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, or search for a specific author or term via the free text search 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.

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  • 2022 • 214 Active Buffer Matrix in Nanoparticle-Based Silicon-Rich Silicon Nitride Anodes Enables High Stability and Fast Charging of Lithium-Ion Batteries
    Kilian, S.O. and Wankmiller, B. and Sybrecht, A.M. and Twellmann, J. and Hansen, M.R. and Wiggers, H.
    Advanced Materials Interfaces 9 (2022)
    A very promising way to improve the stability of silicon in lithium-ion battery (LIB) anodes is the use of nanostructured silicon-rich silicon nitride (SiNx), known as a conversion-type anode material. To investigate the conversion mechanism in this material in detail, SiN0.5 nanoparticles are synthesized and examined as LIB anodes using a combination of ex situ X-ray photoelectron spectroscopy and solid-state 7Li MAS NMR measurements. During the initial cycle, the conversion of SiN0.5 nanoparticles results in the formation of lithium silicides and a buffer matrix consisting of different lithium nitridosilicates and lithium nitride. These phases can be reversibly lithiated and contribute to the total reversible capacity of the silicon nitride active material. The structure of the material after conversion is best described by an amorphous solid solution. Further, it is shown that silicon-rich silicon nitrides possess improved rate capability because of the higher ionic conductivity of the buffer matrix compared to pure silicon, and very fine dispersion of silicon clusters throughout the buffer matrix. Thus, unlike most conversion materials, the silicon-rich silicon nitride exhibits an additional intrinsic active functionality of the buffer matrix that goes far beyond the mere reduction of electrolyte contact area and volume expansion. © 2022 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/admi.202201389
  • 2022 • 213 Analysing the entropy of lithium-ion cells to trace anodic half-cell ageing
    Mertin, G.K. and Wycisk, D. and Stadler, J. and von Kessel, O. and Richter, E. and Oldenburger, M. and Wieck, A.D. and Birke, K.P.
    Journal of Energy Storage 50 (2022)
    The full-cell entropy and its temperature dependency were measured for automotive lithium-ion cells with a graphite anode in dependence of the state of charge. Resulting entropy curves can be related to certain characteristic conditions of the graphite anode. Those characteristics are induced by a certain lithium-ion concentrations within the graphite. Comparing the entropy curves of fresh to aged cells shows a shift in the characteristics of these curves at a similar charge input. Those shifts were assigned to a change in the anodic net capacity, enabling an entropy based state of health estimation of the anode. The execution of the differential voltage analysis leads to similar results. © 2022 Elsevier Ltd
    view abstractdoi: 10.1016/j.est.2022.104109
  • 2022 • 212 Boron in Ni-Rich NCM811 Cathode Material: Impact on Atomic and Microscale Properties
    Roitzheim, C. and Kuo, L.-Y. and Sohn, Y.J. and Finsterbusch, M. and Möller, S. and Sebold, D. and Valencia, H. and Meledina, M. and Mayer, J. and Breuer, U. and Kaghazchi, P. and Guillon, O. and Fattakhova-Rohlfing, D.
    ACS Applied Energy Materials 5 524-538 (2022)
    Doping of Ni-rich cathode active materials with boron is a promising way to improve their cycling stability and mitigate their degradation, but it is still not understood how this effect is achieved and where the boron is located. To receive deeper insights into the impact of doping on atomic and microscale properties, B-doped Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) cathode materials were synthesized by a hydroxide coprecipitation as a model compound to verify the presence and location of boron in B-doped, Ni-rich NCM, as well as its impact on the microstructure and electrochemical properties, by a combined experimental and theoretical approach. Besides X-ray diffraction and Rietveld refinement, DFT calculation was used to find the preferred site of boron absorption and its effect on the NCM lattice parameters. It is found that boron shows a trigonal planar and tetrahedral coordination to oxygen in the Ni layers, leading to a slight increase in lattice parameter c through an electrostatic interaction with Li ions. Therefore, B-doping of NCM811 affects the crystal structure and cation disorder and leads to a change in primary particle size and shape. To experimentally prove that the observations are caused by boron incorporated into the NCM lattice, we detected, quantified, and localized boron in 2 mol % B-doped NCM811 by ion beam analysis and TOF-SIMS. It was possible to quantify boron by NRA with a depth resolution of 2 μm. We found a boron enrichment on the agglomerate surface but also, more importantly, a significant high and constant boron concentration in the interior of the primary particles near the surface, which experimentally verifies that boron is incorporated into the NCM811 lattice. ©
    view abstractdoi: 10.1021/acsaem.1c03000
  • 2022 • 211 Control of spoke movement in DCMS plasmas
    George, M. and Breilmann, W. and Held, J. and von Keudell, A.
    Plasma Sources Science and Technology 31 (2022)
    Spokes appear as zones of increased ionisation in magnetron sputtering discharges. They rotate in front of a 2″ target at a natural frequency between a few 10 kHz and several 100 kHz and move in E → × B → or anti E → × B → direction depending on plasma power. Spokes are known to cause strong gradients in plasma density and potential and can, thus, increase the ion transport from target to substrate. Here, we explore the possibility to control spokes by applying a given frequency f to a set of control probes around the plasma to lock the spoke movement. The efficiency of this locking is analyzed by diagnostic probes and energy resolved mass spectrometry, which measure the integrated ion fluxes leaving the magnetic trap region. It was found that the spoke movement could be locked to the external control signal at frequency f around the natural spoke frequencies f 0. The additional control signal affects the ion flux twofold: (i) a 15% increase in ion flux towards the substrate and a 15% reduction in radial direction irrespective of control frequency is observed, which is explained by a change in plasma confinement since electric fluctuations at the separatrix are induced; (ii) the locking at f causes an increase in ion current in normal as well as in radial direction for f < f 0 and a reduction for f > f 0. This is explained by either longer or shorter residence times of ions in the electric fields caused by the spoke, or by an enhancement of these fields caused by the control. Using this spoke controlling technique an overall increase of ion flux towards the substrate of up to 30% was realized. © 2022 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/ac830e
  • 2022 • 210 Correlative Electrochemical Microscopy for the Elucidation of the Local Ionic and Electronic Properties of the Solid Electrolyte Interphase in Li-Ion Batteries
    Santos, C.S. and Botz, A. and Bandarenka, A.S. and Ventosa, E. and Schuhmann, W.
    Angewandte Chemie - International Edition 61 (2022)
    The solid-electrolyte interphase (SEI) plays a key role in the stability of lithium-ion batteries as the SEI prevents the continuous degradation of the electrolyte at the anode. The SEI acts as an insulating layer for electron transfer, still allowing the ionic flux through the layer. We combine the feedback and multi-frequency alternating-current modes of scanning electrochemical microscopy (SECM) for the first time to assess quantitatively the local electronic and ionic properties of the SEI varying the SEI formation conditions and the used electrolytes in the field of Li-ion batteries (LIB). Correlations between the electronic and ionic properties of the resulting SEI on a model Cu electrode demonstrates the unique feasibility of the proposed strategy to provide the two essential properties of an SEI: ionic and electronic conductivity in dependence on the formation conditions, which is anticipated to exhibit a significant impact on the field of LIBs. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/anie.202202744
  • 2022 • 209 Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties
    Petersen, H. and Stegmann, N. and Fischer, M. and Zibrowius, B. and Radev, I. and Philippi, W. and Schmidt, W. and Weidenthaler, C.
    Inorganic Chemistry 61 2379-2390 (2022)
    Transition-metal phosphates show a wide range of chemical compositions, variations of the valence states, and crystal structures. They are commercially used as solid-state catalysts, cathode materials in rechargeable batteries, or potential candidates for proton-exchange membranes in fuel cells. Here, we report on the successful ab initio structure determination of two novel titanium pyrophosphates, Ti(III)p and Ti(IV)p, from powder X-ray diffraction (PXRD) data. The low-symmetry space groups P21/c for Ti(III)p and P1¯ for Ti(IV)p required the combination of spectroscopic and diffraction techniques for structure determination. In Ti(III)p, trivalent titanium ions occupy the center of TiO6 polyhedra, coordinated by five pyrophosphate groups, one of them as a bidentate ligand. This secondary coordination causes the formation of one-dimensional six-membered ring channels with a diameter dmax of 3.93(2) Å, which is stabilized by NH4+ ions. Annealing Ti(III)p in inert atmospheres results in the formation of a new compound, denoted as Ti(IV)p. The structure of this compound shows a similar three-dimensional framework consisting of [PO4]3- tetrahedra and TiIV+O6 octahedra and an empty one-dimensional channel with a diameter dmax of 5.07(1) Å. The in situ PXRD of the transformation of Ti(III)p to Ti(IV)p reveals a two-step mechanism, i.e., the decomposition of NH4+ ions in a first step and subsequent structure relaxation. The specific proton conductivity and activation energy of the proton migration of Ti(III)p, governed by the Grotthus mechanism, belong to the highest and lowest, respectively, ever reported for this class of materials, which reveals its potential application in electrochemical devices like fuel cells and water electrolyzers in the intermediate temperature range. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.inorgchem.1c02613
  • 2022 • 208 Depth-Adjustable Magnetostructural Phase Transition in Fe60V40Thin Films
    Anwar, M.S. and Cansever, H. and Boehm, B. and Gallardo, R.A. and Hübner, R. and Zhou, S. and Kentsch, U. and Rauls, S. and Eggert, B. and Wende, H. and Potzger, K. and Fassbender, J. and Lenz, K. and Lindner, J. and Hellwig, O. ...
    ACS Applied Electronic Materials 4 3860-3869 (2022)
    Phase transitions occurring within spatially confined regions can be useful for generating nanoscale material property modulations. Here we describe a magneto-structural phase transition in a binary alloy, where a structural transition from short-range order (SRO) to body centered cubic (bcc) results in the formation of depth-adjustable ferromagnetic layers, which reveal application-relevant magnetic properties of high saturation magnetization (Ms) and low Gilbert damping (α). Here we use Fe60V40binary alloy films which transform from initially Ms= 17 kA/m (SRO structure) to 747 kA/m (bcc structure) driven by atomic displacements caused by penetrating ions. Simulations show that an estimated ∼1 displacement per atom triggers a structural transition, forming homogeneous ferromagnetic layers. The thickness of a ferromagnetic layer increases as a step-like function of the ion fluence. Microwave excitations of the ferromagnetic/non-ferromagnetic layered system reveals an α = 0.0027 ± 0.0001. The combination of nanoscale spatial confinement, low α, and high Msprovides a pathway for the rapid patterning of magnetic and microwave device elements. © 2022 American Chemical Society.
    view abstractdoi: 10.1021/acsaelm.2c00499
  • 2022 • 207 Elucidating ion transport mechanism in polyelectrolyte-complex membranes
    Zelner, M. and Stolov, M. and Tendler, T. and Jahn, P. and Ulbricht, M. and Freger, V.
    Journal of Membrane Science 658 (2022)
    Polyelectrolyte-complex (PEC) nanofiltration (NF) membranes attract much attention, however, the mechanisms governing ion separation in PEC films is not well understood. Here, we elucidate the ion transport in PECs using a recently reported Nafion-polyvinylamine (PVAm) membrane prepared via double-coating approach tuned to “rejection neutrality”, i.e., similar rejection of MgCl2 and Na2SO4 as single salts. New insights are gained by examining ion rejection for single- and mixed-salt solutions of NaCl, MgCl2 and Na2SO4 of varying concentrations and pH. The single salt permeability was found to vary with concentration, obeying a power law with an exponent around 0.4, matching neither the Donnan-dielectric nor a proposed PEC dissociation model. This is explained by progressive dissociation of the complex, which raises membrane swelling and dissociation constants, and weakenis dielectric exclusion, when salt concentration increases. Nevertheless, the membrane remains highly stable in all conditions, which is ascribed to the insolubility of Nafion in water. The results also indicate that “rejection-neutral” PEC still possesses a net negative charge, affecting ion selectivity at low salinities. The insights and physical picture proposed here may help understand and tune separation performance of PEC NF membranes and facilitate their implementation in applications such as purification and reuse of contaminated waters, resource recovery, and ion separations. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2022.120757
  • 2022 • 206 Hydration in aqueous NaCl
    Sahle, C.J. and de Clermont Gallerande, E. and Niskanen, J. and Longo, A. and Elbers, M. and Schroer, M.A. and Sternemann, C. and Jahn, S.
    Physical Chemistry Chemical Physics 24 16075-16084 (2022)
    Atomistic details about the hydration of ions in aqueous solutions are still debated due to the disordered and statistical nature of the hydration process. However, many processes from biology, physical chemistry to materials sciences rely on the complex interplay between solute and solvent. Oxygen K-edge X-ray excitation spectra provide a sensitive probe of the local atomic and electronic surrounding of the excited sites. We used ab initio molecular dynamics simulations together with extensive spectrum calculations to relate the features found in experimental oxygen K-edge spectra of a concentration series of aqueous NaCl with the induced structural changes upon solvation of the salt and distill the spectral fingerprints of the first hydration shells around the Na+- and Cl−-ions. By this combined experimental and theoretical approach, we find the strongest spectral changes to indeed result from the first hydration shells of both ions and relate the observed shift of spectral weight from the post- to the main-edge to the origin of the post-edge as a shape resonance. © 2022 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d2cp00162d
  • 2022 • 205 Ion-induced secondary electron emission of oxidized nickel and copper studied in beam experiments
    Buschhaus, R. and Prenzel, M. and Von Keudell, A.
    Plasma Sources Science and Technology 31 (2022)
    Ion-induced secondary electron emission at a target surface is an essential mechanism for laboratory plasmas, i.e. magnetron sputtering discharges. Electron emission, however, is strongly affected by the target condition itself such as oxidation. Data of oxidized targets, however, are very sparse and prone to significant systematic errors, because they were often determined by modeling the complex behavior of the plasma. Thus, it is difficult to isolate the process of ion-induced electron emission from all other plasma-surface-interactions. By utilizing ion beams, the complex plasma environment is avoided and electron yields are determined with higher accuracy. In this study, ion-induced secondary electron emission coefficients (SEECs) of clean, untreated (air-exposed), and intentionally oxidized copper and nickel surfaces were investigated in such a particle beam experiment. Pristine and oxidized metal foils were exposed to beams of singly charged argon ions with energies of 0.2 keV-10 keV. After the ion beam treatment, the surface conditions were analyzed by ex-situ X-ray photoelectron spectroscopy measurements. Further, a model for the electron emission of a partly oxidized surface is presented, which is in agreement with the experimental data. It was found, that oxidized and untreated/air-exposed surfaces do not show the same SEEC: for intentionally oxidized targets, the electron yields were smaller by a factor of 2 than for untreated/air-exposed surfaces. SEECs of oxides were found to be between the values for clean and for untreated metal surfaces. Further, the SEEC was at maximum for untreated/air-exposed surfaces and at minimum for clean surfaces; the electron yields of untreated/air-exposed and clean surfaces were in agreement with values reported in the literature. © 2022 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/ac4c4c
  • 2022 • 204 MD studies of methanol confined in the metal-organic framework MOF MIL-88B-Cl
    Siwaipram, S. and Bopp, P.A. and Ponchai, P. and Soetens, J.-C. and Hasegawa, J.-Y. and Schmid, R. and Bureekaew, S.
    Journal of Molecular Liquids 359 (2022)
    The lattice of the flexible Metal–Organic Framework (MOF) MIL-88B(Fe)-Cl is strongly modified when it is subjected to methanol vapor, increasing its volume by more than 130 %. We use a newly developed interaction model belonging to the extended MOF-FF family to perform classical Molecular Dynamics (MD) simulations of this MOF with varying amounts of methanol guest molecules. This work focuses on the evolving intermolecular structure of the counterions and guest molecules when their number is increased from 1 to 30 per cavity. Two mobile Cl−-counterions are, on the average, present in each lattice cavity to neutralize the framework charges. At low loadings (in the closed (or semi-closed) systems), the methanol molecules aggregate around these ions, which are themselves pegged, at the time scale of the simulation, to the Fe3-centers of the MOF. At loadings just below the transition, such methanol aggregates may link two counterions on opposite Fe3-centers, thus preventing the MOF from opening unless more methanol is added. In all closed systems, the methanol self-diffusion is almost two orders of magnitude lower than in the bulk liquid. Once the MOF opens, i.e., at loadings higher than about 12 to 13 methanol molecules per cavity, structural features typical of liquid methanol become more and more apparent. However, the evolution is not monotonous, there is a transitional region up to about 22 molecules par cavity. Increasing the loading further, all features more and more resemble the ones of bulk liquid methanol. © 2022 Elsevier B.V.
    view abstractdoi: 10.1016/j.molliq.2022.119252
  • 2022 • 203 Spatial Distribution of Intracellular Ion Concentrations in Aggregate-Forming HeLa Cells Analyzed by μ-XRF Imaging
    Gräfenstein, A. and Rumancev, C. and Pollak, R. and Hämisch, B. and Galbierz, V. and Schroeder, W.H. and Garrevoet, J. and Falkenberg, G. and Vöpel, T. and Huber, K. and Ebbinghaus, S. and Rosenhahn, A.
    ChemistryOpen 11 (2022)
    Protein aggregation is a hallmark of several severe neurodegenerative disorders such as Huntington's, Parkinson's, or Alzheimer's disease. Metal ions play a profound role in protein aggregation and altered metal-ion homeostasis is associated with disease progression. Here we utilize μ-X-ray fluorescence imaging in combination with rapid freezing to resolve the elemental distribution of phosphorus, sulfur, potassium, and zinc in huntingtin exon-1-mYFP expressing HeLa cells. Using quantitative XRF analysis, we find a threefold increase in zinc and a 10-fold enrichment of potassium that can be attributed to cellular stress response. While the averaged intracellular ion areal masses are significantly different in aggregate-containing cells, a local intracellular analysis shows no different ion content at the location of intracellular inclusion bodies. The results are compared to corresponding experiments on HeLa cells forming pseudoisocyanine chloride aggregates. As those show similar results, changes in ion concentrations are not exclusively linked to huntingtin exon-1 amyloid formation. © 2022 The Authors. Published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/open.202200024
  • 2022 • 202 Unravelling Anion Solvation in Water-Alcohol Mixtures by Single Entity Electrochemistry
    Saw, E.N. and Kanokkanchana, K. and Amin, H.M.A. and Tschulik, K.
    ChemElectroChem (2022)
    Single entity electrochemistry is employed to gain insights into ion solvation in solvent mixtures. To this end, the time required for the oxidation of individual indicator nanoparticles to sparingly soluble products is used to probe ionic diffusion, and hence gain new insights into the solvation properties of solvent mixtures. Herein, water-ethanol or water-methanol mixtures of different compositions are analyzed following this new approach, using silver nanoparticle oxidation in the presence of chloride and iodide as a complementary indicator reaction. For increasing concentrations of the bulkier alcohol molecules in the mixtures with water, an increasing content of alcohol molecules in the halide's solvation shell is detected by the observation of hindered halide diffusion. The extent of this solvent replacement is shown to scale with the charge density of the ions and the experimental results are rationalized with respect to literature-derived thermodynamic data, highlighting the ability of single entity electrochemistry to explore solvation in solvent mixtures. © 2022 The Authors. ChemElectroChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/celc.202101435
  • 2022 • 201 Voltammetric Behaviour of LMO at the Nanoscale: A Map of Reversibility and Diffusional Limitations
    Gavilán-Arriazu, E.M. and Mercer, M.P. and Barraco, D.E. and Hoster, H.E. and Leiva, E.P.M.
    ChemPhysChem 23 (2022)
    Understanding and optimizing single particle rate behaviour is normally challenging in composite commercial lithium-ion electrode materials. In this regard, recent experimental research has addressed the electrochemical Li-ion intercalation in individual nanosized particles. Here, we present a thorough theoretical analysis of the Li+ intercalation voltammetric behaviour in single nano/micro-scale LiMn2O4 (LMO) particles, incorporating realistic interactions between inserted ions. A transparent 2-dimensional zone diagram representation of kinetic-diffusional behaviour is provided that allows rapid diagnosis of the reversibility and diffusion length of the system depending on the particle geometry. We provide an Excel file where the boundary lines of the zone diagram can be rapidly recalculated by setting input values of the rate constant, (Formula presented.) and diffusion coefficient, (Formula presented.). The model framework elucidates the heterogeneous behaviour of nanosized particles with similar sizes but different shapes. Hence, we present here an outlook for realistic multiscale modelling of real materials. © 2021 Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cphc.202100700
  • 2022 • 200 Zeeman and Davydov splitting of Frenkel excitons in the antiferromagnet CuB2 O4
    Kopteva, N.E. and Kudlacik, D. and Yakovlev, D.R. and Eremin, M.V. and Nurmukhametov, A.R. and Bayer, M. and Pisarev, R.V.
