds, namely the bis[4-(2-ethoxyethyl-imino)-3-pentanonato] copper, [Cu(EEKI)(2)], and bis[4-(3-methoxypropylimino)- 3-pentanonato] copper, [Cu(MPKI)(2)], were characterized by means of elemental and thermogravimetric analysis (TGA), as well as electron impact mass spectrometry (EI-MS). The advantages of these compounds are that they are liquid and possess excellent solubility in common organic solvents in addition to an optimum reactivity towards ambient moisture that enables a facile solution-based approach to nanoscale copper oxide thin films. Moreover, no additives or aging is needed to stabilize the solution processing of the copper oxide layers. [Cu(MPKI)(2)] was tested in detail for the deposition of copper oxide thin films by spin coating. Upon one-step annealing, high-quality, uniform, crystalline copper oxide thin films were deposited on Si, SiO2, as well as on quartz substrates. Structural, morphological and compositional characteristics of the copper oxide nanostructures were investigated in detail by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and a combined analysis using Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA). It was possible to control the copper oxide phases (CuO and Cu2O) by systematic tuning of the post-deposition annealing conditions. The functional properties in terms of optical band gap were investigated using UV/Vis spectroscopy, while the transport properties, such as resistivity, mobility and carrier concentration were analyzed employing Hall measurements, which confirmed the p-type conductivity of the copper oxide layers.
    view abstractdoi: 10.1039/c6dt04399b
  • 2017 • 254 Graphene oxide reduction induced by femtosecond laser irradiation
    Kasischke, M. and Maragkaki, S. and Volz, S. and Gurevich, E.L. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 10356 (2017)
    A promising fabrication method for graphene is the reduction of graphene oxide (GO), this can be achieved photochemically by laser irradiation. In this study, we examine the results of latter method by a femtosecond fiber laser (1030 nm, 280 fs). The chemical properties of the irradiated areas were analyzed by Raman and X-ray photoelectron spectroscopy (XPS) and electrical properties were evaluated using sheet resistance measurements. We found that, within a wide range of fluences (8.5 mJ/cm2to 57.8 mJ/cm2) at high overlapping rates (>99.45 %), photochemical oxygen reduction can be achieved. However, hybridization transition of sp3 to sp2 graphene-like structures only takes place at upper fluences of the mentioned range. © 2017 SPIE.
    view abstractdoi: 10.1117/12.2274976
  • 2017 • 253 Antibacterial activity of microstructured sacrificial anode thin films by combination of silver with platinum group elements (platinum, palladium, iridium)
    Köller, M. and Bellova, P. and Javid, S.M. and Motemani, Y. and Khare, C. and Sengstock, C. and Tschulik, K. and Schildhauer, T.A. and Ludwig, Al.
    Materials Science and Engineering C 74 536-541 (2017)
    Five different Ag dots arrays (16 to 400dots/mm2) were fabricated on a continuous platinum, palladium, or iridium thin film and for comparison also on titanium film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Staphylococcus aureus (S. aureus) were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards . S. aureus was induced by Ag dot arrays on each of the platinum group thin film (sacrificial anode system for Ag) in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag). Among platinum group elements the Ir-Ag system exerted the highest antibacterial activity which was accompanied by most advanced dissolution of the Ag dots and Ag ion release compared to Ag dots on Pt or Pd. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2016.12.075
  • 2017 • 252 Electronic structure of metastable bcc Cu-Cr alloy thin films: Comparison of electron energy-loss spectroscopy and first-principles calculations
    Liebscher, C.H. and Freysoldt, C. and Dennenwaldt, T. and Harzer, T.P. and Dehm, G.
    Ultramicroscopy 178 96-104 (2017)
    Metastable Cu-Cr alloy thin films with nominal thickness of 300nm and composition of Cu67Cr33 (at%) are obtained by co-evaporation using molecular beam epitaxy. The microstructure, chemical phase separation and electronic structure are investigated by transmission electron microscopy (TEM). The thin film adopts the body-centered cubic crystal structure and consists of columnar grains with ~50nm diameter. Aberration-corrected scanning TEM in combination with energy dispersive X-ray spectroscopy confirms compositional fluctuations within the grains. Cu- and Cr-rich domains with composition of Cu85Cr15 (at%) and Cu42Cr58 (at%) and domain size of 1-5nm are observed. The alignment of the interface between the Cu- and Cr-rich domains shows a preference for (110)-type habit plane. The electronic structure of the Cu-Cr thin films is investigated by electron energy loss spectroscopy (EELS) and is contrasted to an fcc-Cu reference sample. The experimental EEL spectra are compared to spectra computed by density functional theory. The main differences between bcc-and fcc-Cu are related to differences in van Hove singularities in the electron density of states. In Cu-Cr solid solutions with bcc crystal structure a single peak after the L3-edge, corresponding to a van Hove singularity at the N-point of the first Brillouin zone is observed. Spectra computed for pure bcc-Cu and random Cu-Cr solid solutions with 10at% Cr confirm the experimental observations. The calculated spectrum for a perfect Cu50Cr50 (at%) random structure shows a shift in the van Hove singularity towards higher energy by developing a Cu-Cr d-band that lies between the delocalized d-bands of Cu and Cr. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2016.07.011
  • 2017 • 251 The effect of dynamical compressive and shear strain on magnetic anisotropy in a low symmetry ferromagnetic film
    Linnik, T.L. and Kats, V.N. and Jager, J. and Salasyuk, A.S. and Yakovlev, D.R. and Rushforth, A.W. and Akimov, A.V. and Kalashnikova, A.M. and Bayer, M. and Scherbakov, A.V.
    Physica Scripta 92 (2017)
    Dynamical strain generated upon excitation of a metallic film by a femtosecond laser pulse may become a versatile tool enabling control of the magnetic state of thin films and nanostructures via inverse magnetostriction on a picosecond time scale. Here, we explore two alternative approaches to manipulate magnetocrystalline anisotropy and excite magnetization precession in a low-symmetry film of a magnetic metallic alloy galfenol (Fe,Ga), either by injecting a picosecond strain pulse into it from a substrate, or by generating dynamical strain of a complex temporal profile in the film directly. In the former case, we realize ultrafast excitation of magnetization dynamics solely by strain pulses. In the latter case, optically-generated strain emerging abruptly in the film modifies its magnetocrystalline anisotropy, competing with heat-induced change of anisotropy parameters. We demonstrate that the optically-generated strain remains efficient for launching magnetization precession, when the heat-induced changes of anisotropy parameters do not trigger the precession any more. We emphasize that in both approaches the ultrafast change of magnetic anisotropy mediating the precession excitation relies on the mixed, compressive, and shear character of the dynamical strain, which emerges due to low-symmetry of the metallic film under study. © 2017 The Royal Swedish Academy of Sciences.
    view abstractdoi: 10.1088/1402-4896/aa6943
  • 2017 • 250 Atomic/molecular layer deposition of hybrid inorganic–organic thin films from erbium guanidinate precursor
    Mai, L. and Giedraityte, Z. and Schmidt, M. and Rogalla, D. and Scholz, S. and Wieck, A.D. and Devi, A. and Karppinen, M.
    Journal of Materials Science 52 6216-6224 (2017)
    Luminescent erbium-based inorganic–organic hybrid materials play an important role in many frontier nano-sized applications, such as amplifiers, detectors and OLEDs. Here, we demonstrate the possibility to fabricate high-quality thin films comprising both erbium and an appropriate organic molecule as a luminescence sensitizer utilizing the combined atomic layer deposition and molecular layer deposition (ALD/MLD) technique. We employ tris(N,N′-diisopropyl-2-dimethylamido guanidinato)erbium(III) [Er(DPDMG)3] together with 3,5-pyridine dicarboxylic acid as precursors. With the appreciably high film deposition rate achieved (6.4 Å cycle−1), the guanidinate precursor indeed appears as an interesting new addition to the ALD/MLD precursor variety toward novel materials. Our erbium–organic thin films showed highly promising UV absorption properties and a photoluminescence at 1535 nm for a 325-nm excitation, relevant to possible future luminescence applications. © 2017 Springer Science+Business Media New York
    view abstractdoi: 10.1007/s10853-017-0855-6
  • 2017 • 249 Effect of annealing on the size dependent deformation behavior of thin cobalt films on flexible substrates
    Marx, V.M. and Cordill, M.J. and Többens, D.M. and Kirchlechner, C. and Dehm, G.
    Thin Solid Films 624 34-40 (2017)
    The effect of film thickness as well as the influence of heat treatment on the deformation behavior of thin cobalt films (50–2000 nm) on polyimide substrates was investigated using various tensile tests. Straining under an optical light microscope provides information about the fracture strain and cracking behavior. The annealed films exhibit enhanced crack onset strains between 4 and 7% compared to the as-deposited films with fracture strains of 1–2%. This is partly achieved by a mechanically induced martensitic phase transformation of cobalt from the face-centered cubic (FCC) to the hexagonal-closed packed (HCP) phase. Thereby, it was shown that the heat treatment can be used to increase the amount of metastable FCC phase. Complementary synchrotron diffraction experiments were used to determine the lattice strains which initially increase during straining. After reaching a maximum, the lattice strains decrease in the case of the as-deposited films due to crack formation and in the case of the annealed films due the strain-induced phase transformation and localized plastic deformation in the form of necks. At higher engineering strains, the formation of cracks is also observed in the heat treated samples. Additionally, a decrease of the maximum lattice strain could be found for the HCP phase below a film thickness of 200 nm and grain size of 50 nm in the as-deposited films which is caused by cracking. © 2017
    view abstractdoi: 10.1016/j.tsf.2017.01.011
  • 2017 • 248 Soluble metal oxo alkoxide inks with advanced rheological properties for inkjet-printed thin-film transistors
    Meyer, S. and Pham, D.V. and Merkulov, S. and Weber, D. and Merkulov, A. and Benson, N. and Schmechel, R.
    ACS Applied Materials and Interfaces 9 2625-2633 (2017)
    Semiconductor inks containing an indium-based oxo alkoxide precursor material were optimized regarding rheology requirements for a commercial 10 pL inkjet printhead. The rheological stability is evaluated by measuring the dynamic viscosity of the formulations for 12 h with a constant shear rate stress under ambient conditions. It is believed that the observed superior stability of the inks is the result of effectively suppressing the hydrolysis and condensation reaction between the metal oxo alkoxide precursor complex and atmospheric water. This can be attributed to a strong precursor coordination and the resulting reduction in ligand exchange dynamics of the solvent tetrahydrofurfuryl alcohol which is used as the main solvent in the formulations. It is also shown that with a proper selection of cosolvents, having high polar Hansen solubility parameter values, the inks drop formation properties and wettability can be finetuned by maintaining the inks rheological stability. Good drop jetting performance without satellite formation and high drop velocities of 8.25 m/s were found with the support of dimensionless numbers and printability windows. By printing single 10 pL ink dots onto short channel indium-tin-oxide electrodes, In2O3 calcination at 350 °C and a solution-processed back-channel protection, high average saturation mobility of approximately 10 cm2/(V s) are demonstrated in a bottom-contact coplanar thinfilm transistor device structure. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b12586
  • 2017 • 247 Tailoring microstructure, mechanical and tribological properties of NiTi thin films by controlling in-situ annealing temperature
    Momeni, S. and Biskupek, J. and Tillmann, W.
    Thin Solid Films 628 13-21 (2017)
    Magnetron sputtered near equiatomic NiTi thin films were deposited on Si (100) and hot work tool steel substrates. The deposited thin films were in-situ annealed at four different temperatures viz., 80 °C, 305 °C, 425 °C, and 525 °C. The effect of the in-situ annealing temperature on the microstructure of the film, the morphology, as well as mechanical and tribological properties was studied using X-ray diffraction, synchrotron diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, ball-on-disc, scratch test, and three dimensional optical microscopy. The obtained results revealed how the variation of in-situ annealing temperature affects the crystallization, microstructure evolution, as well as mechanical and tribological properties of NiTi thin films. © 2017
    view abstractdoi: 10.1016/j.tsf.2017.02.052
  • 2017 • 246 Identification of a ternary μ-phase in the Co-Ti-W system – An advanced correlative thin-film and bulk combinatorial materials investigation
    Naujoks, D. and Eggeler, Y.M. and Hallensleben, P. and Frenzel, J. and Fries, S.G. and Palumbo, M. and Koßmann, J. and Hammerschmidt, T. and Pfetzing-Micklich, J. and Eggeler, G. and Spiecker, E. and Drautz, R. and Ludwig, Al.
    Acta Materialia 138 100-110 (2017)
    The formation of a ternary μ-phase is documented for the system Co-Ti-W. The relevant compositional stability range is identified by high-throughput energy dispersive X-ray spectroscopy, electrical resistance and X-ray diffraction maps from a thin-film materials library (1 μm thickness). Bulk samples of the identified compositions were fabricated to allow for correlative film and bulk studies. Using analytical scanning and transmission electron microscopy, we demonstrate that in both, thin film and bulk samples, the D85 phase (μ-phase) coexists with the C36-phase and the A2-phase at comparable average chemical compositions. Young's moduli and hardness values of the μ-phase and the C36-phase were determined by nanoindentation. The trends of experimentally obtained elastic moduli are consistent with density functional theory (DFT) calculations. DFT analysis also supports the experimental findings, that the μ-phase can solve up to 18 at.% Ti. Based on the experimental and DFT results it is shown that CALPHAD modeling can be modified to account for the new findings. © 2017 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2017.07.037
  • 2017 • 245 Unusual application of aluminium-doped ZnO thin film developed by metalorganic chemical vapour deposition for surface temperature sensor
    Nebatti, A. and Pflitsch, C. and Atakan, B.
    Thin Solid Films 636 532-536 (2017)
    A relatively new promising method for surface temperature measurement is the use of thermographic phosphors. For this purpose, the temperature-dependent photoluminescence (PL) properties of aluminium-doped ZnO thin films were studied. The films have been successfully deposited on substrate of Si(100)-orientation by metalorganic chemical vapour deposition (MOCVD) method. For the use of the films as temperature sensors, the Photoluminescence (PL) properties are most important. Consequently, the emission peaks are observed in the undoped and Al-doped films deposited at 550 °C and annealed at 900 °C for 2 h after ultraviolet laser excitation (355 nm). The results show that with increasing temperature the PL intensity is quenched for the Al-doped ZnO film (n(Al)/n(Zn) = 0.051). As a result, the area under the spectrum changes significantly with temperature, making it useful for temperature evaluation. Al-doped ZnO films can be used as temperature sensors within the range of room temperature to 300 °C. Beyond this range the spectrum is no longer sensitive to temperature change.
    view abstractdoi: 10.1016/j.tsf.2017.07.002
  • 2017 • 244 High-throughput study of binary thin film tungsten alloys
    Nikolić, V. and Wurster, S. and Savan, A. and Ludwig, Al. and Pippan, R.
    International Journal of Refractory Metals and Hard Materials 69 40-48 (2017)
    Combinatorial magnetron co-sputtering from elemental sources was applied to produce W-alloy thin film composition spread materials libraries with well-defined, continuous composition gradients (film thicknesses between 1 and 2.5 μm). Three systems were studied: W-Fe (0–7 at.%), W-Ti (0–15 at.%) and W-Ir (0–12 at.%). High-throughput characterization of the materials libraries comprised of chemical, morphological and microstructural analyses. Scanning electron microscope investigations revealed that the films have a columnar structure of inverted cone-like units separated by voided boundaries, with a strong correlation to the alloying element content. Significant morphological changes occurred with an increase in the amount of the added element; W films with lower at.% of the alloying element had higher density and tighter grain boundaries, altering towards an increased amount of voids as the concentration of the alloying element increased. Electron backscatter diffraction scanning was used to determine microstructural components (grain size, grain shape, texture evolution), in dependence on the concentration of the alloying element. © 2017 Elsevier Ltd
    view abstractdoi: 10.1016/j.ijrmhm.2017.07.017
  • 2017 • 243 Low temperature growth of gallium oxide thin films via plasma enhanced atomic layer deposition
    O'Donoghue, R. and Rechmann, J. and Aghaee, M. and Rogalla, D. and Becker, H.-W. and Creatore, M. and Wieck, A.D. and Devi, A.
    Dalton Transactions 46 16551-16561 (2017)
    Herein we describe an efficient low temperature (60-160 °C) plasma enhanced atomic layer deposition (PEALD) process for gallium oxide (Ga2O3) thin films using hexakis(dimethylamido)digallium [Ga(NMe2)3]2 with oxygen (O2) plasma on Si(100). The use of O2 plasma was found to have a significant improvement on the growth rate and deposition temperature when compared to former Ga2O3 processes. The process yielded the second highest growth rates (1.5 Å per cycle) in terms of Ga2O3 ALD and the lowest temperature to date for the ALD growth of Ga2O3 and typical ALD characteristics were determined. From in situ quartz crystal microbalance (QCM) studies and ex situ ellipsometry measurements, it was deduced that the process is initially substrate-inhibited. Complementary analytical techniques were employed to investigate the crystallinity (grazing-incidence X-ray diffraction), composition (Rutherford backscattering analysis/nuclear reaction analysis/X-ray photoelectron spectroscopy), morphology (X-ray reflectivity/atomic force microscopy) which revealed the formation of amorphous, homogeneous and nearly stoichiometric Ga2O3 thin films of high purity (carbon and nitrogen <2 at.%) under optimised process conditions. Tauc plots obtained via UV-Vis spectroscopy yielded a band gap of 4.9 eV and the transmittance values were more than 80%. Upon annealing at 1000 °C, the transformation to oxygen rich polycrystalline β-gallium oxide took place, which also resulted in the densification and roughening of the layer, accompanied by a slight reduction in the band gap. This work outlines a fast and efficient method for the low temperature ALD growth of Ga2O3 thin films and provides the means to deposit Ga2O3 upon thermally sensitive polymers like polyethylene terephthalate. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7dt03427j
  • 2017 • 242 Optical control of magnetization dynamics in Gd-Fe-Co films with different compositions
    Ohkochi, T. and Fujiwara, H. and Kotsugi, M. and Takahashi, H. and Adam, R. and Sekiyama, A. and Nakamura, T. and Tsukamoto, A. and Schneider, C. M. and Kuroda, H. and Arguelles, E.F. and Sakaue, M. and Kasai, H. and Tsunoda, M. a...
    Applied Physics Express 10 (2017)
    Perpendicularly magnetized ferrimagnetic Gd-Fe-Co thin films with different compositions and multilayer arrangements were subjected to femtosecond laser pulses. The pulses triggered different magnetization dynamics in the various thin films. In the Gd26Fe66Co8 film, which has an angular-momentum-compensation temperature (TA) well above ambient temperature (Texp), monotonic magnetization reversal occurred, whereas the Gd22Fe70Co8 film (where TA is well below Texp) exhibited remarkable wavelike spin modulation with spatial inhomogeneity during relaxation of the laser-induced nonequilibrium state. These findings can enable broad-range tuning of the magneto-optical responses of Gd-Fe-Co alloys, facilitating advances in materials engineering. © 2017 The Japan Society of Applied Physics.
    view abstractdoi: 10.7567/APEX.10.103002
  • 2017 • 241 Photoactive Zinc Ferrites Fabricated via Conventional CVD Approach
    Peeters, D. and Taffa, D.H. and Kerrigan, M.M. and Ney, A. and Jöns, N. and Rogalla, D. and Cwik, S. and Becker, H.-W. and Grafen, M. and Ostendorf, A. and Winter, C.H. and Chakraborty, S. and Wark, M. and Devi, A.
    ACS Sustainable Chemistry and Engineering 5 2917-2926 (2017)
    Owing to its narrow band gap and promising magnetic and photocatalytic properties, thin films of zinc ferrite (ZFO, ZnFe2O4) are appealing for fabrication of devices in magnetic recording media and photoelectrochemical cells. Herein we report for the first time the fabrication of photactive zinc ferrites via a solvent free, conventional CVD approach, and the resulting ZFO layers show promise as a photocatalyst in PEC water-splitting. For large scale applications, chemical vapor deposition (CVD) routes are appealing for thin film deposition; however, very little is known about ZFO synthesis following CVD processes. The challenge in precisely controlling the composition for multicomponent material systems, such as ZFO, via conventional thermal CVD is an issue that is caused mainly by the mismatch in thermal properties of the precursors. The approach of using two different classes of precursors for zinc and iron with a close match in thermal windows led to the formation of polycrystalline spinel type ZFO. Under the optimized process conditions, it was possible to fabricate solely ZFO in the desired phase. This work demonstrates the potential of employing CVD to obtain photoactive ternary material systems in the right composition. For the first time, the application of CVD grown ZFO films for photoelectrochemical applications is being demonstrated, showing a direct band gap of 2.3 eV and exhibiting activity for visible light driven photoelectrochemical water splitting. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acssuschemeng.6b02233
  • 2017 • 240 Controlling the conductivity of Ti3C2 MXenes by inductively coupled oxygen and hydrogen plasma treatment and humidity
    Römer, F.M. and Wiedwald, U. and Strusch, T. and Halim, J. and Mayerberger, E. and Barsoum, M.W. and Farle, M.
    RSC Advances 7 13097-13103 (2017)
    We report on the effects of plasma treatment and humidity on the electrical conductivities of Ti3C2 MXene thin films. The latter-spincoated from a colloidal solution produced by LiF/HCl etching of Ti3AlC2 powders-were 13 nm thick with an area of 6.8 mm2. The changes in the films exposed to hydrogen (H) and oxygen (O) plasmas in vacuum were analyzed by X-ray photoelectron spectroscopy. We find that the film resistivities can be switched reproducibly by plasma treatment between 5.6 μΩm (oxidized state) to 4.6 μΩm (reduced state). Both states show metallic like conductivity. In high vacuum, the film resistivity was 243 Ω; when the relative humidity was 80% the film resistance increased to 6340 Ω, a 26 fold increase. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ra27505b
  • 2017 • 239 Low-Temperature Phase c-axis Oriented Manganese Bismuth Thin Films with High Anisotropy Grown from an Alloy Mn55Bi45 Target
    Sabet, S. and Hildebrandt, E. and Römer, F.M. and Radulov, I. and Zhang, H. and Farle, M. and Alff, L.
    IEEE Transactions on Magnetics 53 (2017)
    Manganese bismuth thin films were deposited from a Mn55Bi45 (at.%) alloy target onto glass substrates at room temperature using dc magnetron sputtering. The ferromagnetic low-temperature phase (LTP) of MnBi was formed through a subsequent vacuum annealing step. The resulting thin films were highly c-axis textured. Magnetic measurement shows a maximum saturation magnetization of 600 eμcm3 (0.60 MA/m). A magnetic uniaxial anisotropy energy density of \sim 1.86 {\cdot 10{7}} erg/cm3 (1.86 MJ/m3) was measured by torque magnetometry. The coercive field has a positive temperature coefficient and reaches 12 kOe (1.2 T) and 14 kOe (1.4 T) at 300 K for the out-of-plane and in-plane direction, respectively. Density functional theory calculations have confirmed that the magnetocrystalline anisotropy energy increases with increasing temperature as a result of a spin-reorientation occurring around 100 K. Growing LTP MnBi thin films directly from an alloy Mn55Bi45 target is an important step toward facilitating the synthesis of multilayers for spintronics or in an exchange spring magnet configuration. © 1965-2012 IEEE.
    view abstractdoi: 10.1109/TMAG.2016.2636817
  • 2017 • 238 Analytical model for thin-film SOI PIN-diode leakage current
    Schmidt, A. and Dreiner, S. and Vogt, H. and Goehlich, A. and Paschen, U.
    Solid-State Electronics 130 4-8 (2017)
    An analytical model for the thin-film silicon-on-insulator pin-diode leakage current is presented. Particularly the back-gate potential influence on the leakage current is addressed. The two-dimensional Poisson equation is simplified and then solved including the influence of the back-gate potential. Subsequently the analytical model is verified by comparison with numerical simulation and measurements. For the verification of the model the dependence on the back-gate potential, reverse voltage, device geometry, doping concentration and -polarity is considered. In this procedure the interface recombination velocity is used as fitting parameter. The model verification shows an accurate modeling of the leakage current at full depletion in combination with a back-gate potential dependence. The usage of the model is limited to back-gate and reverse potentials close to full depletion state of the pin-diode. © 2017 Elsevier Ltd
    view abstractdoi: 10.1016/j.sse.2017.01.004
  • 2017 • 237 Formation of nanometer-sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin-films and their effect on solar cell efficiency
    Schwarz, T. and Cojocaru-Mirédin, O. and Mousel, M. and Redinger, A. and Raabe, D. and Choi, P.-P.
    Acta Materialia 132 276-284 (2017)
    Atom probe tomography and transmission electron microscopy are used to study the formation of nano-sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin-films. For a Cu-rich precursor, which was deposited at 320 °C under Cu- and Zn-rich growth conditions, Cu2-xSe grains at the surface are detected. During annealing the precursor at 500 °C in a SnSe + Se atmosphere most of the Cu2-xSe is transformed to Cu2ZnSnSe4 via the consumption of excessive ZnSe and incorporation of Sn. However, atom probe tomography studies also reveal the formation of various nanometer-sized Cu-Sn-Se particles close to the CdS/Cu2ZnSnSe4 interface. One of those particles has a composition close to the Cu2SnSe3 compound. This phase has a smaller band gap than Cu2ZnSnSe4 and is proposed to lead to a significant drop in the open-circuit voltage and could be the main cause for a detrimental p-n junction and the zero efficiency of the final device. Possible effects of the other phases on solar cell performance and formation mechanisms are discussed as well. © 2017 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2017.04.056
  • 2017 • 236 A correlative investigation of grain boundary crystallography and electronic properties in CdTe thin film solar cells
    Stechmann, G. and Zaefferer, S. and Schwarz, T. and Konijnenberg, P. and Raabe, D. and Gretener, C. and Kranz, L. and Perrenoud, J. and Buecheler, S. and Nath Tiwari, A.
    Solar Energy Materials and Solar Cells 166 108-120 (2017)
    Evaluating the impact of grain boundaries on the functional properties of CdTe thin films, consistent with processes used in photovoltaic solar cells, requires a direct correlation between their crystallography and electronic behavior. In the present work, we propose a novel comprehensive approach, combining focused ion beam/electron backscatter diffraction tomography (3D-EBSD) and quantitative cathodoluminescence (CL). While the former enables a full five parameter characterization of the interfaces, the latter is used to probe the spatial distribution of recombination centers and their characteristics. In addition, critical issues associated with sample preparation are also discussed. Monte Carlo simulations, together with electron channeling contrast imaging (ECCI), are employed to evaluate the effects of ion-sputtering damage on the CL response of CdTe thin films, as well as to overcome the resolution limit of EBSD characterization. The results obtained show that, at the exception of coherent twin boundaries, all interfaces behave as non-radiative recombination centers, exhibiting significant recombination velocities. Furthermore, there is no direct correlation between the misorientation parameters of the interfaces and their recombination properties. In contrast, trends can be observed when considering the crystallography of the boundary planes. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.solmat.2017.03.022
  • 2017 • 235 Review Article: Unraveling synergistic effects in plasma-surface processes by means of beam experiments
    Von Keudell, A. and Corbella, C.
    Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films 35 (2017)
    The interaction of plasmas with surfaces is dominated by synergistic effects between incident ions and radicals. Film growth is accelerated by the ions, providing adsorption sites for incoming radicals. Chemical etching is accelerated by incident ions when chemical etching products are removed from the surface by ion sputtering. The latter is the essence of anisotropic etching in microelectronics, as elucidated by the seminal paper of Coburn and Winters [J. Appl. Phys. 50, 3189 (1979)]. However, ion-radical-synergisms play also an important role in a multitude of other systems, which are described in this article: (1) hydrocarbon thin film growth from methyl radicals and hydrogen atoms; (2) hydrocarbon thin film etching by ions and reactive neutrals; (3) plasma inactivation of bacteria; (4) plasma treatment of polymers; and (5) oxidation mechanisms during reactive magnetron sputtering of metal targets. All these mechanisms are unraveled by using a particle beam experiment to mimic the plasma-surface interface with the advantage of being able to control the species fluxes independently. It clearly shows that the mechanisms in action that had been described by Coburn and Winters [J. Appl. Phys. 50, 3189 (1979)] are ubiquitous. © 2017 Author(s).
    view abstractdoi: 10.1116/1.4983275
  • 2017 • 234 Nano-sized metal organic framework to improve the structural properties and desalination performance of thin film composite forward osmosis membrane
    Zirehpour, A. and Rahimpour, A. and Ulbricht, M.
    Journal of Membrane Science 531 59-67 (2017)
    In the present study, nano-sized metal-organic framework (MOF) particles consisting of silver (I) and 1,3,5-benzene tricarboxylic acid were synthesized and applied to improve the structural properties as well as desalination performance of thin-film composite (TFC) forward osmosis (FO) membranes. The MOF nanocrystals were incorporated into the polyamide layer of membranes through interfacial polymerization. Characterizations by Field emission scanning electron microscopy and X-ray photoelectron spectroscopy enabled the detection of MOF nanocrystals within the selective layer of the resultant membranes. The MOF incorporation led to changes of the membrane active layer in terms of hydrophilicity and transport properties, without detrimental effects on the layer selectivity. These features enhanced pure water permeability of the membranes to 129%, which was provided through 0.04% MOF loading of the organic phase during interfacial polymerization. As a result, the modified membrane exhibited an enhanced FO seawater desalination performance in comparison with the control membrane. The performance stability of TFC membrane was also improved by presence of MOF in active layer (as seen by a water flux decline of about 7% for modified membrane against about 18% for unmodified membrane when tested with real seawater). This study demonstrates the potential of MOF particles to enhance desalination performance of TFC membranes in FO systems. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2017.02.049
  • 2016 • 233 Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se2 thin films for solar cells - a review
    Abou-Ras, D. and Schmidt, S.S. and Schäfer, N. and Kavalakkatt, J. and Rissom, T. and Unold, T. and Mainz, R. and Weber, A. and Kirchartz, T. and Simsek Sanli, E. and van Aken, P.A. and Ramasse, Q.M. and Kleebe, H.-J. and Azulay,...
    Physica Status Solidi - Rapid Research Letters 10 363-375 (2016)
    The present review gives an overview of the various reports on properties of line and planar defects in Cu(In,Ga)(S,Se)2 thin films for high-efficiency solar cells. We report results from various analysis techniques applied to characterize these defects at different length scales, which allow for drawing a consistent picture on structural and electronic defect properties. A key finding is atomic reconstruction detected at line and planar defects, which may be one mechanism to reduce excess charge densities and to relax deep-defect states from midgap to shallow energy levels. On the other hand, nonradiative Shockley-Read-Hall recombination is still enhanced with respect to defect-free grain interiors, which is correlated with substantial reduction of luminescence intensities. Comparison of the microscopic electrical properties of planar defects in Cu(In,Ga)(S,Se)2 thin films with two-dimensional device simulations suggest that these defects are one origin of the reduced open-circuit voltage of the photovoltaic devices. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) This review gives an overview on the current understanding of line and planar defects in Cu(In,Ga)Se2 thin films and their impacts on the corresponding solar-cell devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssr.201510440
  • 2016 • 232 Synthesis of nanostructured LiMn2O4 thin films by glancing angle deposition for Li-ion battery applications
    Borhani-Haghighi, S. and Khare, C. and Trócoli, R. and Dushina, A. and Kieschnick, M. and Lamantia, F. and Ludwig, Al.
    Nanotechnology 27 (2016)
    The development of electric vehicles and portable electronic devices demands lighter and thinner batteries with improved specific charge and rate capabilities. In this work, thin films of LiMn2O4 were fabricated by rf magnetron sputtering. Glancing angle deposition is introduced as a promising approach for fabrication of porous cathode thin films with 2.6 times the capacity in comparison with conventionally sputtered films of the same thickness. Surface morphology and crystallinity of the films are studied along with their electrochemical performance in an aqueous electrolyte. The glancing angle deposited films can reach a rate capability of up to 4 mA cm-2 with minimal energy loss, and a life cycle longer than 100 charge/discharge cycles. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/45/455402
  • 2016 • 231 High-temperature stability and interfacial reactions of Ti and TiN thin films on Al2O3 and ZrO2
    Brust, S. and Röttger, A. and Theisen, W.
    Surface and Coatings Technology 307 47-55 (2016)
    Metallic thin films are used in many applications to modify ceramic surfaces. However, during subsequent processing, chemical interactions may change the properties of the coating. In addition, differences in thermal expansion can lead to delamination of the coating. In this study, titanium and titanium nitride thin films were deposited via physical and chemical vapor deposition (PVD and CVD, respectively) on alumina- and yttria-stabilised zirconia substrates, before being heat-treated at 1200 °C or 1500 °C in static argon atmosphere and analysed via SEM, EDS and XRD to investigate the effect of temperature on the thin films. It was shown that the chemical interactions between TiN and both Al2O3 and ZrO2 are weak. However, partial delamination of the TiN coating on alumina was observed after both annealing temperatures. The TiN coating on zirconia remained adherent. In contrast, the Ti coatings underwent a transformation to cubic TiO on both oxide substrates. This was due to partial reduction of the ZrO2 to ZrO2 − x and dissolution of the Al2O3, which leads to a Ti3Al0.9O1.1 interlayer. The TiO coating which formed remained adherent on the alumina at both annealing temperatures, but delaminated from the ZrO2 substrate after annealing at 1500 °C. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.08.060
  • 2016 • 230 Structural and multifunctional properties of magnetron-sputtered Fe-P(-Mn) thin films
    Decker, P. and Stein, H.S. and Salomon, S. and Brüssing, F. and Savan, A. and Hamann, S. and Ludwig, Al.
    Thin Solid Films 603 262-267 (2016)
    Structural and magnetic properties of magnetron-sputtered Fe-P(-Mn) thin films with compositions around the Fe2P single phase region are reported, revealing the compositional range of the Fe2P-type structure and the change of the magnetic properties within this composition spread. The structural analysis shows that in order to obtain crystalline Fe-P phases the P content must be higher than (Fe0.97Mn0.03)2.33P. A maximum phase fraction of the Fe2P-type structure is obtained in the examined (Fe0.97Mn0.03)1.78P sample. The hysteresis loops for the Fe2P(-Mn) thin films show a two-step magnetic reversal with one part belonging to an amorphous phase fraction and the other to the Fe2P(-Mn) phase. A maximum coercivity of 0.36 T was measured for the Fe2P(-Mn) phase fraction also at the composition of (Fe0.97Mn0.03)1.78P. Furthermore, electrochemical properties of FeP2(-Mn) thin films as hydrogen evolution catalysts (HER) are studied. FeP2(-Mn) shows a HER onset potential about 200 mV lower than that of Pt. Chronoamperometric testing at - 11.5 mA/cm2 for over 3500 s revealed no obvious decay in current density, suggesting good stability under typical working conditions in a photoelectrochemical device. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2016.02.023
  • 2016 • 229 Novel back-reflector architecture with nanoparticle based buried light-scattering microstructures for improved solar cell performance
    Desta, D. and Ram, S.K. and Rizzoli, R. and Bellettato, M. and Summonte, C. and Jeppesen, B.R. and Jensen, P.B. and Tsao, Y.-C. and Wiggers, H. and Pereira, R.N. and Balling, P. and Larsen, A.N.
    Nanoscale 8 12035-12046 (2016)
    A new back-reflector architecture for light-management in thin-film solar cells is proposed that includes a morphologically smooth top surface with light-scattering microstructures buried within. The microstructures are pyramid shaped, fabricated on a planar reflector using TiO2 nanoparticles and subsequently covered with a layer of Si nanoparticles to obtain a flattened top surface, thus enabling growth of good quality thin-film solar cells. The optical properties of this back-reflector show high broadband haze parameter and wide angular distribution of diffuse light-scattering. The n-i-p amorphous silicon thin-film solar cells grown on such a back-reflector show enhanced light absorption resulting in improved external quantum efficiency. The benefit of the light trapping in those solar cells is evidenced by the gains in short-circuit current density and efficiency up to 15.6% and 19.3% respectively, compared to the reference flat solar cells. This improvement in the current generation in the solar cells grown on the flat-topped (buried pyramid) back-reflector is observed even when the irradiation takes place at large oblique angles of incidence. Finite-difference-time-domain simulation results of optical absorption and ideal short-circuit current density values agree well with the experimental findings. The proposed approach uses a low cost and simple fabrication technique and allows effective light manipulation by utilizing the optical properties of micro-scale structures and nanoscale constituent particles. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6nr00259e
  • 2016 • 228 Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth
    Edström, D. and Sangiovanni, D.G. and Hultman, L. and Petrov, I. and Greene, J.E. and Chirita, V.
    Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films 34 (2016)
    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200 K are carried out using incident flux ratios N/Ti = 1, 2, and 4. The films are analyzed as a function of composition, island size distribution, island edge orientation, and vacancy formation. Results show that N/Ti = 1 films are globally understoichiometric with dispersed Ti-rich surface regions which serve as traps to nucleate 111-oriented islands, leading to local epitaxial breakdown. Films grown with N/Ti = 2 are approximately stoichiometric and the growth mode is closer to layer-by-layer, while N/Ti = 4 films are stoichiometric with N-rich surfaces. As N/Ti is increased from 1 to 4, island edges are increasingly polar, i.e., 110-oriented, and N-terminated to accommodate the excess N flux, some of which is lost by reflection of incident N atoms. N vacancies are produced in the surface layer during film deposition with N/Ti = 1 due to the formation and subsequent desorption of N2 molecules composed of a N adatom and a N surface atom, as well as itinerant Ti adatoms pulling up N surface atoms. The N vacancy concentration is significantly reduced as N/Ti is increased to 2; with N/Ti = 4, Ti vacancies dominate. Overall, our results show that an insufficient N/Ti ratio leads to surface roughening via nucleation of small dispersed 111 islands, whereas high N/Ti ratios result in surface roughening due to more rapid upper-layer nucleation and mound formation. The growth mode of N/Ti = 2 films, which have smoother surfaces, is closer to layer-by-layer. © 2016 American Vacuum Society.
    view abstractdoi: 10.1116/1.4953404
  • 2016 • 227 Temperature dependence of perpendicular magnetic anisotropy in CoFeB thin films
    Fu, Y. and Barsukov, I. and Li, J. and Gonçalves, A.M. and Kuo, C.C. and Farle, M. and Krivorotov, I.N.
    Applied Physics Letters 108 (2016)
    We study perpendicular magnetic anisotropy in thin films of Ta/Co20Fe60B20/MgO by ferromagnetic resonance and find a linear temperature dependence for the first and second order uniaxial terms from 5 to 300 K. Our data suggest the possible hybridization of Fe-O orbitals at the CoFeB/MgO interface for the origin of the first order anisotropy. However, we also find that non-interfacial contributions to the anisotropy are present. An easy-cone anisotropy is found for the entire temperature range in the narrow region of film thicknesses around the spin reorientation transition 1.2-1.35 nm. © 2016 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4945682
  • 2016 • 226 Benchmarking the Performance of Thin-Film Oxide Electrocatalysts for Gas Evolution Reactions at High Current Densities
    Ganassin, A. and Maljusch, A. and Colic, V. and Spanier, L. and Brandl, K. and Schuhmann, W. and Bandarenka, A.
    ACS Catalysis 6 3017-3024 (2016)
    Oxide materials are among the state-of-the-art heterogeneous electrocatalysts for many important large-scale industrial processes, including O2 and Cl2 evolution reactions. However, benchmarking their performance is challenging in many cases, especially at high current densities, which are relevant for industrial applications. Serious complications arise particularly due to (i) the formation of a nonconducting gas phase which blocks the surface during the reactions, (ii) problems in determination of the real electroactive electrode area, and (iii) the large influence of surface morphology alterations (stability issues) under reaction conditions, among others. In this work, an approach overcoming many of these challenges is presented, with a focus on electrochemically formed thin-film oxide electrocatalysts. The approach is based on benefits provided by the use of microelectrodes, and it gives comprehensive information about the surface roughness, catalyst activity, and stability. The key advantages of the proposed method are the possibility of characterization of the whole microelectrode surface by means of atomic force microscopy and an accurate assessment of the specific activity (and subsequently stability) of the catalyst, even at very high current densities. Electrochemically deposited CoOx thin films have been used in this study as model catalysts. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b00455
  • 2016 • 225 An efficient PE-ALD process for TiO2 thin films employing a new Ti-precursor
    Gebhard, M. and Mitschker, F. and Wiesing, M. and Giner, I. and Torun, B. and De Los Arcos, T. and Awakowicz, P. and Grundmeier, G. and Devi, A.