    Physical Review B 105 (2022)
    The optical spectra of antiferromagnetic copper metaborate CuB2O4 are characterized by an exceptionally rich structure of narrow absorption lines due to electronic transitions within the magnetic Cu2+ ions, but their unambiguous identification and behavior in magnetic fields have remained far from being fully understood. We study the polarized magnetoabsorption spectra of this tetragonal antiferromagnet with high spectral resolution across the energy range of 1.4055-1.4065 eV in magnetic fields up to 9.5 T for temperatures from 1.6 up to the Néel temperature TN=20 K. We observe a set of eight absorption lines at T=1.6 K in magnetic fields exceeding 1.4 T, which we identify as arising from Frenkel excitons related to the ground and first excited states of the Cu2+ ions. The number of these excitons is defined by the presence of the four Cu2+ ions with doubly degenerate spin state S=1/2 at the 4b positions in the crystallographic unit cell. The energies of these excitons are determined by the exchange interaction of 0.5 meV of the Cu2+ ions in the excited state with the surrounding ions and by the Davydov splitting of 0.12 meV. In large magnetic field the observed Zeeman splitting is controlled by the anisotropic g-factors of both the ground and excited states. We develop a theoretical model of Frenkel excitons in the magnetic field that accounts for specific features of the spin structure and exchange interactions in CuB2O4. The model is used for fitting the experimental data and evaluation of the Frenkel exciton parameters, such as the Davydov splitting, the molecular exchange energy, and the g-factors of the ground and excited states of the Cu2+ ions. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.024421
  • 2021 • 199 Amphiphilic poly(arylene ether sulfone) multiblock copolymers with quaternary ammonium groups for novel thin-film composite nanofiltration membranes
    Wieczorek, J. and Ulbricht, M.
    Polymer 217 (2021)
    Amphiphilic poly(arylene ether sulfone) (PAES) multiblock copolymers with quaternary ammonium groups were evaluated as tunable, size-selective barrier material in thin-film composite (TFC) nanofiltration membranes. Using a two-step synthesis, well-defined PAES multiblock copolymers with molecular weight (Mn) of at least 50 kg/mol were obtained. Conversion to anion-exchange polymers was accomplished by block-selective bromination of methyl side groups at adjusted degree of functionalization and subsequent quantitative amination using triethanolamine. A library of copolymers with varied block length ratios and ion-exchange capacities (IEC; up to 2 mmol/g) was obtained. PAES multiblock copolymers with suited hydrophilic/hydrophobic balance to yield films that are stable in water were further evaluated. Film casting of solutions of anion-exchange copolymers on a porous polyacrylonitrile support and solvent evaporation yielded TFC membranes with barrier layer thickness in the range of 1.5–1.9 μm. Nanofiltration performance was measured with glycerine, glucose, sucrose, NaCl, MgCl2 and FeCl3 in water. While for a random copolymer with similar composition and same thickness, no water flux could be measured, the novel TFC membranes had permeances in the range of 1 L m−2 bar−1·h−1, at >99.9% rejection for glucose. Permeance increased and rejection (for glycerine and salt) decreased systematically with increasing IEC; an additional influence of block length ratio was identified. A membrane made from a block copolymer with longer hydrophobic block and moderate IEC of 0.9 mmol/g showed the best “trade-off” between permeability and selectivity. Furthermore, the stability of the novel membranes under oxidative disinfection conditions was demonstrated. © 2021 Elsevier Ltd
    view abstractdoi: 10.1016/j.polymer.2021.123446
  • 2021 • 198 Direct gas phase synthesis of amorphous Si/C nanoparticles as anode material for lithium ion battery
    Orthner, H. and Wiggers, H. and Loewenich, M. and Kilian, S. and Bade, S. and Lyubina, J.
    Journal of Alloys and Compounds 870 (2021)
    High specific capacity of silicon is very attractive for its application as anode material in lithium ion batteries. However, the implementation of silicon is challenging due to its large volume expansion on lithiation leading to pulverization and buildup of a solid-electrolyte interphase. Nanostructuring and design of silicon alloys are a promising strategy to circumvent these challenges. Here we demonstrate an industrially scalable gas phase synthesis method using thermal decomposition of silane and ethylene to produce novel amorphous silicon/carbon-based particles with enhanced electrochemical performance. Fundamental principles and kinetics considerations for the design of high-performance silicon/carbon-based materials are discussed. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.159315
  • 2021 • 197 ePC-SAFT advanced - Part I: Physical meaning of including a concentration-dependent dielectric constant in the born term and in the Debye-Hückel theory
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 535 (2021)
    The transition from aqueous electrolyte systems to non-aqueous electrolyte systems is highly demanded in industrial applications and especially challenging for physics-based thermodynamic models. Electrolyte thermodynamics is a complex matter, and still not all physico-chemical effects are accounted for in state-of-the-art equations of state. The dielectric constant of non-aqueous electrolyte systems changes drastically compared to aqueous systems. One main consequence is that ions are very differently solvated in non-aqueous medium compared to aqueous medium. The Born term represents a methodology to account for the influence of solvation energies of ions, which is based on influences of solvent and salt on the dielectric constant. Utilizing the Born term in electrolyte models is extensively debated, and it is often reasonably neglected in predominantly aqueous systems. Yet, it has a significant influence on transferability from aqueous to non-aqueous media i.e., systems with a large difference in polarity or permittivity compared to aqueous systems. In this work, a modified Born term was combined with electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) by introducing additionally a salt concentration-dependent dielectric constant, henceforth called altered Born contribution. The new methodology was validated against infinite dilution properties for ion-solvent interactions: Gibbs energy of hydration and Gibbs energy of transfer of alkali halides from water to alcoholic solvents. Further, mean ionic activity coefficients (MIACs) of alkali halides in alcoholic solvents were quantitatively correct predicted with the advanced ePC-SAFT approach. Original ePC-SAFT parameters were applied for all predictions, and no further binary parameters were adjusted. Based on the success of the model predictions, the transferability of pure-ion ePC-SAFT parameters to organic solvents was verified and the incorporation of concentration-dependent dielectric constant into the altered Born contribution and Debye-Hückel theory was proven to be meaningful methods for the transfer of electrolyte thermodynamic models from aqueous to non-aqueous systems. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.112967
  • 2021 • 196 ePC-SAFT advanced – Part II: Application to Salt Solubility in Ionic and Organic Solvents and the Impact of Ion Pairing
    Bülow, M. and Ascani, M. and Held, C.
    Fluid Phase Equilibria 537 (2021)
    The applications of electrolyte thermodynamic models to non-aqueous systems is of great value to reduce experimental effort and gain inside into molecular interactions. A large-scale application is for example the design of advanced battery electrolytes. For non-aqueous electrolyte systems, the Born term was found to be important, as it accounts for the transfer of ions from water into non-aqueous medium. In part one of this study [Bülow et al., Fluid Phase Equilibria 2021, 112967] the Born term was combined with a concentration-dependent dielectric constant within the ePC-SAFT framework (electrolyte Perturbed-Chain Statistical Associating Fluid Theory). In the present work, the Bjerrum treatment for ion pairing was included in the Debye-Hückel framework within ePC-SAFT. The approach was validated by experimental data for the dissociation of salts in organic solvents derived from conductivity measurements. Further, solubility was modeled of alkali halides in organic solvents and in ionic liquids. Modeling solubility required access to the solubility product KSP, which does not depend on the solvent. The approach within this work was to first determine KSP using experimental solubility data in water and the respective ePC-SAFT predicted activity coefficients prior to predict activity coefficients in non-aqueous medium, finally yielding solubility. The so-determined solubility values were found to be in reasonable agreement with the experimental data without fitting model parameters to any data of the non-aqueous solutions. The solubility product requires the solid form of the precipitating salt to be equal for all solvents; as alkali salts precipitate from aqueous solutions as hydrates, the method cannot be applied. Therefore, a methodology is presented to extrapolate the high-temperature KSP of anhydrates to lower temperature. Using the so-extrapolated KSP allowed predicting solubility of non-solvates in other solvents. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2021.112989
  • 2021 • 195 Influence of the sampling probe on flame temperature, species, residence times and on the interpretation of ion signals of methane/oxygen flames in molecular beam mass spectrometry measurements
    Karakaya, Y. and Sellmann, J. and Wlokas, I. and Kasper, T.
    Combustion and Flame 229 (2021)
    Laminar flames are widely used to analyze the fundamentals of combustion processes using molecular beam mass spectrometry. The extraction of a representative sample from a flame by an intrusive sampling technique is challenging because of two main issues. First, the sampling probe itself perturbs the flow and temperature field, affecting the species profiles. These effects need to be characterized by 2-D fluid dynamic simulations to reveal sources of perturbations that are in particular suction and flame cooling. Second, some intermediate species interact with the sampling probe and are removed from the gas sample before analysis. The concentrations of these intermediates in the flames are often low and close to the detection limit. Naturally occurring ions can also be extracted from the flame by molecular beam sampling. Coupled with modern ion optical devices for ion transfer to the mass analyzer very high sensitivity can be reached in the detection of ionic species in flames. Similarities in the shape of measured relative concentration profiles indicate a connection between neutrals and the corresponding protonated molecules by proton transfer reactions. A quantification method of neutral flame species based on signals of the flame-sampled ions is presented and evaluated for the intermediate methanol in methane/oxygen/argon flames. The proposed method is based on equilibrium calculations that depend on temperature. To characterize the sampling process and demonstrate the validity of the quantification approach for ion measurements, the influence of the sampling probe on flame temperature and mole fraction profiles of the main species and the intermediate methanol are investigated by a combined experimental and simulation study. A comparison of the methanol profiles measured by conventional molecular beam sampling and the novel ion sampling technique reveal acceptable agreement. This work shows that if all aspects of sampling are considered as well as possible, the ion sampling technique allows access to kinetic data of neutral intermediates. © 2021
    view abstractdoi: 10.1016/j.combustflame.2021.02.034
  • 2021 • 194 Ion dynamics in capacitively coupled argon-xenon discharges
    Klich, M. and Wilczek, S. and Janssen, J.F.J. and Brinkmann, R.P. and Mussenbrock, T. and Trieschmann, J.
    Plasma Sources Science and Technology 30 (2021)
    An argon-xenon (Ar/Xe) plasma is used as a model system for complex plasmas. Based on this system, symmetric low-pressure capacitively coupled radiofrequency discharges are examined utilizing particle-in-cell/Monte Carlo collisions simulations. In addition to the simulation, an analytical energy balance model fed with the simulation data is applied to analyze the findings further. This work focuses on investigating the ion dynamics in a plasma with two ion species and a gas mixture as background. By varying the gas composition and driving voltage of the single-frequency discharge, fundamental mechanics of the discharge, such as the evolution of the plasma density and the energy dispersion, are discussed. Thereby, close attention is paid to these measures' influence on the ion energy distribution functions at the electrode surfaces. The results show that both the gas composition and the driving voltage can significantly impact the ion dynamics. The mixing ratio of argon to xenon allows for shifting the distribution function for one ion species from collisionless to collision dominated. The mixing ratio serves as a control parameter for the ion flux and the impingement energy of ions at the surfaces. Additionally, a synergy effect between the ionization of argon and the ionization of xenon is found and discussed. © 2021 The Author(s). Published by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/ac02b0
  • 2021 • 193 Laser- and Ion-Induced Defect Engineering in WS2 Monolayers
    Asaithambi, A. and Kozubek, R. and Prinz, G.M. and Reale, F. and Pollmann, E. and Ney, M. and Mattevi, C. and Schleberger, M. and Lorke, A.
    Physica Status Solidi - Rapid Research Letters 15 (2021)
    Tungsten disulfide is one of the prominent transition metal dichalcogenide materials, which shows a transition from an indirect to a direct bandgap as the layer thickness is reduced down to a monolayer. To use (Formula presented.) monolayers in devices, detailed knowledge about the luminescence properties regarding not only the excitonic but also the defect-induced contributions is needed. Herein, (Formula presented.) monolayers are irradiated with (Formula presented.) ions with different fluences to create different defect densities. Apart from the excitonic contributions, two additional emission bands are observed at low temperatures. These bands can be reduced or even suppressed, if the flakes are exposed to laser light with powers up to 1.5 mW. Increasing the temperature up to room temperature leads to recovery of this emission, so that the luminescence properties can be modified using laser excitation and temperature. The defect bands emerging after ion irradiation are attributed to vacancy defects together with physisorbed adsorbates at different defect sites. © 2020 The Authors. Physica Status Solidi (RRL) – Rapid Research Letters published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/pssr.202000466
  • 2021 • 192 Mechanical properties and adhesion behavior of amorphous carbon films with bias voltage controlled TixCy interlayers on Ti6Al4V
    Tillmann, W. and Lopes Dias, N.F. and Franke, C. and Kokalj, D. and Stangier, D. and Thomann, C.A. and Debus, J.
    Diamond and Related Materials 115 (2021)
    Amorphous carbon is a promising functional film material to enhance the surface properties of Ti-based alloys for orthopaedic applications. However, high adhesion of the amorphous carbon film on the orthopaedic implants is essential to fully exploit its potential under high load bearings. Interlayer films are generally employed to improve the adhesion. The applied bias voltage is a decisive deposition parameter and significantly influences the structure and mechanical properties during the interlayer growth, which in turn affect the properties of the amorphous carbon film. Therefore, chemically graded titanium carbide (TixCy) interlayers were deposited using bias voltages of −50, −100, and −150 V with a subsequent hydrogen-free amorphous carbon (a-C) top layer on Ti6Al4V by magnetron sputtering. The mechanical properties and adhesion behavior of single TixCy interlayers were evaluated to analyze the interaction effect of TixCy on bilayered TixCy/a-C structures. A high bias voltage generates dense TixCy of a more disordered and defected structure with high stresses, high hardness of ~16 GPa, and high elastic modulus of ~170 GPa. However, high compressive stresses provoke a low adhesion strength, while low compressive stresses ensure a good adhesion behavior of TixCy. Highly stressed TixCy interlayers lead to overall higher stresses for the entire TixCy/a-C film. Independently of TixCy, the a-C top layer exhibits hardness and elastic modulus values of ~16 and ~160 GPa, respectively. The TixCy/a-C films with TixCy interlayers deposited at high bias voltages possess a low adhesion strength, while a lower bias voltage favors a good adhesion of TixCy/a-C on Ti6Al4V. Therefore, a moderate bias voltage is crucial to deposit lowly stressed TixCy interlayers, which ensure a high adhesion of TixCy/a-C on Ti6Al4V. Consequently, the bias voltage allows controlling the mechanical properties and adhesion behavior of the interlayer and, hence, the adhesion strength of the entire amorphous carbon film structure on Ti-based alloys for orthopaedic applications. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.diamond.2021.108361
  • 2021 • 191 Mixed-Matrix Membrane Adsorbers for the Simultaneous Removal of Different Pharmaceutical Micropollutants from Water
    Uebele, S. and Goetz, T. and Ulbricht, M. and Schiestel, T.
    ACS Applied Polymer Materials (2021)
    The lack of a complete removal of pharmaceutical contaminants from water by conventional wastewater treatment plants requires additional separation processes. In this work, the ability of mixed-matrix membrane (MMM) adsorbers for the simultaneous removal of pharmaceuticals was investigated using three types of strong anion-exchange particles. Diclofenac (DCF), sulfamethoxazole (SMX), carbamazepine (CBZ), and metoprolol (MTP) were used as model substances because they have medical relevance and different chemical characteristics. Spherical nonporous and porous polymer adsorbent particles were synthesized by emulsion and miniemulsion polymerization, respectively, followed by polymer-analogous functionalization. In addition, a commercially available, ground polymer gel ion-exchange adsorbent was used. Adsorption properties of the anion-exchange particles were determined for individual substances and multicomponent mixtures and analyzed via Freundlich and Langmuir isotherm models. All particles showed an excellent adsorption of DCF, revealing Freundlich constants (KF) up to 278 (mg g-1/mg L-1)n. Furthermore, the use of either nonporous or porous adsorber particles enabled the removal of DCF with high adsorption capacities simultaneously with SMX or CBZ, respectively. MMM adsorbers were prepared by incorporation of the adsorber particles into porous poly(vinylidene fluoride) hollow fiber membranes via wet spinning. Dynamic adsorption measurements using the MMM adsorbers for pharmaceuticals at 5 mg L-1 in tap water revealed adsorption capacities up to 13.7 g m-2 (relative to the membrane filter area) for DCF while SMX was adsorbed simultaneously with a capacity of 0.60 g m-2. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acsapm.1c01546
  • 2021 • 190 Molecular Insight into the Swelling of a MOF: A Force-Field Investigation of Methanol Uptake in MIL-88B(Fe)-Cl
    Siwaipram, S. and Bopp, P.A. and Keupp, J. and Pukdeejorhor, L. and Soetens, J.-C. and Bureekaew, S. and Schmid, R.
    Journal of Physical Chemistry C (2021)
    Volume changes are observed in the metal-organic frameworks (MOFs) of the MIL-88 family when they are exposed to certain solvents. We investigate here, at the atomic level, the swelling behavior of MIL-88B absorbing strongly interacting guest molecules, methanol, for which the largest changes are found. The MOF is positively charged and possesses open metal sites at the trimetallic inorganic building units (M3O), with which the counterions and guests coordinate. We develop an extended MOF-FF-type interaction model and perform the first molecular dynamics (MD) simulations to describe the structural changes of the flexible MIL-88B(Fe)-Cl upon insertion of methanol. The newly developed interaction model according to the MOF-FF scheme consists of (I) the intra-MOF interactions, (II) a fully MOF-FF-compatible model for the methanol and the solvated Cl- ion, which was recently published, and (III) specific new terms developed for the interactions between a trimetallic building unit (Fe3O) connected with six benzoate rings and these species. We report the free energy versus volume profiles as a function of loading and temperature, which are matched with the evolution of the unit cell volume versus the methanol loading profile. We discuss radial pair distribution functions (rdf) and some three-dimensional distributions of the counterions around Fe3O. We find that the pore opening is accompanied by characteristic structural changes in the arrangements of the counterions near the central Fe3 units and also of the solvent coordinating these counterions: this illustrates the role of the solvated counterions in the swelling process. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.jpcc.1c01033
  • 2021 • 189 NIR-Sensitized Cationic and Hybrid Radical/Cationic Polymerization and Crosslinking
    Pang, Y. and Shiraishi, A. and Keil, D. and Popov, S. and Strehmel, V. and Jiao, H. and Gutmann, J.S. and Zou, Y. and Strehmel, B.
    Angewandte Chemie - International Edition 60 1465-1473 (2021)
    NIR-sensitized cationic polymerization proceeded with good efficiency, as was demonstrated with epoxides, vinyl ether, and oxetane. A heptacyanine functioned as sensitizer while iodonium salt served as coinitiator. The anion adopts a special function in a series selected from fluorinated phosphates (a: [PF6]−, b: [PF3(C2F5)3]−, c: [PF3(n-C4F9)3]−), aluminates (d: [Al(O-t-C4F9)4]−, e: [Al(O(C3F6)CH3)4]−), and methide [C(O-SO2CF3)3]− (f). Vinyl ether showed the best cationic polymerization efficiency followed by oxetanes and oxiranes. DFT calculations provided a rough pattern regarding the electrostatic potential of each anion where d showed a better reactivity than e and b. Formation of interpenetrating polymer networks (IPNs) using trimethylpropane triacrylate and epoxides proceeded in the case of NIR-sensitized polymerization where anion d served as counter ion in the initiator system. No IPN was formed by UV-LED initiation using the same monomers but thioxanthone/iodonium salt as photoinitiator. Exposure was carried out with new NIR-LED devices emitting at either 805 or 870 nm. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/anie.202010746
  • 2021 • 188 On the possible influence of the Fermi–Dirac statistics on the potential and entropy of galvanic cells
    Mertin, G.K. and Richter, E. and Oldenburger, M. and Hofmann, M.H. and Wycisk, D. and Wieck, A.D. and Birke, K.P.
    Journal of Power Sources 498 (2021)
    The open circuit voltage of galvanic cells is temperature dependent and the effect responsible for this dependency is its entropy. While it is well known that the Nernst equation plays an important role in describing this temperature dependency of the open-circuit voltage, this paper displays another effect. Measurements of the entropy for lithium-ion batteries show a significant temperature dependency, which cannot be explained by the linear Nernst equation. But this temperature dependency can be described by the free electron potential adapting via Fermi–Dirac statistics. This approach results in a quadratic temperature dependence of the measured potentials, which in the here shown cases for commercial lithium ion cells, could explain the measured effect. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jpowsour.2021.229870
  • 2021 • 187 On the structure-property relationships of (Al, Ga, In)-doped spinel cobalt ferrite compounds: A combined experimental and DFT study
    Naveed-Ul-Haq, M. and Hussain, S. and Webers, S. and Salamon, S. and Ahmad, I. and Bibi, T. and Hameed, A. and Wende, H.
    Physical Chemistry Chemical Physics 23 18112-18124 (2021)
    We report a combined experimental and theoretical study of pure and doped cobalt ferrite where 25% of Fe3+ ions were replaced by Al3+, Ga3+, and In3+ ions, respectively, i.e., CoFe1.5X0.5O4 (X = Al, Ga, and In). The ferrite compositions were successfully synthesized using the solid-state reaction method. The X-ray powder diffraction method established that all ferrite samples had a spinel unit cell structure with the Fd3m (No. 227) space group. The lattice constants of ferrites increased from 8.382 Å (for undoped CoFe2O4) to 8.520 Å (for In-doped cobalt ferrite) in direct relation to the dopant ion size. The magnetic properties were obtained at 4.3 K and 300 K. At 4.3 K, the In-doped CoFe2O4 showed the highest saturation magnetic moment of 4.68 μB f.u.-1, while Al-doped CoFe2O4 showed the smallest value of 2.72 μB f.u.-1. The Fe3+ distribution among the spinel tetrahedral and octahedral sites was determined from the Mössbauer spectra. From ultraviolet-visible diffuse reflectance spectroscopy the direct optical bandgaps were determined, which have values between 1.20 eV and 1.28 eV for these ferrites. The ferrite compositions were also studied theoretically using plane-wave density functional theory using the CASTEP code where it was revealed that arrangements of the non-magnetic cations at the tetrahedral and octahedral sites strongly influence the electronic structure, the bandgap value, and the net magnetic moment per formula unit. Light Al3+ ions at the octahedral site give a low value of the net magnetic moment while the heavier Ga3+ and In3+ ions at the tetrahedral sites of the spinel give an enhanced magnetic moment. The magnetic moment values obtained from theoretical calculations match very well with the experimental values. Moreover, the theoretical calculations reveal that there exists a strong p-d hybridization among the oxygen and magnetic ions, which is affected by the non-magnetic dopant ions. The change in hybridization with the non-magnetic ion doping is responsible for the altered magnetic moments of the doped ferrites. Thus, our study provides a comprehensive investigation covering the synthesis and characterization of ferrites along with a good understanding of the phenomenon of how non-magnetic ion doping into spinel ferrites provides a method to tune the electronic and magnetic properties of the spinel ferrite. This journal is © the Owner Societies.
    view abstractdoi: 10.1039/d1cp02625a
  • 2021 • 186 Relative calibration of a retarding field energy analyzer sensor array for spatially resolved measurements of the ion flux and ion energy in low temperature plasmas
    Ries, S. and Schroeder, M. and Woestefeld, M. and Corbella, C. and Korolov, I. and Awakowicz, P. and Schulze, J.
    Review of Scientific Instruments 92 (2021)
    A calibration routine is presented for an array of retarding field energy analyzer (RFEA) sensors distributed across a planar electrode surface with a diameter of 450 mm that is exposed to a low temperature plasma. Such an array is used to measure the ion velocity distribution function at the electrode with radial and azimuthal resolutions as a basis for knowledge-based plasma process development. The presented calibration procedure is tested by exposing such an RFEA array to a large-area capacitively coupled argon plasma driven by two frequencies (13.56 and 27.12 MHz) at a gas pressure of 0.5 Pa. Up to 12 sensors are calibrated with respect to the 13th sensor, called the global reference sensor, by systematically varying the sensor positions across the array. The results show that the uncalibrated radial and azimuthal ion flux profiles are incorrect. The obtained profiles are different depending on the sensor arrangement and exhibit different radial and azimuthal behaviors. Based on the proposed calibration routine, the ion flux profiles can be corrected and a meaningful interpretation of the measured data is possible. The calibration factors are almost independent of the external process parameters, namely, input power, gas pressure, and gas mixture, investigated under large-area single-frequency capacitively coupled plasma conditions (27.12 MHz). Thus, mean calibration factors are determined based on 45 different process conditions and can be used independent of the plasma conditions. The temporal stability of the calibration factors is found to be limited, i.e., the calibration must be repeated periodically. © 2021 Author(s).
    view abstractdoi: 10.1063/5.0059658
  • 2021 • 185 Spin polarization and magnetotransport properties of systematically disordered Fe60Al40 thin films
    Borisov, K. and Ehrler, J. and Fowley, C. and Eggert, B. and Wende, H. and Cornelius, S. and Potzger, K. and Lindner, J. and Fassbender, J. and Bali, R. and Stamenov, P.
    Physical Review B 104 (2021)
    We investigate the evolution of spin polarization, spontaneous Hall angle (SHA), saturation magnetization, and Curie temperature of B2-ordered Fe60Al40 thin films under varying antisite disorder, induced by Ne+-ion irradiation. The spin polarization increases monotonically as a function of ion fluence. A relatively high polarization of 46% and a SHA of 3.1% are achieved on 40 nm films irradiated with 2×1016 ions/cm2 at 30 keV. An interesting divergence in the trends of the magnetization and SHA is observed for low disorder concentrations. The high spin polarization and its broad tunability range make ion-irradiated Fe60Al40 a promising material for application in spin electronic devices. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.104.134417
  • 2021 • 184 The Impact of Lithium Tungstate on the Densification and Conductivity of Phosphate Lithium-Ion Conductors
    Odenwald, P. and Ma, Q. and Davaasuren, B. and Dashjav, E. and Tietz, F. and Wolff, M. and Rheinheimer, W. and Uhlenbruck, S. and Guillon, O. and Fattakhova-Rohlfing, D.
    ChemElectroChem (2021)
    Phosphate lithium-ion conductors are outstanding electrolyte materials for solid-state lithium batteries. As polycrystalline ceramics, they must be sintered at high temperatures. Lithium tungstate Li2WO4 (LWO) is reported for the first time as an effective sintering aid to reduce the sintering temperature for one of the most common solid-state lithium-ion conductors, Li1.5Al0.5Ti1.5(PO4)3 (LATP). While densification of LATP without sintering aids requires temperatures of at least 950 °C to obtain a relative density of 90 %, here relative densities of 90–95 % are achieved even at 775 °C when 5 wt.% of LWO are added. At 800 °C the LATP containing 5–7 wt.% LWO densifies to a relative density of 97.2 %. The ionic conductivity of LWO containing LATP is generally higher than that of pure LATP sintered at the same temperature. LATP containing 7 wt.% LWO shows high ionic conductivity of 4.4×10−4 S/cm after sintering at 825 °C. A significant reduction in sintering temperature, an increase in density and in the ionic conductivity of LATP as well as its non-toxicity render LWO a very promising sintering aid for the development of LATP-based solid state batteries. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/celc.202101366
  • 2021 • 183 Titanium Niobium Oxide Ti2Nb10O29/Carbon Hybrid Electrodes Derived by Mechanochemically Synthesized Carbide for High-Performance Lithium-Ion Batteries
    Budak, Ö. and Srimuk, P. and Aslan, M. and Shim, H. and Borchardt, L. and Presser, V.
    ChemSusChem 14 398-407 (2021)
    This work introduces the facile and scalable two-step synthesis of Ti2Nb10O29 (TNO)/carbon hybrid material as a promising anode for lithium-ion batteries (LIBs). The first step consisted of a mechanically induced self-sustaining reaction via ball-milling at room temperature to produce titanium niobium carbide with a Ti and Nb stoichiometric ratio of 1 to 5. The second step involved the oxidation of as-synthesized titanium niobium carbide to produce TNO. Synthetic air yielded fully oxidized TNO, while annealing in CO2 resulted in TNO/carbon hybrids. The electrochemical performance for the hybrid and non-hybrid electrodes was surveyed in a narrow potential window (1.0–2.5 V vs. Li/Li+) and a large potential window (0.05–2.5 V vs. Li/Li+). The best hybrid material displayed a specific capacity of 350 mAh g−1 at a rate of 0.01 A g−1 (144 mAh g−1 at 1 A g−1) in the large potential window regime. The electrochemical performance of hybrid materials was superior compared to non-hybrid materials for operation within the large potential window. Due to the advantage of carbon in hybrid material, the rate handling was faster than that of the non-hybrid one. The hybrid materials displayed robust cycling stability and maintained ca. 70 % of their initial capacities after 500 cycles. In contrast, only ca. 26 % of the initial capacity was maintained after the first 40 cycles for non-hybrid materials. We also applied our hybrid material as an anode in a full-cell lithium-ion battery by coupling it with commercial LiMn2O4. © 2020 The Authors. ChemSusChem published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/cssc.202002229
  • 2021 • 182 Yttrium oxide freeze-casts: Target materials for radioactive ion beams
    Kröll, E. and Vadalà, M. and Schell, J. and Stegemann, S. and Ballof, J. and Rothe, S. and Lupascu, D.C.
    Materials 14 (2021)
    Highly porous yttrium oxide is fabricated as ion beam target material in order to produce radioactive ion beams via the Isotope Separation On Line (ISOL) method. Freeze casting allows the formation of an aligned pore structure in these target materials to improve the isotope release. Aqueous suspensions containing a solid loading of 10, 15, and 20 vol% were solidified with a unidirectional freeze-casting setup. The pore size and pore structure of the yttrium oxide freeze-casts are highly affected by the amount of solid loading. The porosity ranges from 72 to 84% and the crosslinking between the aligned channels increases with increasing solid loading. Thermal aging of the final target materials shows that an operation temperature of 1400◦ C for 96 h has no significant effect on the microstructure. Thermo-mechanical calculation results, based on a FLUKA simulation, are compared to measured compressive strength and forecast the mechanical integrity of the target materials during operation. Even though they were developed for the particular purpose of the production of short-lived radioactive isotopes, the yttria freeze-cast scaffolds can serve multiple other purposes, such as catalyst support frameworks or high-temperature fume filters. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstractdoi: 10.3390/ma14112864
  • 2020 • 181 Energy deposition of highly charged ions transmitted through single layer MoS2
    Creutzburg, S. and Schwestka, J. and Inani, H. and Tripathi, M.K. and Grande, P.L. and Heller, R. and Klingner, N. and Niggas, A. and Kozubek, R. and Madauß, L. and Facsko, S. and Kotakoski, J. and Schleberger, M. and Aumayr, F. ...
    Journal of Physics: Conference Series 1412 (2020)
    Highly charged ions (HCIs) are an efficient tool for the perforation of suspended 2D materials. Only a fraction of their potential energy is transferred to the atomically thin target during the very short interaction time and is available for pore formation. Charge exchange spectra were measured for highly charged xenon ions transmitted through suspended, single layer MoS2 in order to determine the deposited potential energy available for pore formation. Additionally, charge exchange dependent ion stopping responsible for kinetic sputtering was measured simultaneously. © 2020 Institute of Physics Publishing. All rights reserved.
    view abstractdoi: 10.1088/1742-6596/1412/16/162018
  • 2020 • 180 Fast diffusion mechanism in Li4P2S6: Via a concerted process of interstitial Li ions
    Stamminger, A.R. and Ziebarth, B. and Mrovec, M. and Hammerschmidt, T. and Drautz, R.
    RSC Advances 10 10715-10722 (2020)
    The synthesis of Li superionic conductor Li7P3S11 may be accompanied by the formation of a detrimental Li4P2S6 phase due to a high mixing sensitivity of precursor materials. This phase exhibits a poor ionic conductivity whose origins are not fully understood. Recently Dietrich et al. investigated the energetics of Li ion migration in Li4P2S6 with nudged elastic band (NEB) calculations. The observed large migration barrier of 0.51 eV for purely interstitial diffusion leads to an interpretation of the low ionic conductivity by kinetic limitations. Based on ab initio molecular dynamics simulations (AIMD) we propose a new and energetically much more favorable diffusion path available to interstitial Li ion charge carriers that has not been considered so far. It consists of a concerted process in which a second lithium atom is pushed out from its equilibrium lattice position by the diffusing lithium ion. A detailed analysis with NEB calculations shows that the energy barrier for this concerted diffusion is only 0.08 eV, i.e. an order of magnitude lower than the previously reported value for purely interstitial diffusion. Therefore, the observed low ionic conductivity of Li4P2S6 is likely not originating from kinetic limitations due to high diffusion barriers but rather from thermodynamic reasons associated with a low concentration of free charge carriers. We therefore expect that increasing the charge carrier concentration by doping is a viable design route to optimize the ionic conductivity of this material. © 2020 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ra00932f
  • 2020 • 179 Freestanding LiFe0.2Mn0.8PO4/rGO nanocomposites as high energy density fast charging cathodes for lithium-ion batteries
    Zoller, F. and Böhm, D. and Luxa, J. and Döblinger, M. and Sofer, Z. and Semenenko, D. and Bein, T. and Fattakhova-Rohlfing, D.
    Materials Today Energy 16 (2020)
    Freestanding electrodes for lithium ion batteries are considered as a promising option to increase the total gravimetric energy density of the cells due to a decreased weight of electrochemically inactive materials. We report a simple procedure for the fabrication of freestanding LiFe0.2Mn0.8PO4 (LFMP)/rGO electrodes with a very high loading of active material of 83 wt%, high total loading of up to 8 mg cm−2, high energy density, excellent cycling stability and at the same time very fast charging rate, with a total performance significantly exceeding the values reported in the literature. The keys to the improved electrode performance are optimization of LFMP nanoparticles via nanoscaling and doping; the use of graphene oxide (GO) with its high concentration of surface functional groups favoring the adhesion of high amounts of LFMP nanoparticles, and freeze-casting of the GO-based nanocomposites to prevent the morphology collapse and provide a unique fluffy open microstructure of the freestanding electrodes. The rate and the cycling performance of the obtained freestanding electrodes are superior compared to their Al-foil coated equivalents, especially when calculated for the entire weight of the electrode, due to the extremely reduced content of electrochemically inactive material (17 wt% of electrochemically inactive material in case of the freestanding compared to 90 wt% for the Al-foil based electrode), resulting in 120 mAh g−1 electrode in contrast to 10 mAh g−1 electrode at 0.2 C. The electrochemical performance of the freestanding LFMP/rGO electrodes is also considerably better than the values reported in literature for freestanding LFMP and LMP composites, and can even keep up with those of LFP-based analogues. The freestanding LFMP/rGO reported in this work is additionally attractive due to its high gravimetric energy density (604 Wh kg−1 LFMP at 0.2C). The obtained results demonstrate the advantage of freestanding LiFe0.2Mn0.8PO4/rGO electrodes and their great potential for applications in lithium ion batteries. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.mtener.2020.100416
  • 2020 • 178 Irreversible Structural Changes of Copper Hexacyanoferrate Used as a Cathode in Zn-Ion Batteries
    Lim, J. and Kasiri, G. and Sahu, R. and Schweinar, K. and Hengge, K. and Raabe, D. and La Mantia, F. and Scheu, C.
    Chemistry - A European Journal 26 4917-4922 (2020)
    The structural changes of copper hexacyanoferrate (CuHCF), a Prussian blue analogue, which occur when used as a cathode in an aqueous Zn-ion battery, are investigated using electron microscopy techniques. The evolution of ZnxCu1−xHCF phases possessing wire and cubic morphologies from initial CuHCF nanoparticles are monitored after hundreds of cycles. Irreversible introduction of Zn ions to CuHCF is revealed locally using scanning transmission electron microscopy. A substitution mechanism is proposed to explain the increasing Zn content within the cathode material while simultaneously the Cu content is lowered during Zn-ion battery cycling. The present study demonstrates that the irreversible introduction of Zn ions is responsible for the decreasing Zn ion capacity of the CuHCF cathode in high electrolyte concentration. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/chem.201905384
  • 2020 • 177 Magneto-Optics of Excitons Interacting with Magnetic Ions in CdSe/CdMnS Colloidal Nanoplatelets
    Shornikova, E.V. and Yakovlev, D.R. and Tolmachev, D.O. and Ivanov, V.Y. and Kalitukha, I.V. and Sapega, V.F. and Kudlacik, D. and Kusrayev, Y.G. and Golovatenko, A.A. and Shendre, S. and Delikanli, S. and Demir, H.V. and Bayer, M.
    ACS Nano 14 9032-9041 (2020)
    Excitons in diluted magnetic semiconductors represent excellent probes for studying the magnetic properties of these materials. Various magneto-optical effects, which depend sensitively on the exchange interaction of the excitons with the localized spins of the magnetic ions can be used for probing. Here, we study core/shell CdSe/(Cd,Mn)S colloidal nanoplatelets hosting diluted magnetic semiconductor layers. The inclusion of the magnetic Mn2+ ions is evidenced by three magneto-optical techniques using high magnetic fields up to 15 T: polarized photoluminescence, optically detected magnetic resonance, and spin-flip Raman scattering. We show that the holes in the excitons play the dominant role in exchange interaction with magnetic ions. We suggest and test an approach for evaluation of the Mn2+ concentration based on the spin-lattice relaxation dynamics of the Mn2+ spin system. Copyright © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.0c04048
  • 2020 • 176 Nanocutting mechanism of 6H-SiC investigated by scanning electron microscope online observation and stress-assisted and ion implant-assisted approaches
    Xu, Z. and Liu, L. and He, Z. and Tian, D. and Hartmaier, A. and Zhang, J. and Luo, X. and Rommel, M. and Nordlund, K. and Zhang, G. and Fang, F.
    International Journal of Advanced Manufacturing Technology 106 3869-3880 (2020)
    Nanocutting mechanism of single crystal 6H-SiC is investigated through a novel scanning electron microscope setup in this paper. Various undeformed chip thicknesses on (0001) < 1–100 > orientation are adopted in the nanocutting experiments. Phase transformation and dislocation activities involved in the 6H-SiC nanocutting process are also characterized and analyzed. Two methods of stress-assisted and ion implant-assisted nanocutting are studied to improve 6H-SiC ductile machining ability. Results show that stress-assisted method can effectively decrease the hydrostatic stress and help to activate dislocation motion and ductile machining; ion implant-induced damages are helpful to improve the ductile machining ability from MD simulation and continuous nanocutting experiments under the online observation platform. © 2020, Springer-Verlag London Ltd., part of Springer Nature.
    view abstractdoi: 10.1007/s00170-019-04886-6
  • 2020 • 175 Particle emission from two-dimensional MoS2 induced by highly charged ion impact
    Skopinski, L. and Ernst, P. and Herder, M. and Schleberger, M.
    Journal of Physics: Conference Series 1412 (2020)
    For many attractive applications of single layer MoS2 such as in optoelectronics e.g., the sample is supported by a substrate. Its importance for the modification through ion irradiation is here experimentally investigated by the analysis of sputtered particle of MoS2 on SiO2 and Au substrates under highly charged ion irradiation. The velocity distribution of the sputtered atoms is less affected by the substrate using highly charged projectiles than using slightly charged ones. Furthermore, we can show that potential sputtering causes additional emission of particles with lower kinetic energy. © 2019 Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/1412/20/202007
  • 2020 • 174 Predicting oxidation and spin states by high-dimensional neural networks: Applications to lithium manganese oxide spinels
    Eckhoff, M. and Lausch, K.N. and Blöchl, P.E. and Behler, J.
    Journal of Chemical Physics 153 (2020)
    Lithium ion batteries often contain transition metal oxides such as LixMn2O4 (0 ≤ x ≤ 2). Depending on the Li content, different ratios of MnIII to MnIV ions are present. In combination with electron hopping, the Jahn-Teller distortions of the MnIIIO6 octahedra can give rise to complex phenomena such as structural transitions and conductance. While for small model systems oxidation and spin states can be determined using density functional theory (DFT), the investigation of dynamical phenomena by DFT is too demanding. Previously, we have shown that a high-dimensional neural network potential can extend molecular dynamics (MD) simulations of LixMn2O4 to nanosecond time scales, but these simulations did not provide information about the electronic structure. Here, we extend the use of neural networks to the prediction of atomic oxidation and spin states. The resulting high-dimensional neural network is able to predict the spins of the Mn ions with an error of only 0.03 We find that the Mn eg electrons are correctly conserved and that the number of Jahn-Teller distorted MnIIIO6 octahedra is predicted precisely for different Li loadings. A charge ordering transition is observed between 280 K and 300 K, which matches resistivity measurements. Moreover, the activation energy of the electron hopping conduction above the phase transition is predicted to be 0.18 eV, deviating only 0.02 eV from experiment. This work demonstrates that machine learning is able to provide an accurate representation of both the geometric and the electronic structure dynamics of LixMn2O4 on time and length scales that are not accessible by ab initio MD. © 2020 Author(s).
    view abstractdoi: 10.1063/5.0021452
  • 2020 • 173 Selective proton transport for hydrogen production using graphene oxide membranes
    Madauß, L. and Foller, T. and Plaß, J. and Kumar, P.V. and Musso, T. and Dunkhorst, K. and Joshi, R. and Schleberger, M.