    Journal of Materials Chemistry C 4 1057-1065 (2016)
    An efficient plasma-enhanced atomic layer deposition (PE-ALD) process was developed for TiO2 thin films of high quality, using a new Ti-precursor, namely tris(dimethylamido)-(dimethylamino-2-propanolato)titanium(iv) (TDMADT). The five-coordinated titanium complex is volatile, thermally stable and reactive, making it a potential precursor for ALD and PE-ALD processes. Process optimization was performed with respect to plasma pulse length and reactive gas flow rate. Besides an ALD window, the application of the new compound was investigated using in situ quartz-crystal microbalance (QCM) to monitor surface saturation and growth per cycle (GPC). The new PE-ALD process is demonstrated to be an efficient procedure to deposit stoichiometric titanium dioxide thin films under optimized process conditions with deposition temperatures as low as 60°C. Thin films deposited on Si(100) and polyethylene-terephthalate (PET) exhibit a low RMS roughness of about 0.22 nm. In addition, proof-of-principle studies on TiO2 thin films deposited on PET show promising results in terms of barrier performance with oxygen transmission rates (OTR) found to be as low as 0.12 cm3 x cm-2 x day-1 for 14 nm thin films. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c5tc03385c
  • 2016 • 224 Screening of material libraries for electrochemical CO2 reduction catalysts – Improving selectivity of Cu by mixing with Co
    Grote, J.-P. and Zeradjanin, A.R. and Cherevko, S. and Savan, A. and Breitbach, B. and Ludwig, Al. and Mayrhofer, K.J.J.
    Journal of Catalysis 343 248-256 (2016)
    The efficiency of the direct electrochemical CO2 reduction can be improved by the development of new alloy catalysts, but to do so a highly resolved composition screening remains to be connected to complex sample preparation and time consuming analysis. We have developed a technique that allows a fast and easy initial catalyst composition screening by analyzing thin film composition spread samples, utilizing a scanning flow cell coupled to an online electrochemical mass spectrometer (SFC-OLEMS). As a first case example, the investigation of a Cu–Co thin film material library demonstrates the benefits and high potential of this approach. In particular, a shift in selectivity toward C2 species for low Co content (5–15 at.%) has been found and is discussed as being related to changed adsorption energies of intermediate products and the consequent modification of reaction pathways. © 2016 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2016.02.026
  • 2016 • 223 Epitaxial growth of thermally stable cobalt films on Au(111)
    Haag, N. and Laux, M. and Stöckl, J. and Kollamana, J. and Seidel, J. and Großmann, N. and Fetzer, R. and Kelly, L.L. and Wei, Z. and Stadtmüller, B. and Cinchetti, M. and Aeschlimann, M.
    18 (2016)
    Ferromagnetic thin films play a fundamental role in spintronic applications as a source for spin polarized carriers and in fundamental studies as ferromagnetic substrates. However, it is challenging to produce such metallic films with high structural quality and chemical purity on single crystalline substrates since the diffusion barrier across the metal-metal interface is usually smaller than the thermal activation energy necessary for smooth surface morphologies. Here, we introduce epitaxial thin Co films grown on an Au(111) single crystal surface as a thermally stable ferromagnetic thin film. Our structural investigations reveal an identical growth of thin Co/Au(111) films compared to Co bulk single crystals with large monoatomic Co terraces with an average width of 500 Å, formed after thermal annealing at 575 K. Combining our results from photoemission and Auger electron spectroscopy, we provide evidence that no significant diffusion of Au into the near surface region of the Co film takes place for this temperature and that no Au capping layer is formed on top of Co films. Furthermore, we show that the electronic valence band is dominated by a strong spectral contribution from a Co 3d band and a Co derived surface resonance in the minority band. Both states lead to an overall negative spin polarization at the Fermi energy. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
    view abstractdoi: 10.1088/1367-2630/18/10/103054
  • 2016 • 222 Zinc Ferrite Photoanode Nanomorphologies with Favorable Kinetics for Water-Splitting
    Hufnagel, A.G. and Peters, K. and Müller, A. and Scheu, C. and Fattakhova-Rohlfing, D. and Bein, T.
    Advanced Functional Materials 26 4435-4443 (2016)
    The n-type semiconducting spinel zinc ferrite (ZnFe2O4) is used as a photoabsorber material for light-driven water-splitting. It is prepared for the first time by atomic layer deposition. Using the resulting well-defined thin films as a model system, the performance of ZnFe2O4 in photoelectrochemical water oxidation is characterized. Compared to benchmark α-Fe2O3 (hematite) films, ZnFe2O4 thin films achieve a lower photocurrent at the reversible potential. However, the oxidation onset potential of ZnFe2O4 is 200 mV more cathodic, allowing the water-splitting reaction to proceed at a lower external bias and resulting in a maximum applied-bias power efficiency (ABPE) similar to that of Fe2O3. The kinetics of the water oxidation reaction are examined by intensity-modulated photocurrent spectroscopy. The data indicate a considerably higher charge transfer efficiency of ZnFe2O4 at potentials between 0.8 and 1.3 V versus the reversible hydrogen electrode, attributable to significantly slower surface charge recombination. Finally, nanostructured ZnFe2O4 photoanodes employing a macroporous antimony-doped tin oxide current collector reach a five times higher photocurrent than the flat films. The maximum ABPE of these host–guest photoanodes is similarly increased. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201600461
  • 2016 • 221 Fabrication and physico-mechanical properties of thin magnetron sputter deposited silver-containing hydroxyapatite films
    Ivanova, A.A. and Surmeneva, M.A. and Tyurin, A.I. and Pirozhkova, T.S. and Shuvarin, I.A. and Prymak, O. and Epple, M. and Chaikina, M.V. and Surmenev, R.A.
    Applied Surface Science 360 929-935 (2016)
    As a measure of the prevention of implant associated infections, a number of strategies have been recently applied. Silver-containing materials possessing antibacterial activity as expected might have wide applications in orthopedics and dentistry. The present work focuses on the physico-chemical characterization of silver-containing hydroxyapatite (Ag-HA) coating obtained by radio frequency (RF) magnetron sputtering. Mechanochemically synthesized Ag-HA powder (Ca10-xAgx(PO4)6(OH)2-x, x = 1.5) was used as a precursor for sputtering target preparation. Morphology, composition, crystallinity, physico-mechanical features (Young's modulus and nanohardness) of the deposited Ag-HA coatings were investigated. The sputtering of the nanostructured multicomponent target at the applied process conditions allowed to deposit crystalline Ag-HA coating which was confirmed by XRD and FTIR data. The SEM results revealed the formation of the coating with the grain morphology and columnar cross-section structure. The EDX analysis confirmed that Ag-HA coating contained Ca, P, O and Ag with the Ca/P ratio of 1.6 ± 0.1. The evolution of the mechanical properties allowed to conclude that addition of silver to HA film caused increase of the coating nanohardness and elastic modulus compared with those of pure HA thin films deposited under the same deposition conditions. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2015.11.087
  • 2016 • 220 Semiperiodicity versus periodicity for ultra broadband optical absorption in thin-film solar cells
    Jalali, M. and Nadgaran, H. and Erni, D.
    Journal of Nanophotonics 10 (2016)
    We propose the use of one-dimensional semiperiodic front and back gratings based on Thue-Morse, Fibonacci, and Rudin-Shapiro (RS) binary sequences as promising photon management techniques for enhancing ultra-broadband optical absorption in thin-film solar cells. The semiperiodicity allows an aggregate light in-coupling into the active layer within the range of the solar spectrum that is less weak compared to an inherently broadband random grating, but has a much larger bandwidth than the strong in-coupling via a periodic grating configuration. The proper design procedure proposed here deviates from a canonical double grating synthesis as it adheres to an ultra-broadband design where the spectrally integrated absorption in the active material is the proper subject to optimization, leaving the grating perturbations just a measure to perturb and mold the trapped light field in the active layer accordingly. It is shown that by using a well-defined RS double grating in a 400-nm thick crystalline silicon solar cell, a 110.2% enhancement of the spectrally integrated optical absorption can be achieved relative to the reference case without grating. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).
    view abstractdoi: 10.1117/1.JNP.10.036018
  • 2016 • 219 Thermochromic modulation of surface plasmon polaritons in vanadium dioxide nanocomposites
    Jostmeier, T. and Mangold, M. and Zimmer, J. and Karl, H. and Krenner, H.J. and Ruppert, C. and Betz, M.
    Optics Express 24 17321-17331 (2016)
    We propose and implement a new concept for thermochromic plasmonic elements. It is based on vanadium dioxide (VO2) nanocrystals located in the near field of surface plasmon polaritons supported by an otherwise unstructured gold thin film. When the VO2 undergoes the metal-insulator phase transition, the coupling conditions for conversion of light into propagating surface plasmon polaritons change markedly. In particular, we realize thermochromic plasmonic grating couplers with substantial switching contrast as well as tunable plasmonic couplers in a Kretschmann configuration. The use of VO2 nanocrystals permits highly repetitive switching and room temperature operation. Simulations based on the actual dielectric function of our VO2 nanocrystals agree well with the experiment. © 2016 Optical Society of America.
    view abstractdoi: 10.1364/OE.24.017321
  • 2016 • 218 The effect of silicon-substrate orientation on the local piezoelectric characteristics of LiNbO3 films
    Kiselev, D.A. and Zhukov, R.N. and Ksenich, S.V. and Kubasov, I.V. and Temirov, A.A. and Timushkin, N.G. and Bykov, A.S. and Malinkovich, M.D. and Shvartsman, V.V. and Lupascu, D.C. and Parkhomenko, Y.N.
    Journal of Surface Investigation 10 742-747 (2016)
    The domain structure of lithium-niobate thin films grown on Si(111) and Si(100) substrates coated with a native oxide layer with a thickness of no less than 2 nm is investigated by X-ray diffraction, scanning electron microscopy and piezoresponse force microscopy. The films are synthesized by the rf magnetron sputtering of a single-crystal lithium-niobate target. A high degree of grain orientation in the polycrystalline films is demonstrated. The piezoelectric coefficients dzz of the lithium-niobate films on Si(111) and Si(100) substrates are calculated from the measured dependences of the amplitude of the piezoresponse signal on the ac voltage applied between the cantilever tip and the substrate. Piezoelectric hysteresis loops are obtained in the remanent piezoelectric response regime © 2016, Pleiades Publishing, Ltd.
    view abstractdoi: 10.1134/S1027451016040091
  • 2016 • 217 Strain-induced phase transformation of a thin Co film on flexible substrates
    Marx, V.M. and Kirchlechner, C. and Breitbach, B. and Cordill, M.J. and Többens, D.M. and Waitz, T. and Dehm, G.
    Acta Materialia 121 227-233 (2016)
    The strain-induced FCC to HCP phase transformation of a two phase Co film on polyimide was investigated by performing a tensile test in an X-ray diffractometer. During straining of the 2 μm thick film, the intensity of the (002)FCC peak continuously decreases at engineering strains between 2 and 8% and remains constant at higher strains. Complementary in situ tensile tests under an optical light microscope showed crack formation at 6.7% and crack saturation at around 10% engineering strain. The strain-induced phase transformation starts before the first cracks form leading to a maximum lattice strain of approximately 0.9% as initiation strain measured from the (101¯1)HCP peak with the sin2ψ method which converts to a film stress of approximately 1270 ± 150 MPa. It could be revealed that a strain-induced phase transformation can enhance the ductility and therefore delay the crack onset of a thin cobalt film. © 2016 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2016.09.015
  • 2016 • 216 Thickness effect on the structure, grain size, and local piezoresponse of self-polarized lead lanthanum zirconate titanate thin films
    Melo, M. and Araújo, E.B. and Shvartsman, V.V. and Shur, V.Y. and Kholkin, A.L.
    Journal of Applied Physics 120 (2016)
    Polycrystalline lanthanum lead zirconate titanate (PLZT) thin films were deposited on Pt/TiO2/SiO2/Si substrates to study the effects of the thickness and grain size on their structural and piezoresponse properties at nanoscale. Thinner PLZT films show a slight (100)-orientation tendency that tends to random orientation for the thicker film, while microstrain and crystallite size increases almost linearly with increasing thickness. Piezoresponse force microscopy and autocorrelation function technique were used to demonstrate the existence of local self-polarization effect and to study the thickness dependence of correlation length. The obtained results ruled out the bulk mechanisms and suggest that Schottky barriers near the film-substrate are likely responsible for a build-in electric field in the films. Larger correlation length evidence that this build-in field increases the number of coexisting polarization directions in larger grains leading to an alignment of macrodomains in thinner films. © 2016 Author(s).
    view abstractdoi: 10.1063/1.4960137
  • 2016 • 215 High resolution electron energy loss spectroscopy of spin waves in ultra-thin cobalt films
    Michel, E. and Ibach, H. and Schneider, C.M.
    Surface and Interface Analysis 48 1104-1107 (2016)
    Electron energy loss spectroscopy has successfully established itself as the experimental method to study exchange-dominated, high-momentum spin waves in ultra-thin films. Because of insufficient energy resolution, previous studies were limited to spin waves in the high energy range and to wave vectors larger than about q|| = 0.4 Å−1. In this regime, spin waves are strongly damped by decay into Stoner excitations. Furthermore, the spin wave signal of a multilayer film consists of several overlapping modes. After implementation of several technical modifications, our electron spectrometer now enables the study of spin waves with an energy resolution down to 2 meV, and thereby the discrimination of several spin wave modes in ultra-thin films as well as the study of the intrinsic width of modes down to 1 meV. Examples are presented for fcc and hcp cobalt films and discussed in terms of current theoretical models. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/sia.6127
  • 2016 • 214 Investigation of the self-healing sliding wear characteristics of NiTi-based PVD coatings on tool steel
    Momeni, S. and Tillmann, W.
    Wear 368-369 53-59 (2016)
    Excellent damping capacity and superelasticity of the bulk NiTi shape memory alloy (SMA) makes it a suitable material of choice for tools in machining process as well as tribological systems. Although thin film of NiTi SMA has a same damping capacity as NiTi bulk alloys, it has a poor mechanical properties and undesirable tribological performance. This study aims at eliminating these application limitations for NiTi thin films. In order to achieve this goal, NiTi thin films were magnetron sputtered as an interlayer between reactively sputtered hard TiCN coatings and hot work tool steel substrates. The microstructure, composition, crystallographic phases, mechanical and tribological properties of the deposited thin films were analyzed by using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), nanoindentation, ball-on-disc, scratch test, and three dimensional (3D) optical microscopy. It was found that under a specific coating architecture, the superelasticity of NiTi inter-layer can be combined with high hardness and wear resistance of TiCN protective layers. The obtained results revealed that the thickness of NiTi interlayers is an important factor controlling mechanical and tribological performance of bilayer composite coating systems. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2016.08.004
  • 2016 • 213 Composite cavitation resistant PVD coatings based on NiTi thin films
    Momeni, S. and Tillmann, W. and Pohl, M.
    Materials and Design 110 830-838 (2016)
    As a protective coating, TiCN hard PVD coating was deposited on magnetron sputtered NiTi thin films under various coating architectures. The microstructure, composition, mechanical properties, tribological performance as well as the cavitation resistance of deposited coatings were analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), nanoindentation, ball–on-disc, scratch test, three dimensional (3D) optical microscopy, and the standard ultrasonic cavitation test (ASTM G 32). The obtained results revealed that under a specific coating architecture, the superelasticity of NiTi can be combined with high hardness and wear resistance of TiCN coatings. As a consequence of the combination of these properties, the composite NiTi based coatings are capable of presenting remarkable cavitation resistance and tribological performance. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.matdes.2016.08.054
  • 2016 • 212 Nanostructured Ti-Ta thin films synthesized by combinatorial glancing angle sputter deposition
    Motemani, Y. and Khare, C. and Savan, A. and Hans, M. and Paulsen, A. and Frenzel, J. and Somsen, C. and Mücklich, F. and Eggeler, G. and Ludwig, Al.
    Nanotechnology 27 (2016)
    Ti-Ta alloys are attractive materials for applications in actuators as well as biomedical implants. When fabricated as thin films, these alloys can potentially be employed as microactuators, components for micro-implantable devices and coatings on surgical implants. In this study, Ti100-xTa x (x = 21, 30) nanocolumnar thin films are fabricated by glancing angle deposition (GLAD) at room temperature using Ti73Ta27 and Ta sputter targets. Crystal structure, morphology and microstructure of the nanostructured thin films are systematically investigated by XRD, SEM and TEM, respectively. Nanocolumns of ∼150-160 nm in width are oriented perpendicular to the substrate for both Ti79Ta21 and Ti70Ta30 compositions. The disordered α″ martensite phase with orthorhombic structure is formed in room temperature as-deposited thin films. The columns are found to be elongated small single crystals which are aligned perpendicular to the and planes of α″ martensite, indicating that the films' growth orientation is mainly dominated by these crystallographic planes. Laser pre-patterned substrates are utilized to obtain periodic nanocolumnar arrays. The differences in seed pattern, and inter-seed distances lead to growth of multi-level porous nanostructures. Using a unique sputter deposition geometry consisting of Ti73Ta27 and Ta sputter sources, a nanocolumnar Ti-Ta materials library was fabricated on a static substrate by a co-deposition process (combinatorial-GLAD approach). In this library, a composition spread developed between Ti72.8Ta27.2 and Ti64.4Ta35.6, as confirmed by high-throughput EDX analysis. The morphology over the materials library varies from well-isolated nanocolumns to fan-like nanocolumnar structures. The influence of two sputter sources is investigated by studying the resulting column angle on the materials library. The presented nanostructuring methods including the use of the GLAD technique along with pre-patterning and a combinatorial materials library fabrication strategy offer a promising technological approach for investigating Ti-Ta thin films for a range of applications. The proposed approaches can be similarly implemented for other materials systems which can benefit from the formation of a nanocolumnar morphology. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/49/495604
  • 2016 • 211 Measurements of liquid film thickness, concentration, and temperature of aqueous urea solution by NIR absorption spectroscopy
    Pan, R. and Jeffries, J.B. and Dreier, T. and Schulz, C.
    Applied Physics B: Lasers and Optics 122 (2016)
    A multi-wavelength near-infrared (NIR) diode laser absorption sensor has been developed and demonstrated for real-time monitoring of the thickness, solute concentration, and temperature of thin films of urea–water solutions. The sensor monitors the transmittance of three near-infrared diode lasers through the thin liquid film. Film thickness, urea mass fraction, and liquid temperature were determined from measured transmittance ratios of suitable combinations of lasers. Available laser wavelengths were selected depending on the variation of the NIR absorption spectrum of the solution with temperature and solute concentration. The spectral database was measured by a Fourier transform infrared spectrometer in the range 5500–8000 cm−1 for urea solutions between 5 and 40 wt% and temperatures between 298 and 338 K. A prototype sensor was constructed, and the sensor concept was first validated with measurements using a calibration cell providing liquid layers of variable thickness (200–1500 μm), urea mass fraction (5–40 wt%) and temperature (298–318 K). Temporal variations of film thickness and urea concentration were captured during the constant-temperature evaporation of a liquid film deposited on an optically polished heated quartz flat. © Springer-Verlag Berlin Heidelberg 2016.
    view abstractdoi: 10.1007/s00340-015-6290-y
  • 2016 • 210 Silicon-based nanocomposites for thermoelectric application
    Schierning, G. and Stoetzel, J. and Chavez, R. and Kessler, V. and Hall, J. and Schmechel, R. and Schneider, T. and Petermann, N. and Wiggers, H. and Angst, S. and Wolf, D.E. and Stoib, B. and Greppmair, A. and Stutzmann, M. and B...
    Physica Status Solidi (A) Applications and Materials Science 213 497-514 (2016)
    Here we present the realization of efficient and sustainable silicon-based thermoelectric materials from nanoparticles. We employ a gas phase synthesis for the nanoparticles which is capable of producing doped silicon (Si) nanoparticles, doped alloy nanoparticles of silicon and germanium (Ge), SixGe1-x, and doped composites of Si nanoparticles with embedded metal silicide precipitation phases. Hence, the so-called "nanoparticle in alloy" approach, theoretically proposed in the literature, forms a guideline for the material development. For bulk samples, a current-activated pressure-assisted densification process of the nanoparticles was optimized in order to obtain the desired microstructure. For thin films, a laser annealing process was developed. Thermoelectric transport properties were characterized on nanocrystalline bulk samples and laser-sintered-thin films. Devices were produced from nanocrystalline bulk silicon in the form of p-n junction thermoelectric generators, and their electrical output data were measured up to hot side temperatures of 750°C. In order to get a deeper insight into thermoelectric properties and structure forming processes, a 3D-Onsager network model was developed. This model was extended further to study the p-n junction thermoelectric generator and understand the fundamental working principle of this novel device architecture. Gas phase synthesis of composite nanoparticles; nanocrystalline bulk with optimized composite microstructure; laser-annealed thin film. The authors fabricated thermoelectric nanomaterials from doped silicon and silicon and germanium alloy nanoparticles, as well as composites of Si nanoparticles with embedded metal silicide nanoparticles. Processing was performed applying a current-activated pressure-assisted densification process for bulk samples and a laser annealing process for thin film samples. Devices were produced in the form of pn junction thermoelectric generators. A 3D-Onsager network model was used to understand the fundamental working principle of this novel device architecture. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201532602
  • 2016 • 209 Tuning the Cell Adhesion on Biofunctionalized Nanoporous Organic Frameworks
    Schmitt, S. and Hümmer, J. and Kraus, S. and Welle, A. and Grosjean, S. and Hanke-Roos, M. and Rosenhahn, A. and Bräse, S. and Wöll, C. and Lee-Thedieck, C. and Tsotsalas, M.
    Advanced Functional Materials 26 8455-8462 (2016)
    The ability to control the structure and surface chemistry of biomaterials on a molecular level is crucial for optimizing their performance. Here, a novel type of nanoporous organic framework that is suited for the fabrication of thin films is described. These surface-grafted gels (SURGELs) are prepared and functionalized using two orthogonal, metal-free click chemistries. The SURGELs are shown to be cytocompatible and to efficiently mediate adhesion of osteoblast-like cells. This process can be further enhanced by surface modification. In addition, the use of light-triggered reactions in combination with photomasks allows a patterned functionalization of the substrates. The potential to vary and exactly adjust the parameters within the SURGEL polymer network (including porosity and exact network topology on the nanometer scale as well as addressable functional groups) combined with the ability to functionalize their surfaces with any clickable biomolecule of choice in any desired pattern allow the targeted design of novel SURGEL-based biomaterials for applications in nanomedicine, tissue engineering scaffolds, wound dressing,and medical implants. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201603054
  • 2016 • 208 Revealing the relationships between chemistry, topology and stiffness of ultrastrong Co-based metallic glass thin films: A combinatorial approach
    Schnabel, V. and Köhler, M. and Evertz, S. and Gamcova, J. and Bednarcik, J. and Music, D. and Raabe, D. and Schneider, J.M.
    Acta Materialia 107 213-219 (2016)
    An efficient way to study the relationship between chemical composition and mechanical properties of thin films is to utilize the combinatorial approach, where spatially resolved mechanical property measurements are conducted along a concentration gradient. However, for thin film glasses many properties including the mechanical response are affected by chemical topology. Here a novel method is introduced which enables spatially resolved short range order analysis along concentration gradients of combinatorially synthesized metallic glass thin films. For this purpose a CoZrTaB metallic glass film of 3 μm thickness is deposited on a polyimide foil, which is investigated by high energy X-ray diffraction in transmission mode. Through the correlative chemistry-topology-stiffness investigation, we observe that an increase in metalloid concentration from 26.4 to 32.7 at% and the associated formation of localized (hybridized) metal - metalloid bonds induce a 10% increase in stiffness. Concomitantly, along the same composition gradient, a metalloid-concentration-induced increase in first order metal - metal bond distances of 1% is observed, which infers itinerant (metallic) bond weakening. Hence, the metalloid concentration induced increase in hybridized bonding dominates the corresponding weakening of metallic bonds. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2016.01.060
  • 2016 • 207 Preparation of Organometal Halide Perovskite Photonic Crystal Films for Potential Optoelectronic Applications
    Schünemann, S. and Chen, K. and Brittman, S. and Garnett, E. and Tüysüz, H.
    ACS Applied Materials and Interfaces 8 25489-25495 (2016)
    Herein, a facile method for the preparation of organometal halide perovskite (OHP) thin films in photonic crystal morphology is presented. The OHP photonic crystal thin films with controllable porosity and thicknesses between 2 μm and 6 μm were prepared on glass, fluorine-doped tin oxide (FTO), and TiO2 substrates by using a colloidal crystal of polystyrene microspheres as a template to form an inverse opal structure. The composition of OHP could be straightforwardly tuned by varying the halide anions. The obtained OHP inverse opal films possess large ordered domains with a periodic change of the refractive index, which results in pronounced photonic stop bands in the visible light range. By changing the diameter of the polystyrene microspheres, the position of the photonic stop band can be tuned through the visible spectrum. This developed methodology can be used as blueprint for the synthesis of various OHP films that could eventually be used as more effective light harvesting materials for diverse applications. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b09227
  • 2016 • 206 Combining sensor and protective functionalities in ferromagnetic nanocomposite thin films for applications in harsh environments
    Seemann, K. and Leiste, H. and Stüber, M. and Krüger, K. and Brunken, H. and Ludwig, Al. and Thede, C. and Quandt, E.
    Advanced Engineering Materials 18 739-745 (2016)
    The present paper discusses the development of Fe48Co52/TiN, Fe32Co44Hf12N12/TiN, Fe-Co/Al-N multilayer, and Fe2B single layer films produced by magnetron sputtering processes. These films combine appropriate magnetic and wear resistant multifunctional properties for the employment as sensor components for monitoring the actual state of stress and/or temperature of cutting tools used in the metal processing industry. At this point, the ferromagnetic layers enable the sensor function, whereas the TiN or Al-N layers support mechanical features. Being exposed to stress and/or temperature, the change of polarization or permeability can be utilized as a response for reading-out the sensor component. The paper introduces the development of Fe48Co52/TiN, Fe32Co44Hf12N12/TiN, Fe-Co/Al-N multilayer, and Fe2B single layer films as sensor components for monitoring, e.g., the actual state of stress and/or temperature of cutting tools which are used in metal processing. The films are produced by magnetron sputtering processes. They ought to combine appropriate magnetic property changes and wear resistance. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201500474
  • 2016 • 205 3-Dimensional microstructural characterization of CdTe absorber layers from CdTe/CdS thin film solar cells
    Stechmann, G. and Zaefferer, S. and Konijnenberg, P. and Raabe, D. and Gretener, C. and Kranz, L. and Perrenoud, J. and Buecheler, S. and Tiwari, A.N.
    Solar Energy Materials and Solar Cells 151 66-80 (2016)
    The present work reports on a study on the microstructure and its evolution during processing of CdTe absorber layers from CdTe/CdS thin film solar cells grown by low-temperature processes in substrate configuration. Investigations were performed at different stages of the cell manufacturing, from deposition to the final functional solar cell, with the aim to understand the microstructure formation of the photoactive layer. To this end 3-dimensional microstructure characterization was performed using focused ion beam/electron backscatter diffraction tomography ("3D-EBSD") together with conventional 2D-EBSD. The analyses revealed strong microstructural and textural changes developing across the thickness of the absorber material, between the back contact and the p-n junction interfaces. Based on the 3-dimensional reconstruction of the CdTe thin film, a coherent growth model was proposed, emphasizing the microstructural continuity before and after a typical CdCl2-annealing activation treatment. One of the principal results is that the absorber layer is created by two concomitant processes, deposition and recrystallization, which led to different textures and microstructures. Further changes are the result of subsequent annealing treatments, favoring twinning and promoting well-defined texture components. The results open the possibility for a grain boundary engineering approach applied to the design of such cells. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.solmat.2016.02.023
  • 2016 • 204 Thin film synthesis and characterization of a chemically ordered magnetic nanolaminate (V,Mn)3GaC2
    Tao, Q. and Salikhov, R. and Mockute, A. and Lu, J. and Farle, M. and Wiedwald, U. and Rosen, J.
    APL Materials 4 (2016)
    We report on synthesis and characterization of a new magnetic nanolaminate (V,Mn)3GaC2, which is the first magnetic MAX phase of a 312 stoichiometry. Atomically resolved energy dispersive X-ray mapping of epitaxial thin films reveals a tendency of alternate chemical ordering between V and Mn, with atomic layers composed of primarily one element only. Magnetometry measurements reveal a ferromagnetic response between 50 K and 300 K, with indication of a magnetic ordering temperature well above room temperature. © 2016 Author(s).
    view abstractdoi: 10.1063/1.4961502
  • 2016 • 203 The detachment behavior of polycarbonate on thin films above the glass transition temperature
    Tillmann, W. and Hagen, L. and Hoffmann, F. and Dildrop, M. and Wibbeke, A. and Schöppner, V. and Resonnek, V. and Pohl, M. and Krumm, C. and Tiller, J.C. and Paulus, M. and Sternemann, C.
    Polymer Engineering and Science 56 786-797 (2016)
    When producing mono-axially stretched films made of amorphous polycarbonate, a self-reinforcement is generated due to the stretching process. This leads to an increase of the strength and stiffness. The mono-axial stretching process is conducted at temperatures above the glass transition temperature, whereas better mechanical properties are obtained at higher stretching temperatures. However, the film tends to adhere to the rolls, especially at temperatures from 10°C above the glass transition temperature. The rolls of the mono-axial stretching unit are made of an induction hardened and polished quenched and tempered steel 1.7225 – 42CrMo4. This work reports on the investigation of the detachment behavior of polycarbonate on different coatings as a function of the temperature and contact time. The main intention is to find a suitable coating on which the polycarbonate film adheres only slightly at temperatures clearly exceeding the glass transition temperature. POLYM. ENG. SCI., 56:786–797, 2016. © 2016 Society of Plastics Engineers. © 2016 Society of Plastics Engineers
    view abstractdoi: 10.1002/pen.24307
  • 2016 • 202 Tribological development of TiCN coatings by adjusting the flowing rate of reactive gases
    Tillmann, W. and Momeni, S.
    Journal of Physics and Chemistry of Solids 90 45-53 (2016)
    TiCN coatings were deposited by means of direct current magnetron sputtering of Ti targets in presence of N2 and C2H2 reactive gases. The microstructure, composition, mechanical and tribological properties of the deposited thin films were analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), nanoindentation, ball-on-disc, scratch test, and three dimensional (3D) optical microscopy. The obtained results presents a reproducible processing route for tailoring microstructure, mechanical and tribological behavior of TiCN coatings by controlling flowing rate of the reactive gases. © 2015 Elsevier Ltd.
    view abstractdoi: 10.1016/j.jpcs.2015.11.009
  • 2016 • 201 Magnetic surface domain imaging of uncapped epitaxial FeRh(001) thin films across the temperature-induced metamagnetic transition
    Zhou, X. and Matthes, F. and Bürgler, D.E. and Schneider, C.M.
    AIP Advances 6 (2016)
    The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001) thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA) at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001) surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh. © 2016 Author(s).
    view abstractdoi: 10.1063/1.4940758
  • 2016 • 200 Discriminating between surface and bulk recombination in organic solar cells by studying the thickness dependence of the open-circuit voltage
    Zonno, I. and Krogmeier, B. and Katte, V. and Lübke, D. and Martinez-Otero, A. and Kirchartz, T.
    Applied Physics Letters 109 (2016)
    In case of thin-film solar cells, it is often rather difficult to determine what the dominant recombination mechanism is. In particular, it is difficult to distinguish recombination at the interface between the absorber layer and the electrodes (typically called surface recombination) from recombination in the bulk of the absorber - or in case of organic solar cells at the internal donor-acceptor interfaces. Here, we suggest a method to distinguish surface and bulk recombination in thin-film solar cells based on the thickness dependence of the saturation current density, which we derive from the open-circuit voltage and the photocurrent at short circuit or reverse bias. By means of numerical simulations, we show that surface and bulk recombination currents scale differently with thickness assuming the material properties to be unchanged. We test our predictions on a range of organic solar cell data from our laboratory and from literature and show that in the field of organic photovoltaics the whole range of cases, from mostly surface limited to purely bulk limited, is observed. © 2016 Author(s).
    view abstractdoi: 10.1063/1.4966613
  • 2015 • 199 Distortion of Ultrathin Photocleavable Block Copolymer Films during Photocleavage and Nanopore Formation
    Altinpinar, S. and Zhao, H. and Ali, W. and Kappes, R.S. and Schuchardt, P. and Salehi, S. and Santoro, G. and Theato, P. and Roth, S.V. and Gutmann, J.S.
    Langmuir 31 8947-8952 (2015)
    Highly ordered block copolymer thin films have been studied extensively during the last years because they afford versatile self-assembled morphologies via a bottom-up approach. They promise to be used in applications such as polymeric membranes or templates for nanostructured materials. Among the block copolymer structures, perpendicular cylinders have received strong attention due to their ability to fabricate highly ordered nanopores and nanowires. Nanopores can be created from a thin block copolymer film upon the removal of one block by selective etching or by dissolution of one polymer block. Here we demonstrate the utilization of polystyrene-block-poly(ethylene oxide) diblock copolymer (PS-hν-PEO) with an ortho-nitrobenzyl ester (ONB) as the photocleavable block-linker to create highly ordered thin films. Removal of the PEO block by choosing an appropriate solvent upon photocleavage is expected to yield arrays of nanopores decorated with functional groups, thus lending itself to adsorption or filtration uses. While the feasibility of this approach has been demonstrated, it is crucial to understand the influence of removal conditions (i.e., efficiency of photocleavage as well as best washing solvent) and to evaluate changes in the surface topology and inner structure upon photocleavage. To this end, the time dependence evolution of the surface morphology of block copolymer thin films was studied using grazing-incidence small-angle X-ray scattering (GISAXS) technique in combination with scanning probe microscopy. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.5b00750
  • 2015 • 198 Thin-film composite membranes for organophilic nanofiltration based on photo-cross-linkable polyimide
    Behnke, S. and Ulbricht, M.
    Reactive and Functional Polymers 86 233-242 (2015)
    This work demonstrates that it is possible to prepare new, competitive thin-film composite (TFC) membranes with a polyolefin ultrafiltration membrane as support and with a non-porous photo-cross-linked polyimide as separation layer for organic solvent nanofiltration. The commercial polyimide Lenzing P84® was modified by a polymer-analogous reaction to introduce side groups with carbon-carbon double bonds to increase its photo-reactivity with respect to cross-linking. Polymer characterization revealed that this was successfully achieved at acceptable level of main chain scission. The higher reactivity of the photo-cross-linkable polyimide had been confirmed by comparison with the original polymer; i.e., shorter gelation times upon UV irradiation, higher suppression of swelling by solvents and complete stability in strong solvents for not cross-linked polyimide such as dimethylformamide (DMF) had been obtained. For films from unmodified and modified polyimide, the degree of swelling in various solvents could be adjusted by UV irradiation time. Photo-cross-linking of the original polyimide did not lead to stability in DMF. TFC membranes had been prepared by polymer solution casting on a polyethylene ultrafiltration membrane, UV irradiation of the liquid film and subsequent solvent evaporation. Polyimide barrier film thicknesses between 10 and 1 μm were obtained by variation of cast film thickness. Performance in organic solvent nanofiltration was analyzed by using hexane, toluene, isopropanol and DMF as well as two dyes with molar masses of ∼300 and ∼1000 g/mol. Permeances of TFC membranes from unmodified polyimide were low (< 0.1 L/hm2 bar) while rejections of up to 100% for the dye with ∼1000 g/mol could be achieved. TFC membranes from modified and photo-cross-linked polyimide had adjustable separation performance in DMF with a trade-off between permeance and selectivity, in the same range (e.g.: 0.3 L/hm2 bar and 97% rejection for the dye with ∼1000 g/mol) as a commercial conventional polyimide membrane tested in parallel. The established membrane preparation method is promising because by tuning the degree of cross-linking of the polymeric barrier layer, the membrane separation performance could be tailored within the same manufacturing process. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.reactfunctpolym.2014.09.027
  • 2015 • 197 New Au-Cu-Al thin film shape memory alloys with tunable functional properties and high thermal stability
    Buenconsejo, P.J.S. and Ludwig, Al.
    Acta Materialia 85 378-386 (2015)
    An Au-Cu-Al thin film materials library prepared by combinatorial sputter-deposition was characterized by high-throughput experimentation in order to identify and assess new shape memory alloys (SMAs) in this alloy system. Automated resistance measurements during thermal cycling between -20 and 250 °C revealed a wide composition range that undergoes reversible phase transformations with martensite transformation start temperatures, reverse transformation finish temperatures and transformation hysteresis ranging from -15 to 149 °C, 5 to 185 °C and 8 to 60 K, respectively. High-throughput X-ray diffraction analysis of the materials library confirmed that the phase-transforming compositions can be attributed to the existence of the β-AuCuAl parent phase and its martensite product. The formation of large amount of phases based on face-centered cubic (Au-Cu), Al-Cu and Al-Au is responsible for limiting the range of phase-transforming compositions. Selected alloys in this system show excellent thermal cyclic stability of the phase transformation. The functional properties of these alloys, combined with the inherent properties of Au-based alloys, i.e. aesthetic value, oxidation and corrosion resistance, makes them attractive as smart materials for a wide range of applications, including applications as SMAs for elevated temperatures in harsh environment. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2014.11.035
  • 2015 • 196 Three-Dimensional, Fibrous Lithium Iron Phosphate Structures Deposited by Magnetron Sputtering
    Bünting, A. and Uhlenbruck, S. and Sebold, D. and Buchkremer, H.P. and Vaßen, R.
    ACS Applied Materials and Interfaces 7 22594-22600 (2015)
    Crystalline, three-dimensional (3D) structured lithium iron phosphate (LiFePO4) thin films with additional carbon are fabricated by a radio frequency (RF) magnetron-sputtering process in a single step. The 3D structured thin films are obtained at deposition temperatures of 600 °C and deposition times longer than 60 min by using a conventional sputtering setup. In contrast to glancing angle deposition (GLAD) techniques, no tilting of the substrate is required. Thin films are characterized by X-ray diffraction (XRD), Raman spectrospcopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), and galvanostatic charging and discharging. The structured LiFePO4 + C thin films consist of fibers that grow perpendicular to the substrate surface. The fibers have diameters up to 500 nm and crystallize in the desired olivine structure. The 3D structured thin films have superior electrochemical properties compared with dense two-dimensional (2D) LiFePO4 thin films and are, hence, very promising for application in 3D microbatteries. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsami.5b07090
  • 2015 • 195 Effect of sol-gel reaction time on the morphology transition in mesoporous titania/PS-b-PEO composite films
    Cheng, Y.-J. and Zhou, S. and Wolkenhauer, M. and Bumbu, G.-G. and Lenz, S. and Memesa, M. and Nett, S. and Emmerling, S. and Steffen, W. and Roth, S.V. and Gutmann, J.S.