    Journal of Physical Chemistry Letters 9415-9420 (2020)
    Graphene oxide has shown exceptional properties in terms of water permeability and filtration characteristics. Here the suitability of graphene oxide membranes for the spatial separation of hydronium and hydroxide ions after photocatalytic water splitting is demonstrated. Instead of relying on classical size exclusion by adjusting the membrane laminates' interlayer spacings, nonmodified graphene oxide is used to exploit the presence of its natural functional groups and surface charges for filtration. Despite a significantly larger interlayer spacing inside the membrane compared with the size of the hydrated radii of the ions, highly asymmetric transport behavior and a 6 times higher mobility for hydronium than for hydroxide are observed. DFT simulations reveal that hydroxide ions are more prone to interact and stick to the functional groups of graphene oxide, while diffusion of hydronium ions through the membrane is less impeded and aligns well with the concept of the Grotthuss mechanism. © 2020 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.jpclett.0c02481
  • 2020 • 172 Short range proximity effect induced by exchange interaction in tunnel-coupled CdTe and (Cd,Mn)Te quantum wells
    Kirstein, E. and Kozyrev, N.V. and Afanasiev, M.M. and Mantsevich, V.N. and Krivenko, I.S. and Kalevich, V.K. and Salewski, M. and Chusnutdinow, S. and Wojtowicz, T. and Karczewski, G. and Kusrayev, Y.G. and Zhukov, E.A. and Yakov...
    Physical Review B 101 (2020)
    The coherent spin dynamics of electrons in tunnel-coupled CdTe and (Cd,Mn)Te quantum wells (QWs) is studied by time-resolved pump-probe Kerr rotation. The coupled QWs have different thicknesses; the narrow one is doped by Mn2+ magnetic ions. A short range proximity effect between them is observed: the Zeeman splitting of electrons in the wide QW is given in addition to the intrinsic electron g factor by the exchange interaction with the Mn2+ ions mediated by electron tunneling into the narrow QW. The exchange interaction strength scales with the Cd0.88Mg0.12Te barrier thickness separating the QWs. The Kerr rotation signal measured on the wide QW shows two close frequencies of electron spin Larmor precession in a transverse magnetic field. These components have very different spin dephasing times, 50 ps and 1 ns. The two frequencies originate from electrons in the wide QW being either part of an exciton or being resident. The proximity effect of the exciton electron is smaller due to the binding by Coulomb interaction, which decreases the tunneling to the narrow well. The experimental data are in good agreement with model calculations. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.101.035301
  • 2020 • 171 Vanishing influence of the band gap on the charge exchange of slow highly charged ions in freestanding single-layer MoS2
    Creutzburg, S. and Schwestka, J. and Niggas, A. and Inani, H. and Tripathi, M. and George, A. and Heller, R. and Kozubek, R. and Madauß, L. and McEvoy, N. and Facsko, S. and Kotakoski, J. and Schleberger, M. and Turchanin, A. and...
    Physical Review B 102 (2020)
    Charge exchange and kinetic energy loss of slow highly charged xenon ions transmitted through freestanding monolayer MoS2 are studied. Two distinct exit charge state distributions, characterized by high and low charge states, are observed. They are accompanied by smaller and larger kinetic energy losses, as well as scattering angles, respectively. High charge exchange is attributed to two-center neutralization processes, which take place in close impact collisions with the target atoms. Experimental findings are compared to graphene as a target material and simulations based on a time-dependent scattering potential model. Independent of the target material, experimentally observed charge exchange can be modeled by the same electron capture and de-excitation rates for MoS2 and graphene. A common dependence of the kinetic energy loss on the charge exchange for MoS2 as well as graphene is also observed. Considering the similarities of the zero band-gap material graphene and the 1.9 eV band-gap material MoS2, we suggest that electron transport on the femtosecond timescale is dominated by the strong influence of the ion's Coulomb potential in contrast to the dispersion defined by the material's band structure. © 2020 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.102.045408
  • 2019 • 170 Block copolymer-directed synthesis of porous anatase for lithium-ion battery electrodes
    McRae, O.F. and Xia, Q. and Tjaberings, S. and Gröschel, A.H. and Ling, C.D. and Müllner, M.
    Journal of Polymer Science, Part A: Polymer Chemistry 57 1890-1896 (2019)
    A templating method is developed to produce porous nanocrystalline anatase materials for negative electrodes in lithium-ion batteries (LIBs). Amphiphilic diblock copolymers are used to generate template films with phase-separated internal structure. Subsequent swelling with acidified titanium(IV) bis(ammonium lactato) dihydroxide (TALH) solution yielded structured hybrid films. Upon heating, the formation of TiO2 nanocrystals is induced, resulting in a three-dimensional mesoporous structure directed by the bulk morphology of the polymer template. In comparison to commercial nanosized anatase, the structured anatase shows significant performance improvements in lithium-ion coin cell batteries in terms of capacity, stability, and rate capability. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1890–1896. © 2018 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/pola.29312
  • 2019 • 169 Features of spin dynamics of magnetic ions and charge carriers in self-organized quantum dots CdSe/ZnMnSe
    Kozyrev, N.V. and Kirstein, E. and Namozov, B.R. and Kusrayev, Y.G. and Zhukov, E.A. and Sedova, I.V. and Yakovlev, D.R. and Bayer, M.
    Journal of Physics: Conference Series 1400 (2019)
    Self-organized disk-shaped quantum dots of CdSe embedded in diluted magnetic ZnMnSe barrier were studied by means of pump-probe time-resolved Kerr rotation (TRKR) technique at low temperature T = 7 K. In absence of the external magnetic field TRKR signal exhibits long-living spin dynamics with the decay time exceeding the period between laser pulses. Such spin dynamics is not typical for diluted magnetic semiconductors and nano-structures based on them and could be a trace of a bound magnetic polaron. Resonant spin amplification measured in transversal magnetic field up to 1 T shows the only one peak near B = 0. In B = 1 T the long-living non-precessing signal practically vanishes, while the precessing one appears with the Larmor frequency corresponding to the Mn2+ ions' net spin precession around the magnetic field. It was found that the signal consists of three components with slightly different precession frequencies that could be due to the fine structure of the manganese spin sublevels occurring because of a stress in quantum dots. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/1400/7/077010
  • 2019 • 168 Ionic liquid - Electrode materials interactions studied by NMR spectroscopy, cyclic voltammetry, and impedance spectroscopy
    Zhang, E. and Fulik, N. and Paasch, S. and Borchardt, L. and Kaskel, S. and Brunner, E.
    Energy Storage Materials 19 432-438 (2019)
    The interactions between two selected porous carbon materials and ionic-liquid based electrolyte solutions consisting of the ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4)diluted with acetonitrile are investigated within the present paper by combined use of cyclic voltammetry, electrochemical impedance spectroscopy, and NMR spectroscopy. The commercially available microporous YP50F and the hierarchically organized micro- and mesoporous OM-CDC (ordered mesoporous carbide derived carbon)are selected as model materials to achieve a better understanding of the electrolyte behavior, especially its mobility, in porous carbons. The ionic liquid chosen as electrolyte leads to high specific capacitance approaching 180 F g-1 for OM-CDC. Due to the hierarchical pore system, OM-CDC shows a better rate performance than YP50F. NMR analyses provide an understanding of the molecular processes giving rise to the above-mentioned observations. They reveal a limited accessibility of the narrow pores in YP50F for pure EmimBF4 in contrast to OM-CDC. It was found that about 30% of the entire pore volume of YP50F remain unfilled by electrolyte ions without dilution. Dilution with acetonitrile significantly increased the anion mobility as the NMR signal of adsorbed ions becomes narrower. A mixture containing 60% EmimBF4 and 40% acetonitrile was identified as the optimum for electrochemical applications. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.ensm.2019.03.015
  • 2019 • 167 Measurement and Modeling of Lactose Solubility in Aqueous Electrolyte Solutions
    Choscz, C. and Held, C. and Eder, C. and Sadowski, G. and Briesen, H.
    Industrial and Engineering Chemistry Research 58 20797-20805 (2019)
    Lactose solubility has a significant influence on lactose crystallization. Changes in lactose solubility have an immediate impact on saturation concentration and hence supersaturation, which is used to control the crystallization process. The possibility to model and predict changes in solubility, which are caused by electrolytes, provides a chance to optimize the crystallization processes accordingly. This study explores the influence of different whey salts and salt mixtures on lactose solubility in aqueous solutions. Temperatures from 20 to 50 °C in combination with different salt concentrations are studied. Furthermore, a semipredictive modeling approach using the ePC-SAFT model is presented based on the experimental results. This approach requires pure-component parameters for lactose, dissociated ions, and water, as well as binary interaction parameters for lactose-water, water-ion, and lactose-ion, the latter of which were fitted to lactose solubility data in ternary water-lactose-salt solutions. These parameters have then been applied to successfully predict lactose solubility in multicomponent salt solutions. Until now, a modeling approach for the systems under investigation has not existed in the literature. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.iecr.9b04031
  • 2019 • 166 Native Top-Down Mass Spectrometry and Ion Mobility Spectrometry of the Interaction of Tau Protein with a Molecular Tweezer Assembly Modulator
    Nshanian, M. and Lantz, C. and Wongkongkathep, P. and Schrader, T. and Klärner, F.-G. and Blümke, A. and Despres, C. and Ehrmann, M. and Smet-Nocca, C. and Bitan, G. and Loo, J.A.
    Journal of the American Society for Mass Spectrometry 30 16-23 (2019)
    Native top-down mass spectrometry (MS) and ion mobility spectrometry (IMS) were applied to characterize the interaction of a molecular tweezer assembly modulator, CLR01, with tau, a protein believed to be involved in a number of neurodegenerative disorders, including Alzheimer’s disease. The tweezer CLR01 has been shown to inhibit aggregation of amyloidogenic polypeptides without toxic side effects. ESI-MS spectra for different forms of tau protein (full-length, fragments, phosphorylated, etc.) in the presence of CLR01 indicate a primary binding stoichiometry of 1:1. The relatively high charging of the protein measured from non-denaturing solutions is typical of intrinsically disordered proteins, such as tau. Top-down mass spectrometry using electron capture dissociation (ECD) is a tool used to determine not only the sites of post-translational modifications but also the binding site(s) of non-covalent interacting ligands to biomolecules. The intact protein and the protein-modulator complex were subjected to ECD-MS to obtain sequence information, map phosphorylation sites, and pinpoint the sites of inhibitor binding. The ESI-MS study of intact tau proteins indicates that top-down MS is amenable to the study of various tau isoforms and their post-translational modifications (PTMs). The ECD-MS data point to a CLR01 binding site in the microtubule-binding region of tau, spanning residues K294-K331, which includes a six-residue nucleating segment PHF6 (VQIVYK) implicated in aggregation. Furthermore, ion mobility experiments on the tau fragment in the presence of CLR01 and phosphorylated tau reveal a shift towards a more compact structure. The mass spectrometry study suggests a picture for the molecular mechanism of the modulation of protein-protein interactions in tau by CLR01. [Figure not available: see fulltext.]. © 2018, American Society for Mass Spectrometry.
    view abstractdoi: 10.1007/s13361-018-2027-6
  • 2019 • 165 Perforating Freestanding Molybdenum Disulfide Monolayers with Highly Charged Ions
    Kozubek, R. and Tripathi, M. and Ghorbani-Asl, M. and Kretschmer, S. and Madauß, L. and Pollmann, E. and O'Brien, M. and McEvoy, N. and Ludacka, U. and Susi, T. and Duesberg, G.S. and Wilhelm, R.A. and Krasheninnikov, A.V. and Ko...
    Journal of Physical Chemistry Letters 10 904-910 (2019)
    Porous single-layer molybdenum disulfide (MoS 2 ) is a promising material for applications such as DNA sequencing and water desalination. In this work, we introduce irradiation with highly charged ions (HCIs) as a new technique to fabricate well-defined pores in MoS 2 . Surprisingly, we find a linear increase of the pore creation efficiency over a broad range of potential energies. Comparison to atomistic simulations reveals the critical role of energy deposition from the ion to the material through electronic excitation in the defect creation process and suggests an enrichment in molybdenum in the vicinity of the pore edges at least for ions with low potential energies. Analysis of the irradiated samples with atomic resolution scanning transmission electron microscopy reveals a clear dependence of the pore size on the potential energy of the projectiles, establishing irradiation with highly charged ions as an effective method to create pores with narrow size distributions and radii between ca. 0.3 and 3 nm. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpclett.8b03666
  • 2019 • 164 Phonon Pair Creation by Inflating Quantum Fluctuations in an Ion Trap
    Wittemer, M. and Hakelberg, F. and Kiefer, P. and Schröder, J.-P. and Fey, C. and Schützhold, R. and Warring, U. and Schaetz, T.
    Physical Review Letters 123 (2019)
    Quantum theory predicts intriguing dynamics during drastic changes of external conditions. We switch the trapping field of two ions sufficiently fast to tear apart quantum fluctuations, i.e., create pairs of phonons and, thereby, squeeze the ions' motional state. This process can be interpreted as an experimental analog to cosmological particle creation and is accompanied by the formation of spatial entanglement. Hence, our platform allows one to study the causal connections of squeezing, pair creation, and entanglement and might permit one to cross-fertilize between concepts in cosmology and applications of quantum information processing. © 2019 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.123.180502
  • 2019 • 163 Single entity electrochemistry for the elucidation of lithiation kinetics of TiO 2 particles in non-aqueous batteries
    Löffler, T. and Clausmeyer, J. and Wilde, P. and Tschulik, K. and Schuhmann, W. and Ventosa, E.
    Nano Energy 57 827-834 (2019)
    In battery research, the development of analytical techniques is of key importance for determining intrinsic properties of active materials ultimately dictating the battery performance. We report the application of nano-impact electrochemistry to gain insight into the intrinsic properties of commercial battery materials i.e. TiO 2 particles in non-aqueous media. Potentiostatic lithiation measurements do not only provide qualitative information about the rate-limiting step in the lithiation process, but also demonstrate that nano-impact electrochemistry is a suitable technique in non-aqueous media in complete absence of oxygen and water. Our results reveal that the intrinsic lithiation rate of individual TiO 2 particles is not – as generally assumed – determined by interfacial ion transfer kinetics, mobility of ion and/or electrons in the bulk of the particle, but by the solid-solid electron transfer. These findings have important implications for future studies of fundamental properties of battery materials considering that charge transfer in battery electrodes does not always obey Butler-Volmer kinetics. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.nanoen.2018.12.064
  • 2019 • 162 Single entity electrochemistry for the elucidation of lithiation kinetics of TiO2 particles in non-aqueous batteries
    Löffler, T. and Clausmeyer, J. and Wilde, P. and Tschulik, K. and Schuhmann, W. and Ventosa, E.
    Nano Energy 57 827-834 (2019)
    In battery research, the development of analytical techniques is of key importance for determining intrinsic properties of active materials ultimately dictating the battery performance. We report the application of nano-impact electrochemistry to gain insight into the intrinsic properties of commercial battery materials i.e. TiO2 particles in non-aqueous media. Potentiostatic lithiation measurements do not only provide qualitative information about the rate-limiting step in the lithiation process, but also demonstrate that nano-impact electrochemistry is a suitable technique in non-aqueous media in complete absence of oxygen and water. Our results reveal that the intrinsic lithiation rate of individual TiO2 particles is not – as generally assumed – determined by interfacial ion transfer kinetics, mobility of ion and/or electrons in the bulk of the particle, but by the solid-solid electron transfer. These findings have important implications for future studies of fundamental properties of battery materials considering that charge transfer in battery electrodes does not always obey Butler-Volmer kinetics. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.nanoen.2018.12.064
  • 2019 • 161 Structure and Dynamics of the Liquid-Water/Zinc-Oxide Interface from Machine Learning Potential Simulations
    Quaranta, V. and Behler, J. and Hellström, M.
    Journal of Physical Chemistry C 123 1293-1304 (2019)
    Interfaces between water and metal oxides exhibit many interesting phenomena like dissociation and recombination of water molecules and water exchange between the interface and the bulk liquid. Moreover, a variety of structural motifs can be found, differing in hydrogen-bonding patterns and molecular orientations. Here, we report the structure and dynamics of liquid water interacting with the two most stable ZnO surfaces, (101Ì) and (112Ì), by means of reactive molecular dynamics simulations based on a machine learning high-dimensional neural network potential. For both surfaces, three distinct hydration layers can be observed within 10 Å from the surface with the first hydration layer (nearest to the surface) representing the most interesting region to investigate. There, water molecules dynamically dissociate and recombine, leading to a variety of chemical species at the interface. We characterized these species and their molecular environments by analyzing the properties of the hydrogen bonds and local geometries. At ZnO(112Ì0), some of the adsorbed hydroxide ions bridge two surface Zn ions, which is not observed at ZnO(101Ì0). For both surfaces, adsorbed water molecules always bind to a single Zn ion, and those located in proximity of the substrate are mostly "H-down" oriented for ZnO(101Ì0) and "flat-lying", i.e., parallel to the surface, for ZnO(112Ì0). The time scales for proton-transfer (PT) reactions are quite similar at the two surfaces, with the average lifetime of adsorbed hydroxide ions being around 41 ± 3 ps until recombination. However, water exchange events, in which adsorbed water molecules leave the surface and enter the bulk liquid, happen more frequently at ZnO(112Ì0) than at ZnO(101Ì0). © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b10781
  • 2019 • 160 Structure and Reactivity of 1,8-Bis(naphthalenediyl)dipnictanes
    Dzialkowski, K. and Gehlhaar, A. and Wölper, C. and Auer, A.A. and Schulz, S.
    Organometallics 38 2927-2942 (2019)
    Syntheses and solid-state structures of diarsane Naph2As2 (Naph = 1,8-naphthalenediyl, 1) and (Naph)5Sb4Cl2 3 are reported and the σ-donor capacity of Naph2E2 (E = As 1, Sb 2) was studied in reactions with (coe)Cr(CO)5 (coe = Z-cyclooctene), yielding [Naph2As2][Cr(CO)5]2 (4) and [Naph2E2][Cr(CO)5] (E = As 5, Sb 6). In contrast, reactions of 1 and 3 with Me2SAuCl proceed with oxidation and formation of elemental gold as well as Naph2(AsCl)2 (7) and [NaphSbCl2]2 8. All complexes were characterized by elemental analyses, heteronuclear (1H, 13C) NMR and FT-IR spectroscopy, as well as single crystal X-ray diffraction. Intermolecular E···πinteractions (E = As, Sb), which were observed in 7 and 8, were quantified by use of density functional theory and local coupled cluster electronic structure theory calculations. These allow to assess the nature and relative importance of covalent and noncovalent interactions and illustrate how dispersion interactions change with the electronic structure of the compounds. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.organomet.9b00269
  • 2019 • 159 The fate of the OH radical in molecular beam sampling experiments
    Krüger, D. and Oßwald, P. and Köhler, M. and Hemberger, P. and Bierkandt, T. and Kasper, T.
    Proceedings of the Combustion Institute 37 1563-1570 (2019)
    The collisional history of ionized molecules in a molecular beam mass spectrometric flame experiment is target of our present investigation. Measurements in a double imaging photoelectron photoion coincidence spectroscopy (i2PEPICO) were performed at the Swiss Light Source (SLS) of the Paul Scherrer Institute to use the ion imaging device for separating the molecular beam ions from rethermalized ions. This enables the precise composition study of the individual types of ions. Results show clearly for the OH radical that the complete signal is obtained from the molecular beam, while the signal from other combustion compounds features additional rethermalized molecules. As for OH radicals, the mole fraction is reduced by sampling effects and contact with the ionization vessel walls significantly. Consequently, this leads to signal loss and lower mole fractions, when using ionization cross sections for the quantification. To improve on this, a beam fraction (BF) factor is presented. The factor describes the ratio of the separated beam signal without rethermalized ions with the total ion signal, consisting of the mass to charge ratio from the molecular beam and additional rethermalized ions. Since the detected OH radicals are solely from the molecular beam, a new method of comparing two molecular beam alignments using the OH to H2O signal ratio is presented. This method has a decent potential for the optimization of the quality of molecular beams. Finally, the separated beam signal (without the rethermalized ions) was used to determine mole fraction profiles for the OH radical using ionization cross sections. These profiles are in good agreement with model predictions of the USC-II and the Aramco Mech 2.0 mechanisms, while the total signal leads to factor of 12 smaller OH mole fractions. © 2018 Elsevier Ltd.
    view abstractdoi: 10.1016/j.proci.2018.05.041
  • 2019 • 158 The Key Role of Water Activity for the Operating Behavior and Dynamics of Oxygen Depolarized Cathodes
    Röhe, M. and Botz, A. and Franzen, D. and Kubannek, F. and Ellendorff, B. and Öhl, D. and Schuhmann, W. and Turek, T. and Krewer, U.
    ChemElectroChem 6 5671-5681 (2019)
    Advanced chlor-alkali electrolysis with oxygen depolarized cathodes (ODC) requires 30 % less electrical energy than conventional hydrogen-evolution-based technology. Herein, we confirm that the activities of hydroxide and water govern the ODC performance and its dynamics. Experimental characterization of ODC under varying mass transfer conditions on the liquid side reveals large differences in the polarization curves as well as in potential step responses of the electrodes. Under convective transport in the liquid electrolyte, the ODC is not limited by mass transfer in its current density at j&gt;3.9 kA m−2, whereas transport limitations are already reached at j≈1.3 kA m−2 with a stagnant electrolyte. Since gas phase conditions do not differ significantly between the measurements, these results are in contrast the common assumption that oxygen supply determines ODC performance. A dynamic model reveals the strong influence of the electrolyte mass transfer conditions on oxygen availability and thus performance. Dynamic responses of the current density to step-wise potential changes are dominated by the mass transport of water and hydroxide ions, which is by orders of magnitude faster with convective electrolyte flow. Without convective liquid electrolyte transport, a high accumulation of hydroxide ions significantly lowers the oxygen solubility. Thus, a fast mass transport of water and hydroxide is essential for high ODC performance and needs to be ensured for technical applications. The predicted accumulation of ions is furthermore validated experimentally by means of scanning electrochemical microscopy. We also show how the outlined processes can explain the distinctively different potential step responses with and without electrolyte convection. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/celc.201901224
  • 2019 • 157 The Poisson-Boltzmann model for implicit solvation of electrolyte solutions: Quantum chemical implementation and assessment via Sechenov coefficients
    Stein, C.J. and Herbert, J.M. and Head-Gordon, M.
    Journal of Chemical Physics 151 (2019)
    We present the theory and implementation of a Poisson-Boltzmann implicit solvation model for electrolyte solutions. This model can be combined with arbitrary electronic structure methods that provide an accurate charge density of the solute. A hierarchy of approximations for this model includes a linear approximation for weak electrostatic potentials, finite size of the mobile electrolyte ions, and a Stern-layer correction. Recasting the Poisson-Boltzmann equations into Euler-Lagrange equations then significantly simplifies the derivation of the free energy of solvation for these approximate models. The parameters of the model are either fit directly to experimental observables - e.g., the finite ion size - or optimized for agreement with experimental results. Experimental data for this optimization are available in the form of Sechenov coefficients that describe the linear dependence of the salting-out effect of solutes with respect to the electrolyte concentration. In the final part, we rationalize the qualitative disagreement of the finite ion size modification to the Poisson-Boltzmann model with experimental observations by taking into account the electrolyte concentration dependence of the Stern layer. A route toward a revised model that captures the experimental observations while including the finite ion size effects is then outlined. This implementation paves the way for the study of electrochemical and electrocatalytic processes of molecules and cluster models with accurate electronic structure methods. © 2019 Author(s).
    view abstractdoi: 10.1063/1.5131020
  • 2018 • 156 A short perspective of modeling electrode materials in lithium-ion batteries by the ab initio atomistic thermodynamics approach
    Exner, K.S.
    Journal of Solid State Electrochemistry 22 3111-3117 (2018)
    Atomic-scale insights into the performance of electrode materials in lithium-ion batteries require thermodynamic considerations as first step in order to determine potential surface structures that are relevant for subsequent kinetic studies. Within the last 20 years, research in heterogeneous catalysis as well as in electrocatalysis has been spurred by the ab initio atomistic thermodynamics approach, whose application for electrode materials in lithium-ion batteries is eyed and discussed in this perspective article. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s10008-018-4017-9
  • 2018 • 155 Activity – Stability Volcano Plots for the Investigation of Nano-Sized Electrode Materials in Lithium-Ion Batteries
    Exner, K.S.
    ChemElectroChem 5 3243-3248 (2018)
    In the last two decades, materials design in lithium-ion batteries (LIBs) based on first-principles methods has been spurred mainly by computationally demanding investigations of diffusion pathways, redox mechanisms or activation barriers for lithium-ion migration. However, hitherto an expeditious tool with conceptual simplicity that enables a priori computational screening based on thermodynamic considerations in order to propose potential candidates for the usage as electrode materials in LIBs is missing. Here, a novel method based on the application of Volcano plots from catalysis is introduced which allows assessing lithium intercalation in nano-sized electrode materials of LIBs by means of both activity and stability. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201800838
  • 2018 • 154 All gas-phase synthesis of graphene: Characterization and its utilization for silicon-based lithium-ion batteries
    Münzer, A. and Xiao, L. and Sehlleier, Y.H. and Schulz, C. and Wiggers, H.
    Electrochimica Acta 272 52-59 (2018)
    We report on a gas-phase synthesis method for the preparation of free-standing few-layer graphene in a microwave plasma reactor using pure ethanol as precursor. This scalable synthesis route produces gas-phase graphene (GPG) with lab-scale production rates up to a few hundred mg/h. The physico-chemical properties of the resulting GPG were characterized by XRD, FTIR-, and Raman spectroscopy, electrical conductivity measurements, XPS, and HRTEM in combination with EELS. The materials’ properties were compared with those of reduced graphene oxide (rGO) made by the established Hummers’ method. The results indicate that the gas-phase synthesis method provides highly-ordered few-layer graphene with extraordinary high purity, very low oxygen content of less than 1 at.%, and high specific conductivity. Both graphene materials were processed in combination with gas-phase synthesized silicon nanoparticles towards silicon-graphene nanocomposites for Li-ion battery anodes. Subsequent electrochemical testing revealed that the gas-phase graphene significantly enhances the long-term stability and Coulomb efficiency of the composite compared to pristine silicon and outperforms the composite fabricated from reduced graphene oxide. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2018.03.137
  • 2018 • 153 Atypical titration curves for GaAl12 Keggin-ions explained by a joint experimental and simulation approach
    Sulpizi, M. and Lützenkirchen, J.
    Journal of Chemical Physics 148 (2018)
    Although they have been widely used as models for oxide surfaces, the deprotonation behaviors of the Keggin-ions (MeAl127+) and typical oxide surfaces are very different. On Keggin-ions, the deprotonation occurs over a very narrow pH range at odds with the broad charging curve of larger oxide surfaces. Depending on the Me concentration, the deprotonation curve levels off sooner (high Me concentration) or later (for low Me concentration). The leveling off shows the onset of aggregation before which the Keggin-ions are present as individual units. We show that the atypical titration data previously observed for some GaAl12 solutions in comparison to the originally reported data can be explained by the presence of Ga2Al11 ions. The pKa value of aquo-groups bound to octahedral Ga was determined from ab initio molecular dynamics simulations relative to the pure GaAl12 ions. Using these results within a surface complexation model, the onset of deprotonation of the crude solution is surprisingly well predicted and the ratio between the different species is estimated to be in the proportion 20 (Ga2Al11): 20 (Al13): 60 (GaAl12). © 2018 Author(s).
    view abstractdoi: 10.1063/1.5024201
  • 2018 • 152 Co2+-Doping of Magic-Sized CdSe Clusters: Structural Insights via Ligand Field Transitions
    Yang, J. and Muckel, F. and Choi, B.K. and Lorenz, S. and Kim, I.Y. and Ackermann, J. and Chang, H. and Czerney, T. and Kale, V.S. and Hwang, S.-J. and Bacher, G. and Hyeon, T.
    Nano Letters 18 7350-7357 (2018)
    Magic-sized clusters represent materials with unique properties at the border between molecules and solids and provide important insights into the nanocrystal formation process. However, synthesis, doping, and especially structural characterization become more and more challenging with decreasing cluster size. Herein, we report the successful introduction of Co2+ ions into extremely small-sized CdSe clusters with the intention of using internal ligand field transitions to obtain structural insights. Despite the huge mismatch between the radii of Cd2+ and Co2+ ions (&gt;21%), CdSe clusters can be effectively synthesized with a high Co2+ doping concentration of ∼10%. Optical spectroscopy and mass spectrometry suggest that one or two Co2+ ions are substitutionally embedded into (CdSe)13 clusters, which is known as one of the smallest CdSe clusters. Using magnetic circular dichroism spectroscopy on the intrinsic ligand field transitions between the different 3d orbitals of the transition metal dopants, we demonstrate that the Co2+ dopants are embedded on pseudotetrahedral selenium coordinated sites despite the limited number of atoms in the clusters. A significant shortening of Co-Se bond lengths compared to bulk or nanocrystals is observed, which results in the metastability of Co2+ doping. Our results not only extend the doping chemistry of magic-sized semiconductor nanoclusters, but also suggest an effective method to characterize the local structure of these extremely small-sized clusters. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.8b03627
  • 2018 • 151 Dimensional control of supramolecular assemblies of diacetylene-derived peptide gemini amphiphile: From spherical micelles to foamlike networks
    Jiang, H. and Ehlers, M. and Hu, X.-Y. and Zellermann, E. and Schmuck, C.
    Soft Matter 14 5565-5571 (2018)
    Peptide amphiphiles capable of assembling into multidimensional nanostructures have attracted much attention over the past decade due to their potential applications in materials science. Herein, a novel diacetylene-derived peptide gemini amphiphile with a fluorenylmethyloxycarbonyl (Fmoc) group at the N-terminus is reported to hierarchically assemble into spherical micelles, one-dimensional nanorods, two-dimensional foamlike networks and lamellae. Solvent polarity shows a remarkable effect on the self-assembled structures by changing the balance of four weak noncovalent interactions (hydrogen-bonding, π-π stacking, hydrophobic interaction, and electrostatic repulsion). We also show the time-evolution not only from spherical micelles to helical nanofibers in aqueous solution, but also from branched wormlike micelles to foamlike networks in methanol solution. In this work, the presence of the Fmoc group plays a key role in the self-assembly process. This work provides an efficient strategy for precise morphological control, aiding the future development in materials science. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8sm00512e
  • 2018 • 150 Dynamical heterogeneities of rotational motion in room temperature ionic liquids evidenced by molecular dynamics simulations
    Usui, K. and Hunger, J. and Bonn, M. and Sulpizi, M.
    Journal of Chemical Physics 148 (2018)
    Room temperature ionic liquids (RTILs) have been shown to exhibit spatial heterogeneity or structural heterogeneity in the sense that they form hydrophobic and ionic domains. Yet studies of the relationship between this structural heterogeneity and the ∼picosecond motion of the molecular constituents remain limited. In order to obtain insight into the time scales relevant to this structural heterogeneity, we perform molecular dynamics simulations of a series of RTILs. To investigate the relationship between the structures, i.e., the presence of hydrophobic and ionic domains, and the dynamics, we gradually increase the size of the hydrophobic part of the cation from ethylammonium nitrate (EAN), via propylammonium nitrate (PAN), to butylammonium nitrate (BAN). The two ends of the organic cation, namely, the charged Nhead-H group and the hydrophobic Ctail-H group, exhibit rotational dynamics on different time scales, evidencing dynamical heterogeneity. The dynamics of the Nhead-H group is slower because of the strong coulombic interaction with the nitrate counter-ionic anions, while the dynamics of the Ctail-H group is faster because of the weaker van der Waals interaction with the surrounding atoms. In particular, the rotation of the Nhead-H group slows down with increasing cationic chain length, while the rotation of the Ctail-H group shows little dependence on the cationic chain length, manifesting that the dynamical heterogeneity is enhanced with a longer cationic chain. The slowdown of the Nhead-H group with increasing cationic chain length is associated with a lower number of nitrate anions near the Nhead-H group, which presumably results in the increase of the energy barrier for the rotation. The sensitivity of the Nhead-H rotation to the number of surrounding nitrate anions, in conjunction with the varying number of nitrate anions, gives rise to a broad distribution of Nhead-H reorientation times. Our results suggest that the asymmetry of the cations and the larger excluded volume for longer cationic chain are important for both the structural heterogeneity and the dynamical heterogeneities. The observed dynamical heterogeneities may affect the rates of chemical reactions depending on where the reactants are solvated in ionic liquids and provide an additional guideline for the design of RTILs as solvents. © 2018 Author(s).
    view abstractdoi: 10.1063/1.5005143
  • 2018 • 149 Electrolyte mobility in supercapacitor electrodes – Solid state NMR studies on hierarchical and narrow pore sized carbons
    Fulik, N. and Hippauf, F. and Leistenschneider, D. and Paasch, S. and Kaskel, S. and Brunner, E. and Borchardt, L.
    Energy Storage Materials 12 183-190 (2018)
    Electrical double layer capacitors are in the special focus of current energy storage research due to their high power density. They store charge physically by quick electrosorption of electrolyte ions on the surface of porous carbon electrodes. However, fundamental insight into the storage mechanism, especially on a molecular level is limited despite of the crucial importance to understand and improve this promising technology. We have investigated and quantified the mobility of electrolyte ions in supercapacitor electrodes by means of solid-state nuclear magnetic resonance (NMR) spectroscopy. We could discriminate between the mobility of cations, anions, and solvent molecules. The exchange of these species between different pore systems as well as between pore system and external bulk environment is studied in detail by NMR spectroscopic methods. © 2017
    view abstractdoi: 10.1016/j.ensm.2017.12.008
  • 2018 • 148 Experimental investigations of the magnetic asymmetry effect in capacitively coupled radio frequency plasmas
    Oberberg, M. and Kallahn, J. and Awakowicz, P. and Schulze, J.
    Plasma Sources Science and Technology 27 (2018)
    The electrical asymmetry effect allows control of the discharge symmetry, the DC self-bias, and charged particle energy distribution functions electrically by driving a capacitive radio frequency discharge with multiple consecutive harmonics with fixed, but adjustable relative phases. Recently, Trieschmann et al (2013 J. Phys. D: Appl. Phys. 46 084016) and Yang et al (2017 Plasma Process. Polym. 14 1700087; 2018 Plasma Sources Sci. Technol. 27 035008) computationally predicted that the discharge symmetry can also be controlled magnetically via the magnetic asymmetry effect (MAE). By particle-in-cell simulations they demonstrated that a magnetic field, that is parallel to the electrodes and inhomogeneous in the direction perpendicular to the electrodes, induces a discharge asymmetry due to different ion densities adjacent to both electrodes. This, in turn, is predicted to lead to the generation of a DC self-bias as a function of the difference of the magnetic field at both electrodes. In this way the MAE should allow control of the mean ion energy at both electrodes as a function of the magnetic field configuration. Here, we present the first experimental investigation of the MAE. In a low pressure discharge operated in argon at 13.56 MHz, we use a magnetron-like magnetic field configuration at the powered electrode, which leads to an inhomogeneous profile of the magnetic field perpendicular to the electrodes. By measuring the DC self-bias and the ion flux-energy distribution function at the grounded electrode as a function of the magnetic field strength at the powered electrode, the driving voltage amplitude and the neutral gas pressure we experimentally verify the concept of the MAE and demonstrate this technology to be a powerful method to control the discharge symmetry and process relevant energy distribution functions. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6595/aae199
  • 2018 • 147 Formation of Polymeric Particles by Direct Polymerization on the Surface of a Supramolecular Template
    Li, M. and Zellermann, E. and Schmuck, C.
    Chemistry - A European Journal 24 9061-9065 (2018)
    Formation of polymeric materials on the surface of supramolecular assemblies is rather challenging because of the often weak noncovalent interactions between the self-assembled template and the monomers before polymerization. We herein show that the introduction of a supramolecular anion recognition motif, the guanidiniocarbonyl pyrrole cation (GCP), into a short Fmoc-dipeptide 1 leads to self-assembled spherical nanoparticles in aqueous solution. Negatively charged diacetylene monomers can be attached onto the surface of these nanoparticles, which, after UV polymerization, leads to the formation of a polymer shell around the self-assembled template. The hybrid supramolecular and polymeric nanoparticles demonstrate intriguing thermal hysteresis phenomena. The template nanoparticles could be disassembled upon treatment with organic base, which cleaved the Fmoc moiety on 1. This strategy thus showed that a supramolecular anion recognition motif allows the post-assembly formation of polymeric nanomaterials from anionic monomers around a cationic self-assembled template. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201705209
  • 2018 • 146 Formation of the Solid Electrolyte Interphase at Constant Potentials: A Model Study on Highly Oriented Pyrolytic Graphite
    Antonopoulos, B.K. and Maglia, F. and Schmidt-Stein, F. and Schmidt, J.P. and Hoster, H.E.
    Batteries and Supercaps 1 110-121 (2018)
    The solid electrolyte interphase (SEI) on graphite anodes is a key enabler for rechargeable lithium-ion batteries (LIBs). It ensures that only Li+ ions and no damaging electrolyte components enter the anode and hinders electrolyte decomposition. Its growth should be confined to the initial SEI formation process and stop once the battery is in operation to avoid capacity/power loss. In technical LIB cells, the SEI is formed at constant current, with the potential of the graphite anode slowly drifting from higher to lower voltages. SEI formation rate, composition, and structure depend on the potential and on the chemical properties of the anode surface. Here, we characterize SEIs formed at constant potentials on the chemically inactive basal plane of highly oriented pyrolytic graphite (HOPG). X-ray photoemission spectroscopy (XPS) detects carbonate species only at lower formation potentials. Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) with Fc/Fc+ as an electrochemical probe demonstrate how the formation potential influences ion transport and electrochemical kinetics to and at the anode surface, respectively. Breaking the EIS data down to a Distribution of Relaxation Times (DRT) reveals distinct kinetics and transport related peaks with varying Arrhenius-type temperature dependencies. We discuss our findings in the context of previous electrochemical studies and existing SEI models and of SEI formation protocols suitable for industry. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/batt.201800029
  • 2018 • 145 Impact of local electrostatic field rearrangement on field ionization
    Katnagallu, S. and Dagan, M. and Parviainen, S. and Nematollahi, A. and Grabowski, B. and Bagot, P.A.J. and Rolland, N. and Neugebauer, J. and Raabe, D. and Vurpillot, F. and Moody, M.P. and Gault, B.
    Journal of Physics D: Applied Physics 51 (2018)
    Field ion microscopy allows for direct imaging of surfaces with true atomic resolution. The high charge density distribution on the surface generates an intense electric field that can induce ionization of gas atoms. We investigate the dynamic nature of the charge and the consequent electrostatic field redistribution following the departure of atoms initially constituting the surface in the form of an ion, a process known as field evaporation. We report on a new algorithm for image processing and tracking of individual atoms on the specimen surface enabling quantitative assessment of shifts in the imaged atomic positions. By combining experimental investigations with molecular dynamics simulations, which include the full electric charge, we confirm that change is directly associated with the rearrangement of the electrostatic field that modifies the imaging gas ionization zone. We derive important considerations for future developments of data reconstruction in 3D field ion microscopy, in particular for precise quantification of lattice strains and characterization of crystalline defects at the atomic scale. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aaaba6
  • 2018 • 144 Influence of average ion energy and atomic oxygen flux per Si atom on the formation of silicon oxide permeation barrier coatings on PET
    Mitschker, F. and Wißing, J. and Hoppe, C. and De Los Arcos, T. and Grundmeier, G. and Awakowicz, P.
    Journal of Physics D: Applied Physics 51 (2018)
    The respective effect of average incorporated ion energy and impinging atomic oxygen flux on the deposition of silicon oxide (SiOx) barrier coatings for polymers is studied in a microwave driven low pressure discharge with additional variable RF bias. Under consideration of plasma parameters, bias voltage, film density, chemical composition and particle fluxes, both are determined relative to the effective flux of Si atoms contributing to film growth. Subsequently, a correlation with barrier performance and chemical structure is achieved by measuring the oxygen transmission rate (OTR) and by performing x-ray photoelectron spectroscopy. It is observed that an increase in incorporated energy to 160 eV per deposited Si atom result in an enhanced cross-linking of the SiOx network and, therefore, an improved barrier performance by almost two orders of magnitude. Furthermore, independently increasing the number of oxygen atoms to 10 500 per deposited Si atom also lead to a comparable barrier improvement by an enhanced cross-linking. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aab1dd
  • 2018 • 143 Influence of spokes on the ionized metal flux fraction in chromium high power impulse magnetron sputtering
    Biskup, B. and Maszl, C. and Breilmann, W. and Held, J. and Böke, M. and Benedikt, J. and Von Keudell, A.