    Science of Advanced Materials 7 924-933 (2015)
    A morphology transition from the coexistence of spherical and worm-like mesopores to highly branched wormlike mesopores within the titania thin films has been realized by varying the sol-gel reaction time from 51 minutes to 50 hours in the four-component templating system of PS-b-PEO, 1,4-dioxane, concentrated HCl, and Titanium tetraisopropoxide (TTIP). The impact of sol-gel reaction time on the local structure, long range lateral structure, and vertical structure of the as-prepared, calcined, and UV degraded thin films, and structure change in solution have been systematically investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), grazing incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR), and dynamic light scattering (DLS) respectively. With the sol-gel reaction time up to 5 hours, the morphology does not change significantly. Both spherical and worm-like domains exist, which are converted to spherical and worm-like mesopores after calcination or UV degradation due to the removal of the PS block. However, with the sol-gel reaction time extended to 25 and 50 hours, highly branched worm-like domains appear. As a result, highly porous mesopores are formed by calcination or UV degradation. The GISAXS results prove that the local structure change revealed by AFM and SEM is representative over macroscopic scale. X-ray reflectivity results indicate that an additional thin layer exists beneath the mesoporous titania layer due to the presence of large amount of worm-like domains. Dynamic light scattering (DLS) studies imply that the morphology transition is due to the fusion process of the worm-like micelles in solution. © 2015 by American Scientific Publishers.
    view abstractdoi: 10.1166/sam.2015.1957
  • 2015 • 194 Insights into the structural, electronic, and magnetic properties of Fe2−xTixO3/Fe2O3 thin films with x = 0.44 grown on Al2O3 (0001)
    Dennenwaldt, T. and Lübbe, M. and Winklhofer, M. and Müller, A. and Döblinger, M. and Nabi, H.S. and Gandman, M. and Cohen-Hyams, T. and Kaplan, W.D. and Moritz, W. and Pentcheva, R. and Scheu, C.
    Journal of Materials Science 50 122-137 (2015)
    The interface between hematite (α-Fe2 IIIO3) and ilmenite (FeIITiO3), a weak ferrimagnet and an antiferromagnet, respectively, has been suggested to be strongly ferrimagnetic due to the formation of a mixed valence layer of Fe2+/Fe3+ (1:1 ratio) caused by compensation of charge mismatch at the chemically abrupt boundary. Here, we report for the first time direct experimental evidence for a chemically distinct layer emerging at heterointerfaces in the hematite—Ti-doped-hematite system. Using molecular beam epitaxy, we have grown thin films (~25 nm thickness) of α-Fe2O3 on α-Al2O3 (0001) substrates, which were capped with a ~25 nm thick Fe2−xTixO3 layer (x = 0.44). An additional 3 nm cap of α-Fe2O3 was deposited on top. The films were structurally characterized in situ with surface X-ray diffraction, which showed a partial low index orientation relationship between film and substrate in terms of the [0001] axis and revealed two predominant domains with (Formula presented.) one with (Formula presented.) and a twin domain with (Formula presented.). Electron energy loss spectroscopy profiles across the Fe2−xTixO3/Fe2O3 interface show that Fe2+/Fe3+ ratios peak right at the interface. This strongly suggests the formation of a chemically distinct interface layer, which might also be magnetically distinct as indicated by the observed magnetic enhancement in the Fe2−xTixO3/α-Fe2O3/Al2O3 system compared to the pure α-Fe2O3/Al2O3 system. © 2014, Springer Science+Business Media New York.
    view abstractdoi: 10.1007/s10853-014-8572-x
  • 2015 • 193 Temperature dependent low-field measurements of the magnetocaloric Δ T with sub-mK resolution in small volume and thin film samples
    Döntgen, J. and Rudolph, J. and Gottschall, T. and Gutfleisch, O. and Salomon, S. and Ludwig, Al. and Hägele, D.
    Applied Physics Letters 106 (2015)
    We present temperature dependent ΔT measurements of the magnetocaloric effect in a thin film sample of Gd, employing magnetomodulation and detection of thermal radiation. A bulk sample of the metamagnetic material LaFe11.05Co0.91Si1.04 shows a strong broadening of the ΔT peak for increasing field amplitudes between 4 and 45mT. Bulk Gd in comparison shows only a weak broadening. All investigated samples exhibit a clear quadratic dependence of ΔT on the external field Hext at the ΔT peak maximum, contrary to earlier predictions. An analytic expression is derived that interpolates between the Hext2-behavior at low and the well-known Hext2/3-behavior at high fields. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4906426
  • 2015 • 192 Interplay of strain and interdiffusion in Heusler alloy bilayers
    Dutta, B. and Hickel, T. and Neugebauer, J. and Behler, C. and Fähler, S. and Behler, A. and Waske, A. and Teichert, N. and Schmalhorst, J.-M. and Hütten, A.
    Physica Status Solidi - Rapid Research Letters 9 321-325 (2015)
    Combining conventional and inverse magnetocaloric materials promises to enhance solid state refrigeration. As a first step here we present epitaxial Ni-Mn-Ga/Ni-Mn-Sn bilayer films. We examine the dependence of the lateral and normal lattice constants on the deposition sequence by combining experimental and ab initio techniques. Structural properties are determined with X-ray diffraction as well as highresolution transmission electron microscopy, while ab initio calculations explain the interplay of strain, local relaxations and the interdiffusion of atoms. The latter is confirmed by Auger electron spectroscopy and is expected to have a noticeable impact on the functional properties of the Heusler materials. ( © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssr.201510070
  • 2015 • 191 Spin-resolved low-energy and hard x-ray photoelectron spectroscopy of off-stoichiometric Co2MnSi Heusler thin films exhibiting a record TMR
    Fetzer, R. and Ouardi, S. and Honda, Y. and Liu, H.-X. and Chadov, S. and Balke, B. and Ueda, S. and Suzuki, M. and Uemura, T. and Yamamoto, M. and Aeschlimann, M. and Cinchetti, M. and Fecher, G.H. and Felser, C.
    48 (2015)
    Half-metallic Co<inf>2</inf>MnSi-based Heusler compounds have attracted attention because they yield very high tunnelling magnetoresistance (TMR) ratios. Record TMR ratios of 1995% (at 4.2 K) are obtained from off-stoichiometric Co<inf>2</inf>MnSi-based magnetic tunnel junctions. This work reports on a combination of band structure calculations and spin-resolved and photon-polarisation-dependent photoelectron spectroscopy for off-stoichiometric Heusler thin films with the composition Co<inf>2</inf>Mn<inf>1.30</inf>Si<inf>0.84</inf>. Co and Mn are probed by magnetic dichroism in angle-resolved photoelectron spectroscopy at the 2p core level. In contrast to the delocalised Co 3d states, a pronounced localisation of the Mn 3d states is deduced from the corresponding 2p core level spectra. The valence states are investigated by linear dichroism using both hard x-ray and very-low-photon-energy excitation. When a very low photon energy is used for excitation, the valence bands exhibit a spin polarisation of about 30% at the Fermi energy. First principles calculations reveal that the low spin polarisation might be caused by a spin-flip process in the photoelectron final states. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/48/16/164002
  • 2015 • 190 Microscopic analysis of the composition driven spin-reorientation transition in NixPd1-x/Cu(001)
    Gottlob, D.M. and Doğanay, H. and Nickel, F. and Cramm, S. and Krug, I.P. and Nemšák, S. and Schneider, C.M.
    Ultramicroscopy 159 503-507 (2015)
    The spin-reorientation transition (SRT) in epitaxial NixPd1-x/Cu(001) is studied by photoemission microscopy utilizing the X-ray magnetic circular dichroism effect at the Ni L2,3 edge. In a composition/thickness wedged geometry, a composition driven SRT could be observed between 37ML and 60ML, and 0 and 38% of Pd. Microspectroscopy in combination with azimuthal sample rotation confirms a magnetization preference changing from the [001] to an in-plane easy axis. At this increased thickness, the domain patterns arrange comparable to SRTs in ultrathin films. The images document domains equivalent to a canted state SRT, at which an additional effect of in-plane anisotropies could be identified. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2015.05.022
  • 2015 • 189 Nanostructure and mechanical behavior of metastable Cu-Cr thin films grown by molecular beam epitaxy
    Harzer, T.P. and Djaziri, S. and Raghavan, R. and Dehm, G.
    Acta Materialia 83 318-332 (2015)
    Metastable binary Cu-Cr alloys with nominal film thicknesses of 300 nm and chemical compositions in the range of 4-93 at.% Cr were synthesized via co-evaporation using molecular beam epitaxy. All films were grown onto Si (1 0 0) substrates at deposition rates of ∼0.05 nm s-1. The film microstructures were studied by using transmission electron microscopy and X-ray diffraction. The mechanical properties were investigated by the nanoindentation technique. Depending on the chemical composition, three types of thin film microstructures are observed, which all exhibit tensile residual stresses. For a Cr concentration of 4 at.% a single-phase face-centered cubic (fcc) film was formed, whereas single-phase body-centered cubic (bcc) films were observed for Cr concentrations ≥ 33 at.%. In the case of a Cu85Cr15 film, a two-phase fcc and bcc structure is formed. An increase of the atomic fraction of Cr induces a significant refinement of grain sizes, from ∼100 nm for a Cu96Cr4 alloy to ∼30 nm in the case of a Cu20Cr80 alloy. Consequently, the hardness of the alloy films increased from 5.5 to 11.8 GPa. In addition, the formation of supersaturated solid solutions of Cr in single-phase fcc Cu films and Cu in single-phase bcc films was observed. Predictions of existing models of solid solution and grain boundary strengthening were evaluated and correlated with the mechanical properties of the films with respect to film compositions and grain sizes. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2014.10.013
  • 2015 • 188 Influence of initial microstructure on thermomechanical fatigue behavior of Cu films on substrates
    Heinz, W. and Robl, W. and Dehm, G.
    Microelectronic Engineering 137 5-10 (2015)
    During a switch event in a power semiconductor device temperature changes of up to 300 K can occur in the Cu layer. Repeated switching operations causes cyclic thermal cycling which may finally lead to thermomechanical fatigue with severe microstructural changes. In this study, the influence of the starting microstructure and film thickness (600 nm and 5000 nm) on thermomechanical fatigue was investigated for epitaxial and polycrystalline Cu films for up to 1000 thermal cycles. Severe surface roughening and a texture change (crystal rotation) are detected during thermal cycling for the polycrystalline Cu films, while the epitaxial films maintain their microstructure. Controlling the initial microstructure of a Cu layer in a device exposed to cyclic thermomechanical straining is a route to delay surface damage. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.mee.2014.10.024
  • 2015 • 187 Nanocellulose-Templated Porous Titania Scaffolds Incorporating Presynthesized Titania Nanocrystals
    Ivanova, A. and Fravventura, M.C. and Fattakhova-Rohlfing, D. and Rathouský, J. and Movsesyan, L. and Ganter, P. and Savenije, T.J. and Bein, T.
    Chemistry of Materials 27 6205-6212 (2015)
    Nanocrystalline cellulose (NCC) is an abundant biogenic nanomaterial with unique properties that enables the efficient synthesis of mesoporous crystalline titania. We significantly enhance the photocatalytic activity of titania thin films by introducing solvothermally synthesized preformed anatase nanoparticles into a sol-gel based biotemplated titania scaffold. The resulting dual source titania thin films containing different amounts of preformed crystalline species were investigated by time-resolved microwave conductivity (TRMC) measurements and tested in the photocatalytic conversion of 4-chlorophenol. The gradual addition of preformed nanoparticles leads to a consistent increase of the mean size of titania crystalline domains, whereas the porosity of the composite is well-preserved due to the shape-persistent nature of the NCC template. Microwave conductivity studies establish increased photoconductivity of the films containing preformed anatase nanoparticles in comparison to that of films made without the nanoparticles. The synergistic features of the dual source titania, namely the improved crystalline properties brought by the preformed nanocrystals in combination with the high surface area provided by the NCC-templated sol-gel titania, result in a very high photocatalytic activity of the films in the photocatalytic decomposition of 4-chlorophenol. In quantitative terms, the dual source titania films prepared with 75% nanoparticles exhibit a first order degradation rate constant of 0.53 h-1 (1.47 × 10-4 sec-1), which strongly outperforms the activity of commercial P90 nanopowder showing a rate constant of 0.17 h-1 (0.47 × 10-4 sec-1) under the same conditions. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.5b00770
  • 2015 • 186 High-Quality Solution-Processed Silicon Oxide Gate Dielectric Applied on Indium Oxide Based Thin-Film Transistors
    Jaehnike, F. and Pham, D.V. and Anselmann, R. and Bock, C. and Kunze, U.
    ACS Applied Materials and Interfaces 7 14011-14017 (2015)
    A silicon oxide gate dielectric was synthesized by a facile sol-gel reaction and applied to solution-processed indium oxide based thin-film transistors (TFTs). The SiO<inf>x</inf> sol-gel was spin-coated on highly doped silicon substrates and converted to a dense dielectric film with a smooth surface at a maximum processing temperature of T = 350 °C. The synthesis was systematically improved, so that the solution-processed silicon oxide finally achieved comparable break downfield strength (7 MV/cm) and leakage current densities (<10 nA/cm2 at 1 MV/cm) to thermally grown silicon dioxide (SiO<inf>2</inf>). The good quality of the dielectric layer was successfully proven in bottom-gate, bottom-contact metal oxide TFTs and compared to reference TFTs with thermally grown SiO<inf>2</inf>. Both transistor types have field-effect mobility values as high as 28 cm2/(Vs) with an on/off current ratio of 108, subthreshold swings of 0.30 and 0.37 V/dec, respectively, and a threshold voltage close to zero. The good device performance could be attributed to the smooth dielectric/semiconductor interface and low interface trap density. Thus, the sol-gel-derived SiO<inf>2</inf> is a promising candidate for a high-quality dielectric layer on many substrates and high-performance large-area applications. (Graph Presented). © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsami.5b03105
  • 2015 • 185 Metal-organic CVD of Y2O3 Thin Films using Yttrium tris-amidinates
    Karle, S. and Dang, V.-S. and Prenzel, M. and Rogalla, D. and Becker, H.-W. and Devi, A.
    Chemical Vapor Deposition 21 335-342 (2015)
    Thin films of Y2O3 are deposited on Si(100) and Al2O3 (0001) substrates via metal-organic (MO)CVD for the first time using two closely related yttrium tris-amidinate compounds as precursors in the presence of oxygen in the temperature range 400-700 °C. The structural, morphological, and compositional features of the films are investigated in detail. At deposition temperatures of 500 °C and higher both the precursors yield polycrystalline Y2O3 thin films in the cubic phase. The compositional analysis revealed the formation of nearly stoichiometric Y2O3. The optical band gaps are estimated using UV-Vis spectroscopy. Preliminary electrical measurements are performed in the form of a metal oxide semiconductor (MOS) structure of Al/Y2O3/p-Si/Ag. Leakage currents and dielectric constants are also determined. Y2O3 thin films are grown by MOCVD at 400-700 °C using yttrium amidinate presursors in the presence of oxygen. The films, which are polycrystalline in case of deposition temperatures &gt; 400 °C, are dense and exhibit good purity and homogeneity. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cvde.201507189
  • 2015 • 184 Redox-stable high-performance thin-film solid oxide fuel cell
    Keuter, T. and Roehrens, D. and Menzler, N.H. and Vaßen, R.
    ECS Transactions 68 2001-2009 (2015)
    In this work, a mechanically redox-stable SOFC with a 1 μm thin-film sol-gel electrolyte is presented. With this electrolyte a power output larger than 1.25 W/cm2 at 0.7 V and an operating temperature of 600°C could be demonstrated. Half cells were re-oxidized in excess air, in order to test the redox stability of these SOFCs. No cracks were found in the sol-gel electrolyte after re-oxidation for 4 hours at 600°C and 30 minutes at 800°C, respectively. Due to the fact, that the energy release rate is proportional to the thickness of the thin-film, a thinner film is more stable against cracking than a thicker film at constant tensile stresses. The SOFC with the thin-film sol-gel electrolyte can be considered as stable against re-oxidation, because the long re-oxidation time of 4 hours at an operating temperature of 600°C is unlikely to happen under real conditions. © The Electrochemical Society.
    view abstractdoi: 10.1149/06801.2001ecst
  • 2015 • 183 MOCVD of TiO2 thin films from a modified titanium alkoxide precursor
    Kim, S.J. and Dang, V.-S. and Xu, K. and Barreca, D. and Maccato, C. and Carraro, G. and Bhakta, R.K. and Winter, M. and Becker, H.-W. and Rogalla, D. and Sada, C. and Fischer, R.A. and Devi, A.
    Physica Status Solidi (A) Applications and Materials Science 212 1563-1570 (2015)
    A new titanium precursor, [Ti(OPri)<inf>2</inf>(deacam)<inf>2</inf>] (deacam = N,N-diethylacetoacetamide), was developed by the reaction of the parent Ti alkoxide with the β-ketoamide. The compound, obtained as a monomeric six-coordinated complex, was used in metal organic chemical vapor deposition (MOCVD) of TiO<inf>2</inf> both as a single source precursor (SSP) and in the presence of oxygen. The high thermal stability of [Ti(OPri)<inf>2</inf>(deacam)<inf>2</inf>] enabled the fabrication of TiO<inf>2</inf> films over a wide temperature range, with steady growth rates between 500 and 800 °C. The microstructure of the obtained systems was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, whereas atomic force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) measurements were performed to investigate the surface morphology and nanoorganization. Film composition was investigated by complementary techniques like Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The electrical properties of the layers were investigated by performing capacitance voltage (C-V) and leakage current measurements. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/pssa.201532271
  • 2015 • 182 Antibacterial activity of microstructured Ag/Au sacrificial anode thin films
    Köller, M. and Sengstock, C. and Motemani, Y. and Khare, C. and Buenconsejo, P.J.S. and Geukes, J. and Schildhauer, T.A. and Ludwig, Al.
    Materials Science and Engineering C 46 276-280 (2015)
    Ten different Ag dot arrays (16 to 625 microstructured dots per square mm) were fabricated on a continuous Au thin film and for comparison also on Ti film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Escherichia coli and Staphylococcus aureus were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards both bacterial strains was induced by Ag dot arrays on fabricated Au thin film (sacrificial anode system for Ag), due to the release of Ag ions from dissolution of Ag dots in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag) which remained intact to the original dot shape. The required number of Ag dots on gold film to achieve complete bactericidal effects for both bacterial strains was seven times lower than that observed with Ag dot arrays on Ti film. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.msec.2014.10.058
  • 2015 • 181 X-ray photoelectron spectroscopy investigations of the surface reaction layer and its effects on the transformation properties of nanoscale Ti51Ni38Cu11 shape memory thin films
    König, D. and Naujoks, D. and De Los Arcos, T. and Grosse-Kreul, S. and Ludwig, Al.
    Advanced Engineering Materials 17 669-673 (2015)
    The depth-dependent chemical constitution of Ti<inf>51</inf>Ni<inf>38</inf>Cu<inf>11</inf> thin films of different total film thickness from 400 to 50-nm was characterized using X-ray photoelectron spectroscopy (XPS). It was analyzed how reaction layers, which form on the surface of the film significantly change the chemical composition of the transforming phase, which leads in turn to altered phase transformation properties. For thinner films, the deviation from the nominal chemical composition increases. For a film thickness of 50-nm, a Ti loss of ≈9-at% is observed. The Ni content is increased by ≈5-at%, whereas the Cu content stays relatively constant for films of different thickness. The results are summarized in a layer model, which supports designing nanoscale shape memory thin films. Ti<inf>51</inf>Ni<inf>38</inf>Cu<inf>11</inf> thin films of different film thickness are investigated regarding the influence of the reaction layers on the chemical composition of the transforming phase and the corresponding functional properties. A model is proposed describing the different reaction layers on the surface of the thin film and at the substrate/thin film interface. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201400317
  • 2015 • 180 High-Throughput Investigation of the Oxidation and Phase Constitution of Thin-Film Ni-Al-Cr Materials Libraries
    König, D. and Eberling, C. and Kieschnick, M. and Virtanen, S. and Ludwig, Al.
    Advanced Engineering Materials 17 1365-1373 (2015)
    Thin-film materials libraries of the intermetallic model system Ni-Al-Cr were fabricated and their oxidation behavior was studied by compositional, optical, electrical, and structural high-throughput characterization methods. The study reveals the compositional regions of the binary and ternary compositions which withstand longest to annealing in air (up to 700 C), and are, therefore, resistant to oxidation and delamination under these conditions. A complete ternary thin-film phase diagram for the Ni-Al-Cr system in its state after 9 h annealing in air at 500 C was determined. Optical high-throughput characterization is shown to be valid for rapid identification of oxidizing phases. Generally, the initially metallic phases show different oxidation behavior in air. We find that the ternary compositions are more resistant to oxidation than the binary phases. Compositions around Ni<inf>25</inf>Al<inf>12.5</inf>Cr<inf>62.5</inf> were found to show very good oxidation resistance. These results were supported by additional information from corresponding electrical and optical property investigations. The presented high-throughput approach is generic for the efficient study of multinary thin-film materials in harsh environments. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201500023
  • 2015 • 179 Wet Nanoindentation of the Solid Electrolyte Interphase on Thin Film Si Electrodes
    Kuznetsov, V. and Zinn, A.-H. and Zampardi, G. and Borhani-Haghighi, S. and La Mantia, F. and Ludwig, Al. and Schuhmann, W. and Ventosa, E.
    ACS Applied Materials and Interfaces 7 23554-23563 (2015)
    The solid electrolyte interphase (SEI) film formed at the surface of negative electrodes strongly affects the performance of a Li-ion battery. The mechanical properties of the SEI are of special importance for Si electrodes due to the large volumetric changes of Si upon (de)insertion of Li ions. This manuscript reports the careful determination of the Young's modulus of the SEI formed on a sputtered Si electrode using wet atomic force microscopy (AFM)-nanoindentation. Several key parameters in the determination of the Young's modulus are considered and discussed, e.g., wetness and roughness-thickness ratio of the film and the shape of a nanoindenter. The values of the Young's modulus were determined to be 0.5-10 MPa under the investigated conditions which are in the lower range of those previously reported, i.e., 1 MPa to 10 GPa, pointing out the importance of the conditions of its determination. After multiple electrochemical cycles, the polymeric deposits formed on the surface of the SEI are revealed, by force-volume mapping in liquid using colloidal probes, to extend up to 300 nm into bulk solution. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acsami.5b06700
  • 2015 • 178 Copper-based nanostructured coatings for low-temperature brazing applications
    Lehmert, B. and Janczak-Rusch, J. and Pigozzi, G. and Zuraw, P. and La Mattina, F. and Wojarski, L. and Tillmann, W. and Jeurgens, L.P.H.
    Materials Transactions 56 1015-1018 (2015)
    This feasibility study demonstrates the possibility to apply nanostructured filler materials for novel low-temperature brazing applications by exploiting the size-dependent melting behavior of metals and alloys when confined to the nano-scale regime. As an example, a copper-based nanostructured brazing filler is presented, which allows metal brazing of coated Ti-6Al-4V components at 750°C, much below the bulk melting point of copper (1083°C). The copper-based nanostructured brazing fillers can be produced in the form of coatings and free-standing brazing foils. The nano-confinement of Cu is abrogated after brazing and, consequently, the brazed joints can be operated well above their reduced brazing temperatures. © 2015 The Japan Institute of Metals and Materials.
    view abstractdoi: 10.2320/matertrans.MI201419
  • 2015 • 177 The influence of a brittle Cr interlayer on the deformation behavior of thin Cu films on flexible substrates: Experiment and model
    Marx, V.M. and Toth, F. and Wiesinger, A. and Berger, J. and Kirchlechner, C. and Cordill, M.J. and Fischer, F.D. and Rammerstorfer, F.G. and Dehm, G.
    Acta Materialia 89 278-289 (2015)
    Thin metal films deposited on polymer substrates are used in flexible electronic devices such as flexible displays or printed memories. They are often fabricated as complicated multilayer structures. Understanding the mechanical behavior of the interface between the metal film and the substrate as well as the process of crack formation under global tension is important for producing reliable devices. In the present work, the deformation behavior of copper films (50-200 nm thick), bonded to polyimide directly or via a 10 nm chromium interlayer, is investigated by experimental analysis and computational simulations. The influence of the various copper film thicknesses and the usage of a brittle interlayer on the crack density as well as on the stress magnitude in the copper after saturation of the cracking process are studied with in situ tensile tests in a synchrotron and under an atomic force microscope. From the computational point of view, the evolution of the crack pattern is modeled as a stochastic process via finite element based cohesive zone simulations. Both, experiments and simulations show that the chromium interlayer dominates the deformation behavior. The interlayer forms cracks that induce a stress concentration in the overlying copper film. This behavior is more pronounced in the 50 nm than in the 200 nm copper films. © Acta Materialia Inc. Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.actamat.2015.01.047
  • 2015 • 176 Adhesion measurement of a buried Cr interlayer on polyimide
    Marx, V.M. and Kirchlechner, C. and Zizak, I. and Cordill, M.J. and Dehm, G.
    Philosophical Magazine 95 1982-1991 (2015)
    A fundamental knowledge and understanding of the adhesion behaviour of metal-polymer systems is important as interface failure leads to a complete breakdown of flexible devices. A combination of in situ atomic force microscopy for studying topological changes and in situ synchrotron based stress measurements both during film tensile testing were used to estimate the adhesion energy of a thin bilayer film. The film systems consisted of 50-200 nm Cu with a 10 nm Cr adhesion layer on 50 μm thick polyimide. If the Cu film thickness is decreased to 50 nm the Cr interlayer starts dominating the system behaviour. An apparent transition from plastic to predominantly brittle deformation behaviour of the Cu can be observed. Then, compressive stresses in the transverse direction are high enough to cause delamination and buckling of the Cr interlayer from the substrate. This opens a new route to induce buckling of a brittle interlayer between a ductile film and a compliant substrate which is used to determine the interfacial adhesion energy. © 2015 Taylor & Francis.
    view abstractdoi: 10.1080/14786435.2014.920543
  • 2015 • 175 High-throughput screening of thin-film semiconductor material libraries II: Characterization of Fe-W-O libraries
    Meyer, R. and Sliozberg, K. and Khare, C. and Schuhmann, W. and Ludwig, Al.
    ChemSusChem 8 1279-1285 (2015)
    Metal oxides are promising materials for solar water splitting. To identify suitable materials within the ternary system Fe-W-O, thin-film material libraries with combined thickness and compositional gradients were synthesized by combinatorial reactive magnetron sputtering. These libraries (>1000 different samples) were investigated by means of structural and functional high-throughput characterization techniques to establish correlations between composition, crystallinity, morphology, thickness, and photocurrent density in the compositional range between (Fe<inf>6</inf>W<inf>94</inf>)O<inf>x</inf> and (Fe<inf>61</inf>W<inf>39</inf>)O<inf>x</inf>. In addition to the well-known phase WO<inf>3</inf>, the binary phase W<inf>5</inf>O<inf>14</inf> and the ternary phase Fe<inf>2</inf>O<inf>6</inf>W show enhanced photoelectrochemical activity. The highest photocurrent density of 65 μA cm-2 was achieved for the composition (Fe<inf>15</inf>W<inf>85</inf>)O<inf>x</inf>, which contains the W<inf>5</inf>O<inf>14</inf> phase and has a thickness of 1060 nm. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cssc.201402918
  • 2015 • 174 Microstructure, Shape Memory Effect and Functional Stability of Ti67Ta33 Thin Films
    Motemani, Y. and Kadletz, P.M. and Maier, B. and Rynko, R. and Somsen, C. and Paulsen, A. and Frenzel, J. and Schmahl, W.W. and Eggeler, G. and Ludwig, Al.
    Advanced Engineering Materials 17 1425-1433 (2015)
    Ti-Ta based alloys are an interesting class of high-temperature shape memory materials. When fabricated as thin films, they can be used as high-temperature micro-actuators with operation temperatures exceeding 100 °C. In this study, microstructure, shape memory effect and thermal cycling stability of room-temperature sputter deposited Ti<inf>67</inf>Ta<inf>33</inf> thin films are investigated. A disordered α martensite (orthorhombic) phase is formed in the as-deposited Ti<inf>67</inf>Ta<inf>33</inf> films. The films show a columnar morphology with the columns being oriented perpendicular to the substrate surface. They are approximately 200 nm in width. XRD texture analysis reveals a martensite fiber texture with {120} and {102} fiber axes. The XRD results are confirmed by TEM analysis, which also shows columnar grains with long axes perpendicular to the {120} and {102} planes of α martensite. The shape memory effect is analyzed in the temperature range of -10 to 240 °C using the cantilever deflection method, with special emphasis placed on cyclic stability. Ti<inf>67</inf>Ta<inf>33</inf> thin films undergo a forward martensitic transformation at M<inf>s</inf> ≈ 165 °C, with a stress relaxation of approximately 33 MPa during the transformation. The actuation response of the film actuators degrades significantly during thermal cycling. TEM analysis shows that this degradation is related to the formation of nanoscale ω precipitates (5-13 nm) which form above the austenite finish temperature. These precipitates suppress the martensitic transformation, as they act as obstacles for the growth of martensite variants. Ti-Ta thin films can be used as high-temperature micro-actuators. In this study, microstructure, shape memory effect, and functional stability of room-temperature sputter deposited Ti<inf>67</inf>Ta<inf>33</inf> thin films are systematically investigated. The actuation response of the film actuators degrades significantly during thermal cycling. This degradation is related to the formation of nanoscale ω precipitates (5-13 nm) which form above the austenite finish temperature. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201400576
  • 2015 • 173 Exploration of ternary subsystems of superalloys by high-throughput thin film experimentation: Optical and electrical data of the Co-Al-W system
    Naujoks, D. and Koenig, D. and Ludwig, Al.
    Materials Research Society Symposium Proceedings 1760 145-150 (2015)
    The complete ternary system Co-Al-W was fabricated as a thin film materials library by combinatorial magnetron sputtering. The materials library was investigated using high-throughput characterization methods such as optical measurements as well as automated resistance screening. The obtained data indicate possible phase regions and compositional regions which show early surface oxidation. The demonstrated approach illustrates that using high-throughput measurement methods provides a fast access to data of relatively unexplored materials systems. The gained data provides a valuable basis for further in-depth studies of the investigated materials systems. © 2015 Materials Research Society.
    view abstractdoi: 10.1557/opl.2015.56
  • 2015 • 172 Transition from shear to stress-assisted diffusion of copper-chromium nanolayered thin films at elevated temperatures
    Raghavan, R. and Wheeler, J.M. and Harzer, T.P. and Chawla, V. and Djaziri, S. and Thomas, K. and Philippi, B. and Kirchlechner, C. and Jaya, B.N. and Wehrs, J. and Michler, J. and Dehm, G.
    Acta Materialia 100 73-80 (2015)
    The mechanical behavior of Cu-Cr nanolayered films and an alloy film of nominal composition Cu<inf>20</inf>Cr<inf>80</inf> at.% was studied by microcompression testing at temperatures from 25 °C to 300 °C. Comparing nanolayered films, plastic deformation and failure occurred at consistently higher stress levels in the film with the smaller layer thicknesses. Plasticity in the nanolayered films always initiated in the softer Cu layers followed by a finite strain-hardening response in the stress-strain curves. Failure indicated by a strain-softening response following the higher peak strength due to shearing and tearing at columnar boundaries of Cr was observed in the nanolayered films at 25 °C and 100 °C. A transition from shearing and crack formation across the Cu-Cr interfaces leading to anomalous grain growth or beading of the nanocrystalline Cu layers was observed at elevated temperatures of 200 °C and 300 °C. On the other hand, the Cu<inf>20</inf>Cr<inf>80</inf> at.% alloy film exhibited failure by columnar buckling consistently at elevated temperatures, but shearing promoted by buckling at the highest strengths among the films at ambient temperature. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2015.08.016
  • 2015 • 171 Comparing small scale plasticity of copper-chromium nanolayered and alloyed thin films at elevated temperatures
    Raghavan, R. and Harzer, T.P. and Chawla, V. and Djaziri, S. and Phillipi, B. and Wehrs, J. and Wheeler, J.M. and Michler, J. and Dehm, G.
    Acta Materialia 93 175-186 (2015)
    Abstract The yield strengths and deformation mechanisms of Cu-Cr nanolayered and alloyed thin films were studied by microcompression testing at elevated temperatures. The mechanical response of the films with alternating layers of Cu and Cr with sub-100 nm interlayer thicknesses and alloyed films of the same average composition was compared to determine the role of the interfaces on deformation. Higher resistance to plastic flow at elevated temperatures was exhibited by the nanolayered films with smaller interlayer thickness among the layered films, while the alloyed film revealed an anomalous increase in strength with temperature exhibiting a deformation mechanism similar to the pure Cr film. © 2015 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2015.04.008
  • 2015 • 170 Combinatorial synthesis and high-throughput characterization of the thin film materials system Co-Mn-Ge: Composition, structure, and magnetic properties
    Salomon, S. and Hamann, S. and Decker, P. and Savan, A. and Meshi, L. and Ludwig, Al.
    Physica Status Solidi (A) Applications and Materials Science 212 1969-1974 (2015)
    Co-Mn-Ge is a system of interest for magnetocaloric applications as a solid state magnetic refrigerant. A thin film materials library covering a large fraction of the Co-Mn-Ge ternary composition space was fabricated by sputter deposition. After deposition, it was annealed at 600°C for 3 h and quenched subsequently. An energy-dispersive X-ray spectroscopy and X-ray diffraction-based cluster analysis revealed the regions of existence for the CoMnGe and the Co<inf>2</inf>MnGe single phase areas. Furthermore, high intensity diffraction peaks revealed the presence of the hexagonal (Co, Mn)<inf>7</inf>Ge<inf>6</inf> phase in a region that also featured the CoMnGe phase. In this region, a non-linear, symmetric, and hysteretic shift of the (200) diffraction peak of the (Co, Mn)<inf>7</inf>Ge<inf>6</inf> phase was observed by temperature-dependent X-ray diffraction for Co<inf>23</inf>Mn<inf>33</inf>Ge<inf>44</inf>, indicating a structural phase transition taking place between 350 and 375 K upon heating and 325 and 300 K upon cooling. This coincides with a magnetic transition near 325 K from the ferromagnetic to the paramagnetic state. However, no magnetostructural coupling was identified in the temperature range from 330 to 300 K upon cooling. Magnetostriction and an undetected structural transition of the CoMnGe phase were ruled out as probable causes for the non-linear shifts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201532075
  • 2015 • 169 Thin-film SOI PIN-diode leakage current dependence on back-gate-potential and HCI traps
    Schmidt, A. and Dreiner, S. and Vogt, H. and Paschen, U.
    European Solid-State Device Research Conference 2015-November 290-293 (2015)
    We investigated the leakage current of thin film silicon-on-insulator (SOI) pin-diodes in dependence of the back-gate potential and hot carrier induced traps. Leakage current of virgin and hot-carrier stressed diodes was measured at distinct back-gate potentials. TCAD simulations were used to determine the mechanisms of leakage current generation at specific back-gate potentials. Traps were introduced to study the impact of hot-carrier stress on the leakage current. Location, polarity and density of traps were considered. For a virgin device tunneling is predominant in inversion and accumulation. In full depletion surface generation dominates the leakage behavior. Surface and oxide traps shift the leakage current and alter its mechanism with increasing density, i.e. stress time. In inversion trap generation dominates at the top SOI interface. In depletion top and bottom interface traps are generated. © 2015 IEEE.
    view abstractdoi: 10.1109/ESSDERC.2015.7324771
  • 2015 • 168 Covalently bonded compounds of heavy group 15/16 elements - Synthesis, structure and potential application in material sciences
    Schulz, S.
    Coordination Chemistry Reviews 297-298 49-76 (2015)
    Our understanding on the nature of weak intermolecular metal-metal interactions as well as of multiple bonding in group 15/16 chemistry, in particular of compounds containing the heaviest elements of both groups - Sb, Bi, Se, and Te - is still scarce. These types of interactions are particularly important for the chemical and physical properties of such main group element compounds. For instance, the formation and disruption of weak intermolecular metal-metal interactions are the origin of the so-called thermochroism. The structural characterization of compounds containing sterically less demanding organic substituents is therefore of particular interest, since the capability of small substituents to kinetically stabilize the respective metal centers - and hence to suppress intermolecular interactions - is expected to be rather less pronounced. We will herein summarize the most recent results reported for the synthesis and structural characterization of group 15/16 compounds containing a direct (polar-covalent) element-element bond including compounds containing a terminal, formally double bond. In addition, the capability of selected compounds to serve as single-source precursor for the synthesis of the corresponding nanomaterials, in particular Sb<inf>2</inf>Te<inf>3</inf> and Bi<inf>2</inf>Te<inf>3</inf>, by using wet chemical methods as well as gas phase approaches such as metal organic chemical vapor deposition (MOCVD) processes will be demonstrated. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.ccr.2014.11.003
  • 2015 • 167 Detection of Cu2Zn5SnSe8 and Cu2Zn6SnSe9 phases in co-evaporated Cu2ZnSnSe4 thin-films
    Schwarz, T. and Marques, M.A.L. and Botti, S. and Mousel, M. and Redinger, A. and Siebentritt, S. and Cojocaru-Mirédin, O. and Raabe, D. and Choi, P.-P.
    Applied Physics Letters 107 (2015)
    Cu2ZnSnSe4 thin-films for photovoltaic applications are investigated using combined atom probe tomography and ab initio density functional theory. The atom probe studies reveal nano-sized grains of Cu2Zn5SnSe8 and Cu2Zn6SnSe9 composition, which cannot be assigned to any known phase reported in the literature. Both phases are considered to be metastable, as density functional theory calculations yield positive energy differences with respect to the decomposition into Cu2ZnSnSe4 and ZnSe. Among the conceivable crystal structures for both phases, a distorted zinc-blende structure shows the lowest energy, which is a few tens of meV below the energy of a wurtzite structure. A band gap of 1.1 eV is calculated for both the Cu2Zn5SnSe8 and Cu2Zn6SnSe9 phases. Possible effects of these phases on solar cell performance are discussed. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4934847
  • 2015 • 166 Atom probe tomography study of internal interfaces in Cu2ZnSnSe4 thin-films
    Schwarz, T. and Cojocaru-Mirédin, O. and Choi, P. and Mousel, M. and Redinger, A. and Siebentritt, S. and Raabe, D.
    Journal of Applied Physics 118 (2015)
    We report on atom probe tomography studies of the composition at internal interfaces in Cu<inf>2</inf>ZnSnSe<inf>4</inf> thin-films. For Cu<inf>2</inf>ZnSnSe<inf>4</inf> precursors, which are deposited at 320 °C under Zn-rich conditions, grain boundaries are found to be enriched with Cu irrespective of whether Cu-poor or Cu-rich growth conditions are chosen. Cu<inf>2</inf>ZnSnSe<inf>4</inf> grains are found to be Cu-poor and excess Cu atoms are found to be accumulated at grain boundaries. In addition, nanometer-sized ZnSe grains are detected at or near grain boundaries. The compositions at grain boundaries show different trends after annealing at 500 °C. Grain boundaries in the annealed absorber films, which are free of impurities, are Cu-, Sn-, and Se-depleted and Zn-enriched. This is attributed to dissolution of ZnSe at the Cu-enriched grain boundaries during annealing. Furthermore, some of the grain boundaries of the absorbers are enriched with Na and K atoms, stemming from the soda-lime glass substrate. Such grain boundaries show no or only small changes in composition of the matrix elements. Na and K impurities are also partly segregated at some of the Cu<inf>2</inf>ZnSnSe<inf>4</inf>/ZnSe interfaces in the absorber, whereas for the precursors, only Na was detected at such phase boundaries possibly due to a higher diffusivity of Na compared to K. Possible effects of the detected compositional fluctuations on cell performance are discussed. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4929874
  • 2015 • 165 High-Throughput Screening of Thin-Film Semiconductor Material Libraries I: System Development and Case Study for Ti-W-O
    Sliozberg, K. and Schäfer, D. and Erichsen, T. and Meyer, R. and Khare, C. and Ludwig, Al. and Schuhmann, W.
    ChemSusChem 8 1270-1278 (2015)
    An automated optical scanning droplet cell (OSDC) enables high-throughput quantitative characterization of thin-film semiconductor material libraries. Photoelectrochemical data on small selected measurement areas are recorded including intensity-dependent photopotentials and -currents, potentiodynamic and potentiostatic photocurrents, as well as photocurrent (action) spectra. The OSDC contains integrated counter and double-junction reference electrodes and is fixed on a precise positioning system. A Xe lamp with a monochromator is coupled to the cell through a thin poly(methyl methacrylate) (PMMA) optical fiber. A specifically designed polytetrafluoroethylene (PTFE) capillary tip is pressed on the sample surface and defines through its diameter the homogeneously illuminated measurement area. The overall and wavelength-resolved irradiation intensities and the cell surface area are precisely determined and calibrated. System development and its performance are demonstrated by means of screening of a Ti-W-O thin film. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cssc.201402917
  • 2015 • 164 A combinatorial study of photoelectrochemical properties of Fe-W-O thin films
    Sliozberg, K. and Schäfer, D. and Meyer, R. and Ludwig, Al. and Schuhmann, W.