    Journal of Physics D: Applied Physics 51 (2018)
    High power impulse magnetron sputtering (HiPIMS) discharges are an excellent tool for deposition of thin films with superior properties. By adjusting the plasma parameters, an energetic metal and reactive species growth flux can be controlled. This control requires, however, a quantitative knowledge of the ion-to-neutral ratio in the growth flux and of the ion energy distribution function to optimize the deposited energy per incorporated atom in the film. This quantification is performed by combining two diagnostics, a quartz crystal microbalance (QCM) combined with an ion-repelling grid system (IReGS) to discriminate ions versus neutrals and a HIDEN EQP plasma monitor to measure the ion energy distribution function (IEDF). This approach yields the ionized metal flux fraction (IMFF) as the ionization degree in the growth flux. This is correlated to the plasma performance recorded by time resolved ICCD camera measurements, which allow to identify the formation of pronounced ionization zones, so called spokes, in the HiPIMS plasma. Thereby an automatic technique was developed to identify the spoke mode number. The data indicates two distinct regimes with respect to spoke formation that occur with increasing peak power, a stochastic regime with no spokes at low peak powers followed by a regime with distinct spokes at varying mode numbers at higher peak powers. The IMFF increases with increasing peak power reaching values of almost 80% at very high peak powers. The transition in between the two regimes coincides with a pronounced change in the IMFF. This change indicates that the formation of spokes apparently counteracts the return effect in HiPIMS. Based on the IMFF and the mean energy of the ions, the energy per deposited atom together with the overall energy flux onto the substrate is calculated. This allows us to determine an optimum for the peak power density around 0.5 kW cm-2 for chromium HiPIMS. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aaac15
  • 2018 • 142 Insight into induced charges at metal surfaces and biointerfaces using a polarizable Lennard-Jones potential
    Geada, I.L. and Ramezani-Dakhel, H. and Jamil, T. and Sulpizi, M. and Heinz, H.
    Nature Communications 9 (2018)
    Metallic nanostructures have become popular for applications in therapeutics, catalysts, imaging, and gene delivery. Molecular dynamics simulations are gaining influence to predict nanostructure assembly and performance; however, instantaneous polarization effects due to induced charges in the free electron gas are not routinely included. Here we present a simple, compatible, and accurate polarizable potential for gold that consists of a Lennard-Jones potential and a harmonically coupled core-shell charge pair for every metal atom. The model reproduces the classical image potential of adsorbed ions as well as surface, bulk, and aqueous interfacial properties in excellent agreement with experiment. Induced charges affect the adsorption of ions onto gold surfaces in the gas phase at a strength similar to chemical bonds while ions and charged peptides in solution are influenced at a strength similar to intermolecular bonds. The proposed model can be applied to complex gold interfaces, electrode processes, and extended to other metals. © 2018 The Author(s).
    view abstractdoi: 10.1038/s41467-018-03137-8
  • 2018 • 141 Ion-mediated growth of ultra thin molybdenum disulfide layers on highly oriented pyrolytic graphite
    Pollmann, E. and Ernst, P. and Madauß, L. and Schleberger, M.
    Surface and Coatings Technology 349 783-786 (2018)
    Van der Waals (vdW) heterostructures composed of different two-dimensional (2D) materials are at the center of many novel devices. To prepare vdW heterostructures which are of the highest quality and suitable for applications, chemical vapour deposition (CVD) can be used to grow the 2D materials directly on top of each other and thus build the vdW heterostructure in a bottom-up fashion. However, obtaining layers of uniform quality by precisely controlling their growth poses a severe challenge. The aim of our work is to understand the growth mechanisms and we have chosen MoS2 layers on highly oriented pyrolytic graphite (HOPG) as a model system for the MoS2-graphene interface. In our model system we observe, that MoS2 layers do not grow on the HOPG terraces but are more likely to grow at HOPG edges, one-dimensional defects, which obviously acts as growth seeds. In graphene however, step edges are absent and the ever-improving quality of commercially available CVD graphene yields less and less defects per unit area. While this is clearly an advantage for most devices, in the light of our findings it constitutes a major disadvantage for the bottom-up preparation of vdW heterostructures. To overcome this obstacle we artificially introduce defects into the HOPG surface by highly charged ion irradiation. In this way we induce an easily controllable number of quasi zero-dimensional defects before the chemical vapour deposition of MoS2 takes place. We show that this treatment results in MoS2 island growth on top HOPG terraces. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2018.05.031
  • 2018 • 140 Local Activities of Hydroxide and Water Determine the Operation of Silver-Based Oxygen Depolarized Cathodes
    Botz, A. and Clausmeyer, J. and Öhl, D. and Tarnev, T. and Franzen, D. and Turek, T. and Schuhmann, W.
    Angewandte Chemie - International Edition 57 12285-12289 (2018)
    Local ion activity changes in close proximity to the surface of an oxygen depolarized cathode (ODC) were measured by scanning electrochemical microscopy (SECM). While the operating ODC produces OH− ions and consumes O2 and H2O through the electrocatalytic oxygen reduction reaction (ORR), local changes in the activity of OH− ions and H2O are detected by means of a positioned Pt microelectrode serving as an SECM tip. Sensing at the Pt tip is based on the pH-dependent reduction of PtO and obviates the need for prior electrode modification steps. It can be used to evaluate the coordination numbers of OH− ions and H2O, and the method was exploited as a novel approach of catalyst activity assessment. We show that the electrochemical reaction on highly active catalysts can have a drastic influence on the reaction environment. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201807798
  • 2018 • 139 Making Ultrafast High-Capacity Anodes for Lithium-Ion Batteries via Antimony Doping of Nanosized Tin Oxide/Graphene Composites
    Zoller, F. and Peters, K. and Zehetmaier, P.M. and Zeller, P. and Döblinger, M. and Bein, T. and Sofer, Z. and Fattakhova-Rohlfing, D.
    Advanced Functional Materials 28 (2018)
    Tin oxide-based materials attract increasing attention as anodes in lithium-ion batteries due to their high theoretical capacity, low cost, and high abundance. Composites of such materials with a carbonaceous matrix such as graphene are particularly promising, as they can overcome the limitations of the individual materials. The fabrication of antimony-doped tin oxide (ATO)/graphene hybrid nanocomposites is described with high reversible capacity and superior rate performance using a microwave assisted in situ synthesis in tert-butyl alcohol. This reaction enables the growth of ultrasmall ATO nanoparticles with sizes below 3 nm on the surface of graphene, providing a composite anode material with a high electric conductivity and high structural stability. Antimony doping results in greatly increased lithium insertion rates of this conversion-type anode and an improved cycling stability, presumably due to the increased electrical conductivity. The uniform composites feature gravimetric capacity of 1226 mAh g−1 at the charging rate 1C and still a high capacity of 577 mAh g−1 at very high charging rates of up to 60C, as compared to 93 mAh g−1 at 60C for the undoped composite synthesized in a similar way. At the same time, the antimony-doped anodes demonstrate excellent stability with a capacity retention of 77% after 1000 cycles. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201706529
  • 2018 • 138 Molecular dynamics simulation of silicon ion implantation into diamond and subsequent annealing
    Fu, X. and Xu, Z. and He, Z. and Hartmaier, A. and Fang, F.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms (2018)
    Ion implantation is one of the best methods to manufacture silicon-vacancy (SiV) centers in diamond, which can be used as qubits. In this work, molecular dynamics (MD) simulation was conducted to analyze the damage evolution and distribution during the process of silicon ion implantation into bulk diamond and subsequent annealing. Tersoff-ZBL (Ziegler-Biersack-Littmark) potential was used to describe the atomic interaction. Identify Diamond Structure (IDS) and Wigner-Seitz defect analysis methods were used to calculate damages and vacancies. After 2393 K annealing, about 42.5% of ion induced IDS damages were recovered. During the temperature cooling down from 2393 K to 293 K, the movements of silicon atoms along the implantation direction were sensitive to the temperature variation, while vacancies were almost insensitive. MD simulation is helpful to illustrate the ion implant induced damages’ dynamic evolution and Si-V related defects, which can assist a deeper understanding of SiV center's manufacturing. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.nimb.2018.04.027
  • 2018 • 137 On the Ni-Ion release rate from surfaces of binary NiTi shape memory alloys
    Ševčíková, J. and Bártková, D. and Goldbergová, M. and Kuběnová, M. and Čermák, J. and Frenzel, J. and Weiser, A. and Dlouhý, A.
    Applied Surface Science 427 434-443 (2018)
    The study is focused on Ni-ion release rates from NiTi surfaces exposed in the cell culture media and human vascular endothelial cell (HUVEC) culture environments. The NiTi surface layers situated in the depth of 70 μm below a NiTi oxide scale are affected by interactions between the NiTi alloys and the bio-environments. The finding was proved with use of inductively coupled plasma mass spectrometry and electron microscopy experiments. As the exclusive factor controlling the Ni-ion release rates was not only thicknesses of the oxide scale, but also the passivation depth, which was two-fold larger. Our experimental data strongly suggested that some other factors, in addition to the Ni concentration in the oxide scale, admittedly hydrogen soaking deep below the oxide scale, must be taken into account in order to rationalize the concentrations of Ni-ions released into the bio-environments. The suggested role of hydrogen as the surface passivation agent is also in line with the fact that the Ni-ion release rates considerably decrease in NiTi samples that were annealed in controlled hydrogen atmospheres prior to bio-environmental exposures. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.08.235
  • 2018 • 136 Revising the Concept of Pore Hierarchy for Ionic Transport in Carbon Materials for Supercapacitors
    Borchardt, L. and Leistenschneider, D. and Haase, J. and Dvoyashkin, M.
    Advanced Energy Materials 8 (2018)
    Rapid motion of electrolyte ions is a crucial requirement to ensure the fast charging/discharging and the high power densities of supercapacitor devices. This motion is primarily determined by the pore size and connectivity of the used porous carbon electrodes. Here, the diffusion characteristics of each individual electrolyte component, that is, anion, cation, and solvent confined to model carbons with uniform and well-defined pore sizes are quantified. As a result, the contributions of micropores, mesopores, and hierarchical pore architectures to the overall transport of adsorbed mobile species are rationalized. Unexpectedly, it is observed that the presence of a network of mesopores, in addition to smaller micropores—the concept widely used in heterogeneous catalysis to promote diffusion of sorbates—does not necessarily enhance ionic transport in carbon materials. The observed phenomenon is explained by the stripping off the surrounding solvent shell from the electrolyte ions entering the micropores of the hierarchical material, and the resulting enrichment of solvent molecules preferably in the mesopores. It is believed that the presented findings serve to provide fundamental understanding of the mechanisms of electrolyte diffusion in carbon materials and depict a quantitative platform for the future designing of supercapacitor electrodes on a rational basis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/aenm.201800892
  • 2018 • 135 Solid electrolyte interphase: Can faster formation at lower potentials yield better performance?
    Antonopoulos, B.K. and Stock, C. and Maglia, F. and Hoster, H.E.
    Electrochimica Acta 269 331-339 (2018)
    To make a Lithium Ion Battery (LIB) reliably rechargeable over many cycles, its graphite-based negative electrode requires the solid electrolyte interphase (SEI) as a protection layer. The SEI is formed through chemical and particularly electrochemical side reactions of electrolyte components in the first charging cycle(s) after manufacturing of a LIB. The SEI ideally serves two purposes: (i) act as a sieve permeable to Li ions but not to other electrolyte components and (ii) passivate the electrode against further electrolyte decomposition. Core element of conventional SEI formation is a lengthy, low-current galvanostatic charging step, which due to its time consumption contributes heavily to cell manufacturing costs. Here, we report on some non-conventional SEI formation protocols for composite carbon electrodes, inspired by recent experimental findings at smooth model electrodes. Acknowledging that the SEI forms in two main steps, taking place in a high-potential and a low-potential region, respectively, we demonstrate that less time spent in the high-potential region not only makes the process faster but even yields SEIs with superior kinetic properties. We tentatively explain this via basic rules of thin film growth and the role of grain boundaries for ion transport. We also report on the positive influence of multi-frequency potential modulations applied between high-potential and low-potential formation. Given that any new cell chemistry in principle requires its own tailor-made formation process, technologic success of future LIB cells will benefit from a systematic, well-understood toolbox of formation protocols. This paper is meant as a first step, highlighting potentially low-hanging fruits, but also flagging the demand for further systematic studies on model systems and on commercially manufactured cells. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2018.03.007
  • 2018 • 134 Solvent-induced ion separation of a beryllium scorpionate complex
    Naglav, D. and Tobey, B. and Dzialkowski, K. and Bläser, D. and Wölper, C. and Jansen, G. and Schulz, S.
    Dalton Transactions 47 12511-12515 (2018)
    Spontaneous ion separation of the scorpionate beryllium complex, TpBeI 1 (Tp = 1-trispyrazolylborate), occurs upon treatment with THF, yielding [TpBe(thf)]I 2, which was characterized by heteronuclear NMR spectroscopy (1H, 9Be, 13C) and structurally characterized by single crystal X-ray diffraction. 2 represents a rare example of a structurally characterized monocationic beryllium complex, and to the best of our knowledge, the synthesis of 2 by a solvent-induced ion separation has previously only been observed in the reactions of beryllium dihalides with strong Lewis bases. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8dt01640b
  • 2018 • 133 Surface structure modification of single crystal graphite after slow, highly charged ion irradiation
    Alzaher, I. and Akcöltekin, S. and Ban-d'Etat, B. and Manil, B. and Dey, K.R. and Been, T. and Boduch, P. and Rothard, H. and Schleberger, M. and Lebius, H.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 420 23-26 (2018)
    Single crystal graphite was irradiated by slow, highly charged ions. The modification of the surface structure was studied by means of Low-Energy Electron Diffraction. The observed damage cross section increases with the potential energy, i.e. the charge state of the incident ion, at a constant kinetic energy. The potential energy is more efficient for the damage production than the kinetic energy by more than a factor of twenty. Comparison with earlier results hints to a strong link between early electron creation and later target atom rearrangement. With increasing ion fluence, the initially large-scale single crystal is first transformed into μm-sized crystals, before complete amorphisation takes place. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.nimb.2018.01.024
  • 2018 • 132 The role of radiative de-excitation in the neutralization process of highly charged ions interacting with a single layer of graphene
    Schwestka, J. and Wilhelm, R.A. and Gruber, E. and Heller, R. and Kozubek, R. and Schleberger, M. and Facsko, S. and Aumayr, F.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 422 63-67 (2018)
    X-ray emission of slow (&lt;1 a.u.) highly charged Argon and Xenon ions is measured for transmission through a freestanding single layer of graphene. To discriminate against X-ray emission originating from the graphene's support grid a coincidence technique is used. X-ray emission of 75 keV Ar17+ and Ar18+ ions with either one or two K-shell vacancies is recorded. Using a windowless Bruker XFlash detector allows us to measure additionally Ar KLL and KLM Auger electrons and determine the branching ratio of radiative vs. non-radiative decay of Ar K-shell holes. Furthermore, X-ray spectra for 100 keV Xe22+-Xe35+ ions are compared, showing a broad M-line peak for all cases, where M-shell vacancies are present. All these peaks are accompanied by emission lines at still higher energies indicating the presence of a hollow atom during X-ray decay. We report a linear shift of the main M-line peak to higher energies for increasing incident charge state, i.e. increasing number of M-shell holes. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.nimb.2018.02.022
  • 2017 • 131 A widely applicable tool for modeling precipitation processes
    Haderlein, M. and Güldenpfennig, A. and Segets, D. and Peukert, W.
    Computers and Chemical Engineering 98 197-208 (2017)
    This work presents a generalized tool for modeling precipitation processes for the parallel formation of multiple solid phases. A symmetric mixing model for T-mixers is presented which mimics the mixing process in a numerically highly efficient way. This model can easily be extended to other reactor types such as stirred tank reactors following the implementation given in this work. Modelling ion activities and ion complexation is strongly accelerated by the analytical formulation of the Jacobian of the corresponding system of equations. Solid formation processes are described via the numerically efficient Direct Quadrature Method of Moments (DQMOM) which is parallelized for treating multiple solid phases simultaneously. Expressions for agglomeration of multiple solid phases and for particle transfer between different mixer zones are given. Both the models of the individual processes and the entire precipitation tool are validated and tested in multiple scenarios proving the flexibility of the tool. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.compchemeng.2016.12.007
  • 2017 • 130 Constrained Ab Initio Thermodynamics: Transferring the Concept of Surface Pourbaix Diagrams in Electrocatalysis to Electrode Materials in Lithium-Ion Batteries
    Exner, K.S.
    ChemElectroChem 4 3231-3237 (2017)
    DFT-based ab initio Pourbaix diagrams represent a powerful tool to resolve the stable surface structure of an electrocatalyst under different environmental parameters such as the applied electrode potential and pH. Herein, a general approach for anode and cathode materials in lithium-ion batteries (LIBs) is presented that enables to transfer the concept of surface Pourbaix diagrams from electrocatalysis to electrode materials employed in LIBs. This novel approach is exemplified at the example of the (111) facet for a single-crystalline spinel lithium titanate (LTO) model electrode by combining constrained thermodynamics and density functional theory calculations. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201700754
  • 2017 • 129 Electric potential screening on metal targets submitted to reactive sputtering
    Corbella, C. and Marcak, A. and Von Keudell, A. and De Los Arcos, T.
    Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films 35 (2017)
    A very thin oxide layer is formed on top of metal surfaces that are submitted to reactive magnetron sputtering in an oxygen atmosphere. Having a few atomic monolayers thickness (1-5 nm), this oxide top layer shows properties of an electric insulator that retards the flux of incident ions. Here, the authors show that this layer can be modeled as a parallel combination of capacitance and resistance. The basic sputtering processes on the oxide layer have been mimicked by means of particle beam experiments in an ultra-high-vacuum reactor. Hence, quantified beams of argon ions and oxygen molecules have been sent to aluminum, chromium, titanium, and tantalum targets. The formation and characteristics of the oxide top layer have been monitored in situ by means of an electrostatic collector and quartz crystal microbalance. The charge build-up at the oxide layer interfaces generates a screening potential of the order of 1-10 V, which shows linear correlation with the total current through the target. The secondary electron yields of the oxides show the expected behavior with ion energies (500-1500 eV), thereby showing that this parameter is not significantly distorted by the screening potential. Charging kinetics of the oxide layer is investigated by means of time-resolved current measurements during bombardment with square-wave modulated ion fluxes. Finally, the dependence of secondary electron emission with surface oxidation state and surface charging issues in pulsed plasmas are studied within the context of the Berg's model. © 2016 American Vacuum Society.
    view abstractdoi: 10.1116/1.4972566
  • 2017 • 128 Focused ion beam supported growth of monocrystalline wurtzite InAs nanowires grown by molecular beam epitaxy
    Scholz, S. and Schott, R. and Labud, P.A. and Somsen, C. and Reuter, D. and Ludwig, Ar. and Wieck, A.D.
    Journal of Crystal Growth 470 46-50 (2017)
    We investigate monocrystalline InAs nanowires (NWs) which are grown catalyst assisted by molecular beam epitaxy (MBE) and create the catalyst by focused ion beam (FIB) implanted Au spots. With this combination of methods an aspect ratio, i.e. the length to width ratio, of the grown NWs up to 300 was achieved. To control the morphology and crystalline structure of the NWs, the growth parameters like temperature, flux ratios and implantation fluence are varied and optimized. Furthermore, the influence of the used molecular arsenic species, in particular the As2 to As4 ratio, is investigated and adjusted. In addition to the high aspect ratio, this optimization results in the growth of monocrystalline InAs NWs with a negligible number of stacking faults. Single NWs were placed site-controlled by FIB implantation, which supplements the working field of area growth. © 2017
    view abstractdoi: 10.1016/j.jcrysgro.2017.04.013
  • 2017 • 127 Identification of Intrahelical Bifurcated H-Bonds as a New Type of Gate in K+ Channels
    Rauh, O. and Urban, M. and Henkes, L.M. and Winterstein, T. and Greiner, T. and Van Etten, J.L. and Moroni, A. and Kast, S.M. and Thiel, G. and Schroeder, I.
    Journal of the American Chemical Society 139 7494-7503 (2017)
    Gating of ion channels is based on structural transitions between open and closed states. To uncover the chemical basis of individual gates, we performed a comparative experimental and computational analysis between two K+ channels, KcvS and KcvNTS. These small viral encoded K+ channel proteins, with a monomer size of only 82 amino acids, resemble the pore module of all complex K+ channels in terms of structure and function. Even though both proteins share about 90% amino acid sequence identity, they exhibit different open probabilities with ca. 90% in KcvNTS and 40% in KcvS. Single channel analysis, mutational studies and molecular dynamics simulations show that the difference in open probability is caused by one long closed state in KcvS. This state is structurally created in the tetrameric channel by a transient, Ser mediated, intrahelical hydrogen bond. The resulting kink in the inner transmembrane domain swings the aromatic rings from downstream Phes in the cavity of the channel, which blocks ion flux. The frequent occurrence of Ser or Thr based helical kinks in membrane proteins suggests that a similar mechanism could also occur in the gating of other ion channels. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/jacs.7b01158
  • 2017 • 126 Improved CO2 Electroreduction Performance on Plasma-Activated Cu Catalysts via Electrolyte Design: Halide Effect
    Gao, D. and Scholten, F. and Roldan Cuenya, B.