    ChemPlusChem 80 136-140 (2015)
    A continuous mixed Fe-W-O thin-films materials library was fabricated by means of reactive co-sputtering from elemental iron and tungsten targets in argon/oxygen. The materials library was screened for its local photoelectrochemical properties by using an automated optical scanning droplet cell. Local scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX) measurements of the materials library were performed to correlate the composition, morphology, and photocurrents. The iron content was varied in the range from Fe32W68Ox to Fe81W19Ox. A strong dependence of the film morphology and the measured photocurrents on the composition was observed with a maximal photocurrent from a measurement area containing 55 at% iron. The most photoactive area showed a porous structure with a high surface area. The bandgap values of these materials were assessed by photocurrent spectroscopy and showed a systematic variation of the bandgap values with the composition. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cplu.201402277
  • 2015 • 163 Thickness-dependent electron-lattice equilibration in laser-excited thin bismuth films
    Sokolowski-Tinten, K. and Li, R.K. and Reid, A.H. and Weathersby, S.P. and Quirin, F. and Chase, T. and Coffee, R. and Corbett, J. and Fry, A. and Hartmann, N. and Hast, C. and Hettel, R. and Horn-Von Hoegen, M. and Janoschka, D. ...
    New Journal of Physics 17 (2015)
    Electron-phonon coupling processes determine electronic transport properties of materials and are responsible for the transfer of electronic excess energy to the lattice. With decreasing device dimensions an understanding of these processes in nanoscale materials is becoming increasingly important. Here we use time-resolved electron diffraction to directly study energy relaxation in thin bismuth films after optical excitation. Precise measurements of the transient Debye-Waller-effect for various film thicknesses and over an extended range of excitation fluences allow to separate different contributions to the incoherent lattice response. While phonon softening in the electronically excited state is responsible for an immediate increase of the r.m.s. atomic displacement within a few hundred fs, 'ordinary' electron-phonon coupling leads to subsequent heating of the material on a few ps time-scale. The data reveal distinct changes in the energy transfer dynamics which becomes faster for stronger excitation and smaller film thickness, respectively. The latter effect is attributed to a cross-interfacial coupling of excited electrons to phonons in the substrate. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
    view abstractdoi: 10.1088/1367-2630/17/11/113047
  • 2015 • 162 Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds
    Steil, D. and Schmitt, O. and Fetzer, R. and Kubota, T. and Naganuma, H. and Oogane, M. and Ando, Y. and Rodan, S. and Blum, C.G.F. and Balke, B. and Wurmehl, S. and Aeschlimann, M. and Cinchetti, M.
    48 (2015)
    Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demagnetization studies can, thus, help to understand the impact of stoichiometry and order on ultrafast spin dynamics. Here, we present a comparative study of the structural ordering and magnetization dynamics for thin films and bulk single crystals of the family of Heusler alloys with composition Co2Fe1 - xMnxSi. The local ordering is studied by 59Co nuclear magnetic resonance (NMR) spectroscopy, while the time-resolved magneto-optical Kerr effect gives access to the ultrafast magnetization dynamics. In the NMR studies we find significant differences between bulk single crystals and thin films, both regarding local ordering and stoichiometry. The ultrafast magnetization dynamics, on the other hand, turns out to be mostly unaffected by the observed structural differences, especially on the time scale of some hundreds of femtoseconds. These results confirm hole-mediated spin-flip processes as the main mechanism for ultrafast demagnetization and the robustness of this demagnetization channel against defect states in the minority band gap as well as against the energetic position of the band gap with respect to the Fermi energy. The very small differences observed in the magnetization dynamics on the picosecond time-scale, on the other hand, can be explained by considering the differences in the electronic structure at the Fermi energy and in the heat diffusion of thin films and bulk crystals. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/48/16/164016
  • 2015 • 161 A structure zone diagram obtained by simultaneous deposition on a novel step heater: A case study for Cu2O thin films
    Stein, H. and Naujoks, D. and Grochla, D. and Khare, C. and Gutkowski, R. and Grützke, S. and Schuhmann, W. and Ludwig, Al.
    Physica Status Solidi (A) Applications and Materials Science 212 2798-2804 (2015)
    In thin film deposition processes, the deposition temperature is one of the crucial process parameters for obtaining films with desired properties. Usually the optimum deposition temperature is found by conducting several depositions sequentially in a time consuming process. This paper demonstrates a facile and rapid route of the simultaneous thin film deposition at six different deposition temperatures ranging from 100 to 1000 °C. Cuprite (Cu2O) was chosen for the study as this material is of interest for energy applications. The thin films are assessed for their crystallographic, microstructural, Raman scattering, and photoelectrochemical properties. The results show that the utilization of a step heater leads to the rapid optimization of thin film microstructures of an absorber material used in photoelectrochemistry. This results in a structure zone diagram for Cu2O. For a substrate temperature of 600 °C, an optimum between crystallinity and morphology occurs. © 2015 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201532384
  • 2015 • 160 Influence of film thickness and composition on the martensitic transformation in epitaxial Ni-Mn-Sn thin films
    Teichert, N. and Auge, A. and Yüzüak, E. and Dincer, I. and Elerman, Y. and Krumme, B. and Wende, H. and Yildirim, O. and Potzger, K. and Hütten, A.
    Acta Materialia 86 279-285 (2015)
    Two series of epitaxial Ni-Mn-Sn thin films of different thickness are investigated for the thickness and composition dependence of the martensitic transformation. Thin films ranging in thickness from 20 to 200 nm (series A) and 10 to 100 nm (series B) were prepared by magnetron co-sputtering and deposited on heated MgO(0 0 1) substrates. The structural characterization was done by temperature-dependent X-ray diffraction measurements. Magnetization and resistivity measurements were performed to investigate the transformation characteristics. We find a strong influence of the film thickness on the relative amount of material undergoing the martensitic transformation, the temperature range of the transformation, and the transformation temperatures. The main contribution originates from the rigid substrate which delays the transformation of the Ni-Mn-Sn near the interface and even leads to a layer of residual austenite at low temperatures. Another issue are size effects which presumably broaden the martensitic transformation and decrease the transformation temperatures. By variation of the thin film composition we find changes of the substrate influence due to a different mismatch between the lattice of MgO and austenite. A better phase compatibility between martensite and austenite, denoted by λ2, not only results in a smaller hysteresis but is also beneficial for the transformation of material close to the substrate. © 2014 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2014.12.019
  • 2015 • 159 Tribological performance of near equiatomic and Ti-rich NiTi shape memory alloy thin films
    Tillmann, W. and Momeni, S.
    Acta Materialia 92 189-196 (2015)
    Near equiatomic and Ti-rich NiTi shape memory alloy thin films were magnetron sputtered with the same processing parameters and thickness of 3 μm. The microstructure, composition, shape memory behavior, mechanical and tribological properties of the deposited thin films were analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), nanoindentation, ball-on-disc, scratch test, and three dimensional (3D) optical microscopy. The obtained results clearly show how the crystallization evolution and precipitation formation of these two sets of thin films can drastically influence their mechanical and tribological performances. © 2015 Acta Materialia Inc. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2015.04.006
  • 2015 • 158 Comparison of NiTi thin films sputtered from separate elemental targets and Ti-rich alloy targets
    Tillmann, W. and Momeni, S.
    Journal of Materials Processing Technology 220 184-190 (2015)
    The kind of sputtering targets can adversely affect the microstructure, phase transformation behavior, mechanical and tribological properties of near equi-atomic NiTi thin films. This new finding was systematically investigated by employing comprehensive characterization and analysis techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), nanoindentation, ball-on-disc, and three dimensional (3D) optical microscopy. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jmatprotec.2015.01.014
  • 2015 • 157 In-situ annealing of NiTi thin films at different temperatures
    Tillmann, W. and Momeni, S.
    Sensors and Actuators, A: Physical 221 9-14 (2015)
    Magnetron sputtered NiTi thin films are usually sputtered at ambient temperature and need a post-annealing treatment to promote crystallization and obtain shape memory effect. However, this treatment could adversely affect the microstructure as well as the morphology of the film. Within this study, NiTi thin films were generated by annealing during the sputtering process. The effect of the sputtering temperature on the morphology of the film, the composition, and shape memory behavior was studied using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), and differential scanning calorimetry (DSC). © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.sna.2014.10.034
  • 2015 • 156 Influence of in-situ and postannealing technique on tribological performance of NiTi SMA thin films
    Tillmann, W. and Momeni, S.
    Surface and Coatings Technology 276 286-295 (2015)
    Magnetron sputtered NiTi thin films were crystallized through two convenient techniques: (i) postannealing and (ii) in-situ annealing during the deposition. The annealing parameters (temperature and time) were kept constant by employing each technique. The microstructure, morphology, phase transformation behavior, mechanical and tribological properties of these thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), 4-point probe resistivity measurement, nanoindentation test, pin-on-disc, scratch test and three dimensional (3D) optical microscopy. The results show how postannealing and in-situ annealing techniques can differently affect properties of NiTi thin films in spite of employing similar annealing temperature and time. © 2015 Elsevier B.V..
    view abstractdoi: 10.1016/j.surfcoat.2015.07.012
  • 2015 • 155 Chemical vapor deposition of Si/SiC nano-multilayer thin films
    Weber, A. and Remfort, R. and Wöhrl, N. and Assenmacher, W. and Schulz, S.
    Thin Solid Films 593 44-52 (2015)
    Stoichiometric SiC films were deposited with the commercially available single source precursor Et3SiH by classical thermal chemical vapor deposition (CVD) as well as plasma-enhanced CVD at low temperatures in the absence of any other reactive gases. Temperature-variable deposition studies revealed that polycrystalline films containing different SiC polytypes with a Si to carbon ratio of close to 1:1 are formed at 1000°C in thermal CVD process and below 100°C in the plasma-enhanced CVD process. The plasma enhanced CVD process enables the reduction of residual stress in the deposited films and offers the deposition on temperature sensitive substrates in the future. In both deposition processes the film thickness can be controlled by variation of the process parameters such as the substrate temperature and the deposition time. The resulting material films were characterized with respect to their chemical composition and their crystallinity using scanning electron microscope, energy dispersive X-ray spectroscopy (XRD), atomic force microscopy, X-ray diffraction, grazing incidence X-ray diffraction, secondary ion mass spectrometry and Raman spectroscopy. Finally, Si/SiC multilayers of up to 10 individual layers of equal thickness (about 450 nm) were deposited at 1000°C using Et3SiH and SiH4. The resulting multilayers features amorphous SiC films alternating with Si films, which feature larger crystals up to 300 nm size as measured by transmission electron microscopy as well as by XRD. XRD features three distinct peaks for Si(111), Si(220) and Si(311). © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2015.08.042
  • 2015 • 154 Molecular-scale hybridization of clay monolayers and conducting polymer for thin-film supercapacitors
    Zhao, J. and Xu, S. and Tschulik, K. and Compton, R.G. and Wei, M. and O'Hare, D. and Evans, D.G. and Duan, X.
    Advanced Functional Materials 25 2745-2753 (2015)
    Development of electrode materials with well-defined architectures is a fruitful and profitable approach for achieving highly-efficient energy storage systems. A molecular-scale hybrid system is presented based on the self-assembly of CoNi-layered double hydroxide (CoNi-LDH) monolayers and the conducting polymer (poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate), denoted as PEDOT:PSS) into an alternating-layer superlattice. Owing to the homogeneous interface and intimate interaction, the resulting CoNi-LDH/PEDOT:PSS hybrid materials possess a simultaneous enhancement in ion and charge-carrier transport and exhibit improved capacitive properties with a high specific capacitance (960 F g-1 at 2 A g-1) and excellent rate capability (83.7% retention at 30 A g-1). In addition, an in-plane supercapacitor device with an interdigital design is fabricated based on a CoNi-LDH/PEDOT:PSS thin film, delivering a significantly enhanced energy and power output (an energy density of 46.1 Wh kg-1 at 11.9 kW kg-1). Its application in miniaturized devices is further demonstrated by successfully driving a photodetector. These characteristics demonstrate that the molecular-scale assembly of LDH monolayers and the conducting polymer is promising for energy storage and conversion applications in miniaturized electronics. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201500408
  • 2014 • 153 Selective laser patterning in organic solar cells
    Abreu Fernandes, S. and Maragkaki, S. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 9180 (2014)
    Selective laser patterning for integrative serious connection has been industrially established in inorganic thin film solar cells based on glass substrates since a few years. In organic solar cells (OSC) the used materials significantly differ in terms of their patterning behavior. Due to their processability by wet chemical methods inverted architectures are often preferred in organic solar cells which allow the patterning by ultrashort laser pulses in substrate and superstrate configuration. Starting with an introduction of the ablation mechanisms taking place in OSC thin films, an overview of the current state-of-the-art in laser patterning of organic solar cells is presented. Besides progress in research also current achievements in industrial applications are illustrated. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2061248
  • 2014 • 152 Thermopower engineering of Bi2Te3 without alloying: The interplay between nanostructuring and defect activation
    Bae, C. and Böhnert, T. and Gooth, J. and Lim, S. and Lee, S. and Kim, H. and Heimann, S. and Schulz, S. and Shin, H. and Nielsch, K.
    Semiconductor Science and Technology 29 (2014)
    We report on the interplay between nanostructuring and defect activation in dense polycrystalline Bi2Te3 thin films in terms of the thermopower engineering. The Bi2Te3 thin films were prepared at relatively low temperatures (100-160 °C) by atomic layer deposition and their grains showed different sizes in the range of 50-200 nm according to the deposition temperatures. We monitored the conductivity, Seebeck coefficient, and power factor of all samples from the temperature of 50-400 K. By increasing the growth temperature, remarkably, we observed the gradual defect activation from the nominal p-type to n-type in our binary end compound, Bi2Te3 without any alloying. The present results give us an insight on the optimization of thermoelectric materials not only by nanostructuring (i.e., phonon engineering) but also by controlled defect activation (i.e., electron engineering). © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0268-1242/29/6/064003
  • 2014 • 151 Novel β-ketoiminato complexes of zirconium: Synthesis, characterization and evaluation for solution based processing of ZrO2 thin films
    Banerjee, M. and Seidel, R.W. and Winter, M. and Becker, H.-W. and Rogalla, D. and Devi, A.
    Dalton Transactions 43 2384-2396 (2014)
    Treatment of tetrakis(diethylamido)zirconium(iv); [Zr(NEt2) 4] with a series of β-ketoimines ({[RHN]C(CH3)C(H) C(CH3)O} where R is a functionalized side-chain; 4-(2- methoxyethylamino)pent-3-en-2-one, Hmeap; 4-(3-methoxypropylamino)pent-3-en-2- one, Hmpap; 4-(2-(dimethylamino)ethylamino)pent-3-en-2-one, Hdeap; 4-(3-(dimethylamino)propylamino)pent-3-en-2-one, Hdpap) leads to an amine substitution reaction that yielded novel monomeric heteroleptic mixed amido-ketoiminato complexes of the type bis(4-(2-methoxyethylamino)pent-3-en-2- onato)bis(diethylamido)zirconium(iv) (1), bis(4-(3-methoxypropylamino)pent-3-en- 2-onato)bis(diethylamido)zirconium(iv) (2), and bis(4-(3-(dimethylamino) propylamino)pent-3-en-2-onato)bis(diethylamido)zirconium(iv) (3), and eight-coordinated homoleptic complexes tetrakis(4-(2-methoxyethylamino)pent-3- en-2-onato)zirconium(iv) (4) and tetrakis(4-(2-(dimethylamino)ethylamino)pent-3- en-2-onato)zirconium(iv) (5), depending on the ratio of the ligand to zirconium. Adopting a similar strategy with zirconium alkoxide, namely [Zr(O iPr)4·iPrOH], with β-ketoimine Hmeap, leads to the formation of a dimer, bis(μ2-isopropoxo)bis(4- (2-methoxyethylamino)pent-3-en-2-onato)tetrakis(isopropoxo)dizirconium(iv) (6). The newly synthesised complexes were characterized by NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, elemental analysis and thermal analysis. The low decomposition temperature facilitated by the stepwise elimination of the ketominate ligand from the complex and the stability of the complexes obtained in air as well as in solution makes them highly suitable for solution based processing of ZrO2 thin films, which is demonstrated using compound 5 on Si(100) substrates. High quality ZrO2 films were obtained and were investigated for their structure, morphology, composition and optical properties. Low temperature crystallisation of ZrO2 is achieved by a simple chemical deposition process using the new class of Zr precursors and the films exhibit an optical transmittance above 90%. © 2014 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3dt52335g
  • 2014 • 150 MOCVD of TiO2 thin films using a heteroleptic titanium complex: Precursor evaluation and investigation of optical, photoelectrochemical and electrical properties
    Banerjee, M. and Dang, V.-S. and Bledowski, M. and Beranek, R. and Becker, H.-W. and Rogalla, D. and Edengeiser, E. and Havenith, M. and Wieck, A.D. and Devi, A.
    Chemical Vapor Deposition 20 224-233 (2014)
    A new heteroleptic titanium precursor with a mixed oxygen/nitrogen coordination sphere [Ti(dmap)2(NMe2)2] (Hdmap=1-dimethylamino-2-propanol) is synthesized by a simple elimination reaction on tetrakis-dimethylaminotitanium(IV) [Ti(NMe2)4]. The compound shows encouraging results in terms of chemical and thermal stability compared to the parent alkyl amide [Ti(NMe2)4], and is therefore more suitable for MOCVD applications. TiO2 thin films are grown on Si(100) and ITO-coated borosilicate glass substrates via MOCVD in the temperature range 500-800°C. The deposition temperature has a significant effect on the phase and microstructure of the TiO2 films obtained, which influences the functional properties. The optical bandgaps of the films are in the range 2.92-3.36eV. The best photocurrent response (1.5mAcm-2 under AM 1.5G conditions) in aqueous electrolytes is observed for films grown at 700°C having improved crystallinity and porous columnar structure. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cvde.201407125
  • 2014 • 149 On the mechanism that leads to vanishing thermal hysteresis of the B2-R phase transformation in multilayered (TiNi)/(W) shape memory alloy thin films
    Buenconsejo, P.J.S. and Zarnetta, R. and Young, M. and Brunken, H. and Mehta, A. and Ludwig, Al.
    Thin Solid Films 564 79-85 (2014)
    The film stresses in two-phase (TiNi)/(W) shape memory alloy (SMA) multilayer thin films were evaluated using synchrotron diffraction analysis. The phase transforming B2-TiNi phase is under tensile stress due to the mismatch of the coefficient-of-thermal-expansion (αB2-TiNi &gt; αW &gt; αSi-substrate) and the elastic modulus (EW &gt; ESi &gt; EB2-TiNi) with respect to the bcc-W layers and the Si-substrate. The amount of stress on the B2-TiNi phase increases with increasing W amount in the film, which is proportional to the W layer thickness. This led to important changes in the behavior of the B2-R transformation. On cooling, a B2-R transformation proceeds under increasing tensile stress which increases the transformation start temperature (R s). Upon transformation to the R phase, the TiNi layers undergo stress-relaxation by reorientation of R phase variants to accommodate the mismatch. During heating the film always starts from a relaxed stress-state, so the reverse transformation proceeds without adversely affecting the reverse transformation temperature (Af). With increasing amount of W in the film Rs increases more on cooling, while Af is not significantly affected on heating, and this leads to vanishing thermal hysteresis (ΔTB2-R = Af - Rs). © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2014.05.010
  • 2014 • 148 From spherical mesopores to worm-shaped mesopores: Morphology transition in titania-polystyrene-b-poly(ethylene oxide) composite films with increasing sol-gel reaction time
    Cheng, Y.-J. and Zhou, S. and Wolkenhauer, M. and Bumbu, G.-G. and Lenz, S. and Memesa, M. and Nett, S. and Emmerling, S. and Steffen, W. and Roth, S.V. and Gutmann, J.S.
    European Journal of Inorganic Chemistry 2014 836-844 (2014)
    A morphology transition from spherical mesopores to worm-shaped mesopores within titania block copolymer composite thin films has been observed by varying the sol-gel reaction time from 40 min to 48 h in the four-component templating system of polystyrene-b-poly(ethylene oxide) (PS-b-PEO), 1,4-dioxane, concentrated HCl, and titanium tetraisopropoxide (TTIP) with a PS-b-PEO mass concentration of 0.25 wt.-%. The impact of the sol-gel reaction time on the local structure, long-range lateral structure, and vertical structure of the as-prepared, calcined, and UV-degraded thin films as well as the structural changes in solution have been systematically investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), grazing-incidence small-angle X-ray scattering (GISAXS), X-ray reflectivity (XRR), and dynamic light scattering (DLS). With sol-gel reaction times of up to 5 h, hexagonally organized spherical micelles are present within the as-prepared composite films, in which the core of the spherical micelles is composed of the polystyrene (PS) block, and the corona is composed of the poly(ethylene oxide)-titania (PEO-titania) hybrid. Upon calcination or UV exposure, ordered mesoporous structures are formed owing to the removal of the PS block. With the sol-gel reaction time extended to 25 and 48 h, worm-shaped micelles appear, and their quantity increases with increasing sol-gel reaction time. Worm-shaped mesopores are formed by calcination or UV degradation. The GISAXS results prove that the local structural changes are representative over a macroscopic scale. The XRR results suggest that with the sol-gel reaction time extended to 48 h there is an additional thin layer beneath the mesoporous titania layer owing to the presence of a large amount of worm-shaped micelles. The results of the DLS studies imply that the morphology transition from spherical micelles to worm-shaped micelles is caused by a fusion process of the spherical micelles in solution. A morphology transition from spherical mesopores to worm-shaped mesopores within titania-polystyrene-b-poly(ethylene oxide) (titania-PS-b-PEO) composite thin films is achieved by varying the sol-gel reaction time from 40 min to 48 h with 0.25 wt.-% PS-b-PEO and fixed solution composition, as confirmed by imaging and scattering techniques. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ejic.201301251
  • 2014 • 147 Electrical and optical properties of TiO2 thin films prepared by plasma-enhanced atomic layer deposition
    Dang, V.-S. and Parala, H. and Kim, J.H. and Xu, K. and Srinivasan, N.B. and Edengeiser, E. and Havenith, M. and Wieck, A.D. and De Los Arcos, T. and Fischer, R.A. and Devi, A.
    Physica Status Solidi (A) Applications and Materials Science 211 416-424 (2014)
    We report on the electrical and optical characterisation of the high-permittivity (high-κ) TiO2 thin films grown by plasma enhanced atomic layer deposition on Si (100) and glass substrates, respectively. TiO2 films were incorporated in metal-oxide semiconductor (MOS) capacitor structures with an Al metal gate electrode. The as-deposited films were amorphous; however upon annealing in the temperature range 500-900°C, crystalline TiO2 in the anatase phase was formed. This was further confirmed by performing Raman measurements where the characteristic features corresponding to the anatase phase were observed. Transmittance and absorption spectra of the as-deposited and annealed films were performed by UV-Vis measurements showing more than 70% of transmittance. The formation of stoichiometric TiO2 was revealed by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS) analysis performed on annealed samples (500-900°C). The dielectric constants were calculated from capacitance-voltage (C-V) curves of the MOS structure on the as-deposited film and annealed films revealing a significant improvement of the dielectric constants from 10 to 75 at AC frequencies of 100 kHz for the 700°C annealed TiO2 thin films. The increase in the dielectric constant for annealed films could be attributed to the transformation of film structure from amorphous to polycrystalline (anatase). However, the transformation of amorphous to crystalline phase, leads to an increase in the leakage current which was also found best fitted with Schottky emission mechanism at moderated electric fields. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201330115
  • 2014 • 146 Characterization of Ta-Ti Thin Films by using a Scanning Droplet Cell in Combination with AC Linear Sweep Voltammetry
    Fan, M. and Sliozberg, K. and La Mantia, F. and Miyashita, N. and Hagymási, M. and Schnitter, C. and Ludwig, Al. and Schuhmann, W.
    ChemElectroChem 1 903-908 (2014)
    A binary Ta-Ti thin film composition-spread materials library is prepared through magnetron sputter co-deposition. An automated microelectrochemical investigation on selected surface areas, corresponding to a concentration gradient of Ti varying from 0.5 to 36at%, is achieved by using a scanning droplet cell. Simultaneously, during the anodic oxide growth, a small alternating current (AC) voltage is superimposed on the increasing direct current (DC) potential in order to record the capacitance of the mixed-metal oxide by using alternating current linear sweep voltammetry (AC-LSV). Valve metal behavior, with the current stabilizing after an initial rapid increase, is found for all investigated compositions. AC-LSV allows the ratio of the formation factor to the relative permittivity for different compositions to be calculated. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201300153
  • 2014 • 145 Mechanism of tailored magnetic anisotropy in amorphous Co 68Fe24Zr8 thin films
    Fu, Y. and Barsukov, I. and Meckenstock, R. and Lindner, J. and Raanaei, H. and Hjörvarsson, B. and Farle, M.
    Applied Physics Letters 104 (2014)
    The mechanism of tailored magnetic anisotropy in amorphous Co 68Fe24Zr8 thin films was investigated by ferromagnetic resonance (FMR) on samples deposited without an applied magnetic field, with an out-of-plane field and an in-plane field. Analysis of FMR spectra profiles, high frequency susceptibility calculations, and statistical simulations using a distribution of local uniaxial magnetic anisotropy reveal the presence of atomic configurations with local uniaxial anisotropy, of which the direction can be tailored while the magnitude remains at an intrinsically constant value of 3.0(2) kJ/m3. The in-plane growth field remarkably sharpens the anisotropy distribution and increases the sample homogeneity. The results benefit designing multilayer spintronic devices based on highly homogeneous amorphous layers with tailored magnetic anisotropy. © 2014 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4865369
  • 2014 • 144 Ruthenium complexes as precursors for chemical vapor-deposition (CVD)
    Gaur, R. and Mishra, L. and Siddiqi, M.A. and Atakan, B.
    RSC Advances 4 33785-33805 (2014)
    Ruthenium and its compounds are often used as thin films and can be deposited by chemical vapor deposition. The quality of the films strongly depends on the inorganic precursors, their evaporation behaviour and thermochemistry. This is an area where different aspects of inorganic chemistry and chemical engineering must fit together to provide good thin films. It was noticed that providing firsthand information in one place especially for a learner of this area of research, and collection of reports on different types of ruthenium complexes as CVD precursors would be timely. Thus, in this review a bird's eye view of ruthenium complexes suitable for CVD technology, together with the presentation of different precursors, their synthesis, evaporation, decomposition and film formation is presented. A brief summary of the CVD technique is also presented with future-design, synthesis and usefulness of CVD precursors. This journal is © the Partner Organisations 2014.
    view abstractdoi: 10.1039/c4ra04701j
  • 2014 • 143 Indium-tris-guanidinates: A promising class of precursors for water assisted atomic layer deposition of In2O3 thin films
    Gebhard, M. and Hellwig, M. and Parala, H. and Xu, K. and Winter, M. and Devi, A.
    Dalton Transactions 43 937-940 (2014)
    Two closely related mononuclear homoleptic indium-tris-guanidinate complexes have been synthesized and characterized as precursors for atomic layer deposition (ALD) of In2O3. In a water assisted ALD process, high quality In2O3 thin films have been fabricated for the first time using the new class of precursors as revealed by the promising ALD growth characteristics and film properties. © The Royal Society of Chemistry 2014.
    view abstractdoi: 10.1039/c3dt52746h
  • 2014 • 142 Epitaxial Cu(001) films grown on a Cr/Ag/Fe/GaAs(001) buffer system
    Gottlob, D.M. and Jansen, T. and Hoppe, M. and Bürgler, D.E. and Schneider, C.M.
    Thin Solid Films 562 250-253 (2014)
    We present a procedure to prepare single-crystalline, high-purity Cu(001) films (templates) suitable as substrates for subsequent epitaxial thin-film growth. The template films were grown in a dedicated molecular-beam epitaxy system on a Cr/Ag/Fe/GaAs(001) buffer layer system. Low-energy electron diffraction and X-ray diffraction were applied to determine the surface orientation and the epitaxial relationship between all layers of the stack. Post-annealing at moderate temperatures enhances the quality of the film as shown by low-energy electron diffraction and atomic force microscopy. X-ray photoemission and Auger electron spectroscopy confirm that no atoms of the buffer layers diffuse into the Cu film during the initial preparation and the post-annealing treatment. The completed Cu(001) template system can be exposed to air and afterwards refurbished by Ar+-ion bombardment and annealing, enabling the transfer between vacuum systems. The procedure provides suitable conductive thin film templates for studies of epitaxial thin films, e.g. on the magnetic and magnetotransport properties of Co and Ni based films and multilayers. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2014.04.078
  • 2014 • 141 Wide-range structural and chemical stability of the magnetic oxide NiFe2O4 Grown by O2-assisted pulsed laser deposition
    Hoppe, M. and Gorgoi, M. and Schneider, C. M. and Muller, M.
    IEEE Transactions on Magnetics 50 (2014)
    We present a study of the structural and chemical properties of the magnetic insulator NiFe2O4 on conductive Nb-doped SrTiO3 (001) substrates. Special regard is given to the dependence of the thin film properties on the O2:Ar ratio during pulsed laser deposition. Using stoichiometric NiFe2O4 target material and varying the O2 partial pressure from 0% to 100%, we find a nonzero oxygen threshold for heteroepitaxial growth and a stoichiometric Fe:Ni cation distribution. Moreover, our study clearly demonstrates that NiFe2O4 thin films grow with high quality over a wide range of oxygen partial pressures. These optimized NiFe2O4/SrTiO3 heterostructures are envisioned as efficient spin filter tunnel contacts for room temperature application. © 1965-2012 IEEE.
    view abstractdoi: 10.1109/TMAG.2014.2322378
  • 2014 • 140 Antibacterial AgNPs/CaP biocomposites
    Ivanova, A.A. and Surmenev, R.A. and Surmeneva, M.A. and Mukhametkaliyev, T. and Sharonova, A.A. and Grubova, I.Y. and Loza, K. and Chernousova, S. and Prymak, O. and Epple, M.
    2014 9th International Forum on Strategic Technology, IFOST 2014 472-474 (2014)
    The modification of implant surface is in the focus of many scientists worldwide. In this study, multifunctional biocomposite on the basis of calcium phosphate coating and silver nanoparticles has been fabricated through the use of nanofabrication techniques. Dense nanocrystalline HA film was deposited over AgNPs. The properties as well as the in vitro behavior of the developed biocomposites have been studied. The diffraction patterns of the biocomposites revealed the peaks of crystalline HA and silver (Ag). The release of Ag from the developed biocomposites was evaluated. The concentration of the released silver ions for 7 days of dissolution was 0.27±0.02 μg/mL and 0.54±0.02 μg/mL for phosphate and acetate buffers, respectively. In order to estimate the cytotoxicity of the samples the functional activity of osteoclasts, in particular, cell morphology, multinuclearity, actin ring and resorption pit on the substrates coated with HA and AgNPs-HA have been evaluated. © 2014 IEEE.
    view abstractdoi: 10.1109/IFOST.2014.6991166
  • 2014 • 139 Tailoring the morphology of mesoporous titania thin films through biotemplating with nanocrystalline cellulose
    Ivanova, A. and Fattakhova-Rohlfing, D. and Kayaalp, B.E. and Rathouský, J. and Bein, T.
    Journal of the American Chemical Society 136 5930-5937 (2014)
    The tunable porosity of titania thin films is a key factor for successful applications in photovoltaics, sensing, and photocatalysis. Here, we report on nanocrystalline cellulose (NCC) as a novel shape-persistent templating agent enabling the straightforward synthesis of mesoporous titania thin films. The obtained structures are highly porous anatase morphologies having well-defined, narrow pore size distributions. By varying the titania-to-template ratio, it is possible to tune the surface area, pore size, pore anisotropy, and dimensions of titania crystallites in the films. Moreover, a post-treatment at high humidity and subsequent slow template removal can be used to achieve pore widening; this treatment is also beneficial for the multilayer deposition of thick films. The resulting homogeneous transparent films can be directly spin- or dip- coated on glass, silicon, and transparent conducting oxide (TCO) substrates. The mesoporous titania films show very high activity in the photocatalytic NO conversion and in the degradation of 4-chlorophenol. Furthermore, the films can be successfully applied as anodes in dye-sensitized solar cells. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/ja411292u
  • 2014 • 138 Investigation of the thin-film phase diagram of the Cr-Ni-Re system by high-throughput experimentation
    Janghorban, A. and Pfetzing-Micklich, J. and Frenzel, J. and Ludwig, Al.
    Advanced Engineering Materials 16 588-593 (2014)
    The Cr-Ni-Re system was investigated over the whole composition range using combinatorial fabrication methods combined with high-throughput characterization techniques in order to establish its thin film phase diagram. After annealing at 940 and 1100°C, the phase equilibrium was reached in the Ni-rich part of the ternary in agreement with the published bulk phase diagram. Annealing the materials library at 940°C is not sufficient to achieve the equilibrium state in the Re-rich part of the system, however by annealing the materials library at 1100°C the formation of expected phases (three solid-solutions and a topologically close packed compound) could be observed. As a result of this study, a thin film phase diagram of the complete Cr-Ni-Re at 1100°C was established, which is well comparable to the bulk phase diagram. This shows that the combinatorial thin film phase diagram approach is feasible and especially promising for materials systems with expensive and/or high melting point constituents. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201300430
  • 2014 • 137 Plasma spray physical vapor deposition of La1-x Sr x Co y Fe1-y O3-δ Thin-film oxygen transport membrane on porous metallic supports
    Jarligo, M.O. and Mauer, G. and Bram, M. and Baumann, S. and Vaßen, R.
    Journal of Thermal Spray Technology 23 213-219 (2014)
    Plasma spray physical vapor deposition (PS-PVD) is a very promising route to manufacture ceramic coatings, combining the efficiency of thermal spray processes and characteristic features of thin PVD coatings. Recently, this technique has been investigated to effectively deposit dense thin films of perovskites particularly with the composition of La0.58Sr 0.4Co0.2Fe0.8O3-δ (LSCF) for application in gas separation membranes. Furthermore, asymmetric type of membranes with porous metallic supports has also attracted research attention due to the advantage of good mechanical properties suitable for use at high temperatures and high permeation rates. In this work, both approaches are combined to manufacture oxygen transport membranes made of gastight LSCF thin film by PS-PVD on porous NiCoCrAlY metallic supports. The deposition of homogenous dense thin film is challenged by the tendency of LSCF to decompose during thermal spray processes, irregular surface profile of the porous metallic substrate and crack and pore-formation in typical ceramic thermal spray coatings. Microstructure formation and coating build-up during PS-PVD as well as the annealing behavior at different temperatures of LSCF thin films were investigated. Finally, measurements of leak rates and oxygen permeation rates at elevated temperatures show promising results for the optimized membranes. © 2013 ASM International.
    view abstractdoi: 10.1007/s11666-013-0004-y
  • 2014 • 136 Self-directed localization of ZIF-8 thin film formation by conversion of ZnO nanolayers
    Khaletskaya, K. and Turner, S. and Tu, M. and Wannapaiboon, S. and Schneemann, A. and Meyer, R. and Ludwig, Al. and Van Tendeloo, G. and Fischer, R.A.
    Advanced Functional Materials 24 4804-4811 (2014)
    Control of localized metal-organic framework (MOF) thin film formation is a challenge. Zeolitic imidazolate frameworks (ZIFs) are an important sub-class of MOFs based on transition metals and imidazolate linkers. Continuous coatings of intergrown ZIF crystals require high rates of heterogeneous nucleation. In this work, substrates coated with zinc oxide layers are used, obtained by atomic layer deposition (ALD) or by magnetron sputtering, to provide the Zn 2+ ions required for nucleation and localized growth of ZIF-8 films ([Zn(mim)2]; Hmim = 2-methylimidazolate). The obtained ZIF-8 films reveal the expected microporosity, as deduced from methanol adsorption studies using an environmentally controlled quartz crystal microbalance (QCM) and comparison with bulk ZIF-8 reference data. The concept is transferable to other MOFs, and is applied to the formation of [Al(OH)(1,4-ndc)]n (ndc = naphtalenedicarboxylate) thin films derived from Al2O3 nanolayers. The self-template route for the manufacturing of ZIF-8 films on silicon (Si) and quartz crystal microbalance (QCM) substrates involves the pre-deposition of ZnO films prepared by sputtering or atomic layer deposition methods and the subsequent conversion of the immobilized ZnO phase into crystalline and homogeneously dense ZIF-8 films via microwave-assisted synthesis. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201400559
  • 2014 • 135 Synthesis of WO3 nanoblades by the dealloying of glancing angle deposited W-Fe nanocolumnar thin films
    Khare, C. and Stepanovich, A. and Buenconsejo, P.J.S. and Ludwig, Al.
    Nanotechnology 25 (2014)
    Glancing angle co-deposition of well-separated W-Fe nanocolumns was carried out using a W oblique angle sputter source and a Fe confocal incidence source. As-deposited nanocolumns with an overall composition of W64.6Fe35.4 (at.%) exhibited an average column width w nc of 77 ± 15 nm with predominant growth in the β-W phase. With the aim of synthesizing highly porous nanostructures, the as-deposited precursor W-Fe nanocolumnar thin films were immersed in aqueous HNO3 solution for various dealloying durations (t d ). Formation of nanoflake-, nanocactus-, and nanoblade-like structures were observed during the dealloying treatment, as a result of selective dissolution of Fe from the W-Fe precursor films and simultaneous oxidation of W adatoms. By increasing the dealloying duration, the Fe concentration within the film reduced drastically and the film thickness increased by about three times in comparison to the as-deposited film. The dealloyed film exhibited an overall composition of W95.6Fe4.4, where the effective surface area of the film increased substantially. It was found that W adatom diffusion and subsequent rearrangement are crucially important in determining the resultant thin film morphology. The morphological development, corresponding compositions and crystallographic properties of different nanostructures were found to be significantly dependent on the dealloying duration. For optimized processing parameters, the selective dissolution process led to formation of single crystal monoclinic WO3 nanoblades, with growth along [002] and [020] axes. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/25/20/205606
  • 2014 • 134 Investigation of ternary subsystems of superalloys by thin-film combinatorial synthesis and high-throughput analysis
    König, D. and Pfetzing-Micklich, J. and Frenzel, J. and Ludwig, Al.
    MATEC Web of Conferences 14 (2014)
    A Co-Ti-W thin film materials library was fabricated by magnetron sputtering. By using automated high-throughput measurement techniques (resistance mapping, automated XRD measurements) and cluster analysis a yet unknown phase region was revealed. The existence region of the new ternary phase is close to the composition Co60Ti15W25. In order to transfer the results from thin film to bulk material, a bulk sample was prepared by arc melting and subsequent heat treatment. Scanning electron microscopy and chemical micro-analysis data support that a yet unknown ternary phase exists in the system Co-Ti-W. © 2014 Owned by the authors, published by EDP Sciences.
    view abstractdoi: 10.1051/matecconf/20141418002
  • 2014 • 133 Recent advances using guanidinate ligands for Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD) applications
    Kurek, A. and Gordon, P.G. and Karle, S. and Devi, A. and Barry, S.T.
    Australian Journal of Chemistry 67 989-996 (2014)
    Volatile metal complexes are important for chemical vapour deposition (CVD) and atomic layer deposition (ALD) to deliver metal components to growing thin films. Compounds that are thermally stable enough to volatilize but that can also react with a specific substrate are uncommon and remain unknown for many metal centres. Guanidinate ligands, as discussed in this review, have proven their utility for CVD and ALD precursors for a broad range of metal centres. Guanidinate complexes have been used to deposit metal oxides, metal nitrides and pure metal films by tuning process parameters. Our review highlights use of guanidinate ligands for CVD and ALD of thin films over the past five years, design trends for precursors, promising precursor candidates and discusses the future outlook of these ligands. © CSIRO 2014.
    view abstractdoi: 10.1071/CH14172
  • 2014 • 132 Structural, optical, and magnetic properties of highly-resistive Sm-implanted GaN thin films
    Lo, F.-Y. and Huang, C.-D. and Chou, K.-C. and Guo, J.-Y. and Liu, H.-L. and Ney, V. and Ney, A. and Shvarkov, S. and Pezzagna, S. and Reuter, D. and Chia, C.-T. and Chern, M.-Y. and Wieck, A.D. and Massies, J.
    Journal of Applied Physics 116 (2014)
    Samarium ions of 200 keV in energy were implanted into highly-resistive molecular-beam-epitaxy grown GaN thin films with a focused-ion-beam implanter at room temperature. The implantation doses range from 1 × 1014 to 1 × 1016cm-2. Structural properties studied by x-ray diffraction and Raman-scattering spectroscopy revealed Sm incorporation into GaN matrix without secondary phase. The optical measurements showed that the band gap and optical constants changed very slightly by the implantation. Photoluminescence measurements showed emission spectra similar to p-type GaN for all samples. Magnetic investigations with a superconducting quantum interference device identified magnetic ordering for Sm dose of and above 1 × 1015cm-2 before thermal annealing, while ferromagnetism was only observed after thermal annealing from the sample with highest Sm dose. The long-range magnetic ordering can be attributed to interaction of Sm ions through the implantation-induced Ga vacancy. © 2014 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4891226
  • 2014 • 131 A method for calculating the complex refractive index of inhomogeneous thin films
    Manley, P. and Yin, G. and Schmid, M.
    Journal of Physics D: Applied Physics 47 (2014)
    We calculate the complex refractive index of inhomogeneous thin films using the transfer matrix method and reflection/transmission measurements. To this end we have developed a model for both the 3D distribution of inhomogeneities inside thin films and for light propagation through the inhomogeneities. The model involves splitting the light into contributions from the homogeneous section of the film (modelled coherently) and the inhomogeneous sections (modelled incoherently). Measurements of the film implied an isotropic inhomogeneity distribution, which was replicated in the simulation. The model for light propagation inside a film was implemented into a transfer matrix program allowing for the evaluation of the reflection and transmission of the thin film on a substrate. Using this result and experimental data for the reflection and transmission, the complex refractive index, n+ik, of an inhomogeneous CuInSe2 film was calculated. The resulting n and k were in much closer agreement to the n and k for a homogeneous CuInSe2 film than those for the standard transfer matrix approach applied to the data of the inhomogeneous sample. The n value at short wavelengths deviates from the homogeneous value suggesting a breakdown of the scalar scattering theory for short wavelengths. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/47/20/205301
  • 2014 • 130 Electrochemistry on binary valve metal combinatorial libraries: Niobium-tantalum thin films
    Mardare, A.I. and Ludwig, Al. and Savan, A. and Hassel, A.W.
    Electrochimica Acta 140 366-375 (2014)
    A Nb-Ta thin film compositional spread obtained from a co-sputtering process was analysed. The microstructure and crystallographic investigations revealed the presence of a compositional threshold at Nb-60 at.%Ta where the change from tetragonal to cubic symmetry was evidenced by a mixed tetragonal-cubic phase. The electrochemical properties of the anodic oxides were studied via cyclic voltammetry and the oxide formation factors were mapped along the entire compositional spread. Values ranging from 1.8 nm·V -1 at the Ta-rich side to 2.6 nm·V-1 at the Nb-rich side of the library were measured. All Nb-Ta mixed anodic oxides were found to exhibit a type-n semiconducting behaviour as evidenced by Mott-Schottky analysis. The chemical composition of the surface anodic oxides differed from the composition of the parent metal alloys and no clear trend could be identified regarding their mismatch. © 2014 Elsevier Ltd.
    view abstractdoi: 10.1016/j.electacta.2014.02.138
  • 2014 • 129 Properties of anodic oxides grown on a hafnium-tantalum-titanium thin film library
    Mardare, A.I. and Ludwig, Al. and Savan, A. and Hassel, A.W.
    Science and Technology of Advanced Materials 15 (2014)
    A ternary thin film combinatorial materials library of the valve metal system Hf-Ta-Ti obtained by co-sputtering was studied. The microstructural and crystallographic analysis of the obtained compositions revealed a crystalline and textured surface, with the exception of compositions with Ta concentration above 48 at.% which are amorphous and show a flat surface. Electrochemical anodization of the composition spread thin films was used for analysing the growth of the mixed surface oxides. Oxide formation factors, obtained from the potentiodynamic anodization curves, as well as the dielectric constants and electrical resistances, obtained from electrochemical impedance spectroscopy, were mapped along two dimensions of the library using a scanning droplet cell microscope. The semiconducting properties of the anodic oxides were mapped using Mott-Schottky analysis. The degree of oxide mixing was analysed qualitatively using x-ray photoelectron spectroscopy depth profiling. A quantitative analysis of the surface oxides was performed and correlated to the as-deposited metal thin film compositions. In the concurrent transport of the three metal cations during oxide growth a clear speed order of Ti > Hf > Ta was proven. © 2014 National Institute for Materials Science.
    view abstractdoi: 10.1088/1468-6996/15/1/015006
  • 2014 • 128 Plasmonic improvement of microcavity biomedical sensor spectroscopic characteristics
    Saetchnikov, V.A. and Tcherniavskaia, E.A. and Saetchnikov, A.V. and Schweiger, G. and Ostendorf, A. and Ghadiri, R.
    Progress in Biomedical Optics and Imaging - Proceedings of SPIE 8957 (2014)
    New opportunity to improve a sensetivity of a label-free biomolecule detection in sensing systems based on microcavity evanescent wave optical sensors has been recently found and is being under intensive development. Novel technique based on combination of optical resonance on microring structures with plasmon resonance. Recently developed tools based on neural network data processing can realize real-Time identification of biological agents. So combining advantages of plasmon enhancing optical microcavity resonance with identification tools can give a new platform for ulta sensitive label-free biomedical sensor. Our developed technique used standard glass and polymer microspheres as sensetive elements. They are fixed in the solution flow by adhesive layer on the surface being in the field of evanescence wave. Sensitive layer have been treated by gold nanoparticel (GN) solution. Another technique used thin film gold layers deposited on the substrate below adhesive. The light from a tuneable diode laser is coupled into the microsphere through a prism and was sharply focussed on the single microsphere. Images were recorded by CMOS camera. Normalized by free spectral range resonance shift of whispering gallery mode (WGM) and a relative efficiency of their excitation were used as input data for biomolecule classification. Both biomolecules and NP injection was obtained caused WGM spectra modification. But after NP treatment spectral shift and intensity of WGM resonances in biomolecule solutions increased. WGM resonances in microspheres fixed on substrate with gold layer with optimized layer thickness in biomolecule solutions also had higher intensity and spectra modification then without gold layer. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2039049
  • 2014 • 127 Composition-Dependent Oxygen Reduction Activity and Stability of Pt-Cu Thin Films
    Schuppert, A.K. and Topalov, A.A. and Savan, A. and Ludwig, Al. and Mayrhofer, K.J.J.
    ChemElectroChem 1 358-361 (2014)
    Catalyst considerations: Pt-Cu alloys are prepared as a thin-film material library with a composition gradient. By using a scanning flow cell coupled to on-line mass spectrometry, this library can be screened over to measure the activity towards the oxygen reduction reaction as well as the time-resolved dissolution of both alloy components in parallel. This results in comprehensive insights into the composition-dependent performance of the Pt-Cu system. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201300078
  • 2014 • 126 Structure-related antibacterial activity of a titanium nanostructured surface fabricated by glancing angle sputter deposition
    Sengstock, C. and Lopian, M. and Motemani, Y. and Borgmann, A. and Khare, C. and Buenconsejo, P.J.S. and Schildhauer, T.A. and Ludwig, Al. and Köller, M.
    Nanotechnology 25 (2014)
    The aim of this study was to reproduce the physico-mechanical antibacterial effect of the nanocolumnar cicada wing surface for metallic biomaterials by fabrication of titanium (Ti) nanocolumnar surfaces using glancing angle sputter deposition (GLAD). Nanocolumnar Ti thin films were fabricated by GLAD on silicon substrates. S. aureus as well as E. coli were incubated with nanostructured or reference dense Ti thin film test samples for one or three hours at 37 °C. Bacterial adherence, morphology, and viability were analyzed by fluorescence staining and scanning electron microscopy and compared to human mesenchymal stem cells (hMSCs). Bacterial adherence was not significantly different after short (1 h) incubation on the dense or the nanostructured Ti surface. In contrast to S. aureus the viability of E. coli was significantly decreased after 3 h on the nanostructured film compared to the dense film and was accompanied by an irregular morphology and a cell wall deformation. Cell adherence, spreading and viability of hMSCs were not altered on the nanostructured surface. The results show that the selective antibacterial effect of the cicada wing could be transferred to a nanostructured metallic biomaterial by mimicking the natural nanocolumnar topography. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/25/19/195101
  • 2014 • 125 Fabrication of a Ni-Cu thin film material library using pulsed electrodeposition
    Srinivas, P. and Hamann, S. and Wambach, M. and Ludwig, Al. and Dey, S.R.
    Journal of the Electrochemical Society 161 D504-D509 (2014)
    A thin film composition gradient library of the Ni-Cu alloy system is generated through an electrodeposition technique using a complexing citrate electrolyte bath in a modified Hull cell. Energy dispersive X-ray spectroscopy, scanning electron microscopy and automated X-ray diffraction are performed to assess composition, surface morphology, and crystallographic structure of the deposited film as a function of the lateral position on the materials library. The results confirmed deposition of single phase polycrystalline f.c.c. Ni-Cu alloy system with varied lateral composition and lattice parameter, afcc as well. © 2014 The Electrochemical Society. All rights reserved.
    view abstractdoi: 10.1149/2.0451410jes
  • 2014 • 124 MOCVD of tungsten nitride thin films: Comparison of precursor performance and film characteristics
    Srinivasan, N.B. and Thiede, T.B. and De Los Arcos, T. and Rogalla, D. and Becker, H.-W. and Devi, A. and Fischer, R.A.
    Physica Status Solidi (A) Applications and Materials Science 211 260-266 (2014)
    Two different all nitrogen coordinated tungsten complexes, [W(N tBu)2(NMe2)2] (1) and [W(N tBu)2(NMe2){(iPrN) 2C(NMe2)}] (2) were compared for metal organic chemical vapour deposition (MOCVD) of tungsten nitride (WN) thin films in a state-of-the-art commercial MOCVD reactor. Precursor performances of both complexes were investigated under single source precursor (SSP) conditions and in the presence of ammonia as reactive gas where WN thin films were deposited on Si (100) substrates in a temperature range of 500-800°C. The X-ray diffraction (XRD) analysis showed that the films deposited under SSP conditions contained a mixture of carbide and nitride phases; while upon the addition of ammonia crystalline WN thin films were formed at higher temperatures (T ≥ 600°C). Elemental composition investigated by complementary techniques such as Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS) revealed that the films grown in the presence of ammonia had increased levels of nitrogen and a decreased carbon content in comparison to films grown under SSP conditions. WN films deposited in the presence of ammonia show higher resistivity values than those deposited under SSP conditions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201330127
  • 2014 • 123 Thermal conductivity of mesoporous films measured by Raman spectroscopy
    Stoib, B. and Filser, S. and Petermann, N. and Wiggers, H. and Stutzmann, M. and Brandt, M.S.
    Applied Physics Letters 104 (2014)
    We measure the in-plane thermal conductance of mesoporous Ge and SiGe thin films using the Raman-shift method and, based on a finite differences simulation accounting for the geometry of the sample, extract the in-plane thermal conductivity. For a suspended thin film of laser-sintered SiGe nanoparticles doped with phosphorus, we find an effective in-plane thermal conductivity of 0.05 W/m K in vacuum for a temperature difference of 400 K and a mean temperature of 500 K. Under similar conditions, the effective in-plane thermal conductivity of a laser-sintered undoped Ge nanoparticle film is 0.5 W/m K. Accounting for a porosity of approximately 50%, the normalized thermal conductivities are 0.1 W/m K and 1 W/m K, respectively. The thermoelectric performance is discussed, considering that the electrical in-plane conductivity is also affected by the mesoporosity. © 2014 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4873539
  • 2014 • 122 Deposition of superelastic composite NiTi based films
    Tillmann, W. and Momeni, S.
    Vacuum 104 41-46 (2014)
    In recent years, NiTi shape memory alloys (SMA) thin films have been widely used as promising high-performance materials in the field of biomedical and microelectromechanical (MEMS) systems. However, there are still important problems such as their unsatisfactory mechanical and tribological properties including a limited hardness and wear resistance. This study aimed at deposition of layered composite thin films made of NiTi and TiCN thin films on Si (100) substrate by means of DC magnetron sputtering. Subsequently, microstructures, mechanical properties and shape memory behavior of these bilayers were investigated using Nanoindentation, X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results of this study confirmed that the presence of TiCN layer on NiTi thin film modifies its mechanical properties while maintaining the shape memory effects. The initial findings of this research work are suggestive of the potential for fabrication of self-healed composite NiTi based films. © 2014 Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.vacuum.2013.12.010
  • 2014 • 121 Nanostructured Er2O3 thin films grown by metalorganic chemical vapour deposition
    Xu, K. and Dang, V.-S. and Ney, A. and De Los Arcos, T. and Devi, A.
    Journal of Nanoscience and Nanotechnology 14 5095-5102 (2014)
    Metalorganic chemical vapor deposition (MOCVD) of nanostructured Er 2O3 thin films was performed using the Er-tris-guanidinate precursor [Er(DPDMG)3] (DPDMG = diisopropyl-2- dimethylamidoguanidinato) as the Er source and oxygen. Film deposition was carried out on Si(100) and quartz glass substrates and the process parameters namely temperature, pressure and oxygen flow rate were varied. The resulting thin films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) for investigating the crystallinity and morphology, respectively. The chemical composition of the film was investigated by X-ray photoelectron spectroscopy (XPS) measurements. Transmittance and absorption spectra of the 600 °C film grown on glass substrates were performed by UV-vis measurements revealing more than 80% transmittance. The potential of Er2O3 thin films as gate dielectrics was verified by carrying out capacitance-voltage (C-V ) and current-voltage (I-V ) measurements. Dielectric constants estimated from the accumulation capacitance were found to be in the range of 10-12 in AC frequencies of 1 MHz down to 10 kHz and the leakage current of the order of 2×10-8 A/cm2 at the applied field of 1 MV cm-1 was measured for films deposited under optimised process conditions. The low leakage current and high dielectric constant implies good quality of the Er2O3 layers relevant for high-k applications. These layers were found to be paramagnetic with a slightly reduced magnetic moment of the Er3+ ions. Copyright © 2014 American Scientific Publishers All rights reserved.
    view abstractdoi: 10.1166/jnn.2014.8848
  • 2014 • 120 Influence of substrate and its temperature on the optical constants of CuIn1-xGaxSe2 thin films
    Yin, G. and Manley, P. and Schmid, M.
    Journal of Physics D: Applied Physics 47 (2014)
    We investigate the influence of substrate and its temperature on the optical constants of CuIn1-xGaxSe2 (CIGSe) thin films using the transfer-matrix method. The optical constants of a CIGSe layer on top of a transparent conducting oxide (TCO) layer were calculated considering the realistic optical constants of the TCO layer after CIGSe deposition. It was found that TCO substrates could influence the optical constants of CIGSe layers and that the ITO (Sn doped In2O3) substrate had a greater impact than IMO (Mo doped In2O3) for the CIGSe (x = 0.4) film when compared to a reference on bare glass substrate. Additionally, the varied substrate temperatures did not impact the optical constants of CGSe (x = 1). For CIGSe (x = 0.4), the refractive index n stayed relatively independent although at low temperature the grain size was reduced and the Ga/(Ga+In) profile was altered compared to that at high temperature (610 °C). In contrast, the extinction coefficient k at low temperature showed higher absorption at longer wavelengths because of a lower minimum bandgap (E g,min) originating from reduced inter-diffusion of Ga-Se at a low substrate temperature. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/47/13/135101
  • 2014 • 119 Mechanical properties of SiLix thin films at different stages of electrochemical Li insertion
    Zinn, A.-H. and Borhani-Haghighi, S. and Ventosa, E. and Pfetzing-Micklich, J. and Wieczorek, N. and Schuhmann, W. and Ludwig, Al.
    Physica Status Solidi (A) Applications and Materials Science 211 2650-2656 (2014)
    The mechanical properties of amorphous Si thin films, lithiated electrochemically to different Si£Li compositions are studied by ex situ nanoindentation. The compositions of the films are adjusted using an electrochemical routine that corrects for the Li consumed by SEI layer growth during initial lithiation. The mechanical properties such as Young's modulus and hardness are derived from nanoindentation. For compositions between Si and SiLi<inf>2.5</inf> the Young's modulus decreases with increasing Li content from ∼160 GPa to ∼8 GPa and the hardness decreases from ∼14 GPa to ∼0.1 GPa. The yield strength values, as deduced from hardness measurements, decrease from ∼5 GPa to 0.05 GPa. AFM imaging is used on the electrochemically cycled films to assess the SEIs impact on the nanomechanical measurements. XPS depth-profiling of the electrochemically cycled sample indicated a Li concentration gradient across the film thickness. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201431303
  • 2014 • 118 Interface reactions of Ag@TiO2 nanocomposite films
    Zuo, J. and Rao, J. and Eggeler, G.
    Materials Chemistry and Physics 145 90-98 (2014)
    TiO2 films were sputtered on 100-nm-thick Ag layers at various O2 partial pressures to study forming processes at the interface. The interfacial reactions during the deposition process were investigated by means of transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and UV-vis reflection spectra. The sputtering process led to formation of Ag nanoparticles surrounded by Ag 2O and TiO2 in the TiO2 film matrix as well as on the surface. The presence of oxygen in the plasma resulted in enrichment of silver oxides on the surface and an intermixing of Ag in the TiO2 matrix. The film structures could be explained based on the interplay among the formation of silver oxide, the nucleation and growth of TiO2, as well as the mobility of silver and silver oxides within the growing TiO2 films. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2014.01.041
  • 2013 • 117 Internal detection of surface plasmon coupled chemiluminescence during chlorination of potassium thin films
    Becker, F. and Krix, D. and Hagemann, U. and Nienhaus, H.
    Journal of Chemical Physics 138 (2013)
    The interaction of chlorine with potassium surfaces is a prototype reaction with a strong non-adiabatic energy transfer leading to exoemission and chemiluminescence. Thin film K/Ag/p-Si(111) Schottky diodes with 8 nm potassium on a 5-200 nm thick Ag layer are used as 2π-photodetectors for the chemiluminescence during chlorination of the K film at 110 K. The observed photocurrent shows a sharp maximum for small exposures and decreases gradually with the increasing chloride layer. The time dependence can be explained by the reaction kinetics, which is governed initially by second-order adsorption processes followed by an electric field-assisted diffusion. The detector current corresponds to a yield of a few percent of elementary charge per reacting chlorine molecule and is orders of magnitude larger than for external detection. The photoyield can be enhanced by increasing the Ag film thickness. For Ag films of 30 and 50 nm, the yield exhibits a maximum indicating surface plasmon coupled chemiluminescence. Surface plasmon polaritons in the Ag layer are excited by the reaction and decay radiatively into Si leading to the observed currents. A model calculation for the reverse process in attenuated total reflection is applied to explain the observed current yield maxima. © 2013 American Institute of Physics.
    view abstractdoi: 10.1063/1.4776156
  • 2013 • 116 Thickness dependent exchange bias in martensitic epitaxial Ni-Mn-Sn thin films
    Behler, A. and Teichert, N. and Dutta, B. and Waske, A. and Hickel, T. and Auge, A. and Hütten, A. and Eckert, J.
    AIP Advances 3 (2013)
    A thickness dependent exchange bias in the low temperature martensitic state of epitaxial Ni-Mn-Sn thin films is found. The effect can be retained down to very small thicknesses. For a Ni50Mn32Sn18 thin film, which does not undergo a martensitic transformation, no exchange bias is observed. Our results suggest that a significant interplay between ferromagnetic and antiferromagnetic regions, which is the origin for exchange bias, is only present in the martensite. The finding is supported by ab initio calculations showing that the antiferromagnetic order is stabilized in the phase. © 2013 Author(s).
    view abstractdoi: 10.1063/1.4849795
  • 2013 • 115 Morphology evolution in mesoporous titania block copolymer composite films with increasing Sol-Gel reaction time
    Cheng, Y.-J. and Zhou, S. and Wolkenhauer, M. and Bumbu, G.-G. and Lenz, S. and Memesa, M. and Nett, S. and Emmerling, S. and Steffen, W. and Gutmann, J.S.
    European Journal of Inorganic Chemistry 1127-1133 (2013)
    A morphology evolution of thin films of titania from spherical mesopores to worm-shaped mesopores was realized by simply varying the sol-gel reaction time from 46 min to 25 h in the quadruple system consisting of polystyrene-block- poly(ethylene oxide) (PS-b-PEO), 1,4-dioxane, concentrated HCl, and titanium tetraisopropoxide (TTIP). Imaging techniques including scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to investigate the local structure change of the as-prepared, calcined, and UV-degraded composite films. Grazing incidence small angle X-ray scattering (GISAXS) experiments prove that the structure change in local areas is representative of that over the macroscopic scale. An X-ray reflectivity (XRR) investigation reveals that the vertical structure change happens when the sol-gel reaction is extended from 5 to 25 h. A combination of imaging and scattering techniques provides a powerful tool to elucidate the impact of the sol-gel reaction time on the morphology evolution of the composite films. Dynamic light scattering (DLS) studies imply that the morphology evolution within the films is due to the structure change in solution. A mechanism of the morphology evolution with sol-gel reaction time is proposed on the basis of these results, which provide not only a new way to control the morphology of titania block copolymer composite films but also deep insights into the kinetics of the amphiphilic block copolymer templating process. Evolution of the morphology of TiO 2 thin films from spherical mesopores to worm-shaped mesopores has been achieved by simply varying the sol-gel reaction time of titanium tetraisopropoxide (TTIP) in the quadruple templating system copolymer PS-b-PEO, 1,4-dioxane, conc. HCl, and TTIP. Effective horizontal and vertical structure control is demonstrated at both the local and macroscopic scale. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ejic.201201366
  • 2013 • 114 Structural phase transitions in ferroelectric crystals and thin films studied by VUV spectroscopic ellipsometry with synchrotron radiation
    Dorywalski, K. and Andriyevsky, B. and Piasecki, M. and Kityk, I. and Cobet, C. and Esser, N. and Patryn, A.
    Phase Transitions 86 932-940 (2013)
    Results of thermo-optical investigations for lead germanate (Pb5Ge3O11), potassium dihydrogen phosphate (KH2PO4) ferroelectric crystals, and lead titanate (PbTiO3) thin films expitaxially deposited on (001) SrTiO3 substrate are presented in this article. The measurements were performed using VUV spectroscopic ellipsometry with synchrotron radiation in the temperature range comprising structural phase transitions (PTs) in the materials under study. Distinct anomalies in the temperature dependencies of complex dielectric permittivity and the intensity of reflected synchrotron light are found in the vicinity of ferroelectric-to-paraelectric PT point and discussed. Different temperature points of the characteristic anomalies at the PT of the real and imaginary components of the pseudo-dielectric function are observed for Pb5Ge3O11 and KH2PO4. It is crucial that anomalies in the measured temperature dependences for PbTiO3 thin films on SrTiO3 substrates are observed at the temperature near 105 K, corresponding to the PT in the SrTiO3 single crystal. © 2013 Copyright Taylor and Francis Group, LLC.
    view abstractdoi: 10.1080/01411594.2012.745540
  • 2013 • 113 Chemical and Physical Sputtering of Polyethylene Terephthalate (PET)
    Grosse-Kreul, S. and Corbella, C. and von Keudell, A.
    Plasma Processes and Polymers 10 225--234 (2013)
    The polymer polyethylene terephthalate (PET) has been exposed to quantified beams of argon ions and oxygen atoms and molecules. The etch rate (ER) and the surface composition of PET thin films have been analyzed by real time in situ Fourier transform infrared spectroscopy (FTIR). After the onset of the exposure of PET to the ion beam, the ER decreases rapidly by one order of magnitude irrespective of the ion energy. This slowing down of the ER is caused by cross-linking of the polymer surface. The steady state etch yields are generally orders of magnitude higher than predicted by computer calculations. The addition of oxygen to the particle flux is only changing the surface composition. At low ion energies, chemical sputtering dominates causing very high sputter yields. In addition, no threshold ion energy is observed. [GRAPHICS] .
    view abstractdoi: 10.1002/ppap.201200094
  • 2013 • 112 Compositional trends and magnetic excitations in binary and ternary Fe-Pd-X magnetic shape memory alloys
    Gruner, M.E. and Hamann, S. and Brunken, H. and Ludwig, Al. and Entel, P.
    Journal of Alloys and Compounds 577 S333-S337 (2013)
    High throughput thin film experiments and first-principles calculations are combined in order to get insight into the relation between finite temperature transformation behavior and structural ground state properties of ternary Fe-Pd-X alloys. In particular, we consider the binding surface, i.e., the energy of the disordered alloy calculated along the Bain path between bcc and fcc which we model by a 108 atom supercell. We compare stoichiometric Fe 75Pd25 with ternary systems, where 4.6% of the Fe atoms were substituted by Cu and Mn, respectively. The computational trends are related to combinatorial experiments on thin film libraries for the systems Fe-Pd-Mn and Fe-Pd-Cu which reveal a systematic evolution of the martensitic start temperature with composition within the relevant concentration range for magnetic shape memory (MSM) applications. Our calculations include atomic relaxations, which were shown to be relevant for a correct description of the structural properties. Furthermore, we find that magnetic excitations can substantially alter the binding surface. The comparison of experimental and theoretical trends indicates that, both, compositional changes and magnetic excitations contribute significantly to the structural stability which may thus be tailored by specifically adding antiferromagnetic components. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jallcom.2012.02.033
  • 2013 • 111 Synthesis of Au microwires by selective oxidation of Au-W thin-film composition spreads
    Hamann, S. and Brunken, H. and Salomon, S. and Meyer, R. and Savan, A. and Ludwig, Al.
    Science and Technology of Advanced Materials 14 (2013)
    We report on the stress-induced growth of Au microwires out of a surrounding Au-W matrix by selective oxidation, in view of a possible application as 'micro-Velcro'. The Au wires are extruded due to the high compressive stress in the tungsten oxide formed by oxidation of elemental W. The samples were fabricated as a thin-film materials library using combinatorial sputter deposition followed by thermal oxidation. Sizes and shapes of the Au microwires were investigated as a function of the W to Au ratio. The coherence length and stress state of the Au microwires were related to their shape and plastic deformation. Depending on the composition of the Au-W precursor, the oxidized samples showed regions with differently shaped Au microwires. The Au48W52 composition yielded wires with the maximum length to diameter ratio due to the high compressive stress in the tungsten oxide matrix. The values of wire length (35 μm) and diameter (2 μm) achieved at the Au48W52 composition are suitable for micro-Velcro applications. © 2013 National Institute for Materials Science.
    view abstractdoi: 10.1088/1468-6996/14/1/015003
  • 2013 • 110 Transmission electron microscopy characterization of CrN films on MgO(001)
    Harzer, T.P. and Daniel, R. and Mitterer, C. and Dehm, G. and Zhang, Z.L.
    Thin Solid Films 545 154-160 (2013)
    Two CrN(001) films with different thickness were grown on MgO(001) substrates using unbalanced d.c.magnetron sputtering.The morphology and interfacial structure of the films are characterized by using conventional transmission electron microscopy, weak-beam dark-field microscopy and spherical aberration (CS)-corrected high-resolution transmission electron microscopy.The microscopy studies revealed the well-known cube-on-cube orientation relationship.While an interface dislocation network with b→=1/2aCrN< 100&gt; edge dislocations was identified, only part of the lattice mismatch is relaxed.The misfit dislocation structure and growth defects are analyzed and discussed based on the weak-beam dark-field and high-resolution transmission electron microscopy results.© 2013 Elsevier B.V.All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2013.07.064
  • 2013 • 109 Preparation of thin film Cu-Pt(1 1 1) near-surface alloys: One small step towards up-scaling model single crystal surfaces
    Henry, J.B. and Maljusch, A. and Tymoczko, J. and Schuhmann, W. and Bandarenka, A.S.
    Electrochimica Acta 112 887-893 (2013)
    A method for the preparation of Pt(1 1 1) like thin films and thin film Cu-Pt(1 1 1) near-surface alloys (where Cu is preferentially located in the subsurface region) is reported in detail. Cyclic voltammograms of the resultant Pt(1 1 1)-like thin films in 0.1 M HClO4 demonstrate characteristic "butterfly" peaks attributed to the disorder/order phase transition in the adsorbed*OH layer, typical for a large Pt(1 1 1) crystals. Modification of the film surface with a monolayer of Cu and subsequent annealing in a reducing Ar/H2(5%) atmosphere, the voltammograms resemble those obtained for Cu-Pt(1 1 1) near-surface alloys prepared on commercial bulk single crystals. This method shows promise for the fabrication of extended (1 1 1)-type alloy surfaces of Pt and its alloys and can additionally be used to up-scale model objects for wider industrial and laboratory applications. © 2012 Elsevier Ltd.
    view abstractdoi: 10.1016/j.electacta.2012.11.139
  • 2013 • 108 Electrochemical formation and surface characterisation of Cu 2-xTe thin films with adjustable content of Cu
    Huang, M. and Maljusch, A. and Calle-Vallejo, F. and Henry, J.B. and Koper, M.T.M. and Schuhmann, W. and Bandarenka, A.S.
    RSC Advances 3 21648-21654 (2013)
    Electrochemically driven "intercalation" of Cu into Te was used to prepare Cu<inf>2-x</inf>Te (0.2 < x ≤ 2) thin films and accurately control the composition of the resulting samples. A thorough theoretical analysis of the system using density functional theory (DFT) calculations showed that in the absence of external electric fields the driving forces for Cu atoms to move into the subsurface layers of the Te electrodes depend on the surface coverage of copper atoms. The Cu atoms tend to preferentially occupy the subsurface layers in the telluride films. The effective electric charge on Cu atoms inside the Te-electrodes is positive. These effective charge differences with respect to pure Cu and pure Te are only 0.2 e-. Scanning Kelvin probe (SKP), atomic force microscopy (AFM) and electrochemical techniques were used to characterise the surface status of the obtained samples. Both, DFT-calculated work function differences and the SKP-measured contact potential differences (CPD) change non-linearly with the variation of the film composition. Interfacial (solid/liquid) properties evaluated using electrochemical impedance spectroscopy depend on the nominal composition of the samples and display an abrupt change that correlates with a large change in the work function and CPD. While the proposed electrochemical synthetic route can efficiently and accurately control the composition of the Cu<inf>2-x</inf>Te thin films, SKP-measurements performed under close to ambient conditions in combination with DFT calculations can provide a promising tool to link fundamental surface properties and parameters which define the interface between solids and liquids. © The Royal Society of Chemistry 2013.
    view abstractdoi: 10.1039/c3ra42504e
  • 2013 • 107 Aging-induced optical anisotropy in thermally grown thin ZnTPP films on Si
    Kate, S.P. and Pop, S. and Esser, N. and Rappich, J. and Zhang, X. and Hinrichs, K.
    Physica Status Solidi (B) Basic Research 250 1791-1794 (2013)
    We present reflection anisotropy spectroscopy (RAS) as a powerful optical technique for degradation studies of structurally changing thin organic films, here the case of porphyrin films. The measured optical anisotropy of a thin (d=16nm) ZnTPP (Zinc tetraphenylporphyrin) film grown by thermal evaporation on silicon using reflectance anisotropy spectroscopy was studied before and after aging in ambient conditions. The observed absorption features, also found by standard transmission spectroscopy, are correlated with the π-π*electronic transitions of the Q and Soret bands of the molecule. Simulation of RAS spectra revealed blue-shifted resonances, which are in agreement with a preferential face-to-face (stacking) arrangement of the ZnTPP molecules. The findings are in agreement with atomic force microscopy studies of the surface morphology showing with aging a transition from a closed film to separated aggregates. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssb.201248538
  • 2013 • 106 Intrinsic nitrogen-doped CVD-grown TiO2 thin films from all-N-coordinated Ti precursors for photoelectrochemical applications
    Kim, S.J. and Xu, K. and Parala, H. and Beranek, R. and Bledowski, M. and Sliozberg, K. and Becker, H.-W. and Rogalla, D. and Barreca, D. and Maccato, C. and Sada, C. and Schuhmann, W. and Fischer, R.A. and Devi, A.
    Chemical Vapor Deposition 19 45-52 (2013)
    N-doped titanium dioxide (TiO2) thin films are grown on Si(100) and indium tin oxide (ITO)-coated borosilicate glass substrates by metal-organic (MO)CVD. The intrinsic doping of TiO2 thin films is achieved using all-nitrogen-coordinated Ti precursors in the presence of oxygen. The titanium amide-guanidinate complex, [Ti(NMe2)3(guan)] (guan = N,N′-diisopropyl-2-dimethylamidoguanidinato) has been developed to compensate for the thermal instability of the parent alkylamide [Ti(NMe 2)4]. Both of these amide-based compounds are tested and compared as precursors for intrinsically N-doped TiO2 at various deposition temperatures in the absence of additional N sources. The structure and morphology of TiO2 thin films are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Rutherford back scattering (RBS), nuclear reaction analysis (NRA), and secondary ion mass spectrometry (SIMS) analyses are performed to determine N content and distribution in the films. The optical and photoelectrochemical properties of TiO2 thin films on ITO substrates are also examined. N-doped TiO2 thin films, grown from [Ti(NMe 2)3(guan)] at 600 °C, exhibit the lowest optical absorption edge (3.0 eV) and the highest visible light photocurrent response. When compared to undoped TiO2, while in UV light photoconversion efficiency decreases significantly, the intrinsically N-doped TiO2 shows enhanced photocurrents under visible light irradiation. The intrinsic doping of TiO2 thin films with nitrogen by MOCVD and the investigation of the photo-electrochemical properties of the films are reported. N-doped anatase phase TiO2 thin films are grown on Si(100) and ITO substrates under specific processing conditions, using [Ti(NMe2) 4] (1) and [Ti(NMe2)3(guan)] (2) (guan = N,N′-diisopropyl-2-dimethylamidoguanidinato) as precursors. The films grown from [Ti(NMe2)3(guan)] at 600 °C show relatively large surface roughness and lower bandgap related with high N content. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cvde.201206996
  • 2013 • 105 Scanning droplet cell microscopy on a wide range hafnium-niobium thin film combinatorial library
    Mardare, A.I. and Ludwig, Al. and Savan, A. and Hassel, A.W.
    Electrochimica Acta 110 539-549 (2013)
    A wide-range thin film Hf-Nb combinatorial library deposited by co-sputtering is studied. The microstructure and crystallographic properties of the thin film alloys locally investigated by SEM and GIXRD are mapped along the entire compositional spread from 14 to 94 at.% Nb. Scanning droplet cell microscopy (SDCM) is used for mapping the electrochemical properties of the naturally oxidised metallic surfaces. Anodisation of the Hf-Nb thin films alloys is achieved with a high throughput due to computer-controlled scanning, made with a composition resolution of 1 at.%. The electrical properties of the anodic oxides are mapped by EIS and a maximum electrical permittivity close to 75 was found for Hf-33 at.% Nb. Semiconducting properties of the mixed anodic oxides are studied using Mott-Schottky analysis and their composition and mixing is investigated by XPS depth profiling.© 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.electacta.2013.03.065
  • 2013 • 104 Structure and magnetization in CoPd thin films and nanocontacts
    Morgan, C. and Schmalbuch, K. and García-Sánchez, F. and Schneider, C.M. and Meyer, C.
    Journal of Magnetism and Magnetic Materials 325 112-116 (2013)
    We present results showing the structural and magnetic properties of MBE-grown extended films and nanostructured elements of various CoPd alloys. X-ray diffraction studies show that the thin films are polycrystalline, yet exhibit a strong preferential growth orientation along the (111) direction. Magnetic force microscopy and SQUID are used to gain an understanding of the magnetic behavior of the CoPd system with respect to competing anisotropy contributions, based on temperature-dependent SQUID data, collected between 4 and 300 K. The idea and potential implications of using CoPd as a contact material to achieve spin injection in carbon nanotube-based devices is discussed. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jmmm.2012.07.052
  • 2013 • 103 Electronic structure, surface morphology, and topologically protected surface states of Sb2Te3 thin films grown on Si(111)
    Plucinski, L. and Herdt, A. and Fahrendorf, S. and Bihlmayer, G. and Mussler, G. and Döring, S. and Kampmeier, J. and Matthes, F. and Bürgler, D.E. and Grützmacher, D. and Blügel, S. and Schneider, C.M.
    Journal of Applied Physics 113 (2013)
    We have performed a combined spectroscopy and microscopy study on surfaces of Sb2Te3/Si(111) thin films exposed to air and annealed under ultra-high vacuum conditions. Scanning tunneling microscopy images, with atomic resolution present in most areas of such processed surfaces, show a significant amount of impurities and defects. Scanning tunneling spectroscopy reveals the bulk band gap of ∼ 170 meV centered ∼ 65 meV above the Fermi level. This intrinsic p-type doping behavior is confirmed by high-resolution angle-resolved photoemission spectra, which show the dispersions of the lower Dirac cone and the spectral weight of the bulk valence bands crossing the Fermi level. Spin-polarized photoemission revealed up to ∼15% in-plane spin polarization for photoelectrons related to the topologically protected Dirac cone states near the Fermi level, and up to ∼40% for several states at higher binding energies. The results are interpreted using ab initio electronic structure simulations and confirm the robustness of the time-reversal symmetry protected topological surface states in Sb2 Te3 in the presence of impurities and defects. © 2013 American Institute of Physics.
    view abstractdoi: 10.1063/1.4789353
  • 2013 • 102 Transition metal nitride thin films grown by MOCVD using amidinato based complexes [M(NtBu)2{(iPrN)2CMe}2] (M=Mo, W) as precursors
    Srinivasan, N.B. and Thiede, T.B. and de los Arcos, T. and Gwildies, V. and Krasnopolski, M. and Becker, H.-W. and Rogalla, D. and Devi, A. and Fischer, R.A.
    Surface and Coatings Technology 230 130-136 (2013)
    Thin films of molybdenum nitride and tungsten nitride were deposited by metal organic chemical vapour deposition (MOCVD) employing the mixed amidinato-imido compounds [M(NtBu)2{(iPrN)2CMe}2] (M=Mo (1), W (2)) as potential precursors under single source precursor (SSP) condition and in the presence of ammonia at substrate temperatures of 500°C-800°C. Under SSP conditions, the films consisted of the nitride and carbide phases for both the material systems, while the addition of ammonia during the MOCVD process led to the formation of the respective metal nitrides. The films were smooth and amorphous at 500°C, and comprised of very fine grains at higher temperatures. Elemental composition investigated by complementary techniques such as Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS) revealed that the films grown in the presence of ammonia had increased levels of nitrogen and decreased carbon content relative to films grown under SSP condition. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2013.06.024
  • 2013 • 101 Surface morphology of MnSi thin films grown on Si(111)
    Suzuki, T. and Lutz, T. and Geisler, B. and Kratzer, P. and Kern, K. and Costantini, G.
    Surface Science 617 106-112 (2013)
    The surface morphology of MnSi thin films grown on Si(111)-7 × 7 substrates was investigated by systematically changing the amount of deposited Mn. A new 3 × 3 surface reconstruction was found at the very initial growth stages, whose atomic configuration was analyzed both experimentally and theoretically. At a coverage of 0.1 monolayers, the formation of nanometer-sized MnSi islands was observed in coexistence with Mn nanoclusters that fit within the 7 × 7 half unit cell. With increasing Mn deposition, the MnSi islands grow, develop extended flat tops and eventually coalesce into an atomically flat film with a high corrugated 3×3 reconstruction punctuated by several holes. The successive film growth mode is characterized by the formation of MnSi quadlayers with a low corrugated 3×3 reconstruction. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.susc.2013.08.005
  • 2013 • 100 A study of mechanical and tribological properties of self-lubricating TiAlVN coatings at elevated temperatures
    Tillmann, W. and Momeni, S. and Hoffmann, F.