    ACS Catalysis 7 5112-5120 (2017)
    As a sustainable pathway for energy storage and to close the carbon cycle, CO2 electroreduction has recently gained significant interest. We report here the role of the electrolyte, in particular of halide ions, on CO2 electroreduction over plasma-oxidized polycrystalline Cu foils. It was observed that halide ions such as I- can induce significant nanostructuring of the oxidized Cu surface, even at open circuit potential, including the formation of Cu crystals with well-defined shapes. Furthermore, the presence of Cl-, Br-, and I- was found to lower the overpotential and to increase the CO2 electroreduction rate on plasma-activated preoxidized Cu catalyst in the order Cl- &lt; Br- &lt; I-, without sacrificing their intrinsically high C2-C3 product selectivity (∼65% total Faradaic efficiency at -1.0 V vs RHE). This enhancement in catalytic performance is mainly attributed to the specific adsorption of halides with a higher coverage on our oxidized Cu surface during the reaction, which have been previously reported to facilitate the formation and stabilization of the carboxyl (∗COOH) intermediate by partial charge donation from the halide ions to CO2. (Graph Presented). © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.7b01416
  • 2017 • 125 Ion-induced interdiffusion of surface GaN quantum dots
    Rothfuchs, C. and Semond, F. and Portail, M. and Tottereau, O. and Courville, A. and Wieck, A.D. and Ludwig, Ar.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 409 107-110 (2017)
    In the flourishing fields of quantum technology gallium nitride (GaN) quantum dots (QDs) have great appeal by providing high stability and room-temperature operation. Here, we report on the ion implantation of surface GaN QDs grown in the hexagonal crystal structure. An uncapped sample (S1) and two samples capped by 8 ML (S2) and 16 ML (S3) of AlN are subjected to a 100 keV gallium (S1, S2) and a 210 keV erbium (S3) ion beam. The fluence ranged from 5×1010 cm−2 to 1×1015 cm−2 (S1, S2) and from 5×1010 cm−2 to 5×1013 cm−2 (S3). QD characterization is performed by cathodoluminescence measurements at 77 K and atomic force microscopy and scanning electron microscopy. Strong interdiffusion processes upon ion impact at the interfaces are evidenced leading besides other effects to a quenching of the quantum confined Stark effect. Moreover, a model for the QD morphology based on a fluence-dependent diffusion coefficient is developed. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.nimb.2017.04.036
  • 2017 • 124 Kinetic investigation of the ion angular distribution in capacitive radio-frequency plasmas
    Shihab, M. and Mussenbrock, T.
    Physics of Plasmas 24 (2017)
    One of the key parameters in the context of plasma assisted processing in semiconductor fabrication using capacitive radio-frequency plasmas is the ion flux distribution at the substrate. Whereas the ion energy distribution function determines the etching rate and selectivity, the ion angular distribution controls the etching profile. In this contribution, we reveal the effect of the ion flux and the sheath potential on the ion angular distribution and the direct ion heat flux at the bottom of etching profiles in geometrically symmetric plasma reactors. The ion angular distribution and the direct ion heat flux are calculated as a function of the sheath potential, the driving frequency, and the phase shift between the two distinct harmonics of the driving voltage of dual frequency discharges. For this task, self-consistent particle-in-cell simulations subject to Monte Carlo collision are carried out. The results from particle-in-cell simulations which are computationally very expensive are compared and verified with those from the novel ensemble-in-spacetime model. It is confirmed that increasing the voltage of the high-frequency component, the high-frequency component, and/or make a phase shift of π/2 between the dual frequency, narrow the ion angular distribution and increase the direct ion heat flux to the etching profile bottom. In all simulation cases, a correlation between the narrowing of the ion angular distribution and the increase of the sheath potential and the sheath ion flux is found. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4994754
  • 2017 • 123 Molecular dynamics study of stability and disintegration of long rod-like micelles: Dodecyltrimethylammonium chloride in solutions of hydroxybenzoates
    Gujt, J. and Bešter-Rogač, M. and Spohr, E.
    Journal of Molecular Liquids 228 150-159 (2017)
    Recently it was found out that different positions of the hydroxylic group on hydroxybenzoate anions (HB) crucially affect the thermodynamics of the self-organization of the cationic surfactant dodecyltrimethylammonium chloride (DTAC) and also the structure of resulting aggregates. In our previous work, the properties of stable long cylindrical DTAC micelles in the presence of NaHB at 1:1 DTAC/NaHB molar ratio in aqueous solutions were investigated by atomistic molecular dynamics simulations. In the present work, we first study the decay of cylindrical DTAC micelles in water without added salt and then extend our research to systems with low NaHB concentrations (DTAC/NaHB molar ratios of 4:1 and 2:1) in order to approach the real experimental conditions more closely. The geometry and structural properties of DTAC micelles in water are investigated, and also the decomposition of long cylindrical micelles and the solvent accessible surface area of micelles is discussed. We observe that the initial DTAC micelle without NaHB quickly disintegrates into smaller stable spherical micelles. At the 2:1 DTAC/NaHB molar ratio we find all initial DTAC micelles to remain stable; however, their geometry deviates significantly from initial cylindrical one. Furthermore, it is observed that o-HB induces a more ordered internal structure of the micelle, and is more strongly oriented than the other two isomers, which agrees well with the experiments and observations reported in our previous work. When the NaHB concentration is decreased to 4:1 DTAC/NaHB molar ratio, an initial DTAC micelle disintegrates forming smaller aggregates of spherical or elongated shapes regardless of the nature of the HB isomer present. The microscopic structure of the resultant micelles is very similar to the structure observed at higher NaHB concentration, however, the effect of HB ions is smaller. It was also observed that the micelle remains stable longer in the presence of o-HB than in the presence of the other two isomers. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.molliq.2016.09.067
  • 2017 • 122 Nanoscale x-ray investigation of magnetic metallofullerene peapods
    Fritz, F. and Westerström, R. and Kostanyan, A. and Schlesier, C. and Dreiser, J. and Watts, B. and Houben, L. and Luysberg, M. and Avdoshenko, S.M. and Popov, A.A. and Schneider, C.M. and Meyer, C.
    Nanotechnology 28 (2017)
    Endohedral lanthanide ions packed inside carbon nanotubes (CNTs) in a one-dimensional assembly have been studied with a combination of high resolution transmission electron microscopy (HRTEM), scanning transmission x-ray microscopy (STXM), and x-ray magnetic circular dichroism (XMCD). By correlating HRTEM and STXM images we show that structures down to 30 nm are resolved with chemical contrast and record x-ray absorption spectra from endohedral lanthanide ions embedded in individual nanoscale CNT bundles. XMCD measurements of an Er3N@C80 bulk sample and a macroscopic assembly of filled CNTs indicate that the magnetic properties of the endohedral Er3+ ions are unchanged when encapsulated in CNTs. This study demonstrates the feasibility of local magnetic x-ray characterisation of low concentrations of lanthanide ions embedded in molecular nanostructures. © 2017 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/aa8b4c
  • 2017 • 121 New insights into methane-oxygen ion chemistry
    Alquaity, A.B.S. and Chen, B. and Han, J. and Selim, H. and Belhi, M. and Karakaya, Y. and Kasper, T. and Sarathy, S.M. and Bisetti, F. and Farooq, A.
    Proceedings of the Combustion Institute 36 1213-1221 (2017)
    External electric fields may reduce emissions and improve combustion efficiency by active control of combustion processes. In-depth, quantitative understanding of ion chemistry in flames enables predictive models to describe the effect of external electric fields on combustion plasma. This study presents detailed cation profile measurements in low-pressure, burner-stabilized, methane/oxygen/argon flames. A quadrupole molecular beam mass spectrometer (MBMS) coupled to a low-pressure (P =30Torr) combustion chamber was utilized to measure ion signals as a function of height above the burner. Lean, stoichiometric and rich flames were examined to evaluate the dependence of ion chemistry on flame stoichiometry. Additionally, for the first time, cataloging of flame cations is performed using a high mass resolution time-of-flight mass spectrometer (TOF-MS) to distinguish ions with the same nominal mass. In the lean and stoichiometric flames, the dominant ions were H3O+, CH3O2 +, C2H7O+, C2H3O+ and CH5O+, whereas large signals were measured for H3O+, C3H3 + and C2H3O+ in the rich flame. The spatial distribution of cations was compared with results from numerical simulations constrained by thermocouple-measured flame temperatures. Across all flames, the predicted H3O+ decay rate was noticeably faster than observed experimentally. Sensitivity analysis showed that the mole fraction of H3O+ is most sensitive to the rate of chemi-ionization CH+O↔CHO+ +E-. To our knowledge, this work represents the first detailed measurements of positive ions in canonical low-pressure methane flames. © 2016.
    view abstractdoi: 10.1016/j.proci.2016.05.053
  • 2017 • 120 Parasitic Reactions in Nanosized Silicon Anodes for Lithium-Ion Batteries
    Gao, H. and Xiao, L. and Plümel, I. and Xu, G.-L. and Ren, Y. and Zuo, X. and Liu, Y. and Schulz, C. and Wiggers, H. and Amine, K. and Chen, Z.
    Nano Letters 17 1512-1519 (2017)
    When designing nano-Si electrodes for lithium-ion batteries, the detrimental effect of the c-Li15Si4 phase formed upon full lithiation is often a concern. In this study, Si nanoparticles with controlled particle sizes and morphology were synthesized, and parasitic reactions of the metastable c-Li15Si4 phase with the nonaqueous electrolyte was investigated. The use of smaller Si nanoparticles (∼60 nm) and the addition of fluoroethylene carbonate additive played decisive roles in the parasitic reactions such that the c-Li15Si4 phase could disappear at the end of lithiation. This suppression of c-Li15Si4 improved the cycle life of the nano-Si electrodes but with a little loss of specific capacity. In addition, the characteristic c-Li15Si4 peak in the differential capacity (dQ/dV) plots can be used as an early-stage indicator of cell capacity fade during cycling. Our findings can contribute to the design guidelines of Si electrodes and allow us to quantify another factor to the performance of the Si electrodes. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.6b04551
  • 2017 • 119 Peptide-Based Probes with an Artificial Anion-Binding Motif for Direct Fluorescence “Switch-On” Detection of Nucleic Acid in Cells
    Maity, D. and Matković, M. and Li, S. and Ehlers, M. and Wu, J. and Piantanida, I. and Schmuck, C.
    Chemistry - A European Journal 23 17356-17362 (2017)
    This work reports two new peptide-based fluorescence probes (1 and 2) for the detection of ds-DNA at physiological pH. Probes 1 and 2 contain a fluorophore, either amino-naphthalimide or diethyl-aminocoumarin, respectively, and two identical peptide arms each equipped with a guanidiniocarbonylpyrrole (GCP) anion-binding motif. These probes show “switch-on” fluorescence response upon binding to ds-DNA, whereby they can differentiate between various types of polynucleotides. For instance, they exhibit more pronounced fluorescence response for AT-rich polynucleotides than GC-rich polynucleotides, and both give only negligible response to ds-RNA. The fluorimetric response of 1 is proportional to the AT-basepair content in DNA, whereas the fluorescence of 2 is sensitive to the secondary structure of the polynucleotide. Fluorescence experiments, thermal melting experiments and circular dichroism studies suggest that 1 interacts with ds-DNA in a combined intercalation and minor groove binding, whereas 2 interacts mainly with the outer surface of DNA/RNA. As 1 and 2 have a very low cytotoxicity, 1 can be applied for the imaging of nuclear DNA in cells. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201703813
  • 2017 • 118 Plasma-Activated Copper Nanocube Catalysts for Efficient Carbon Dioxide Electroreduction to Hydrocarbons and Alcohols
    Gao, D. and Zegkinoglou, I. and Divins, N.J. and Scholten, F. and Sinev, I. and Grosse, P. and Roldan Cuenya, B.
    ACS Nano 11 4825-4831 (2017)
    Carbon dioxide electroreduction to chemicals and fuels powered by renewable energy sources is considered a promising path to address climate change and energy storage needs. We have developed highly active and selective copper (Cu) nanocube catalysts with tunable Cu(100) facet and oxygen/chlorine ion content by low-pressure plasma pretreatments. These catalysts display lower overpotentials and higher ethylene, ethanol, and n-propanol selectivity, resulting in a maximum Faradaic efficiency (FE) of ∼73% for C2 and C3 products. Scanning electron microscopy and energy-dispersive X-ray spectroscopy in combination with quasi-in situ X-ray photoelectron spectroscopy revealed that the catalyst shape, ion content, and ion stability under electrochemical reaction conditions can be systematically tuned through plasma treatments. Our results demonstrate that the presence of oxygen species in surface and subsurface regions of the nanocube catalysts is key for achieving high activity and hydrocarbon/alcohol selectivity, even more important than the presence of Cu(100) facets. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.7b01257
  • 2017 • 117 Polymer conformations in ionic microgels in the presence of salt: Theoretical and mesoscale simulation results
    Kobayashi, H. and Halver, R. and Sutmann, G. and Winkler, R.G.
    Polymers 9 (2017)
    We investigate the conformational properties of polymers in ionic microgels in the presence of salt ions by molecular dynamics simulations and analytical theory. A microgel particle consists of coarse-grained linear polymers, which are tetra-functionally crosslinked. Counterions and salt ions are taken into account explicitly, and charge-charge interactions are described by the Coulomb potential. By varying the charge interaction strength and salt concentration, we characterize the swelling of the polyelectrolytes and the charge distribution. In particular, we determine the amount of trapped mobile charges inside the microgel and the Debye screening length. Moreover, we analyze the polymer extension theoretically in terms of the tension blob model taking into account counterions and salt ions implicitly by the Debye-Hückel model. Our studies reveal a strong dependence of the amount of ions absorbed in the interior of the microgel on the electrostatic interaction strength, which is related to the degree of the gel swelling. This implies a dependence of the inverse Debye screening length k on the ion concentration; we find a power-law increase of k with the Coulomb interaction strength with the exponent 3/5 for a salt-free microgel and an exponent 1/2 for moderate salt concentrations. Additionally, the radial dependence of polymer conformations and ion distributions is addressed. © 2017 by the authors.
    view abstractdoi: 10.3390/polym9010015
  • 2017 • 116 Proton-Transfer-Driven Water Exchange Mechanism in the Na+ Solvation Shell
    Hellström, M. and Behler, J.
    Journal of Physical Chemistry B 121 4184-4190 (2017)
    Ligand exchange plays an important role for organic and inorganic chemical reactions. We demonstrate the existence of a novel water exchange mechanism, the "proton transfer pathway" (PTP), around Na+(aq) in basic (high pH) solution, using reactive molecular dynamics simulations employing a high-dimensional neural network potential. An aqua ligand in the first solvation (hydration) shell around a sodium ion is only very weakly acidic, but if a hydroxide ion is present in the second solvation shell, thermal fluctuations can cause the aqua ligand to transfer a proton to the neighboring OH-, resulting in a transient direct-contact ion pair, Na+-OH-, which is only weakly bound and easily dissociates. The extent to which water exchange events follow the PTP is pH-dependent: in dilute NaOH(aq) solutions, only very few exchanges occur, whereas in saturated NaOH(aq) solutions up to a third of water self-exchange events are induced by proton transfer. The principles and results outlined here are expected to be relevant for chemical synthesis involving bases and alkali metal cations. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcb.7b01490
  • 2017 • 115 Prussian Blue Analogues: A Versatile Framework for Solid-Contact Ion-Selective Electrodes with Tunable Potentials
    Klink, S. and Ishige, Y. and Schuhmann, W.
    ChemElectroChem 4 490-494 (2017)
    The development of solid-contact ion-selective electrodes (SC-ISEs) (e.g. for point-of-care sensors) requires simple inner reference electrodes (iREs) with predictable and reproducible potentials. Intercalation compounds fulfill these requirements, as they respond to target ions present in the ion-selective membrane. Their applicability, however, is limited by the availability of intercalation frameworks capable to intercalate the target ion of interest. We report that Prussian Blue analogues (PBAs) can serve as versatile iREs for a range of target ions of clinical interest, such as Na+, K+, or Ca2+. Combining target-ion intercalated PBAs with ion-selective membranes results in a family of all-solid SC-ISEs, which are capable as ISEs with an inner filling, yet cheap and suitable for mass-production. The SC-ISEs′ standard potential is predictable and can be tuned by altering the PBAs′ redox-active transition metal or by changing its state of charge. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201700091
  • 2017 • 114 Retention of the Zn−Zn bond in [Ge9Zn−ZnGe9]6− and Formation of [(Ge9Zn)−(Ge9)−(ZnGe9)]8− and Polymeric 1∞ [−(Ge9Zn)2−−]1
    Mayer, K. and Jantke, L.-A. and Schulz, S. and Fässler, T.F.
    Angewandte Chemie - International Edition 56 2350-2355 (2017)
    Reactions of ZnI 2L2 (where L=[HC(PPh2NPh)]−) with solutions of the Zintl phase K4Ge9 in liquid ammonia lead to retention of the Zn−Zn bond and formation of the anion [(η4-Ge9)Zn−Zn(η4-Ge9)]6−, representing the first complex with a Zn−Zn unit carrying two cluster entities. The trimeric anion [(η4-Ge9)Zn{μ2(η1:η1Ge9)}Zn(η4-Ge9)]8− forms as a side product, indicating that oxidation reactions also take place. The reaction of Zn2Cp*2 (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) with K4Ge9 in ethylenediamine yielded the linear polymeric unit (Formula presented.) {[Zn[μ2(η4:η1Ge9)]}2− with the first head-to-tail arrangement of ten-atom closo-clusters. All anions were obtained and structurally characterized as [A(2.2.2-crypt)]+ salts (A=K, Rb). Copious computational analyses at a DFT-PBE0/def2-TZVPP/PCM level of theory confirm the experimental structures and support the stability of the two hypothetical ten vertex cluster fragments closo-[Ge9Zn]2− and (paramagnetic) [Ge9Zn]3−. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201610831
  • 2017 • 113 Retention of the Zn−Zn bond in [Ge9Zn−ZnGe9]6−and Formation of [(Ge9Zn)−(Ge9)−(ZnGe9)]8−and Polymeric 1∞ [−(Ge9Zn)2−−]1
    Mayer, K. and Jantke, L.-A. and Schulz, S. and Fässler, T.F.
    Angewandte Chemie - International Edition 56 2350-2355 (2017)
    Reactions of ZnI2L2(where L=[HC(PPh2NPh)]−) with solutions of the Zintl phase K4Ge9in liquid ammonia lead to retention of the Zn−Zn bond and formation of the anion [(η4-Ge9)Zn−Zn(η4-Ge9)]6−, representing the first complex with a Zn−Zn unit carrying two cluster entities. The trimeric anion [(η4-Ge9)Zn{μ2(η1:η1Ge9)}Zn(η4-Ge9)]8−forms as a side product, indicating that oxidation reactions also take place. The reaction of Zn2Cp*2(Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) with K4Ge9in ethylenediamine yielded the linear polymeric unit (Formula presented.) {[Zn[μ2(η4:η1Ge9)]}2−with the first head-to-tail arrangement of ten-atom closo-clusters. All anions were obtained and structurally characterized as [A(2.2.2-crypt)]+salts (A=K, Rb). Copious computational analyses at a DFT-PBE0/def2-TZVPP/PCM level of theory confirm the experimental structures and support the stability of the two hypothetical ten vertex cluster fragments closo-[Ge9Zn]2−and (paramagnetic) [Ge9Zn]3−. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201610831
  • 2017 • 112 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 • 111 Room-temperature electron spin dynamics of Ce3+ ions in a YAG crystal
    Liang, P. and Hu, R.R. and Chen, C. and Belykh, V.V. and Jia, T.Q. and Sun, Z.R. and Feng, D.H. and Yakovlev, D.R. and Bayer, M.
    Applied Physics Letters 110 (2017)
    Circularly polarized optical excitation generates electron spin polarization in the lowest 5d state of rare-earth Ce3+ ions in a YAG crystal. The 5d electron spin dynamics is investigated in transverse and longitudinal magnetic fields by time-resolved pump-probe Faraday rotation. Long lived electron spin coherence with a dephasing time of 2.5 ns is found at room temperature. In a transverse magnetic field of 1 T, the electron spin coherence shows a distinct beating-like amplitude modulation due to several slightly different Larmor frequencies corresponding to different electron g factors of magnetically inequivalent positions of the Ce3+ ions in the crystal lattice. Hyperfine coupling between the 5d electron of Ce3+ ions and environmental nuclear spins dominates the spin relaxation, which can be efficiently suppressed by a longitudinal magnetic field as small as 10 mT. The dependence of electron spin relaxation on both the transverse and longitudinal magnetic fields agrees well with the one predicted theoretically for the hyperfine coupling mechanism. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4984232
  • 2017 • 110 Size Quenching during Laser Synthesis of Colloids Happens Already in the Vapor Phase of the Cavitation Bubble
    Letzel, A. and Gökce, B. and Wagener, P. and Ibrahimkutty, S. and Menzel, A. and Plech, A. and Barcikowski, S.