    Tribology International 66 324-329 (2013)
    There are several manufacturing processes, in which the employment of solid lubricants is limited. In addition, ecological damage and higher production costs are further consequences of using such solid lubricants. This work aims at using the great potential of thin film technology to deposit adaptive, self-lubricating coatings as an alternative to conventional solid lubricants. Using magnetron sputtering process several titanium aluminum vanadium nitride coatings (TiAlVN) were developed in this study. These quaternary coatings possess the ability of forming lubricious oxides, known as Magnéli phases, at elevated temperatures, which significantly reduces the friction coefficient and surface wear. © 2013 Elsevier Ltd.
    view abstractdoi: 10.1016/j.triboint.2013.06.007
  • 2013 • 99 Generalized synthesis of mesoporous rare earth oxide thin films through amphiphilic ionic block copolymer templating
    Xiao, Y. and You, S. and Yao, Y. and Zheng, T. and Lin, C. and Roth, S.V. and Müller-Buschbaum, P. and Steffen, W. and Sun, L.-D. and Yan, C.-H. and Gutmann, J.S. and Yin, M. and Fu, J. and Cheng, Y.-J.
    European Journal of Inorganic Chemistry 1251-1257 (2013)
    A new concept to achieve the generalized synthesis of crystalline mesoporous rare earth (RE) oxide thin films templated with an ionic amphiphilic block copolymer is developed. Mesoporous La2O3, Eu 2O3, Tb2O3, and Yb2O 3 thin films as representatives of the light and heavy RE groups are synthesized by using polystyrene-block-poly(acrylic acid) (PS-b-PAA) as a templating agent. The impact of the concentration of PS-b-PAA on the morphologies of the mesopores is investigated. The local and long-range lateral structures, vertical structures, and crystallinities of the mesoporous thin films are probed by scanning electron microscopy, atomic force microscopy, grazing-incidence small-angle X-ray scattering, X-ray reflectivity, and transmission electron microscopy. The mechanism of formation of the mesoporous RE oxide thin films is discussed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ejic.201201524
  • 2013 • 98 Atomic layer deposition of Er2O3 thin films from Er tris-guanidinate and water: Process optimization, film analysis and electrical properties
    Xu, K. and Chaudhuri, A.R. and Parala, H. and Schwendt, D. and Arcos, T.D.L. and Osten, H.J. and Devi, A.
    Journal of Materials Chemistry C 1 3939-3946 (2013)
    For the first time, the combination of the homoleptic erbium tris-guanidinate metalorganic complex ([Er(NMe2-Guan)3]) simply with water yielded high quality Er2O3 thin films on Si(100) substrates employing the atomic layer deposition (ALD) process. The process optimization to grow good quality Er2O3 layers was performed by varying the Er precursor pulse time, water pulse time and purge time. The high reactivity of the Er compound towards water and good thermal stability in the temperature range of 150-275°C (ALD window) resulted in homogeneous, stoichiometric Er2O3 layers with high growth rates (1.1 Å per cycle) and the as-deposited films crystallized in the cubic phase. The saturation behavior at different temperatures in the ALD window and the linear dependence of film thickness as a function of precursor pulse time confirmed the true ALD process. The potential of Er2O 3 thin films as gate dielectrics was verified by performing capacitance-voltage (C-V) and current-voltage (I-V) measurements. Dielectric constants estimated from the accumulation capacitance were found to be in the range of 10-13 for layers of different thicknesses (15-30 nm). © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3tc30401a
  • 2013 • 97 Thermoelectric transport and Hall measurements of low defect Sb 2Te3 thin films grown by atomic layer deposition
    Zastrow, S. and Gooth, J. and Boehnert, T. and Heiderich, S. and Toellner, W. and Heimann, S. and Schulz, S. and Nielsch, K.
    Semiconductor Science and Technology 28 (2013)
    Sb2Te3 has recently been an object of intensive research since its promising applicability in thermoelectric, in phase-change memory devices and as a topological insulator. In this work, we report highly textured Sb2Te3 thin films, grown by atomic layer deposition on Si/SiO2 wafers based on the reaction of SbCl 3 and (Et3Si)2Te. The low deposition temperature at 80 °C allows the pre-patterning of the Sb2Te 3 by standard lithography processes. A platform to characterize the Seebeck coefficient S, the electrical conductivity σ as well as the Hall coefficient RH on the same film has been developed. Comparing all temperature-dependent transport properties, three different conductive regions in the temperature range of 50-400 K are found. Room temperature values of S = 146 × 10-6 VK-1, σ = 104 Sm -1 and mobility M = 270.5 × 10-4 m2 V-1 s-1 are determined. The low carrier concentration in the range of n = 2.4 × 1018 cm-3 at 300 K quantifies the low defect content of the Sb2Te3 thin films. © 2013 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0268-1242/28/3/035010
  • 2012 • 96 Temperature-driven nucleation of ferromagnetic domains in FeRh thin films
    Baldasseroni, C. and Bordel, C. and Gray, A.X. and Kaiser, A.M. and Kronast, F. and Herrero-Albillos, J. and Schneider, C.M. and Fadley, C.S. and Hellman, F.
    Applied Physics Letters 100 (2012)
    The evolution of ferromagnetic (FM) domains across the temperature-driven antiferromagnetic (AF) to FM phase transition in uncapped and capped epitaxial FeRh thin films was studied by x-ray magnetic circular dichroism and photoemission electron microscopy. The coexistence of the AF and FM phases was evidenced across the broad transition and the different stages of nucleation, growth, and coalescence were directly imaged. The FM phase nucleates into single domain islands and the width of the transition of an individual nucleus is sharper than that of the transition in a macroscopic average. © 2012 American Institute of Physics.
    view abstractdoi: 10.1063/1.4730957
  • 2012 • 95 Fabrication of ZrO 2 and ZrN films by metalorganic chemical vapor deposition employing new Zr precursors
    Banerjee, M. and Srinivasan, N.B. and Zhu, H. and Kim, S.J. and Xu, K. and Winter, M. and Becker, H.-W. and Rogalla, D. and De Los Arcos, T. and Bekermann, D. and Barreca, D. and Fischer, R.A. and Devi, A.
    Crystal Growth and Design 12 5079-5089 (2012)
    The application of new zirconium precursors for the fabrication of ZrO 2 and ZrN thin films by metalorganic chemical vapor deposition (MOCVD) is presented. The all-nitrogen coordinated Zr precursors exhibit improved thermal properties for vapor phase fabrication of thin films. The growth of ZrO 2 thin films was realized by the combination of the Zr complex with oxygen, while the formation of ZrN thin films was achieved for the first time employing a single source precursor (SSP) approach. This was enabled by the presence of nitrogen containing ligands which contributes to the formation of the ZrN phase without the need for any additional nitrogen source in contrast to classical film growth processes for ZrN thin films. In the first step the newly developed precursors were evaluated thoroughly for their use in MOCVD applications, and in the next step they were utilized for the growth of ZrO 2 and ZrN thin films on Si(100) substrates. Polycrystalline ZrO 2 films that crystallized in the monoclinic phase and the fcc-ZrN films oriented in the (200) direction were obtained, and their structure, morphology, and composition were analyzed by a series of techniques. This work shows the potential of tuning precursors for vapor phase fabrication of Zr containing thin films with a goal of obtaining two different classes of material systems (ZrO 2 and ZrN) using one common precursor. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/cg3010147
  • 2012 • 94 Dual frequency capacitive plasmas in Fe and Ni sputter applications: Correlation of discharge properties on thin film properties
    Bienholz, S. and Semmler, E. and Awakowicz, P. and Brunken, H. and Ludwig, Al.
    Plasma Sources Science and Technology 21 (2012)
    Dual frequency capacitively coupled plasmas (CCPs) are widely used in (large area) etching and plasma enhanced chemical vapor deposition processes. However, applications in physical vapor deposition (PVD) are still sparse due to the well-established dc magnetron cathode discharges. Nevertheless, there exist critical applications such as ferromagnetic or ceramic thin film deposition which are difficult to handle even for dc magnetron systems. For these materials systems dual frequency CCPs pose a good alternative, because for insulators charging can be avoided and for ferromagnetic materials the target thickness becomes independent of the magnetron configuration at comparable deposition rates. In this work we investigate two separate subjects. First, in dual frequency capacitive discharges a complex coupling of the applied excitation frequencies can be observed, which from a plasma parameter point of view limits the separability of ion flux (usually controlled by frequencies >60MHz) and ion bombarding energy (usually controlled by frequency <15MHz) onto the sputter target. By performing deposition experiments it was found that by following simple tuning guidelines a very good degree of separability is achievable. Additionally, the deposition homogeneity is not affected. Second, we correlate the growth conditions with crystalline and magnetic properties as well as the degree of O content for Fe and Ni films. Therefore, we applied different signals as a substrate bias to influence thin film growth. It was found that the crystalline and magnetic properties can be influenced for both Fe and Ni films but is more pronounced for Ni. © 2012 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0963-0252/21/1/015010
  • 2012 • 93 Mechanical layer compaction for dispersion processed nanoparticulate zinc oxide thin film transistors
    Bubel, S. and Schmechel, R.
    Microelectronic Engineering 96 36-39 (2012)
    Using rolling as a roll-to-roll compatible compaction process for solution processable electronics, we demonstrate improved layer morphology and field effect transistor performance of nanoparticulate zinc oxide (ZnO) thin films. Semiconducting ZnO layers have been processed from a polyvinylpyrrolidone (PVP) stabilized nanoparticulate dispersion at low temperatures. Maximum saturation mobilities of 7×10-3cm2/V s, improvements in mobility of more than one order of magnitude and a reduction in threshold voltage by more than 30% are shown. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.mee.2012.02.044
  • 2012 • 92 N-type perylene to fill voids in solution processed nanoparticulate zinc oxide thin films
    Bubel, S. and Ringk, A. and Strohriegl, P. and Schmechel, R.
    Physica E: Low-Dimensional Systems and Nanostructures 44 2124-2127 (2012)
    Using nanoparticle dispersions for printing of semiconductors would be the easiest way to evolve from classic printing technologies towards printed electronics. However, nanoparticular thin films are unfavorable in transistor applications due to two reasons: (i) The charge transport in the thin film or at its interfaces to the gate dielectric is disturbed by the voids between the nanoparticles. (ii) These layers are highly sensitive to surface adsorbates due to their high surface to volume ratio. Atmospheric surface adsorbates, e.g. on metal oxides are known to influence the electrical properties of the thin films. In order to overcome the disadvantages of the nanoparticulate thin film, this work targets both issues with a combined approach. By choosing a qualified surface adsorbate, the perturbing surface of the nanoparticles will be passivated. By using the surface adsorbate as a linker to an electron conducting organic molecule, the n-type organic will be eligible for filling the voids between the particles. We present the synthesis of a new pyrrolidone functionalized n-type perylene diimide and its application in hetero-layer nanoparticulate zinc oxide (ZnO) field-effect transistors. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.physe.2012.06.027
  • 2012 • 91 Influence of annealing atmospheres and synthetic air treatment on solution processed zinc oxide thin film transistors
    Busch, C. and Schierning, G. and Theissmann, R. and Schmechel, R.
    Journal of Applied Physics 112 (2012)
    Thin film transistors (TFTs) based on active layers of zinc oxide prepared from a solution process were fabricated under different annealing conditions. The influence of the annealing gas as well as the influence of a subsequent exposure to synthetic air to the device properties is considered. Annealing under N 2 or H 2 atmosphere leads to a strong negative threshold voltage shift. With respect to known defect states in ZnO, two different donor states are suggested to be responsible for the negative threshold voltage. A subsequent synthetic air treatment causes in general a positive threshold voltage shift. However, transistors annealed under H 2 degrade very fast under synthetic air in contrast to transistors annealed under N 2. In order to obtain more information about the density of states (DOS) distribution, a transistor model for thin film transistors in the hopping transport regime (Vissenberg model) was utilized. For positive threshold voltages, the DOS distribution is independent from the gas treatment and the threshold voltage within the experimental accuracy. This indicates a shift of the Fermi-level within an exponentially decaying DOS. The change in the charge carrier density is either due to shallow donors or due to a charge transfer with acceptors at the surface. In contrast, for negative threshold voltages, the DOS distribution parameter rises, indicating a flatter DOS distribution. We suggest that the difference is due to the change from accumulation mode to the depletion mode of the device. © 2012 American Institute of Physics.
    view abstractdoi: 10.1063/1.4742976
  • 2012 • 90 Thermoreflectance imaging of percolation effects and dynamic resistance in indium tin oxide nanoparticle layers
    Chavez, R. and Angst, S. and Maize, K. and Gondorf, A. and Schierning, G. and Wolf, D.E. and Lorke, A. and Shakouri, A.
    Journal of Applied Physics 112 (2012)
    Thin films of indium tin oxide nanoparticles are studied using charge-coupled device thoermoreflectance. High resolution sub-micron thermal images confirm that percolation in current conduction induces strongly inhomogeneous heat loads on the thin film. We experimentally show that the inhomogeneous current densities induce thousands of micro-hotspots that can be 20 hotter than the average Joule heating in the thin film layer and show comparable behavior in a resistor network. In addition to the percolation induced micro-hotspots, we report major hotspots, with non-Joule behavior, whose temperature response is greater than I 2. We demonstrate that a temperature dependent resistor can account for an effective exponent larger than 2. Finally, it is shown that while ambient molecules modify the thin film conductivity by at least 20, current conduction and percolation effects remain largely unchanged, but such chemical reactions can be nonetheless detected with thermoreflectance. © 2012 American Institute of Physics.
    view abstractdoi: 10.1063/1.4757960
  • 2012 • 89 A facile route to reassemble titania nanoparticles into ordered chain-like networks on substrate
    Cheng, Y.-J. and Wolkenhauer, M. and Bumbu, G.-G. and Gutmann, J.S.
    Macromolecular Rapid Communications 33 218-224 (2012)
    A facile route to reassemble titania nanoparticles within the titania-block copolymer composite films has been developed. The titania nanoparticles templated by the amphiphilic block copolymer of poly(styrene)-block-poly (ethylene oxide) (PS-b-PEO) were frozen in the continuous PS matrix. Upon UV exposure, the PS matrix was partially degraded, allowing the titania nanoparticles to rearrange into chain-like networks exhibiting a closer packing. The local structures of the Titania chain-like networks were investigated by both AFM and SEM; the lateral structures and vertical structures of the films were studied by GISAXS and X-ray reflectivity respectively. Both the image analysis and X-ray scattering characterization prove the reassembly of the titania nanoparticles after UV exposure. The mechanism of the nanoparticle assembly is discussed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201100638
  • 2012 • 88 Robust mechanical performance of chromium-coated polyethylene terephthalate over a broad range of conditions
    Cordill, M.J. and Taylor, A.A. and Berger, J. and Schmidegg, K. and Dehm, G.
    Philosophical Magazine 92 3346-3362 (2012)
    Mechanical properties of metal films on polymer substrates are normally studied in terms of the fracture and adhesion of the film, while the properties of the polymer substrate and testing conditions are overlooked. Substrate orientation and thickness, as well as strain rate and temperature effects, are examined using Cr films deposited onto polyethylene terephthalate substrates. A faster strain rate affects only the initial fracture strain of the Cr film and not the crack and buckle spacings in the high strain condition. The substrate orientation slightly changes the average crack spacing while the substrate thickness has little effect on the cracking and buckling behaviour. Straining experiments at high temperature increased the average crack spacing and led to a change in buckling mode. The lack of sizeable changes in the mechanical behaviour over the large range of testing procedures leads to a resilient material system for flexible applications. © 2012 Taylor & Francis.
    view abstractdoi: 10.1080/14786435.2012.700418
  • 2012 • 87 Influence of process parameters on the crystallinity, morphology and composition of tungsten oxide-based thin films grown by metalorganic chemical vapor deposition
    De Los Arcos, T. and Cwik, S. and Milanov, A.P. and Gwildies, V. and Parala, H. and Wagner, T. and Birkner, A. and Rogalla, D. and Becker, H.-W. and Winter, J. and Ludwig, Al. and Fischer, R.A. and Devi, A.
    Thin Solid Films 522 11-16 (2012)
    The growth of tungsten oxide (WO 3) based thin films was achieved via metalorganic chemical vapor deposition using an all-nitrogen coordinated tungsten precursor in combination with oxygen. Film growth was performed on Si(100) substrates in the temperature range of 400-800 °C. Employing multi-technique approaches like X-ray diffraction, scanning electron microscopy, atomic force microscopy, Rutherford back scattering, nuclear reaction analysis and X-ray photoelectron spectroscopy, the variation of the growth characteristics and film properties with deposition temperature were studied in terms of crystallinity, structure, surface roughness and composition. Special attention was devoted to the investigation of variations in the film composition for the as-deposited and annealed films. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2011.12.007
  • 2012 • 86 In-Situ TEM Straining Experiments: Recent Progress in Stages and Small-Scale Mechanics
    Dehm, G. and Legros, M. and Kiener, D.
    In-Situ Electron Microscopy: Applications in Physics, Chemistry and Materials Science 227-254 (2012)
    doi: 10.1002/9783527652167.ch10
  • 2012 • 85 Rare-earth substituted HfO2 thin films grown by metalorganic chemical vapor deposition
    Devi, A. and Cwik, S. and Xu, K. and Milanov, A.P. and Noei, H. and Wang, Y. and Barreca, D. and Meijer, J. and Rogalla, D. and Kahn, D. and Cross, R. and Parala, H. and Paul, S.
    Thin Solid Films 520 4512-4517 (2012)
    Thin films of HfGdOx and HfDyOx were deposited by metalorganic chemical vapor deposition (MOCVD) utilizing guanidinate precursors for Hf, Gd and Dy. The close match in the thermal properties of the precursors enabled the MOCVD of rare-earth (RE) substituted HfO2 over a wide temperature window. Film deposition was carried out in the temperature range 300-700 °C in the presence of oxygen on Si(100) substrates. HfGdO x films were analyzed in detail for their structure, composition and morphology using X-ray diffraction, Rutherford backscattering spectrometry, proton induced X-ray emission, X-ray photoelectron spectroscopy and scanning electron microscopy. The electrical properties of HfGdOx in terms of capacitance-voltage and current-voltage characteristics of metal-insulator- semiconductor device structures were evaluated. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2011.10.141
  • 2012 • 84 The biocompatibility and mechanical properties of cylindrical NiTi thin films produced by magnetron sputtering
    Habijan, T. and De Miranda, R.L. and Zamponi, C. and Quandt, E. and Greulich, C. and Schildhauer, T.A. and Köller, M.
    Materials Science and Engineering C 32 2523-2528 (2012)
    Superelastic nickel titanium shape memory alloys (NiTi-SMA) are of biomedical interest due to the large obtainable strains and the constant stress level. Production of NiTi-SMA thin films by magnetron sputtering was developed recently. NiTi sputtered tubes have a high potential for application as vascular implants, e.g. stents. Magnetron sputtering, three dimensional lithography and wet etching were used in order to produce Ti and NiTi stent devices (thickness: 5-15 μm; diameter: 1-5 mm). For tensile tests, specimens were prepared in radial and axial directions in order to compare the mechanical properties of the film in both directions. The specimens - produced for cell culture experiments - were incubated with human mesenchymal stem cells (hMSC) for 7 days. Cell viability was analyzed via fluorescence microscopy after live/dead staining of the cells. Cytokine release from cells was quantified via ELISA. Cylindrical NiTi films showed a strain up to 6%. Tensile parameters were identical for both directions. Best material properties were obtained for deposition and patterning in the amorphous state followed by an ex-situ crystallization using rapid thermal annealing in a high vacuum chamber. First biological tests of the Ti and NiTi-SMA samples showed promising results regarding viability and cytokine release of hMSC. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2012.07.035
  • 2012 • 83 Thin-film Cu-Pt(111) near-surface alloys: Active electrocatalysts for the oxygen reduction reaction
    Henry, J.B. and Maljusch, A. and Huang, M. and Schuhmann, W. and Bondarenko, A.S.
    ACS Catalysis 2 1457-1460 (2012)
    A simple method is presented for the formation of thin films of Cu-Pt(111) near-surface alloys (NSA). In these thin films, the solute metal (Cu) is preferentially located in the second platinum layer and protected by a Pt surface layer. The NSA-films act as active and fairly stable electrocatalysts for the reduction of oxygen with the activity and stability which approach those for bulk single crystalline Pt-alloy surfaces and ∼5 times more active than state-of-the-art Pt thin films. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/cs300165t
  • 2012 • 82 Characteristics of ceramic coatings made by thin film low pressure plasma spraying (LPPS-TF)
    Hospach, A. and Mauer, G. and Vaßen, R. and Stöver, D.
    Journal of Thermal Spray Technology 21 435-440 (2012)
    The thin film low pressure plasma spray process (LPPS-TF) has been developed with the aim of efficient depositing uniform and thin coatings with large area coverage by plasma spraying. At high power input (∼150 kW) and very low pressure (∼100 Pa) the plasma jet properties change considerably and it is even possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This relatively new technique bridges the gap between conventional plasma spraying and physical vapor deposition. In addition, the resulting microstructures are unique and can hardly be obtained by other processes. In this paper, microstructures made by LPPS-TF are shown and the columnar layer growth by vapor deposition is demonstrated. In addition to the ceramic materials TiO 2, Al2 O3 or MgAl2O4, the focus of the research was placed on partially yttria-stabilized zirconia. Variations of the microstructures are shown and discussed concerning potential coating applications. © ASM International.
    view abstractdoi: 10.1007/s11666-012-9748-z
  • 2012 • 81 Thickness-dependence of the B2-B19 martensitic transformation in nanoscale shape memory alloy thin films: Zero-hysteresis in 75 nm thick Ti 51Ni38Cu11 thin films
    König, D. and Buenconsejo, P.J.S. and Grochla, D. and Hamann, S. and Pfetzing-Micklich, J. and Ludwig, Al.
    Acta Materialia 60 306-313 (2012)
    The influence of film thickness on the B2-B19 martensitic transformation properties of nanoscale Ti51Ni38Cu11 thin films with thicknesses ranging from 750 to 50 nm is reported. For these films an unexpected behavior of the phase transformation temperatures was observed: Af and Os initially decrease with decreasing film thickness but increase sharply again for thicknesses < 100 nm. The phase transformation temperatures and thermal hysteresis width range from 58 to 35 °C (Af) and 14 to ∼0 K, respectively. For the first time we can show that substrate-attached Ti-Ni-Cu thin films as thin as 50 nm show reversible B2-B19 phase transformations. Furthermore, it is shown that with decreasing film thickness a change in the tetragonality of the B19 martensite phase occurs. This leads to fulfilling the so-called λ2 criterion, causing a vanishing hysteresis for a film thickness of 75 nm. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2011.09.037
  • 2012 • 80 A quick method for the preparation of Pt(111)-like thin films
    Maljusch, A. and Henry, J.B. and Schuhmann, W. and Bondarenko, A.S.
    Electrochemistry Communications 16 88-91 (2012)
    A simple and quick method for forming Pt(111)-like thin films on Si/Ti substrates for electrochemical and/or electrocatalytic experiments is reported. This method involves physical vapour deposition followed by flame annealing, electrochemical cleaning and a short heat treatment under a controlled atmosphere. Careful selection of the substrate, surface preparation and cooling atmosphere allows production of Pt thin films which show voltammetry features typical of large Pt(111) single crystal electrodes in 0.1 M HClO 4. This technique promises a method for the production of Pt(111) type surfaces on a larger scale. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.elecom.2011.12.004
  • 2012 • 79 Sc 2O 3, Er 2O 3, and Y 2O 3 thin films by MOCVD from volatile guanidinate class of rare-earth precursors
    Milanov, A.P. and Xu, K. and Cwik, S. and Parala, H. and De Los Arcos, T. and Becker, H.-W. and Rogalla, D. and Cross, R. and Paul, S. and Devi, A.
    Dalton Transactions 41 13936-13947 (2012)
    Alternative novel precursor chemistries for the vapor phase deposition of rare-earth (RE) oxide thin films were developed by synthesising the homoleptic guanidinate compounds tris(N,N′-diisopropyl-2-dimethylamidoguanidinato)- scandium(iii) [Sc(DPDMG) 3] (1), tris(N,N′-diisopropyl-2- dimethylamidoguanidinato)-erbium(iii), [Er(DPDMG) 3] (2) and tris(N,N′-diisopropyl-2-dimethylamidoguanidinato)-yttrium(iii), [Y(DPDMG) 3] (3). All three compounds are monomeric as revealed by single crystal X-ray diffraction (XRD) analysis, nuclear magnetic resonance (NMR) and electron impact mass spectrometry (EI-MS). The thermal analysis revealed that the compounds are volatile and very stable under evaporation conditions. Therefore the complexes were evaluated as precursors for the growth of Sc 2O 3, Er 2O 3 and Y 2O 3 thin films, respectively, by metal-organic chemical vapor deposition (MOCVD). Uniform Sc 2O 3, Er 2O 3 and Y 2O 3 films on Si(100) substrates with reproducible quality were grown by MOCVD by the combination of the respective guanidinate precursors and oxygen in the temperature range 350-700 °C. The structural, morphological, compositional and electrical properties of the films were investigated in detail. The most relevant film properties are highlighted in relation to the distinct advantages of the novel precursor chemistries in comparison to the commonly used literature known RE precursors. This study shows that compounds 1-3 are very good precursors for MOCVD yielding Sc 2O 3, Er 2O 3 and Y 2O 3 thin films which are stoichiometric and display suitable electrical properties for their potential use as high dielectric constant (high-k) materials. © 2012 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c2dt31219k
  • 2012 • 78 High mobility ZnO thin film transistors using the novel deposition of high-k dielectrics
    Ngwashi, D.K. and Cross, R.B.M. and Paul, S. and Milanov, A.P. and Devi, A.
    Materials Research Society Symposium Proceedings 1315 71-76 (2012)
    In order to investigate the performance of ZnO-based thin film transistors (ZnO-TFTs), we fabricate devices using amorphous hafnium dioxide (HfO 2) high-k dielectrics. Sputtered ZnO was used as the active channel layer, and aluminium source/drain electrodes were deposited by thermal evaporation, and the HfO 2 high-k dielectrics are deposited by metal-organic chemical vapour deposition (MOCVD). The ZnO-TFTs with high-k HfO 2 gate insulators exhibit good performance metrics and effective channel mobility which is appreciably higher in comparison to SiO 2-based ZnO TFTs fabricated under similar conditions. The average channel mobility, turnon voltage, on-off current ratio and subthreshold swing of the high-k TFTs are 31.2 cm 2V -1s -1, -4.7 V, ∼10 3, and 2.4 V/dec respectively. We compared the characteristics of a typical device consisting of HfO 2 to those of a device consisting of thermally grown SiO 2 to examine their potential for use as high-k dielectrics in future TFT devices. © 2011 Materials Research Society.
    view abstractdoi: 10.1557/opl.2011.721
  • 2012 • 77 Layer-by-layer fabrication of an anatase titania multilayer with gradual sponge-like morphology
    Perlich, J. and Memesa, M. and Diethert, A. and Metwalli, E. and Wang, W. and Roth, S.V. and Gutmann, J.S. and Müller-Buschbaum, P.
    Colloid and Polymer Science 290 119-126 (2012)
    The fabrication of a functional multilayer system with a gradually hierarchical order formed by individual titania thin films of different porosity is investigated. The porous or sponge-like nanostructures are fabricated using a diblock copolymer assisted sol-gel process. The successive spin-coating of the sol-gel solution onto the silicon substrate deposits a thin polymer nanocomposite film which is transformed to purely anatase titania nanostructures via calcination. In total, this procedure is repeated layer by layer for three times. This layer-by-layer approach is monitored with grazing incidence small-angle X-ray scattering (GISAXS) after each fabrication step. The GISAXS investigation is complemented in real space with a scanning electron microscopy characterization of the respective preparation stages. From the characterization, a porous titania multilayer system with gradually structured levels is clearly identified. © Springer-Verlag 2011.
    view abstractdoi: 10.1007/s00396-011-2529-2
  • 2012 • 76 Embedded argon as a tool for sampling local structure in thin plasma deposited aluminum oxide films
    Prenzel, M. and de los Arcos, T. and Kortmann, A. and Winter, J. and von Keudell, A.
    Journal of Applied Physics 112 103306 (2012)
    Al2O3 thin films, either amorphous or of varying degrees of crystallinity, were deposited by two-frequency radio-frequency magnetron sputtering. Film crystallinity was investigated by Fourier transform infrared spectroscopy and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) was employed to determine the amount of Ar naturally trapped within the films during the deposition process. A clear correlation was found between the existence of crystalline phases, as determined by XRD, and a shift towards lower binding energy positions of the Ar2p core levels of embedded gas. The shift is due to differences in the local Al2O3 matrix (amorphous or crystalline) of the embedded gas, thus, providing an XPS fingerprint that can be used to qualitatively determine the presence or absence of crystalline phases in very thin films. (C) 2012 American Institute of Physics. []
    view abstractdoi: 10.1063/1.4767383
  • 2012 • 75 Elastic properties of face-centred cubic Fe-Mn-C studied by nanoindentation and ab initio calculations
    Reeh, S. and Music, D. and Gebhardt, T. and Kasprzak, M. and Jäpel, T. and Zaefferer, S. and Raabe, D. and Richter, S. and Schwedt, A. and Mayer, J. and Wietbrock, B. and Hirt, G. and Schneider, J.M.
    Acta Materialia 60 6025-6032 (2012)
    We have studied experimentally and theoretically the influence of C and Mn content on the Young's modulus of Fe-Mn-C alloys. Combinatorial thin film and bulk samples were characterized regarding their structure, texture and Young's modulus. The following chemical composition range was investigated: 1.5-3.0 at.% C, 28.0-37.5 at.% Mn and 60.6-69.8 at.% Fe. The experimental lattice parameters change marginally within 3.597-3.614 Å with the addition of C and are consistent with ab initio calculations. The Young's modulus data are in the range of 185 ± 12-251 ± 59 GPa for the bulk samples and the thin film, respectively. C has no significant effect on the Young's modulus of these alloys within the composition range studied here. The ab initio calculations are 15-22% larger than the average Young's modulus values of the as-deposited and polished thin film at 3 at.% C. The comparison of thin film and bulk samples results reveals similar elastic properties for equivalent compositions, indicating that the applied research strategy consisting of the combinatorial thin film approach in conjunction with ab initio calculations is useful to study the composition dependence of the structure and elastic properties of Fe-Mn-C alloys. The very good agreement between the presented calculations and the experimentally determined lattice parameters and Young's modulus values implies that the here-adopted simulation strategy yields a reliable description of carbon in Fe-Mn alloys, important for future alloy design. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2012.07.038
  • 2012 • 74 Toughness enhancement in TiAlN-based quarternary alloys
    Sangiovanni, D.G. and Chirita, V. and Hultman, L.
    Thin Solid Films 520 4080-4088 (2012)
    Improved toughness in hard and superhard thin films is a primary requirement for present day ceramic hard coatings, known to be prone to brittle failure during in-use conditions. We use density functional theory calculations to investigate a number of (TiAl) 1 - xM xN thin films in the B1 structure, with 0.06 ≤ x ≤ 0.75, obtained by alloying TiAlN with M = V, Nb, Ta, Mo and W. Results show significant ductility enhancements, hence increased toughness, in these compounds. Importantly, these thin films are also predicted to be superhard, with similar or increased hardness values, compared to Ti 0.5Al 0.5 N. For (TiAl) 1 - xW xN the results are experimentally confirmed. The ductility increase originates in the enhanced occupancy of d-t 2g metallic states, induced by the valence electrons of substitutional elements (V, Nb, Ta, Mo, W). This effect is more pronounced with increasing valence electron concentration, and, upon shearing, leads to the formation of a layered electronic structure in the compound material, consisting of alternating layers of high and low charge density in the metallic sublattice, which in turn, allows a selective response to normal and shear stresses. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2012.01.030
  • 2012 • 73 Strain-induced phase transitions in epitaxial NaNbO3 thin films grown by metal-organic chemical vapour deposition
    Schwarzkopf, J. and Schmidbauer, M. and Remmele, T. and Duk, A. and Kwasniewski, A. and Bin Anooz, S. and Devi, A. and Fornari, R.
    Journal of Applied Crystallography 45 1015-1023 (2012)
    Epitaxially strained NaNbO3 films were grown by liquid-delivery spin metal-organic chemical vapour deposition on several oxide substrates, inducing tensile and compressive lattice strain. High-resolution X-ray diffraction measurements reveal that coherently grown compressively strained NaNbO3 films on NdGaO3 exhibit the orthorhombic c phase. With increasing in-plane strain a first structural phase transition to the monoclinic r phase and, further on, for films grown under tensile strain on rare earth scandates, a second phase transition to the aa phase, are observed. Our results are in good agreement with the pathway of phase transitions predicted by Diéguez, Rabe & Vanderbilt [Phys. Rev. B, (2005), 72, 144101] for NaNbO3 films.
    view abstractdoi: 10.1107/S0021889812035911
  • 2012 • 72 Combinatorial development of nanoporous WO 3 thin film photoelectrodes for solar water splitting by dealloying of binary alloys
    Stepanovich, A. and Sliozberg, K. and Schuhmann, W. and Ludwig, Al.
    International Journal of Hydrogen Energy 37 11618-11624 (2012)
    A combinatorial materials approach is suggested for the development of nanoporous thin film oxides for photoelectrochemical solar water splitting. As a precursor for nanoporous WO 3 films, metallic nanoporous W films were synthesized by dealloying sputtered W 1-xAl x and W 1-xFe x (0.06 < x < 0.67) thin film materials libraries in aqueous HNO 3 solutions with different concentrations for 24 h under open circuit conditions. The variation of the etchant concentration provided different film nanostructures. The films were then transformed into nanoporous WO 3 by controlled thermal oxidation at 500 °C in air. Screening of the photoelectrochemical properties of nanoporous WO 3 films shows a strong porosity- and thickness-dependence of the photocurrent. At the same time the photocurrent density does not depend on precursor composition, because dealloying in acid solutions of certain concentration leads to formation of identical nanostructures in a broad range of precursor compositions. ©, 2012 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ijhydene.2012.05.039
  • 2012 • 71 Detection of filament formation in forming-free resistive switching SrTiO 3 devices with Ti top electrodes
    Stille, S. and Lenser, Ch. and Dittmann, R. and Koehl, A. and Krug, I. and Muenstermann, R. and Perlich, J. and Schneider, C.M. and Klemradt, U. and Waser, R.
    Applied Physics Letters 100 (2012)
    We investigated the influence of Ti top electrodes on the resistive switching properties of SrTiO 3 thin film devices. Above a Ti layer thickness of 5 nm, the initial resistance is strongly reduced, giving rise to forming-free devices. Hard x-ray photoemission experiments reveal the Ti layer to be composed of several oxide phases, induced by the redox-reaction at the Ti/SrTiO 3 interface. Grazing incidence small angle x-ray scattering measurements indicate that the reduction of the SrTiO 3 thin film occurs in a filamentary way. We attribute this behavior to the preferential reduction of SrTiO 3 thin films along highly defective areas. © 2012 American Institute of Physics.
    view abstractdoi: 10.1063/1.4724108
  • 2012 • 70 Laser-sintered thin films of doped SiGe nanoparticles
    Stoib, B. and Langmann, T. and Matich, S. and Antesberger, T. and Stein, N. and Angst, S. and Petermann, N. and Schmechel, R. and Schierning, G. and Wolf, D.E. and Wiggers, H. and Stutzmann, M. and Brandt, M.S.
    Applied Physics Letters 100 (2012)
    We present a study of the morphology and the thermoelectric properties of short-pulse laser-sintered (LS) nanoparticle (NP) thin films, consisting of SiGe alloy NPs or composites of Si and Ge NPs. Laser-sintering of spin-coated NP films in vacuum results in a macroporous percolating network with a typical thickness of 300 nm. The Seebeck coefficient for LS samples is the same as for bulk samples prepared by current-assisted sintering and is typical for degenerate doping. The electrical conductivity of LS films is influenced by two-dimensional percolation effects and rises with increasing temperature, approximately following a power-law. © 2012 American Institute of Physics.
    view abstractdoi: 10.1063/1.4726041
  • 2012 • 69 On the limits of the interfacial yield model for fragmentation testing of brittle films on polymer substrates
    Taylor, A.A. and Cordill, M.J. and Dehm, G.
    Philosophical Magazine 92 3363-3380 (2012)
    Fragmentation testing is frequently used to probe film fracture strain and the interfacial properties of thin brittle films on compliant substrates. A model based upon complete yield of the film/substrate interface is frequently used to analyse data after cracking has saturated. Additionally, the film is either assumed to have a single-valued failure stress or a distribution of strengths described by Weibull statistics. Recent work by the authors showed that consideration of film thickness variations and the application of neighbour ratio analysis brought 96% of the data for an Al x O y /Cu film/substrate system into compliance with the predictions for a film with a single-valued failure stress. In the present work Cr/PI (polyimide) and Cr/PET (polyethylene teraphthalate) systems are analysed according to the same methodology. The Cr films on polymer substrates crack such that the neighbour ratios considerably exceed the predicted limit of 2. The influence of the relative thickness of the film and substrate and the strain rate of the test is investigated. A deviation from the idealised mechanical model due to the large difference in elastic moduli of film and substrate is put forward as a possible cause of the observed behaviour. The importance of these results to the application of the interfacial yield model is discussed. © 2012 Taylor & Francis.
    view abstractdoi: 10.1080/14786435.2012.723145
  • 2012 • 68 Magnetic anomaly and dielectric tunability of (Sr,Mn)TiO 3 thin films
    Tkach, A. and Okhay, O. and Wu, A. and Vilarinho, P.M. and Bedanta, S. and Shvartsman, V.V. and Borisov, P.
    Ferroelectrics 426 274-281 (2012)
    Polycrystalline Sr 0.98Mn 0.02TiO 3 thin films are prepared by sol-gel spin-coating method on Si/SiO 2/TiO 2/Pt substrates. Their dielectric permittivity, polarization, and magnetization are investigated as a function of temperature (from 10 to 300 K), electric and magnetic fields. Temperature dependences of the magnetization M ZFC-FH(T), real part of the dielectric permittivity (T), and dissipation factor tan(T) of Sr 0.98Mn 0.02TiO 3 films show anomalies around 41-45 K, implying an interrelation between polar and magnetic order. Butterfly-like dc bias dependences of the real part of the dielectric permittivity (E dc), as well as slim polarization and magnetization hysteresis loops are observed, suggesting that Sr 0.98Mn 0.02TiO 3 thin films belong to multiglass systems. © Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/00150193.2012.672038
  • 2012 • 67 Incubation effect and its influence on laser patterning of ITO thin film
    Xiao, S. and Gurevich, E.L. and Ostendorf, A.
    Applied Physics A: Materials Science and Processing 107 333-338 (2012)
    Results are presented on the surface damage thresholds of ITO thin films induced by single-and multipulse laser irradiation at a pulse duration of 10 ps and a wavelength of 1064 nm. For multi-pulse ablation the incubation effect results in a reduction of the damage threshold, especially apparent at low pulse numbers and very small film thicknesses. The incubation effect attributes to the accumulation of defect sites and/or the storage of thermal stressstrain energy induced by the incident laser pulses. An incubation coefficient of S = 0.82 has been obtained which is independent on the film thickness in the range of 10-100 nm. In practical applications, the incubation effect determines the laser patterning structure of ITO films while increasing the pulse overlapping rate. The width of the patterned line can be predicted by the proposed model involving the laser fluence, the overlapping rate and the incubation coefficient. © 2012 Springer-Verlag.
    view abstractdoi: 10.1007/s00339-012-6820-y
  • 2012 • 66 Atomic layer deposition of HfO 2 thin films employing a heteroleptic hafnium precursor
    Xu, K. and Milanov, A.P. and Parala, H. and Wenger, C. and Baristiran-Kaynak, C. and Lakribssi, K. and Toader, T. and Bock, C. and Rogalla, D. and Becker, H.-W. and Kunze, U. and Devi, A.
    Chemical Vapor Deposition 18 27-35 (2012)
    The application of a heteroleptic hafnium amide-guanidinate precursor for the deposition of HfO 2 thin films via a water-assisted atomic layer deposition (ALD) process is demonstrated for the first time. HfO 2 films are grown in the temperature range 100-300 °C using the compound [Hf(NMe 2) 2(NMe 2-Guan) 2] (1). This compound shows self-limiting ALD-type growth characteristics with growth rates of the order of 1.0-1.2 Å per cycle in the temperature range 100-225 °C. The saturation behavior and a linear dependence on film thickness as a function of number of cycles are verified at various temperatures within the ALD window. The as-deposited HfO 2 films are characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS), and electrical measurements. For a direct comparison of the precursor performance with that of the parent alkyl amide [Hf(NMe 2) 4] (2), ALD experiments are also performed employing compound 2 under similar process conditions, and in this case no typical ALD characteristics are observed. The application of a heteroleptic hafnium amide-guanidinate precursor [Hf(NMe 2) 2(NMe 2-Guan) 2] for the deposition of HfO 2 thin films via a water assisted ALD process has been demonstrated for the first time. This compound showed self-limiting ALD type growth characteristics with the growth rates as high as 1.0-1.2 Å per cycle in the temperature range 100-225 °C. Typical ALD characteristics such as saturation behavior and linear dependence on the film thickness as a function of number of cycles were verified at different temperatures within the ALD window. The as-deposited HfO 2 films were characterized by AFM, SEM, RBS, XPS and electrical measurements. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cvde.201106934
  • 2012 • 65 Atomic layer deposition of Gd 2O 3 and Dy 2O 3: A study of the ALD characteristics and structural and electrical properties
    Xu, K. and Ranjith, R. and Laha, A. and Parala, H. and Milanov, A.P. and Fischer, R.A. and Bugiel, E. and Feydt, J. and Irsen, S. and Toader, T. and Bock, C. and Rogalla, D. and Osten, H.-J. and Kunze, U. and Devi, A.
    Chemistry of Materials 24 651-658 (2012)
    Gd 2O 3 and Dy 2O 3 thin films were grown by atomic layer deposition (ALD) on Si(100) substrates using the homoleptic rare earth guanidinate based precursors, namely, tris(N,N′- diisopropyl-2-dimethylamido-guanidinato)gadolinium(III) [Gd(DPDMG) 3] (1) and tris(N,N′-diisopropyl-2-dimethylamido-guanidinato)dysprosium(III) [Dy(DPDMG) 3] (2), respectively. Both complexes are volatile and exhibit high reactivity and good thermal stability, which are ideal characteristics of a good ALD precursor. Thin Gd 2O 3 and Dy 2O 3 layers were grown by ALD, where the precursors were used in combination with water as a reactant at reduced pressure at the substrate temperature ranging from 150 °C to 350 °C. A constant growth per cycle (GPC) of 1.1 Å was obtained at deposition temperatures between 175 and 275 °C for Gd 2O 3, and in the case of Dy 2O 3, a GPC of 1.0 Å was obtained at 200-275 °C. The self-limiting ALD growth characteristics and the saturation behavior of the precursors were confirmed at substrate temperatures of 225 and 250 °C within the ALD window for both Gd 2O 3 and Dy 2O 3. Thin films were structurally characterized by grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses for crystallinity and morphology. The chemical composition of the layer was examined by Rutherford backscattering (RBS) analysis and Auger electron spectroscopy (AES) depth profile measurements. The electrical properties of the ALD grown layers were analyzed by capacitance-voltage (C-V) and current-voltage (I-V) measurements. Upon subjection to a forming gas treatment, the ALD grown layers show promising dielectric behavior, with no hysteresis and reduced interface trap densities, thus revealing the potential of these layers as high-k oxide for application in complementary metal oxide semiconductor based devices. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/cm2020862
  • 2012 • 64 Deposition of La 1-xSr xFe 1-yCo yO 3-δ coatings with different phase compositions and microstructures by low-pressure plasma spraying-thin film (LPPS-TF) processes
    Zotov, N. and Hospach A. and Mauer G. and Sebold D. and Vaßen, R.
    Journal of Thermal Spray Technology 21 441-447 (2012)
    Perovskite-type materials with the general chemical formula A 1-xÁ xB́ 1-yB́ yO 3δ have received considerable attention as candidates for oxygen separation membranes. Preparation of La 1-xSr xFe 1-yCo yO 3-δ (LSFC) coatings by low-pressure plasma spraying-thin film processes using different plasma spray parameters is reported and discussed. Deposition with Ar-He plasma leads to formation of coatings containing a mixture of cubic LSFC perovskite, SrLaFeO4, FeCo, and metal oxides. Coatings deposited at higher oxygen partial pressures by pumping oxygen into the vacuum chamber contain more than 85% perovskite and only a few percent Fe32xCoxO4, and/or CoO. The microstructures of the investigated LSFC coatings depend sensitively on the oxygen partial pressure, the substrate temperature, the plasma jet velocities, and the deposition rate. Coatings deposited with Ar-rich plasma, relatively low net torch power, and with higher plasma jet velocities are most promising for applications as oxygen permeation membranes. © ASM International.
    view abstractdoi: 10.1007/s11666-012-9768-8
  • 2011 • 63 Field cooling-induced magnetic anisotropy in exchange biased CoO/Fe bilayer studied by ferromagneticresonance
    Akdoǧan, N. and Kazan, S. and Akta, B. and Özdemir, M. and Inam, H. and Obaida, M. and Dudek, J. and Westerholt, K.
    Journal of Magnetism and Magnetic Materials 323 346-350 (2011)
    Exchange-biased CoO/Fe bilayer grown on MgO (0 0 1) substrate by sputtering, studied by variable angle and temperature ferromagnetic resonance. Room temperature in-plane measurements reveal that the Fe layer was epitaxially grown on MgO substrate with a fourfold cubic symmetry. The data also show that the easy axis of magnetization is in the film plane and makes an angle of 45° with the [1 0 0] crystallographic direction of MgO substrate. The low temperature data exhibit a sudden onset of a field cooling-induced and shifted cubic anisotropy below the Nel temperature of CoO. This results in a twofold uniaxial or fourfold cubic symmetry for in-plane magnetic anisotropy depending on a field cooling direction. Low temperature measurements also present a reduction in the resonance fields due to the antiferromagnetic/ferromagnetic coupling. The developed theoretical model perfectly simulates the experimental data of coupled CoO/Fe bilayer. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jmmm.2010.09.037
  • 2011 • 62 Mechanistic Considerations on Contact-Active Antimicrobial Surfaces with Controlled Functional Group Densities
    Bieser, A.M. and Tiller, J.C.
    Macromolecular Bioscience 11 526-534 (2011)
    A series of N-alkyl-N,N-dimethyldeoxyammonium celluloses is synthesized by converting tosyl celluloses with DBA and DDA, respectively. Surface coatings with these water-insoluble derivatives contain well-defined densities of quaternary ammonium functions and nonactive hydrophobic and hydrophilic groups. It is shown that the antimicrobial activity of such surfaces against S. aureus requires a delicate balance between DDA, BDA, and hydrophobic groups. A mechanism is proposed that involves the selective adhesion of anionic phospholipids from the bacterial cell membrane. This so-called phospholipid sponge effect is supported by the fact that all coatings could be deactivated by treatment with SDS or negatively charged phospholipids, but not with neutral phospholipids. The present work strives to gain better insights in the mechanism of surface grafted antimicrobial groups. To this end a series of water-insoluble cellulose derivatives with well-defined ratios of different quaternary ammonium groups and hydrophobic substituents were synthesized and their films were investigated regarding their antimicrobial potential. From the results we propose a new mechanism for such surface grafted biocides, the "phospholipid sponge effect." © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mabi.201000398
  • 2011 • 61 Electronic properties of polyvinylpyrrolidone at the zinc oxide nanoparticle surface : PVP in ZnO dispersions and nanoparticulate ZnO thin films for thin film transistors
    Bubel, S. and Mechau, N. and Schmechel, R.
    Journal of Materials Science 46 7776-7783 (2011)
    We investigated the electrical effects of polyvinylpyrrolidone (PVP), used as a dispersion agent in zinc oxide (ZnO) nanodispersions. We found PVP reduces the high surface conductivity and atmospheric sensitivity. Compared with polymer free ZnO thin films, the nanoparticulate layers with PVP exhibit a smaller density of thermally active charge carriers, a reduced density of trap states, and a Fermi level shift toward the valence band, yielding improved performance, vanishing hysteresis characteristics and reduced atmospheric sensitivity in thin film transistors (TFT). In addition, we discuss the attachment of PVP to the ZnO surface. © 2011 Springer Science+Business Media, LLC.
    view abstractdoi: 10.1007/s10853-011-5757-4
  • 2011 • 60 A new prototype two-phase (TiNi)-(β-W) SMA system with tailorable thermal hysteresis
    Buenconsejo, P.J.S. and Zarnetta, R. and König, D. and Savan, A. and Thienhaus, S. and Ludwig, Al.
    Advanced Functional Materials 21 113-118 (2011)
    The Ti-Ni-W two-phase shape memory alloy (SMA) thin film system is presented as a prototype for new SMAs with tailorable thermal transformation hysteresis (ΔT). The concept is to combine the SMA TiNi with almost insoluble W to create the two-phase system (TiNi)-(β-W). This system behaves like a pseudobinary TiNi system. Phase transformation behavior for compositions above the solubility limit of W in TiNi exhibit a B2-R phase transformation with characteristically small ΔT. Moreover, ΔT is dependent on the amount of W and it can be tailored to zero and even negative. This phenomenon is rationalized as being due to the mechanical interaction between the phases B2-TiNi and β-W. The presented results are very promising for the development of high-speed Ti-Ni-based SMA actuators. We present an approach to inkjet print high-performance organic transistors by printing the organic semiconductor ink on a thin, continuous, and solvent-absorbing layer of insulating material. The ink spreading is effectively controlled by local dissolution of the layer, and during drying the characteristic circular morphology with high rims and inner plateau forms. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201001697
  • 2011 • 59 A novel high-throughput fatigue testing method for metallic thin films
    Burger, S. and Eberl, C. and Siegel, A. and Ludwig, Al. and Kraft, O.
    Science and Technology of Advanced Materials 12 (2011)
    Thin films are used in a wide variety of computing and communication applications although their fatigue behavior and its dependence on alloying elements are not very well known. In this paper, we present an experimental implementation of a novel high-throughput fatigue testing method for metallic thin films. The methodology uses the fact that the surface strain amplitude of a vibrating cantilever decreases linearly from the fixed end to the free end. Therefore, a thin film attached to a vibrating cantilever will experience a gradient of strain and corresponding stress amplitudes along the cantilever. Each cantilever can be used to extract a lifetime diagram by measuring the fatigue-induced damage front that progresses along the cantilever during up to 10 8 load cycles. © 2011 National Institute for Materials Science.
    view abstractdoi: 10.1088/1468-6996/12/5/054202
  • 2011 • 58 Fatigue testing of thin films
    Burger, S. and Rupp, B. and Ludwig, Al. and Kraft, O. and Eberl, C.
    Key Engineering Materials 465 552-555 (2011)
    Thin film processing has been a driving technology in microelectronics and mechanics for years. The reliability of such devices is often limited by the failure of thin films. Therefore a deeper understanding of fatigue mechanisms of thin films through experiments is necessary to develop physical based lifetime models. Thus, this paper focuses on a novel setup for micro beam bending of thin metal films on Si cantilever substrate and first results will be presented. © (2011) Trans Tech Publications, Switzerland.
    view abstractdoi: 10.4028/
  • 2011 • 57 Influence of the annealing atmosphere on solution based zinc oxide thin film transistors
    Busch, C. and Theissmann, R. and Bubel, S. and Schierning, G. and Schmechel, R.
    Materials Research Society Symposium Proceedings 1359 71-77 (2011)
    Zinc oxide layers with a thickness of less than 10 nanometers have been synthesized from an aqueous solution for the application as active layer in thin film transistors. They have been conditioned by applying different oxidizing and reducing atmospheres during an annealing process at a temperature of 125°C. It is shown that the charge carrier mobility and threshold voltage is strongly influenced by the annealing atmosphere. Samples annealed in 10% forming gas (H 2 in N 2 - reducing atmosphere) show the highest field-effect-mobility of 0.6 cm 2V -1s -1, but no saturation of the drain current, due to a high free carrier concentration. Samples treated under oxygen (strongest oxidizing atmosphere) show significantly lower mobilities. Subsequently, the samples have been exposed to synthetic air, with varying exposure times. Samples which have been annealed under hydrogen atmospheres show a pronounced decay of the drain current if exposed to synthetic air, whereas all samples conditioned under hydrogen-free atmospheres are significantly more stable under synthetic air. This enhanced sensitivity against oxygen after hydrogen treatment is attributed to residual hydrogen content in the sample that supports the formation of OH-groups which act as electron acceptors. © 2011 Materials Research Society.
    view abstractdoi: 10.1557/opl.2011.754
  • 2011 • 56 Microstructure and adhesion of as-deposited and annealed Cu/Ti films on polyimide
    Cordill, M.J. and Taylor, A. and Schalko, J. and Dehm, G.
    International Journal of Materials Research 102 729-734 (2011)
    The ability to measure the adhesion energy of metal thin films on polymer substrates is important for the design of reliable flexible electronic devices. One technique is to create well-defined areas of delamination (buckles) as a consequence of lateral compressive stresses induced by tensile straining of the film-substrate system. The adhesion energy is calculated from the buckle dimensions. In order to improve the adhesion between the metal film and polymer substrate, thin adhesion layers can be incorporated. However, interdiffusion and reactions can occur between the adhesion layer and the metal film when subjected to elevated temperatures. This is detrimental for the interfacial adhesion, as will be discussed for Cu films on polyimide with a Ti interlayer subjected to annealing at 350°C. © Carl Hanser Verlag GmbH & Co. KG.
    view abstractdoi: 10.3139/146.110513
  • 2011 • 55 Self-organized nanopatterns in thin layers of superheated liquid metals
    Gurevich, E.L.
    Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 83 (2011)
    In this paper experimental observations of self-organized patterns in resolidified thin films of liquid superheated metals are reported. The superheated melt layers represent an example of a system driven far from equilibrium, which undergoes explosive boiling and solidifies afterward. The melts appear in the course of single-shot femtosecond laser heating of metal samples. Self-organized cells, solitonlike structures, periodic stripes, and transient patterns are observed. Pattern properties and mechanisms leading to the pattern formation as well as possible applications for nanotechnology are discussed. © 2011 American Physical Society.
    view abstractdoi: 10.1103/PhysRevE.83.031604
  • 2011 • 54 Grain resolved orientation changes and texture evolution in a thermally strained Al film on Si substrate
    Heinz, W. and Dehm, G.
    Surface and Coatings Technology 206 1850-1854 (2011)
    Temperature changes induce thermal stresses in thin films on substrates due to differences in the thermal expansion coefficients. Repeated thermal cycling may finally lead to severe surface roughening and a change in film texture. In this study we investigate the orientation changes for a 600. nm thick Al film during subsequent thermal cycles between 25 °C and 450 °C by analyzing individual grains. The results reveal orientation changes by up to 3° after one thermal cycles and unexpected large orientation gradients within individual grains. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2011.07.046
  • 2011 • 53 Atomic vapor deposition approach to In 2O 3 thin films
    Hellwig, M. and Parala, H. and Cybinksa, J. and Barreca, D. and Gasparotto, A. and Niermann, B. and Becker, H.-W. and Rogalla, D. and Feydt, J. and Irsen, S. and Mudring, A.-V. and Winter, J. and Fischer, R.A. and Devi, A.
    Journal of Nanoscience and Nanotechnology 11 8094-8100 (2011)
    In 2O 3 thin films were grown by atomic vapor deposition (AVD) on Si(100) and glass substrates from a tris-guanidinate complex of indium [In(NiPr 2guanid) 3] under an oxygen atmosphere. The effects of the growth temperature on the structure, morphology and composition of In 2O 3 films were investigated. X-ray diffraction (XRD) measurements revealed that In 2O 3 films deposited in the temperature range 450-700°C crystallised in the cubic phase. The film morphology, studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), was strongly dependent on the substrate temperature. Stoichiometric In 2O 3 films were formed under optimised processing conditions as was confirmed by X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), as well as by Rutherford backscattering spectrometry (RBS). Finally, optical properties were investigated by photoluminescence (PL) measurements, spectroscopic ellipsometry (SE) and optical absorption. In 2O 3 films grown on glass exhibited excellent transparency (≈90%) in the Visible (Vis) spectral region. Copyright © 2011 American Scientific Publishers All rights reserved.
    view abstractdoi: 10.1166/jnn.2011.5024
  • 2011 • 52 Columnar-structured thermal barrier coatings (TBCs) by thin film low-pressure plasma spraying (LPPS-TF)
    Hospach, A. and Mauer, G. and Vaßen, R. and Stöver, D.
    Journal of Thermal Spray Technology 20 116-120 (2011)
    The very low-pressure plasma Spray (VLPPS) process has been developed with the aim of depositing uniform and thin coatings with coverage of a large area by plasma spraying. At typical pressures of 100-200 Pa, the characteristics of the plasma jet change compared to conventional low-pressure plasma-spraying processes (LPPS) operating at 5-20 kPa. The combination of plasma spraying at low pressures with enhanced electrical input power has led to the development of the LPPS-TF process (TF = thin film). At appropriate parameters, it is possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This technique offers new possibilities for the manufacturing of thermal barrier coatings (TBCs). Besides the material composition, the microstructure is an important key to reduce thermal conductivity and to increase strain tolerance. In this regard, columnar microstructures deposited from the vapor phase show considerable advantages. Therefore, physical vapor deposition by electron beam evaporation (EB-PVD) is applied to achieve such columnar-structured TBCs. However, the deposition rate is low, and the line-of-sight nature of the process involves specific restrictions. In this article, the deposition of TBCs by the LPPS-TF process is shown. How the evaporation of the feedstock powder could be improved and to what extent the deposition rates could be increased were investigated. © 2010 ASM International.
    view abstractdoi: 10.1007/s11666-010-9549-1
  • 2011 • 51 Methylated [(benzene)(1,3-butadiene)Ru0] derivatives as novel MOCVD precursors with favorable properties
    Jipa, I. and Siddiqi, M.A. and Siddiqui, R.A. and Atakan, B. and Marbach, H. and Cremer, T. and Maier, F. and Steinrück, H.-P. and Danova, K. and Popovska, N. and Heinemann, F.W. and Zenneck, U.
    Chemical Vapor Deposition 17 15-21 (2011)
    [(Benzene)(2-methyl-1,3-butadiene)Ru0] (1), [(benzene)(2,3- dimethyl-1,3-butadiene)Ru0] (2), and [(2,3-dimethyl-1,3-butadiene) (toluene)Ru0] (3) are prepared and tested as new metal-organic (MO) ruthenium precursor complexes with favorable deposition properties for the CVD of thin ruthenium films. X-ray diffraction (XRD) studies of single crystals of the complexes are characteristic for true Ru0 π-complexes without molecular structure peculiarities or significant intermolecular interactions in the solid state, which can hinder undecomposed evaporation. Differential thermal analysis (DTA) and vapor pressure data qualify the compounds as almost ideal MOCVD precursors. Thin ruthenium films are deposited successfully on silicon wafers at substrate temperatures between 200 and 400°C in a nitrogen gas atmosphere. X-ray photoelectron spectroscopy (XPS), four-point probe conductivity measurements, and atomic force microscopy (AFM) are used to characterize the films. All films consist of polycrystalline metallic ruthenium with a low surface roughness. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cvde.201006853
  • 2011 • 50 Processing and damping properties of sputtered NiTi thin films for tools in machining processes
    Kahleyss, F. and De Miranda, R.L. and Surmann, T. and Zamponi, C. and MacHai, C. and Biermann, D. and Quandt, E.
    Journal of Materials Engineering and Performance 20 500-505 (2011)
    Nowadays, many manufacturing processes require the machining of complex forms with a high aspect ratio or cavities. Tools with a long overhang length are a common method to meet these requirements. Typical examples for this are boring bars for bore-turning and the milling with very long cutters. These tools tend to vibrate strongly due to their slender shape. The stress-induced transformation of austenite to martensite and the distinctive hysteresis loop allow the NiTi shape memory alloys (SMA) to absorb vibration energy. This article describes the innovative approach to dampen process vibrations by coating the tool shafts of cutting tools with long overhang with NiTi thin films. It explores how these thin films can be applied on polished tungsten carbide shafts and how their modal parameters are modified by these coatings. In a further step, this knowledge is used to calculate stability charts of corresponding machining processes. The study reported in this article identified the stabilizing effects of coatings with a thickness of 2-4 lm on milling processes. The minimum stability limit was increased by up to 200%. © ASM International.
    view abstractdoi: 10.1007/s11665-011-9847-x
  • 2011 • 49 Phase transformation, structural and functional fatigue properties of Ti-Ni-Hf shape memory thin films
    König, D. and Zarnetta, R. and Savan, A. and Brunken, H. and Ludwig, Al.
    Acta Materialia 59 3267-3275 (2011)
    The shape memory thin film system Ti-Ni-Hf was investigated with regard to its structural, phase transformation and functional fatigue properties by means of combinatorial and high-throughput methods. Temperature-dependent resistance measurements revealed a broad compositional region showing a reversible phase transformation. A ternary Laves phase was identified using X-ray diffraction as a precipitate phase within the transforming composition region. With increasing Ti content, the amount of the Laves phase increases, which results in an increase in the thermal hysteresis and a simultaneous decrease in the transformation temperatures. Shape memory properties were characterized by temperature-dependent stress change measurements using micromachined Si cantilever array wafers coated with Ti-Ni-Hf. The recovery stress was found to increase for small amounts of Laves phase precipitates. Strengthening of the matrix due to the Laves phase precipitates is concluded to be responsible for the observed increase in recovery stress and improved functional fatigue properties for (Ti,Hf)-rich alloy compositions (Ti 40.0Ni 47.5Hf 12.5). © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2011.01.066
  • 2011 • 48 X-ray photoelectron spectroscopy on implanted argon as a tool to follow local structural changes in thin films
    Lahrood, A. R. and de los Arcos, T. and Prenzel, M. and von Keudell, A. and Winter, J.
    Thin Solid Films 520 1625--1630 (2011)
    Argon ions were implanted in metallic, semiconducting or insulating substrates, and investigated with X-ray photoelectron spectroscopy. Analysis of the Ar2p core level of argon showed clear differences in binding energy position and width as function of the matrix material, implantation energy, and post-annealing treatment. Although argon is not expected to form chemical bonds with the host matrix, the electronic shells within the gas atom can react to their environment according to different effects. It is shown that the precise determination and correct interpretation of the binding energy levels of the embedded gas atoms provides information about the local environment of the matrix such as amorphization of the crystalline structure, defect healing or gas bubble formation. (C) 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2011.07.040
  • 2011 • 47 High-throughput characterization of film thickness in thin film materials libraries by digital holographic microscopy
    Lai, Y.W. and Krause, M. and Savan, A. and Thienhaus, S. and Koukourakis, N. and Hofmann, M.R. and Ludwig, Al.
    Science and Technology of Advanced Materials 12 (2011)
    A high-throughput characterization technique based on digital holography for mapping film thickness in thin-film materials libraries was developed. Digital holographic microscopy is used for fully automatic measurements of the thickness of patterned films with nanometer resolution. The method has several significant advantages over conventional stylus profilometry: it is contactless and fast, substrate bending is compensated, and the experimental setup is simple. Patterned films prepared by different combinatorial thin-film approaches were characterized to investigate and demonstrate this method. The results show that this technique is valuable for the quick, reliable and high-throughput determination of the film thickness distribution in combinatorial materials research. Importantly, it can also be applied to thin films that have been structured by shadow masking. © 2011 National Institute for Materials Science.
    view abstractdoi: 10.1088/1468-6996/12/5/054201
  • 2011 • 46 High-throughput characterization of stresses in thin film materials libraries using Si cantilever array wafers and digital holographic microscopy
    Lai, Y.W. and Hamann, S. and Ehmann, M. and Ludwig, Al.
    Review of Scientific Instruments 82 (2011)
    We report the development of an advanced high-throughput stress characterization method for thin film materials libraries sputter-deposited on micro-machined cantilever arrays consisting of around 1500 cantilevers on 4-inch silicon-on-insulator wafers. A low-cost custom-designed digital holographic microscope (DHM) is employed to simultaneously monitor the thin film thickness, the surface topography and the curvature of each of the cantilevers before and after deposition. The variation in stress state across the thin film materials library is then calculated by Stoneys equation based on the obtained radii of curvature of the cantilevers and film thicknesses. DHM with nanometer-scale out-of-plane resolution allows stress measurements in a wide range, at least from several MPa to several GPa. By using an automatic x-y translation stage, the local stresses within a 4-inch materials library are mapped with high accuracy within 10 min. The speed of measurement is greatly improved compared with the prior laser scanning approach that needs more than an hour of measuring time. A high-throughput stress measurement of an as-deposited Fe-Pd-W materials library was evaluated for demonstration. The fast characterization method is expected to accelerate the development of (functional) thin films, e.g., (magnetic) shape memory materials, whose functionality is greatly stress dependent. © 2011 American Institute of Physics.
    view abstractdoi: 10.1063/1.3600594
  • 2011 • 45 Structural, optical, and magnetic properties of Ho-implanted GaN thin films
    Lo, F.-Y. and Guo, J.-Y. and Ney, V. and Ney, A. and Chern, M.-Y. and Melnikov, A. and Pezzagna, S. and Reuter, D. and Wieck, A.D. and Massies, J.
    Journal of Physics: Conference Series 266 (2011)
    Ho ions were implanted into highly-resistive molecular-beam-epitaxy grown GaN thin films with a 100kV focused-ion-beam implanter at room temperature (RT). The implantation doses of Ho ions ranges from 1014 to 10 16 cm-2. Without thermal annealing, the structural, optical, and magnetic properties of the Ho-implanted thin films were investigated. Structural properties studied by x-ray diffraction revealed Ho incorporation into GaN matrix without secondary phase. The overall photoluminescence of any implanted sample is weaker than that of the non-implanted one. The spectra show neutral-donor-bound exciton emission and defect-related blue luminescence. Blocked superparamagnetic behavior was identified from Ho-implanted samples at temperatures below RT by measurements with a superconducting quantum interference device. The highest ordering temperature is 100 K. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/266/1/012097
  • 2011 • 44 Comparative study of hydrothermal treatment and thermal annealing effects on the properties of electrodeposited micro-columnar ZnO thin films
    Lupan, O. and Pauporté, T. and Tiginyanu, I.M. and Ursaki, V.V. and Şontea, V. and Ono, L.K. and Cuenya, B.R. and Chow, L.
    Thin Solid Films 519 7738-7749 (2011)
    We report a comparison of the role played by different sample treatments, namely, a low-temperature hydrothermal treatment by hot H2O vapor in an autoclave versus thermal annealing in air on the properties of ZnO films grown by electrochemical deposition (ECD). Scanning electron microscopy studies reveal a homogeneous micro-columnar morphology and changes in the film surface for the two different treatments. It is found that post-growth hydrothermal treatments of ECD ZnO films at 150 °C under an aqueous environment enhance their structural and optical properties (photoluminescence, transmission, Raman spectra, etc.) similar to thermal annealing in air at higher temperatures (&gt; 200 °C). The modifications of the structural and optical properties of ZnO samples after thermal annealing in air in the temperature range of 150-600 °C are discussed. The removal of chlorine from the films by the hydrothermal treatment was evidenced which could be the main reason for the improvement of the film quality. The observation of the enhanced photoluminescence peak at 380 nm demonstrates the superior properties of the hydrothermally treated ZnO films as compared to the films annealed in air ambient at the same or higher temperature. This post-growth hydrothermal treatment would be useful for the realization of high performance optoelectronic devices on flexible supports which might not withstand at high temperature annealing treatments. © 2011 Elsevier B.V. All rights reseved.
    view abstractdoi: 10.1016/j.tsf.2011.05.072
  • 2011 • 43 Stepwise deposition of metal organic frameworks on flexible synthetic polymer surfaces
    Meilikhov, M. and Yusenko, K. and Schollmeyer, E. and Mayer, C. and Buschmann, H.-J. and Fischer, R.A.
    Dalton Transactions 40 4838-4841 (2011)
    Thin films of [Cu3(btc)2]n (btc = 1,3,5-benzenetricarboxylate) metal organic framework were deposited in a stepwise manner on surfaces of flexible organic polymers. The thickness of films can be precisely controlled. The deposition of the first cycles was monitored by UV-vis spectroscopy. The porosity was proven by the adsorption of pyrazine, which was monitored by FT-IR and thermogravimetric analysis. The deposition of MOF thin films on flexible polymer surfaces might be a new path for the fabrication of functional materials for different applications, such as protection layers for working clothes and gas separation materials in the textile industry. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0dt01820a
  • 2011 • 42 Small-scale deposition of thin films and nanoparticles by microevaporation sources
    Meyer, R. and Hamann, S. and Ehmann, M. and König, D. and Thienhaus, S. and Savan, A. and Ludwig, Al.
    Journal of Microelectromechanical Systems 20 21-27 (2011)
    This paper reports on a novel miniaturized deposition technique based on micro-hotplates which are used as microevaporation sources (MES) for a localized deposition of thin films and nanoparticles. The feasibility of this small-scale deposition technique and its general properties are shown for depositions of Ag on unpatterned and microstructured substrates. The deposited films are rotationally symmetric and show a distinct lateral thickness change. We take advantage of this latter effect, as, e.g., all stages of film condensation can be observed within one experiment on one sample, in a size suitable for transmission electron microscopy investigations. For realizing the most laterally confined depositions, a micro-Knudsen cell was used. It is shown that the use of MES is also very suitable for the fabrication and deposition of nanoparticles. © 2011 IEEE.
    view abstractdoi: 10.1109/JMEMS.2010.2090506
  • 2011 • 41 Malonate complexes of dysprosium: Synthesis, characterization and application for LI-MOCVD of dysprosium containing thin films
    Milanov, A.P. and Seidel, R.W. and Barreca, D. and Gasparotto, A. and Winter, M. and Feydt, J. and Irsen, S. and Becker, H.-W. and Devi, A.
    Dalton Transactions 40 62-78 (2011)
    A series of malonate complexes of dysprosium were synthesized as potential metalorganic precursors for Dy containing oxide thin films using chemical vapor deposition (CVD) related techniques. The steric bulkiness of the dialkylmalonato ligand employed was systematically varied and its influence on the resulting structural and physico-chemical properties that is relevant for MOCVD was studied. Single crystal X-ray diffraction analysis revealed that the five homoleptic tris-malonato Dy complexes (1-5) are dimers with distorted square-face bicapped trigonal-prismatic geometry and a coordination number of eight. In an attempt to decrease the nuclearity and increase the solubility of the complexes in various solvents, the focus was to react these dimeric complexes with Lewis bases such as 2,2′-biypridyl and pyridine (6-9). This resulted in monomeric tris-malonato mono Lewis base adduct complexes with improved thermal properties. Finally considering the ease of synthesis, the monomeric nature and promising thermal characteristics, the silymalonate adduct complex [Dy(dsml)3bipy] (8) was selected as single source precursor for growing DySixOy thin films by liquid injection metalorganic chemical vapor deposition (LI-MOCVD) process. The as-deposited films were analyzed for their morphology and composition by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Rutherford backscattering (RBS) analysis and X-ray photoelectron spectroscopy. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0dt00455c
  • 2011 • 40 Nanostructuring of titania thin films by a combination of microfluidics and block-copolymer-based sol-gel templating
    Rawolle, M. and Ruderer, M.A. and Prams, S.M. and Zhong, Q. and Magerl, D. and Perlich, J. and Roth, S.V. and Lellig, P. and Gutmann, J.S. and Müller-Buschbaum, P.
    Small 7 884-891 (2011)
    Sol-gel templating of titania thin films with the amphiphilic diblock copolymer poly(dimethyl siloxane)-block-methyl methacrylate poly(ethylene oxide) is combined with microfluidic technology to control the structure formation. Due to the laminar flow conditions in the microfluidic cell, a better control of the local composition of the reactive fluid is achieved. The resulting titania films exhibit mesopores and macropores, as determined with scanning electron microscopy, X-ray reflectivity, and grazing incidence small angle X-ray scattering. The titania morphology has three features that are beneficial for application in photovoltaics: 1) a large surface-to-volume ratio important for charge generation with disordered hexagonally arranged mesopores of 25 nm size and a film porosity of up to 0.79, 2) enhanced light scattering that enables the absorption of more light, and 3) a dense titania layer with a thickness of about 6 nm at the substrate (bottom electrode) to prevent short circuits. An optical characterization complements the structural investigation. Microfluidics and sol-gel templating are combined to design titania thin films with well defined structures. The obtained films consist of mesopores with a diameter of 25 nm and macropores, as seen with scanning electron microscopy and grazing incidence small angle X-ray scattering. This structure is interesting for potential applications in inorganic-organic photovoltaics because of the large surface area and enhanced light scattering as compared to structures templated without microfluidics. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201001734
  • 2011 • 39 Preparation and characterization of ultrathin stainless steel films
    Sahoo, B. and Schlage, K. and Major, J. and Von Hörsten, U. and Keune, W. and Wende, H. and Röhlsberger, R.
    AIP Conference Proceedings 1347 57-60 (2011)
    We report on the preparation of polycrystalline austenitic 310 ( 57Fe0.55Cr0.25Ni0.20) stainless steel (SS) thin films on Si substrates and the characterization of their residual magnetism via 57Fe conversion-electron Mössbauer spectroscopy (CEMS). The films were structurally characterized at room temperature by X-ray diffraction (XRD). The virgin films were found to be structurally disordered. Subsequent annealing at moderate temperatures in ultrahigh vacuum produces the ordered martensitic and austenitic SS phases. Further annealing at higher temperatures (up to temperatures where long-range diffusion into the substrate is still weak) transforms the films into the austenitic phase with no trace of a magnetic hyperfine interaction. However, when a 2 nm thick SS thin film is embedded between two carbon layers, the as prepared disordered SS film does not transform to the martensitic or austenitic SS phase irrespective of the annealing temperature, probably because the interdiffusion with C prohibits the formation of these phases. © 2011 American Institute of Physics.
    view abstractdoi: 10.1063/1.3601785
  • 2011 • 38 High-throughput characterization of Pt supported on thin film oxide material libraries applied in the oxygen reduction reaction
    Schäfer, D. and Mardare, C. and Savan, A. and Sanchez, M.D. and Mei, B. and Xia, W. and Muhler, M. and Ludwig, Al. and Schuhmann, W.
    Analytical Chemistry 83 1916-1923 (2011)
    Thin film metal oxide material libraries were prepared by sputter deposition of nanoscale Ti/Nb precursor multilayers followed by ex situ oxidation. The metal composition was varied from 6 at.% Nb to 27 at.% Nb. Additionally, thin wedge-type layers of Pt with a nominal thickness gradient from 0 to 5 nm were sputter-deposited on top of the oxides. The materials libraries were characterized with respect to metallic film composition, oxide thickness, phases, electrical conductivity, Pt thickness, and electrochemical activity for the oxygen reduction reaction (ORR). Electrochemical investigations were carried out by cyclic voltammetry using an automated scanning droplet cell. For a nominal Pt thickness >1 nm, no significant dependence of the ORR activity on the Pt thickness or the substrate composition was observed. However, below that critical thickness, a strong decrease of the surface-normalized activity in terms of reduction currents and potentials was observed. For such thin Pt layers, the conductivity of the substrate seems to have a substantial impact on the catalytic activity. Results from X-ray photoelectron spectroscopy (XPS) measurements suggest that the critical Pt thickness coincides with the transition from a continuous Pt film into isolated particles at decreasing nominal Pt thickness. In the case of isolated Pt particles, the activity of Pt decisively depends on its ability to exchange electrons with the oxide layer, and hence, a dependence on the substrate conductivity is rationalized. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ac102303u
  • 2011 • 37 High-throughput characterization of the seebeck coefficient of a-(Cr 1 - XSix)1 - yOy thin film materials libraries as verification of the extended thermopower formula
    Sonntag, J. and Ziolkowski, P. and Savan, A. and Kieschnick, M. and Ludwig, Al.
    Journal of Physics Condensed Matter 23 (2011)
    In a previous paper (Sonntag 2010 J. Phys.: Condens. Matter 22 235501) the classical thermopower formula has been argued to be incomplete, because it only takes into account the scattering properties of the carriers, but not the temperature dependence of the electrochemical potential μ caused by variation of the carrier density and/or band edge shift with temperature T. This argument is now checked experimentally by high-throughput measurements of the thermopower (Seebeck coefficient) S of a-(Cr1 - xSix) 1 - yOy thin film materials libraries. The concentration dependences of S differ depending on whether the measurements are done with the complete film (where x ranges continuously from x≈0.3 to 0.8; y≈0.1-0.2) or with the separated pieces (each piece with another average value of x). These differences are especially large if, in addition, an oxygen gradient is present. © 2011 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/23/26/265501
  • 2011 • 36 Thin tantalum films on crystalline silicon - a metallic glass
    Stella, K. and Bürstel, D. and Hasselbrink, E. and Diesing, D.
    Physica Status Solidi - Rapid Research Letters 5 68-70 (2011)
    Thin amorphous tantalum films are prepared on Si(111) substrates in a metallic glassy state. The amorphous monoatomic state of the film is characterized by X-ray diffraction studies. The glassy state leads to a negative temperature coefficient of the resistivity (TCR) for low sample temperatures < 200 K which is attributed to incipient localization. Above 200 K a positive TCR is observed as expected for a normal Boltzmann transport regime. Upon heating the Si substrate to 1200 K TaSi2 is formed out of the amorphous tantalum film and the silicon substrate. The TaSi2 layer is crystalline as evident from X-ray diffraction data. Schematic drawing of the evaporation setup on either glass or silicon samples. Scheme of annealing effects. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssr.201004510
  • 2011 • 35 Plasma and optical thin film technologies
    Stenzel, O. and Wilbrandt, S. and Kaiser, N. and Schmitz, C. and Turowski, M. and Ristau, D. and Awakowicz, P. and Brinkmann, R.P. and Musch, T. and Rolfes, I. and Steffen, H. and Foest, R. and Ohl, A. and Köhler, T. and Dolgonos...
    Proceedings of SPIE - The International Society for Optical Engineering 8168 (2011)
    The PluTO project is aimed at combining thin-film and plasma technologies. Accordingly, the consortium comprises experts in optical coating (Laser Zentrum Hannover, Fraunhofer IOF) and such in plasma technology (INP Greifswald, Ruhr University of Bochum RUB). The process plasmas available, especially the sheath layers, will be thoroughly characterized by means of special probes, so that the types, numbers and energies of the particles participating in the coating formation processes can be determined comprehensively in every detail for the first time. The data thus obtained will provide a basis for a numerical modelling of layer growth at atomic scale (Bremen Center for Computational Materials Science BCCMS). The results are expected to deepen the understanding of the physical mechanisms responsible for the influence of plasma action on the layer properties. In parallel, suitable tools for process monitoring will be identified and made available. Some first results have already been achieved which prove the viability of the approach. © 2011 SPIE.
    view abstractdoi: 10.1117/12.895323
  • 2011 • 34 High performance low temperature solution-processed zinc oxide thin film transistor
    Theissmann, R. and Bubel, S. and Sanlialp, M. and Busch, C. and Schierning, G. and Schmechel, R.
    Thin Solid Films 519 5623-5628 (2011)
    Amorphous zinc oxide thin films have been processed out of an aqueous solution applying a one step synthesis procedure. For this, zinc oxide containing crystalline water (ZnO· × H2O) is dissolved in aqueous ammonia (NH3), making use of the higher solubility of ZnO· × H2O compared with the commonly used zinc oxide. Characteristically, as-produced layers have a thickness of below 10 nm. The films have been probed in standard thin film transistor devices, using silicon dioxide as dielectric layer. Keeping the maximum process temperature at 125 °C, a device mobility of 0.25 cm2V- 1s- 1 at an on/off ratio of 106 was demonstrated. At an annealing temperature of 300 °C, the performance could be optimized up to a mobility of 0.8 cm2V- 1s- 1. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2011.02.073
  • 2011 • 33 Evaluation of homoleptic guanidinate and amidinate complexes of gadolinium and dysprosium for MOCVD of rare-earth nitride thin films
    Thiede, T.B. and Krasnopolski, M. and Milanov, A.P. and De Los Arcos, T. and Ney, A. and Becker, H.-W. and Rogalla, D. and Winter, J. and Devi, A. and Fischer, R.A.
    Chemistry of Materials 23 1430-1440 (2011)
    Metal-organic chemical vapor deposition (MOCVD) of thin films of two representative rare-earth nitrides is reported here for the first time. Four homoleptic, all-nitrogen-coordinated, rare-earth (RE) complexes were evaluated as precursors for the respective nitride thin film materials. Two guanidinato complexes [RE{(iPrN)2C(NMe2)}3] [RE = Gd (1), Dy (2)] and two amidinato complexes [RE{(iPrN) 2CMe}3] [RE = Gd (3), Dy (4)] were compared and used either as single source precursors or together with ammonia for MOCVD of gadolinium nitride (GdN) and dysprosium nitride (DyN), respectively. The thermal properties of the precursors were studied and the fragmentation patterns were characterized by high-resolution electron impact-mass spectrometry (HR EI-MS). The obtained nitride films were investigated using a series of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), nuclear reaction analysis (NRA), Rutherford backscattering (RBS), and X-ray photoelectron spectroscopy (XPS). The films contain preferentially oriented grains of fcc-GdN and DyN and are contaminated with small amounts of carbon and oxygen (significantly below 10 at.-% in the best cases). The temperature-dependent magnetic properties of the films, as measured using a superconducting quantum interference device (SQUID), suggest the existence of small ferromagnetic grains of the rare-earth nitrides that exhibit superparamagnetism. Despite the chemical and structural similarity of the guanidinato and amidinato complexes (1-4), a distinctly different behavior as MOCVD precursors was found for 1 and 2, compared with that for 3 and 4. While the guanidinates operate well as single-source precursors (SSPs), the amidinates are not suited at all as SSPs, but give very good nitride films when used in the presence of ammonia. This characteristic behavior was correlated with the different fragmentation mechanisms, as revealed by EI-MS. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/cm102840v
  • 2011 • 32 Enhanced photoelectrochemical properties of WO3 thin films fabricated by reactive magnetron sputtering
    Vidyarthi, V.S. and Hofmann, M. and Savan, A. and Sliozberg, K. and König, D. and Beranek, R. and Schuhmann, W. and Ludwig, Al.
    International Journal of Hydrogen Energy 36 4724-4731 (2011)
    Polycrystalline WO3 thin films were fabricated by reactive magnetron sputtering at a substrate temperature of 350 °C under different Ar/O2 gas pressures. In order to study the thickness dependence of photoelectrochemical (PEC) behavior of WO3, the thickness-gradient films were fabricated and patterned using a micro-machined Si-shadow mask during the deposition process. The variation of the sputter pressure leads to the evolution of different microstructures of the thin films. The films fabricated at 2 mTorr sputter pressure are dense and show diminished PEC properties, while the films fabricated at 20 mTorr and 30 mTorr are less dense and exhibit enhanced water photooxidation efficiency. The enhanced photooxidation is attributed to the coexistence of porous microstructure and space charge region enabling improved charge carrier transfer to the electrolyte and back contact. A steady-state photocurrent as high as 2.5 mA cm-2 at 1 V vs. an Ag/AgCl (3 M KCl) reference electrode was observed. For WO3 films fabricated at 20 mTorr and 30 mTorr, the photocurrent increases continuously up to a thickness of 600 nm. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ijhydene.2011.01.087
  • 2011 • 31 Picosecond laser direct patterning of poly (3,4-ethylene dioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) thin films
    Xiao, S. and Abreu Fernandes, S. and Esen, C. and Ostendorf, A.
    Journal of Laser Micro Nanoengineering 6 249-254 (2011)
    Laser selective micro patterning of thin film of Poly (3,4-ethylenedioxythiophene):Poly (styrene sulfonate) (PEDOT:PSS) blend is investigated. Picosecond pulsed laser with 355 nm and 1064 nm wavelengths are used to study the ablation behavior of PEDOT:PSS thin film coated on glass. We present and discuss ablation thresholds for different film thicknesses as well as ablation lines with different overlapping rates. The results observed by SEM and white-light interference microscopy reveal that PEDOT:PSS film on glass substrates can be selectively patterned by optimized laser parameters.
    view abstractdoi: 10.2961/jlmn.2011.03.0015
  • 2011 • 30 High-throughput characterization of mechanical properties of Ti-Ni-Cu shape memory thin films at elevated temperature
    Zarnetta, R. and Kneip, S. and Somsen, C. and Ludwig, Al.
    Materials Science and Engineering A 528 6552-6557 (2011)
    Hardness and Young's moduli values for TixNi90-xCu10 (37at.%< x< 67at.%) thin films from a continuous composition spread type materials library, annealed at 500°C for 1h, were determined at room temperature (martensitic state) and 80°C (austenitic state) using high-throughput nanoindentation experiments. These values are found to increase as the compositions deviate from Ti contents close to 50at.%. The increases in hardness is correlated to the presence of Ti-rich and (Ni,Cu)-rich precipitates resulting in precipitate hardening and grain size refinement (Hall-Petch effect). The increase of the Young's moduli is rationalized by considering the significantly higher Young's moduli of the different precipitate phases and applying the rule of mixtures. The contributions of the precipitate phases and the matrix to the combined Young's modulus were estimated by evaluating the load-displacement curves in detail. The obtained results are in good agreement with the Young's moduli determined from thin film curvature measurements [R. Zarnetta et al., Smart Mater. Struct. 19 (2010) 65032]. Thus, the experimental restrictions for nanoindentation experiments at elevated temperatures are concluded to not adversely affect the validity of the results. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2011.05.006
  • 2010 • 29 Tailoring spin relaxation in thin films by tuning extrinsic relaxation channels
    Barsukov, I. and Meckenstock, R. and Lindner, J. and Moller, M. and Hassel, C. and Posth, O. and Farle, M. and Wende, H.
    IEEE Transactions on Magnetics 46 2252-2255 (2010)
    The importance of extrinsic spin relaxation processes such as magnonmagnon scattering for the overall damping in ferromagnetic thin films has been shown for low relaxation rate systems. Due to its anisotropic behavior, it offers an opportunity for controlling and tailoring the spin relaxation. In this paper, a ferromagnetic resonance study of a system with pure Gilbert damping Fe 94.5Si5.5/MgO(001) is shown. Fe3 Si/MgO(001) systems with native magnonmagnon scattering are discussed. Possibilities for inducing magnonmagnon scattering by volume and surface defects in these systems are presented, offering a method for controlled tailoring of the overall damping in thin films. © 2006 IEEE.
    view abstractdoi: 10.1109/TMAG.2010.2044482
  • 2010 • 28 Volatile, monomeric, and fluorine-free precursors for the metal organic chemical vapor deposition of zinc oxide
    Bekermann, D. and Rogalla, D. and Becker, H.-W. and Winter, M. and Fischer, R.A. and Devi, A.
    European Journal of Inorganic Chemistry 1366-1372 (2010)
    Two new bis(ketoiminato)zinc(II) compounds that show excellent precursor properties for the chemical vapor deposition (CVD) of zinc oxide materials are presented. The synthesis of the ketoiminato zinc complexes [Zn{[(CH 2)x-OCH3]NC(CH3)=C(H)C(CH 3)=O}2] (1: x = 2; 2: x = 3) is straightforward and can easily be scaled up. Compounds 1 and 2 were analyzed by 1H and 13C NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, and electron ionization mass spectrometry. The compounds exist as monomers with a distorted tetrahedral zinc center. Thermogravimetric studies, sublimation, and solubility tests reveal very promising properties for metal-organic CVD related applications. Preliminary metal-organic CVD experiments with the use of compound 1 were performed as a screening for the suitability of the new bis(ketoiminato)zinc complexes as precursors for the growth of ZnO thin films in the presence of oxygen. The films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive analysis of X-ray, and Rutherford backscattering measurements. The as-deposited ZnO films were stoichiometric; the crystalline films exhibited strong preferred orientation along the c-axis. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/ejic.200901037
  • 2010 • 27 Structural, static and dynamic magnetic properties of Co2MnGe thin films on a sapphire a-plane substrate
    Belmeguenai, M. and Zighem, F. and Chauveau, T. and Faurie, D. and Roussigń, Y. and Ch́rif, S.M. and Moch, P. and Westerholt, K. and Monod, P.
    Journal of Applied Physics 108 (2010)
    Magnetic properties of Co2 MnGe thin films of different thicknesses (13, 34, 55, 83, 100, and 200 nm), grown by rf sputtering at 400 °C on single crystal sapphire substrates, were studied using vibrating sample magnetometry and conventional or microstrip line ferromagnetic resonance. Their behavior is described assuming a magnetic energy density showing twofold and fourfold in-plane anisotropies with some misalignment between their principal directions. For all the samples, the easy axis of the fourfold anisotropy is parallel to the c -axis of the substrate while the direction of the twofold anisotropy easy axis varies from sample to sample and seems to be strongly influenced by the growth conditions. Its direction is most probably monitored by the slight unavoidable miscut angle of the Al2 O 3 substrate. The twofold in-plane anisotropy field Hu is almost temperature independent, in contrast with the fourfold field H 4 which is a decreasing function of the temperature. Finally, we study the frequency dependence of the observed line-width of the resonant mode and we conclude to a typical Gilbert damping constant α value of 0.0065 for the 55-nm-thick film. © 2010 American Institute of Physics.
    view abstractdoi: 10.1063/1.3475501
  • 2010 • 26 Microstructure and magnetic properties of FeCo/Ti thin film multilayers annealed in nitrogen
    Brunken, H. and Somsen, C. and Savan, A. and Ludwig, Al.
    Thin Solid Films 519 770-774 (2010)
    Multifunctional nanocomposites consisting of at least one ferromagnetic phase (e.g. FeCo) and one protective, wear resistant phase (e.g. TiN) are of interest for applications as sensors or actuators in harsh environments. This paper reports on the fabrication and characterization of nanocomposite thin films, prepared from FeCo/Ti metallic precursor multilayer composition spreads using a combinatorial sputter-deposition system. After deposition, the composition spread was annealed in nitrogen (5 × 10 5 Pa pressure) at 850 °C for 1.5 h, leading to preferential nitriding of Ti to TiN, thus forming the protective phase. Automated energy dispersive X-ray analysis, Auger electron spectroscopy, X-ray diffraction measurements, transmission electron microscopy (TEM) and vibrating sample magnetometry were used for the characterization of the as deposited and nitrided composition spreads. As an unexpected result, the appearance of a Heusler phase (Co 2FeSi) in the nanocomposite was observed by TEM. After N 2 annealing, the nanocomposites show reduced saturation magnetization values μ 0M S between 0.5 and 0.95 T and improved coercive field values μ 0H c between 4 and 13.8 mT, dependent on the TiN content. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2010.09.008
  • 2010 • 25 Trap states and space charge limited current in dispersion processed zinc oxide thin films
    Bubel, S. and Mechau, N. and Hahn, H. and Schmechel, R.
    Journal of Applied Physics 108 (2010)
    The electric transport properties of nanoparticulate zinc oxide (ZnO) thin films are investigated in nitrogen and ambient atmosphere with respect to the effects of polymer adsorbates, in order to study the origin of hysteresis behavior of ZnO thin film transistors. A strong dependence on the polymer adsorbate of the conductivity in nitrogen atmosphere is observed. Utilizing the space charge limited current theory, the trap depth and concentration in the films have been estimated. According to this analysis, the low conductivity of polymer free thin films in ambient atmosphere is caused by an increase in deep traps, compensating free charge carriers and not by a reduction in donorlike defect states. Furthermore, polymeric additives seem to induce similar trap states, which make the transport properties less sensitive against atmospheric influences. However, the strongly compensated semiconductor created in this way, causes a slow trap and release behavior resulting in a strong hysteresis in the transistor characteristics and long-term instabilities. It is shown, that ignoring these time-dependent characteristics, straight forward derived transistor parameters like the field effect mobility can be easily overestimated. © 2010 American Institute of Physics.
    view abstractdoi: 10.1063/1.3524184
  • 2010 • 24 Adhesion energies of Cr thin films on polyimide determined from buckling: Experiment and model
    Cordill, M.J. and Fischer, F.D. and Rammerstorfer, F.G. and Dehm, G.
    Acta Materialia 58 5520-5531 (2010)
    For the realization of flexible electronic devices, the metal-polymer interfaces upon which they are based need to be optimized. These interfaces are prone to fracture in such systems and hence form a weak point. In order to quantify the interfacial adhesion, novel mechanical tests and modeling approaches are required. In this study, a tensile testing approach that induces buckling of films by lateral contraction of the substrate is employed to cause delamination of the film. Based on a newly developed energy balance model, the adhesion energy of Cr films on polyimide substrates is determined by measuring the buckle geometry induced by the tensile test. The obtained minimum values for the adhesion energy (about 4.5 J m-2) of 50-190 nm thick films compare well to those found in the literature for metal films on polymer substrates. © 2010 Acta Materialia Inc. Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.actamat.2010.06.032
  • 2010 • 23 Fracture and delamination of chromium thin films on polymer substrates
    Cordill, M.J. and Taylor, A. and Schalko, J. and Dehm, G.
    Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 41 870-875 (2010)
    New emerging technologies in the field of flexible electronic devices require that metal films adhere well and flex with polymer substrates. Common thin film materials used for these applications include copper (Cu) with an adhesion interlayer of chromium (Cr). Copper can be quite ductile and easily move with the polymer substrate. However, Cr is more brittle and fractures at lower strains than Cu. This study aims to examine the fracture and subsequent buckling and delamination of strained Cr films on polyimide (PI). In-situ scanning electron microscope (SEM) straining is used to systematically study the influence of film thickness on fracture and buckling strains. Film fracture and delamination depend on film thickness, and increases in crack and buckle density with decreasing thickness are explored by a shear lag model. © 2009 The Minerals, Metals & Materials Society and ASM International.
    view abstractdoi: 10.1007/s11661-009-9988-9
  • 2010 • 22 Growth and characterization of ti-ta-o thin films on si substrates by liquid injection MOCVD for high-k applications from modified titanium and tantalum precursors
    Devi, A. and Hellwig, M. and Barreca, D. and Parala, H. and Thomas, R. and Becker, H.-W. and Katiyar, R.S. and Fischer, R.A. and Tondello, E.
    Chemical Vapor Deposition 16 157-165 (2010)
    Titanium oxide (TiO2) and titanium-tantalum oxide (Ti-Ta-O) thin films are deposited by liquid injection (LI) metal-organic (MO) CVD using metal amide-malonate complexes, [Ti(NR2)2 (dbml) 2], and tantalum, [Ta(NMe2)2 (dbml)] (R Me, Et; dbml di-tert-butylmalonato). TiO2 and Ti-Ta-O films are deposited on Si(100) in the temperature ranges 350-650°C and 500-700°C, respectively. The structure, morphology, and chemical composition of the films are evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), and X-ray photoelectron spectroscopy (XPS). The electrical properties of the films, namely the dielectric properties, are assessed by carrying out capacitance-voltage (C-V) measurements on metal-oxide-semiconductor (MOS) capacitor structures.
    view abstractdoi: 10.1002/cvde.200906813
  • 2010 • 21 Thin films of the Heusler alloys Cu2MnAl and Co2MnSi: Recovery of ferromagnetism via solid-state crystallization from the x-ray amorphous state
    Erb, D. and Nowak, G. and Westerholt, K. and Zabel, H.
    Journal of Physics D: Applied Physics 43 (2010)
    X-ray amorphous thin films of the Heusler alloys Cu2MnAl and Co2MnSi have been prepared by magnetron sputter deposition at room temperature. In the amorphous state the Cu2MnAl phase is non-ferromagnetic; Co2MnSi is weakly ferromagnetic with a ferromagnetic Curie temperature of 170 K. By solid-state crystallization at high temperatures strong ferromagnetic order and high Curie temperatures are established in both alloys. The saturation magnetization of the Co 2MnSi alloy reaches 5.1μB/f.u. at 4 K, corresponding to 100% of the theoretical value; for Cu2MnAl we obtain 2.8μB/f.u. at 4 K, which corresponds to 87.5% of the theoretical value. In samples of the Co2MnSi phase with optimum saturation magnetization Bragg reflections as indicators of a long-range chemical order are missing, whereas for the Cu2MnAl phase Bragg reflections confirm epitaxial quality and long-range L21 order. © 2010 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/43/28/285001
  • 2010 • 20 The ferromagnetic shape memory system Fe-Pd-Cu
    Hamann, S. and Gruner, M.E. and Irsen, S. and Buschbeck, J. and Bechtold, C. and Kock, I. and Mayr, S.G. and Savan, A. and Thienhaus, S. and Quandt, E. and Fähler, S. and Entel, P. and Ludwig, Al.
    Acta Materialia 58 5949-5961 (2010)
    A new ferromagnetic shape memory thin film system, Fe-Pd-Cu, was developed using ab initio calculations, combinatorial fabrication and high-throughput experimentation methods. Reversible martensitic transformations are found in extended compositional regions, which have increased fcc-fct transformation temperatures in comparison to previously published results. High resolution transmission electron microscopy verified the existence of a homogeneous ternary phase without precipitates. Curie temperature, saturation polarization and orbital magnetism are only moderately decreased by alloying with nonmagnetic Cu. Compared to the binary system; enhanced Invar-type thermal expansion anomalies in terms of an increased volume magnetostriction are predicted. Complementary experiments on splat-fabricated bulk Fe-Pd-Cu samples showed an enhanced stability of the disordered transforming Fe70Pd30 phase against decomposition. From the comparison of bulk and thin film results, it can be inferred that, for ternary systems, the Fe content, rather than the valence electron concentration, should be regarded as the decisive factor determining the fcc-fct transformation temperature. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2010.07.011
  • 2010 • 19 Investigation of the fatigue behavior of Al thin films with different microstructure
    Heinz, W. and Pippan, R. and Dehm, G.
    Materials Science and Engineering A 527 7757-7763 (2010)
    Cyclic compressive and tensile stresses occur in metallic films and interconnects applied in sensors and microelectronic devices when exposed to temperature changes. The stresses are induced by differences in the thermal expansion coefficients of the adjacent materials. Repeated cycling leads to damage evolution and, eventually, to failure. In this study we report on a successful strategy how to avoid thermal stress induced fatigue damage. We analysed the deformation structures of 0.2-2μm thick Al films subjected to thermal cycling between 100°C and 450°C up to 10,000 times. The investigations reveal that a reduction in film thickness or controlling the Al texture and the Al/substrate interface structure can be used to prevent thermo-mechanical fatigue damage. The findings are explained by orientation dependent plasticity and differences in dislocation mechanisms for different interface structures, and less accumulated plastic strain for thinner films. The approach is expected to apply in general for metallic films on substrates. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2010.08.046
  • 2010 • 18 Metal-free and electrocatalytically active nitrogen-doped carbon nanotubes synthesized by coating with polyaniline
    Jin, C. and Nagaiah, T.C. and Xia, W. and Spliethoff, B. and Wang, S. and Bron, M. and Schuhmann, W. and Muhler, M.
    Nanoscale 2 981-987 (2010)
    Nitrogen doping of multi-walled carbon nanotubes (CNTs) was achieved by the carbonization of a polyaniline (PANI) coating. First, the CNTs were partially oxidized with KMnO4 to obtain oxygen-containing functional groups. Depending on the KMnO4 loading, thin layers of birnessite-type MnO2 (10 wt% and 30 wt%) were obtained by subsequent thermal decomposition. CNT-supported MnO2 was then used for the oxidative polymerization of aniline in acidic solution, and the resulting PANI-coated CNTs were finally heated at 550 °C and 850 °C in inert gas. The samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. A thin layer of carbonized PANI was observed on the CNT surface, and the surface nitrogen concentration of samples prepared from 30% MnO 2 was found to amount to 7.6 at% and 3.8 at% after carbonization at 550 °C and 850 °C, respectively. These CNTs with nitrogen-containing shell were further studied by electrochemical impedance spectroscopy and used as catalysts for the oxygen reduction reaction. The sample synthesized from 30 wt% MnO2 followed by carbonization at 850 °C showed the best electrochemical performance indicating efficient nitrogen doping. © 2010 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/b9nr00405j
  • 2010 • 17 Micro- to nanostructured devices for the characterization of scaling effects in shape-memory thin films
    König, D. and Ehmann, M. and Thienhaus, S. and Ludwig, Al.
    Journal of Microelectromechanical Systems 19 1264-1269 (2010)
    Two microfabricated devices designed as test platforms for the investigation of scaling effects in micro- to nanosized substrate-attached shape-memory alloy (SMA) thin films as well as freestanding (suspended) thin-film microbridges are presented. These micromachined test platforms allow for simultaneous nanomechanical, electrical, and thermal tests on thin-film microbridges and can be seen as a basis for nanoscale SMA thin-film applications. The functionality of these devices is demonstrated for Ti 52 Ni32 Cu16 thin films as active material. The martensitic phase-transition temperatures for the thin films as substrate-attached or suspended microstructures as well as the dependence on the lateral dimensions were examined. It was found that decreasing the bridge width from 4 to 1 μm leads to a substantial and asymmetrical decrease of the phase-transition temperatures: 20% [austenite finish temperature (Af) and martensite start temperature (Ms)] and 80% [austenite start temperature (As
    view abstractdoi: 10.1109/JMEMS.2010.2067441
  • 2010 • 16 Effective reaction rates of a thin catalyst layer
    Lenzinger, M. and Schweizer, B.
    Mathematical Methods in the Applied Sciences 33 974-984 (2010)
    The catalyst layer in a fuel cell can be described with a system of reaction diffusion equations for the oxygen concentration and the protonic overpotential. The Tafel law gives an exponential expression for the reaction rate, and the Tafel slope is a coefficient in this law. We present a rigorous thin layer analysis for two reaction regimes. In the case of thin catalyst layers and bounded potentials, the original Tafel law enters as an effective boundary condition. Instead, in the case of large protonic overpotentials, we derive an exponential law that contains the doubled Tafel slope. Copyright © 2009 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/mma.1223
  • 2010 • 15 A review of crystallographic textures in chemical vapor-deposited diamond films
    Liu, T. and Raabe, D. and Mao, W.-M.
    Signal, Image and Video Processing 4 1-16 (2010)
    Diamond is one of the most important functional materials for film applications due to its extreme physical and mechanical properties, many of which depend on the crystallographic texture. The influence of various deposition parameters matters to the texture formation and evolution during chemical vapor deposition (CVD) of diamond films. In this overview, the texture evolutions are presented in terms of both simulations and experimental observations. The crystallographic textures in diamond are simulated based on the van der Drift growth selection mechanism. The film morphology and textures associated with the growth parameters α (proportional to the ratio of the growth rate along the 〈100〉 direction to that along the 〈111〉 direction) are presented and determined by applying the fastest growth directions. Thick films with variations in substrate temperature, methane concentration, film thickness, and nitrogen addition were analyzed using high-resolution electron back-scattering diffraction (HR-EBSD) as well as X-ray diffraction (XRD), and the fraction variations of fiber textures with these deposition parameters were explained. In conjunction with the focused ion beam (FIB) technique for specimen preparation, the grain orientations in the beginning nucleation zones were studied using HR-EBSD (50 nm step size) in another two sets of thin films deposited with variations in methane concentration and substrate material. The microstructures, textures, and grain boundary character were characterized. Based on the combination of an FIB unit for serial sectioning and HR-EBSD, diamond growth dynamics was observed using a 3D EBSD technique, with which individual diamond grains were investigated in 3D. Microscopic defects were observed in the vicinity of the high-angle grain boundaries by using the transmission electron microscopy (TEM) technique, and the advances of TEM orientation microscopy make it possible to identify the grain orientations in nano-crystalline diamond. © 2010 Higher Education Press and Springer Berlin Heidelberg.
    view abstractdoi: 10.1007/s11760-008-0099-7
  • 2010 • 14 Effects of annealing on properties of ZnO thin films prepared by electrochemical deposition in chloride medium
    Lupan, O. and Pauporté, T. and Chow, L. and Viana, B. and Pellé, F. and Ono, L.K. and Roldan Cuenya, B. and Heinrich, H.
    Applied Surface Science 256 1895-1907 (2010)
    The development of cost-effective and low-temperature synthesis techniques for the growth of high-quality zinc oxide thin films is paramount for fabrication of ZnO-based optoelectronic devices, especially ultraviolet (UV)-light-emitting diodes, lasers and detectors. We demonstrate that the properties, especially UV emission, observed at room temperature, of electrodeposited ZnO thin films from chloride medium (at 70 °C) on fluor-doped tin oxide (FTO) substrates is strongly influenced by the post-growth thermal annealing treatments. X-ray diffraction (XRD) measurements show that the films have preferably grown along (0 0 2) direction. Thermal annealing in the temperature range of 150-400 °C in air has been carried out for these ZnO thin films. The as-grown films contain chlorine which is partially removed after annealing at 400 °C. Morphological changes upon annealing are discussed in the light of compositional changes observed in the ZnO crystals that constitute the film. The optical quality of ZnO thin films was improved after post-deposition thermal treatment at 150 °C and 400 °C in our experiments due to the reducing of defects levels and of chlorine content. The transmission and absorption spectra become steeper and the optical bandgap red shifted to the single-crystal value. These findings demonstrate that electrodeposition have potential for the growth of high-quality ZnO thin films with reduced defects for device applications. © 2009 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2009.10.032
  • 2010 • 13 Biomimetic formation of thin, coherent iron oxide films under Langmuir monolayers
    Maas, M. and Degen, P. and Rehage, H. and Nebel, H. and Epple, M.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 354 149-155 (2010)
    This study focuses on the biomimetic formation and growth of thin iron oxide films under Langmuir monolayers. These coherent film structures were formed in the presence of different iron chloride solutions during the addition of an ammonia atmosphere. Stearic acid, stearyl amine and stearyl alcohol were used as film forming surfactants while the subphase contained FeCl2, FeCl3 or a mixture of both salts. The thin, coherent films consisted of X-ray amorphous iron oxide, hydroxide or oxyhydroxide. The films were studied by scanning electron microscopy, atomic force microscopy, X-ray diffraction, dynamic light scattering and surface potential measurements. Based on the experimental results we propose a growth mechanism that is guided by the formation of nanoparticles in the subphase and their assembly and aggregation underneath the Langmuir films. © 2009 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.colsurfa.2009.04.049
  • 2010 • 12 Combinatorial investigation of Hf-Ta thin films and their anodic oxides
    Mardare, A.I. and Ludwig, Al. and Savan, A. and Wieck, A.D. and Hassel, A.W.
    Electrochimica Acta 55 7884-7891 (2010)
    A co-sputtering technique was used for the fabrication of a thin film combinatorial library (Hf-21 at.% Ta to 91 at.% Ta) based on alloying of Hf and Ta. The microstructure and crystallography of individual metallic alloy compositions were analyzed using SEM and XRD mapping, respectively. Three different zones of microstructure were identified within the range of alloys, going from hexagonal to tetragonal through an intermediate amorphous region. The local oxidation of Hf-Ta parent metal alloys at different compositions was investigated in steps of 1 at.% using an automated scanning droplet cell in the confined droplet mode. Potentiodynamic anodisation cycles combined with in situ impedance spectroscopy provide basic knowledge regarding the oxide formation and corresponding electrical properties. Dielectric constants were mapped for the entire composition range and XPS depth profiles allowed investigation of the oxide compositions. © 2010 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.electacta.2010.03.066
  • 2010 • 11 Growth of crystalline Gd2O3 thin films with a high-quality interface on Si(100) by low-temperature H2O-assisted atomic layer deposition
    Milanov, A.P. and Xu, K. and Laha, A. and Bugiel, E. and Ranjith, R. and Schwendt, D. and Osten, H.J. and Parala, H. and Fischer, R.A. and Devi, A.
    Journal of the American Chemical Society 132 36-37 (2010)
    (Figure Presented) This work documents the first example of deposition of high-quality Gd2O3 thin films in a surface-controlled, self-limiting manner by a water-based atomic layer deposition (ALD) process using the engineered homoleptic gadolinium guanidinate precursor [Gd(DPDMG) 3]. The potential of this class of compound is demonstrated in terms of a true ALD process, exhibiting pronounced growth rates, a high-quality interface between the film and the substrate without the need for any additional surface treatment prior to the film deposition, and most importantly, encouraging electrical properties. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ja909102j
  • 2010 • 10 PS-b-PEO block copolymer thin films as structured reservoirs for nanoscale precipitation reactions
    Ochsmann, J.W. and Lenz, S. and Emmerling, S.G.J. and Kappes, R.S. and Nett, S.K. and Lechmann, M.C. and Roth, S.V. and Gutmann, J.S.
    Journal of Polymer Science, Part B: Polymer Physics 48 1569-1573 (2010)
    Thin films of PS-b-PEO block copolymers were utilized as structured reservoirs for localized nanoscale precipitation reactions. By consecutively immersing the film into solutions of thioacetamide and cadmium chloride, we were able to obtain a monolayer of cadmium sulfide nanostructures on top of the block copolymer film. AFM and grazing incidence small angle X-ray scattering revealedspherical nanostructures (d = 15 nm) corresponding to the dimensions given by the block copolymer film. © 2010 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/polb.21967
  • 2010 • 9 In situ TEM study of microplasticity and Bauschinger effect in nanocrystalline metals
    Rajagopalan, J. and Rentenberger, C. and Peter Karnthaler, H. and Dehm, G. and Saif, M.T.A.
    Acta Materialia 58 4772-4782 (2010)
    In situ transmission electron microscopy straining experiments with concurrent macroscopic stress-strain measurements were performed to study the effect of microstructural heterogeneity on the deformation behavior of nanocrystalline metal films. In microstructurally heterogeneous gold films (mean grain size dm = 70 nm) comprising randomly oriented grains, dislocation activity is confined to relatively larger grains, with smaller grains deforming elastically, even at applied strains approaching 1.2%. This extended microplasticity leads to build-up of internal stresses, inducing a large Bauschinger effect during unloading. Microstructurally heterogeneous aluminum films (dm = 140 nm) also show similar behavior. In contrast, microstructurally homogeneous aluminum films comprising mainly two grain families, both favorably oriented for dislocation glide, show limited microplastic deformation and minimal Bauschinger effect despite having a comparable mean grain size (dm = 120 nm). A simple model is proposed to describe these observations. Overall, our results emphasize the need to consider both microstructural size and heterogeneity in modeling the mechanical behavior of nanocrystalline metals. © 2010 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2010.05.013
  • 2010 • 8 Downscaling of defect-passivated Gd2O3 thin films on p-Si(0 0 1) wafers grown by H2O-assisted atomic layer deposition
    Ranjith, R. and Laha, A. and Bugiel, E. and Osten, H.J. and Xu, K. and Milanov, A.P. and Devi, A.
    Semiconductor Science and Technology 25 (2010)
    Crystalline thin films of Gd2O3 of varying thicknesses were grown on 2 inch p-Si(1 0 0) wafers by H2O-assisted atomic layer deposition (ALD) using a homoleptic gadolinium tris-guanidinate precursor [Gd(iPr-Me2N-Guan)3]. The Gd 2O3 layers grown at 225 °C were polycrystalline with columnar growth morphology. The as-grown films were electrically characterized as a metal oxide semiconductor (MOS) capacitor and exhibited instability in the flat-band voltage. Upon subjection to post-deposition defect-passivation treatment, they exhibited promising electrical characteristics. More importantly, the vertical downscaling of Gd2O3 thin films through the H2O-assisted ALD process could be realized through the capacitance equivalent thickness versus physical thickness studies. © 2010 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0268-1242/25/10/105001
  • 2010 • 7 Passivation of Si(111) surfaces with electrochemically grafted thin organic films
    Roodenko, K. and Yang, F. and Hunger, R. and Esser, N. and Hinrichs, K. and Rappich, J.
    Surface Science 604 1623-1627 (2010)
    Ultra thin organic films (about 5 nm thick) of nitrobenzene and 4-methoxydiphenylamine were deposited electrochemically on p-Si(111) surfaces from benzene diazonium compounds. Studies based on atomic force microscopy, infrared spectroscopic ellipsometry and x-ray photoelectron spectroscopy showed that upon exposure to atmospheric conditions the oxidation of the silicon interface proceed slower on organically modified surfaces than on unmodified hydrogen passivated p-Si(111) surfaces. Effects of HF treatment on the oxidized organic/Si interface and on the organic layer itself are discussed. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.susc.2010.06.005
  • 2010 • 6 Depositions of SrRuO3 thin films on oxide substrates with liquid-delivery spin MOCVD
    Schwarzkopf, J. and Dirsyte, R. and Devi, A. and Schmidbauer, M. and Wagner, G. and Fornari, R.
    Thin Solid Films 518 4675-4679 (2010)
    Systematic variations of the deposition conditions for thin epitaxial SrRuO3 films with a liquid-delivery spin MOCVD were performed in order to get a detailed understanding of the physical and chemical issues in the growth process. We have observed that at very low as well as at high growth rates the structural ordering of the films and the lattice strain is low, while for optimized conditions (∼ 0.14-0.2 nm/min) films can be grown under high compressive strain on SrTiO3 and under tensile strain on DyScO 3, showing an electrical resistivity of ∼ 250 μΩcm. Films on NdGaO3 are nearly totally plastically relaxed. In contrast to PLD, step-flow growth could not be detected due to significantly higher carbon incorporation. © 2009 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2009.12.057
  • 2010 • 5 Synchrotron infrared spectroscopic ellipsometry for characterization of biofunctional surfaces
    Sun, G. and Rosu, D.M. and Zhang, X. and Hovestädt, M. and Pop, S. and Schade, U. and Aulich, D. and Gensch, M. and Ay, B. and Holzhütter, H.-G. and Zahn, D.R.T. and Esser, N. and Volkmer, R. and Rappich, J. and Hinrichs, K.
    Physica Status Solidi (B) Basic Research 247 1925-1931 (2010)
    The structural and thickness homogeneity of different biofunctional surfaces after coating an Au substrate was studied by infrared spectroscopic ellipsometry (IRSE). Monolayer coverage was achieved by washing the samples in aqueous solution. A selected cysteine-modified CHL peptide and an antiglutathione S-transfer (GST) antibody produced a characteristic change in the IR ellipsometric spectra after peptide and antibody adsorption, confirming the biosensing ability of this technique. IR ellipsometric mapping at the synchrotron storage ring BESSY II in Berlin allowed laterally resolved characterization of the protein films. The IR ellipsometric tanψ and δ maps revealed that the protein films are inhomogeneous in structure and thickness after adsorption of the peptide and antibody. The absolute thickness of the protein films varied considerably by up to 3 to 7 nm. We also studied cytosine films with different thicknesses (d = 58 nm and 125 nm) and a guanine film (d = 84 nm). For the two cytosine films the synchrotron spectra revealed that the thicker film in particular was rather homogeneous in thickness but inhomogeneous in structure. For the guanine film the shape of vibrational bands in the ellipsometric spectra correlated with anisotropic molecular orientations. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssb.200983945
  • 2010 • 4 Microplasticity phenomena in thermomechanically strained nickel thin films
    Taylor, A.A. and Oh, S.H. and Dehm, G.
    Journal of Materials Science 45 3874-3881 (2010)
    Magnetron sputtered Ni thin films on both oxidised Si (100) and α-Al2O3 (0001) substrates of thickness 150-1000 nm were tested thermomechanically with a wafer curvature system, as well as in situ in a transmission electron microscope. The films on oxidised Si have a {111}-textured columnar microstructure with a mean grain size similar to the film thickness. On (0001) α-Al2O3 a near single crystal epitaxy with two growth variants is achieved leading to a significantly larger grain size. The thermomechanical testing was analysed in terms of the room temperature/high temperature flow stresses in the films and the observed thermoelastic slopes. It was found that the room temperature flow stresses increased with decreasing film thickness until a plateau of ∼1100 MPa was reached for films thinner than 400 nm. This plateau is attributed to the present experiments exerting insufficient thermal strain to induce yielding in these thinner films. At 500 °C the compressive flow stresses of the films show a competition between dislocation and diffusion mediated plasticity. A size effect is also observed in the thermoelastic slopes of the films, with thinner films coming closer to the slope predicted by mismatch in thermal expansion coefficients. It is put forward here that this is due to a highly inhomogeneous stress distribution in the films arising from the grain size distribution. © 2010 Springer Science+Business Media, LLC.
    view abstractdoi: 10.1007/s10853-010-4445-0
  • 2010 • 3 Enhanced light trapping in thin amorphous silicon solar cells by directionally selective optical filters
    Ulbrich, C. and Peters, M. and Tayyib, M. and Blaesi, B. and Kirchartz, T. and Gerber, A. and Rau, U.
    Proceedings of SPIE - The International Society for Optical Engineering 7725 (2010)
    Optical absorption losses limit the efficiency of thin-film solar cells. We demonstrate how to increase the absorption in hydrogenated amorphous silicon solar cells by using a directionally selective optical multilayer filter covering the front glass. The filter transmits perpendicularly incident photons in the wavelength range 350 nm - 770 nm. In the regime of low absorptance, i.e. large optical absorption lengths, however, it blocks those photons impinging under oblique angles. Thus, the incoming radiation is transmitted with almost no loss while the emitted radiation is mostly blocked due to its wider angle distribution. We determine the enhancement in the optical path length from reflectivity measurements. In the weakly absorbing high wavelength range (650 nm - 770 nm) we observe a peak optical path length enhancement of κ ∼3.5. The effective path length enhancement κ ∼ calculated from the external quantum efficiency of the solar cell with filter, however, peaks at a lower value of only κ ∼1.5 in the same wavelength range. Parasitic absorption in the layers adjacent to the photovoltaic absorber limit the increase in the effective light path enhancement. Nonetheless we determine an increase of 0.2 mAcm-2 in the total short circuit current density. © 2010 Copyright SPIE - The International Society for Optical Engineering.
    view abstractdoi: 10.1117/12.853799
  • 2010 • 2 Identification of optimized Ti-Ni-Cu shape memory alloy compositions for high-frequency thin film microactuator applications
    Zarnetta, R. and Ehmann, M. and Savan, A. and Ludwig, Al.
    Smart Materials and Structures 19 (2010)
    Ti-Ni-Cu shape memory thin films within a broad composition range were investigated by the cantilever deflection method using combinatorial methods. Optimal compositions with improved functional properties, i.e.large recovery stress, high transformation temperatures, low thermal hysteresis width and small temperature interval of transformation, were identified using a newly defined figure of merit. Of the investigated alloys, Ti50Ni 41Cu9 and Ti45Ni46Cu9 exhibit the best shape memory properties for compositions showing a B2 → B19 and a B2 → R-phase transformation, respectively. © 2010 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0964-1726/19/6/065032
  • 2010 • 1 Effects of annealing time on the structural and magnetic properties of L10 FePt thin films
    Zotov, N. and Hiergeist, R. and Savan, A. and Ludwig, Al.
    Thin Solid Films 518 4977-4985 (2010)
    Thermal annealing of [Fe 1.65 nm/Pt 1.84 nm]50 multilayers at 673 K for various annealing times between 60 and 12000 s leads to the direct formation of the fully ordered L10 FePt phase with (111) texture. The average grain sizes, determined from X-ray diffraction size-strain analysis, are smaller than the critical size for multi-domain FePt particles, suggesting the presence of single-domain (SD) grains. The coercivity increases with annealing time and increasing grain size and reaches values of about 955 kA/m. The remanence values are typical for randomly oriented weakly-interacting particles. A decrease of the remanence with annealing time suggests a decrease of the intergrain exchange interactions with annealing time. Analysis of minor loops and the initial magnetization curves shows the presence of a broad distribution of critical fields, which the individual SD particles have to overcome for the magnetization reversal. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2010.03.076