    Journal of Physical Chemistry C 121 5356-5365 (2017)
    Although nanoparticle synthesis by pulsed laser ablation in liquids (PLAL) is gaining wide applicability, the mechanism of particle formation, in particular size-quenching effects by dissolved anions, is not fully understood yet. It is well-known that the size of small primary particles (d ≤ 10 nm), secondary particles (spherical particles d > 10 nm), and agglomerates observed ex situ is effectively reduced by the addition of small amounts of monovalent electrolyte to the liquid prior to laser ablation. In this study, we focus on the particle formation and evolution inside the vapor filled cavitation bubble. This vapor phase is enriched with ions from the afore added electrolyte. By probing the cavitation bubbles' interior by means of small-angle X-ray scattering (SAXS), we are able to examine whether the size quenching reaction between nanoparticles and ions starts already during cavitation bubble confinement or if these reactions are subjected to the liquid phase. We find that particle size quenching occurs already within the first bubble oscillation (approximately 100 μs after laser impact), still inside the vapor phase. Thereby we demonstrate that nanoparticle-ion interactions during PLAL are in fact a gas phase phenomenon. These interactions include size reduction of both primary and secondary particles and a decreased abundance of the latter as shown by in situ SAXS and confirmed by ex situ particle analysis (e.g., static SAXS and TEM). (Figure Presented). © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.6b12554
  • 2017 • 109 Solid electrolyte interphase (SEI) at TiO2 electrodes in li-ion batteries: Defining apparent and effective SEI based on evidence from X-ay photoemission spectroscopy and scanning electrochemical microscopy
    Ventosa, E. and Madej, E. and Zampardi, G. and Mei, B. and Weide, P. and Antoni, H. and La Mantia, F. and Muhler, M. and Schuhmann, W.
    ACS Applied Materials and Interfaces 9 3123-3130 (2017)
    The high (de)lithiation potential of TiO2 (ca. 1.7 V vs Li/ Li+ in 1 M Li+) decreases the voltage and, thus, the energy density of a corresponding Li-ion battery. On the other hand, it offers several advantages such as the (de)lithiation potential far from lithium deposition or absence of a solid electrolyte interphase (SEI). The latter is currently under controversial debate as several studies reported the presence of a SEI when operating TiO2 electrodes at potentials above 1.0 V vs Li/Li+. We investigate the formation of a SEI at anatase TiO2 electrodes by means of X-ray photoemission spectroscopy (XPS) and scanning electrochemical microscopy (SECM). The investigations were performed in different potential ranges, namely, during storage (without external polarization), between 3.0-2.0 V and 3.0-1.0 V vs Li/Li+, respectively. No SEI is formed when a completely dried and residues-free TiO2 electrode is cycled between 3.0 and 2.0 V vs Li/Li+. A SEI is detected by XPS in the case of samples stored for 6 weeks or cycled between 3.0 and 1.0 V vs Li/Li+. With use of SECM, it is verified that this SEI does not possess the electrically insulating character as expected for a "classic" SEI. Therefore, we propose the term apparent SEI for TiO2 electrodes to differentiate it from the protecting and ef fective SEI formed at graphite electrodes. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b13306
  • 2017 • 108 The effect of realistic heavy particle induced secondary electron emission coefficients on the electron power absorption dynamics in single- and dual-frequency capacitively coupled plasmas
    Daksha, M. and Derzsi, A. and Wilczek, S. and Trieschmann, J. and Mussenbrock, T. and Awakowicz, P. and Donkó, Z. and Schulze, J.
    Plasma Sources Science and Technology 26 (2017)
    doi: 10.1088/1361-6595/aa7c88
  • 2016 • 107 Altering the luminescence properties of self-assembled quantum dots in GaAs by focused ion beam implantation
    Rothfuchs, C. and Kukharchyk, N. and Greff, M.K. and Wieck, A.D. and Ludwig, Ar.
    Applied Physics B: Lasers and Optics 122 (2016)
    Using quantum dots (QDs) as single-photon sources draws the attention in many quantum communication technologies. One pathway towards manufacturing single-photon sources is focused ion beam (FIB) implantation in molecular beam epitaxy-grown QD samples to disable all QDs around an intentional one for single photoluminescence (PL) emission. In this paper, we investigate the lattice disorders in the vicinity of InAs/GaAs QDs introduced by FIB implantation of gallium and indium ions. For high fluences, we achieve total elimination of the QDs photoluminescence. The impact of the different ion species and fluences is studied by low-temperature PL measurements. Furthermore, we deduce a simple model based on the trap-assisted recombination for the description of the degradation of the PL emission. It allows the determination of the fluences at which the PL emission is suppressed. Moreover, we identify the implantation-induced non-radiative defects by temperature-dependent PL measurements. © 2016, Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00340-015-6305-8
  • 2016 • 106 Capillary pore membranes with grafted diblock copolymers showing reversibly changing ultrafiltration properties with independent response to ions and temperature
    Gajda, M. and Ulbricht, M.
    Journal of Membrane Science 514 510-517 (2016)
    Track-etched polyethylene terephthalate membranes with a pore size of 110 nm have been modified by a grafted diblock copolymer structure in order to obtain dual-responsive ultrafiltration membranes. The temperature-responsive poly-N-isopropylacrylamide (PNIPAAm) and the ion-responsive poly-N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium betaine (PSPE) were grafted from the pore walls by sequential surface-initiated atom transfer radical polymerization. To achieve a well controlled pore functionalization, the polymerization rate had been adjusted to a very slow chain growth. A successful grafting of PSPE as first block and of PNIPAAm as second block could be demonstrated. To study the temperature and ion responsivity, hydraulic permeability and dextran diffusion experiments at 25 °C and 40 °C with different salt solutions had been carried out. It could be shown that such membranes can change their barrier pore size from a more open to a more closed state in dependency of temperature as well as kind of ions and their concentration in the feed. The grafted layer thickness showed a particularly strong increase in the presence of KClO4. Like expected for a well defined polymer brush, an expanded or collapsed state for each of the individual blocks could be obtained. In presence of KClO4 at 25 °C both blocks are expanded and the pores are in a more closed state. If one of these stimuli is changed, for example when temperature is increased to 40 °C or ions are removed, the block copolymer brushes collapse partially what leads to more open pores. However, if both stimuli are applied together, i.e. if temperature is 40 °C and no ions are in solution, diblock copolymers collapse fully what leads to fully opened pores. It had also been demonstrated that this dual responsivity and the magnitude of the effects depend very strongly on the absolute degree of grafting and the ratio between the two different responsive polymer blocks. Furthermore, the ability of changing effective membrane barrier pore size by ions and temperature has been investigated in more detail by dextran diffusion experiments, and very pronounced and reversible changes of molecular sieving curve and molecular weight cut-off could be obtained. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2016.05.001
  • 2016 • 105 Concentration-Dependent Proton Transfer Mechanisms in Aqueous NaOH Solutions: From Acceptor-Driven to Donor-Driven and Back
    Hellström, M. and Behler, J.
    Journal of Physical Chemistry Letters 7 3302-3306 (2016)
    Proton transfer processes play an important role in many fields of chemistry. In dilute basic aqueous solutions, proton transfer from water molecules to hydroxide ions is aided by "presolvation", i.e., thermal fluctuations that modify the hydrogen-bonding environment around the proton-receiving OH- ion to become more similar to that of a neutral H2O molecule. In particular at high concentrations, however, the underlying mechanisms and especially the role of the counterions are little understood. As a prototypical case, we investigate aqueous NaOH solutions using molecular dynamics simulations employing a reactive high-dimensional neural-network potential constructed from density functional theory reference data. We find that with increasing concentration the predominant proton transfer mechanism changes from being "acceptor-driven", i.e., governed by the presolvation of OH-, to "donor-driven", i.e., governed by the presolvation of H2O, and back to acceptor-driven near the room-temperature solubility limit of 19 mol/L, which corresponds to an extremely solvent-deficient system containing only about one H2O molecule per ion. Specifically, we identify concentration ranges where the proton transfer rate is mostly affected by OH- losing an accepted hydrogen bond, OH- forming a donated hydrogen bond, H2O forming an accepted hydrogen bond, or H2O losing a coordinated Na+. Presolvation also manifests itself in the shortening of the Na+-OH2 distances, in that the Na+ "pushes" one of the H2O protons away. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpclett.6b01448
  • 2016 • 104 Controlling the Photocorrosion of Zinc Sulfide Nanoparticles in Water by Doping with Chloride and Cobalt Ions
    Weide, P. and Schulz, K. and Kaluza, S. and Rohe, M. and Beranek, R. and Muhler, M.
    Langmuir 32 12641-12649 (2016)
    Photodegradation under UV light irradiation is a major drawback in photocatalytic applications of sulfide semiconductors. ZnS nanoparticles were doped with very low amounts of chloride or cobalt ions in the ppm range and codoped with chloride and cobalt ions during their synthesis by precipitation in aqueous solution followed by calcination. The high-temperature wurtzite phase annealed at 800 °C had a high susceptibility to UV irradiation in water, while the low-temperature zincblende phase annealed at 400 °C was found to be stable. Chlorine doping increased the rate of photocorrosion in water, whereas cobalt doping led to a stabilization of the ZnS nanoparticles. Based on photochemical and spectroscopic investigations applying UV/vis, X-ray photoelectron, and photoluminescence spectroscopy, the increased susceptibility of Cl-doped ZnS is ascribed to a higher number of surface point defects, whereas the stabilization by Co2+ is caused by additional recombination pathways for the charge carriers in the bulk, thus avoiding photocorrosion processes at the surface. Additional doping of Cl-doped ZnS with cobalt ions was found to counteract the detrimental effect of the chloride ions efficiently. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.6b03385
  • 2016 • 103 Current density distribution in cylindrical Li-Ion cells during impedance measurements
    Osswald, P.J. and Erhard, S.V. and Noel, A. and Keil, P. and Kindermann, F.M. and Hoster, H. and Jossen, A.
    Journal of Power Sources 314 93-101 (2016)
    In this work, modified commercial cylindrical lithium-ion cells with multiple separate current tabs are used to analyze the influence of tab pattern, frequency and temperature on electrochemical impedance spectroscopy. In a first step, the effect of different current tab arrangements on the impedance spectra is analyzed and possible electrochemical causes are discussed. In a second step, one terminal is used to apply a sinusoidal current while the other terminals are used to monitor the local potential distribution at different positions along the electrodes of the cell. It is observed that the characteristic decay of the voltage amplitude along the electrode changes non-linearly with frequency, where high-frequent currents experience a stronger attenuation along the current collector than low-frequent currents. In further experiments, the decay characteristic is controlled by the cell temperature, driven by the increasing resistance of the current collector and the enhanced kinetic and transport properties of the active material and electrolyte. Measurements indicate that the ac current distribution depends strongly on the frequency and the temperature. In this context, the challenges for electrochemical impedance spectroscopy as cell diagnostic technique for commercial cells are discussed. © 2016 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jpowsour.2016.02.070
  • 2016 • 102 Designing molecular complexes using free-energy derivatives from liquid-state integral equation theory
    Mrugalla, F. and Kast, S.M.
    Journal of Physics Condensed Matter 28 (2016)
    Complex formation between molecules in solution is the key process by which molecular interactions are translated into functional systems. These processes are governed by the binding or free energy of association which depends on both direct molecular interactions and the solvation contribution. A design goal frequently addressed in pharmaceutical sciences is the optimization of chemical properties of the complex partners in the sense of minimizing their binding free energy with respect to a change in chemical structure. Here, we demonstrate that liquid-state theory in the form of the solute-solute equation of the reference interaction site model provides all necessary information for such a task with high efficiency. In particular, computing derivatives of the potential of mean force (PMF), which defines the free-energy surface of complex formation, with respect to potential parameters can be viewed as a means to define a direction in chemical space toward better binders. We illustrate the methodology in the benchmark case of alkali ion binding to the crown ether 18-crown-6 in aqueous solution. In order to examine the validity of the underlying solute-solute theory, we first compare PMFs computed by different approaches, including explicit free-energy molecular dynamics simulations as a reference. Predictions of an optimally binding ion radius based on free-energy derivatives are then shown to yield consistent results for different ion parameter sets and to compare well with earlier, orders-of-magnitude more costly explicit simulation results. This proof-of-principle study, therefore, demonstrates the potential of liquid-state theory for molecular design problems. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/28/34/344004
  • 2016 • 101 Employing ionic liquids to deposit cellulose on PET fibers
    Textor, T. and Derksen, L. and Gutmann, J.S.
    Carbohydrate Polymers 146 139-147 (2016)
    Several ionic liquids are excellent solvents for cellulose. Starting from that finishing of PET fabrics with cellulose dissolved in ionic liquids like 1-ethyl-3-methyl imidazolium acetate, diethylphosphate and chloride, or the chloride of butyl-methyl imidazolium has been investigated. Finishing has been carried out from solutions of different concentrations, using microcrystalline cellulose or cotton and by employing different cross-linkers. Viscosity of solutions has been investigated for different ionic liquids, concentrations, cellulose sources, linkers and temperatures. Since ionic liquids exhibit no vapor pressure, simple pad-dry-cure processes are excluded. Before drying the ionic liquid has to be removed by a rinsing step. Accordingly rinsing with fresh ionic liquid followed by water or the direct rinsing with water have been tested. The amount of cellulose deposited has been investigated by gravimetry, zinc chloride iodine test as well as reactive dyeing. Results concerning wettability, water up-take, surface resistance, wear-resistance or washing stability are presented. © 2016 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.carbpol.2016.03.053
  • 2016 • 100 Formation and Effect of NH4 + Intermediates in NH3-SCR over Fe-ZSM-5 Zeolite Catalysts
    Chen, P. and Jabłońska, M. and Weide, P. and Caumanns, T. and Weirich, T. and Muhler, M. and Moos, R. and Palkovits, R. and Simon, U.
    ACS Catalysis 6 7696-7700 (2016)
    With the help of a technique combining in situ electrical impedance spectroscopy and DRIFT spectroscopy, we observed directly the formation of ammonium ion (NH4 +) intermediates resulting from the interaction of NO and NH3 on Fe-ZSM-5 catalysts for selective catalytic reduction by NH3 (NH3-SCR). The formed NH4 + intermediates, indicating the activation of NO in the presence of adsorbed NH3, were found to be strongly related to the NH3-SCR activity of Fe-ZSM-5 catalysts at low temperatures. These findings, which are not easily achievable by conventional methods, provide new and important perspectives to understand mechanistically the NH3-SCR reaction over Fe-zeolite catalysts. (Graph Presented). © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b02496
  • 2016 • 99 High-yield and scalable synthesis of a Silicon/Aminosilane-functionalized Carbon NanoTubes/Carbon (Si/A-CNT/C) composite as a high-capacity anode for lithium-ion batteries
    Sehlleier, Y.H. and Dobrowolny, S. and Plümel, I. and Xiao, L. and Mahlendorf, F. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Journal of Applied Electrochemistry 46 229-239 (2016)
    In this study, we present a novel anode architecture for high-performance lithium-ion batteries based on a Silicon/3-aminosilane-functionalized CNT/Carbon (Si/A-CNT/C) composite. A high-yield, low-cost approach has been developed to stabilize and support silicon as an active anode material. Silicon (Si) nanoparticles synthesized in a hot-wall reactor and aminosilane-functionalized carbon nanotubes (A-CNT) were dispersed in styrene and divinylbenzene (DVB) and subsequently polymerized forming a porous Si/A-CNT/C composite. Transmission electron microscopy showed that this method enables the interconnection and a uniform encapsulation of Si nanoparticles within a porous carbon matrix especially using aminosilane-functionalized CNT (A-CNT). Electrochemical characterization shows that this material can deliver a delithiation capacity of 2293 mAh g−1 with a capacity retention of more than 90 % after 200 cycles at lithiation and delithiation rate of 0.5 C. We conclude that the porous Si/A-CNT/C composite material can accommodate sufficient space for Si volume expansion and extraction and improve the electronic and ionic conduction. Excellent electrochemical performance during repeated cycling can thus be achieved. © 2015, Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s10800-015-0897-x
  • 2016 • 98 Intercalation Compounds as Inner Reference Electrodes for Reproducible and Robust Solid-Contact Ion-Selective Electrodes
    Ishige, Y. and Klink, S. and Schuhmann, W.
    Angewandte Chemie - International Edition 55 4831-4835 (2016)
    With billions of assays performed every year, ion-selective electrodes (ISEs) provide a simple and fast technique for clinical analysis of blood electrolytes. The development of cheap, miniaturized solid-contact (SC-)ISEs for integrated systems, however, remains a difficult balancing act between size, robustness, and reproducibility, because the defined interface potentials between the ion-selective membrane and the inner reference electrode (iRE) are often compromised. We demonstrate that target cation-sensitive intercalation compounds, such as partially charged lithium iron phosphate (LFP), can be applied as iREs of the quasi-first kind for ISEs. The symmetrical response of the interface potentials towards target cations ultimately results in ISEs with high robustness towards the inner filling (ca. 5 mV dec-1 conc.) as well as robust and miniaturized SC-ISEs. They have a predictable and stable potential derived from the LiFePO4/FePO4 redox couple (97.0±1.5 mV after 42 days). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201600111
  • 2016 • 97 Interchannel Hopping in Single Crystalline Lithium Triborate Probed by 7Li NMR: Spin Relaxation, Line Shape Analysis, Selective-Inversion Spin Alignment, and Two-Dimensional Exchange Spectra
    Storek, M. and Böhmer, R.
    Journal of Physical Chemistry C 120 7767-7777 (2016)
    The ion dynamics of single crystalline lithium triborate, LiB3O5, an important material in nonlinear optics, is studied using various 7Li and 11B nuclear magnetic resonance (NMR) techniques at temperatures from about 480 to 780 K in order to elucidate the apparent discrepancies underlying previous interpretations of NMR line shape analyses and results from dielectric spectroscopy. Rotating frame spin-lattice relaxation as well as line shape measurements are carried out and are combined with selective-inversion spin alignment as well as two-dimensional chemical exchange spectroscopy to track the temperature-dependent Li ion motion. From symmetry considerations the latter is clearly identified as interchannel hopping. By combining the present results with those from the published, yet so far not fully analyzed, dielectric loss spectra, it is shown how seeming differences in energy barriers hindering the ion motion and in the evolution of the distribution of correlation times can be reconciled. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.6b01347
  • 2016 • 96 Ions and solvation at biointerfaces
    Valtiner, M. and Erbe, A. and Rosenhahn, A.
    Biointerphases 11 (2016)
    doi: 10.1116/1.4942207
  • 2016 • 95 Irradiation of graphene field effect transistors with highly charged ions
    Ernst, P. and Kozubek, R. and Madauß, L. and Sonntag, J. and Lorke, A. and Schleberger, M.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 382 71-75 (2016)
    In this work, graphene field-effect transistors are used to detect defects due to irradiation with slow, highly charged ions. In order to avoid contamination effects, a dedicated ultra-high vacuum set up has been designed and installed for the in situ cleaning and electrical characterization of graphene field-effect transistors during irradiation. To investigate the electrical and structural modifications of irradiated graphene field-effect transistors, their transfer characteristics as well as the corresponding Raman spectra are analyzed as a function of ion fluence for two different charge states. The irradiation experiments show a decreasing mobility with increasing fluences. The mobility reduction scales with the potential energy of the ions. In comparison to Raman spectroscopy, the transport properties of graphene show an extremely high sensitivity with respect to ion irradiation: a significant drop of the mobility is observed already at fluences below 15 ions/μm2, which is more than one order of magnitude lower than what is required for Raman spectroscopy. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.nimb.2016.03.043
  • 2016 • 94 Modeling the density of ionic liquids with ePC-SAFT
    Ji, X. and Held, C.
    Fluid Phase Equilibria 410 9-22 (2016)
    ePC-SAFT was used to model the densities of ionic liquids (ILs) up to high pressures and temperatures. The ILs under consideration contained one of the IL-cations [Cnmim]+, [Cnpy]+, [Cnmpy]+, [Cnmpyr]+ or [THTDP]+, and one of the IL-anions [Tf2N]-, [PF6]-, [BF4]-, [tfo]-, [DCA]-, [SCN]-, [C1SO4]-, [C2SO4]-, [eFAP]-, Cl-, [Ac]- or Br-, respectively. Within the ePC-SAFT framework, IL-ion specific parameters were applied that are valid independent of the IL they are part of. Each IL-ion was modeled as a non-spherical species exerting repulsive, dispersive and Coulomb forces. The ePC-SAFT parameters for [Cnmim]+ (n = 2, 4, 6 and 8), [Tf2N]-, [PF6]-, and [BF4]- were taken from our previous work (Fluid Phase Equilibria 2012 (335) 64-73). Based on these parameters, all parameters of the other IL-ions were fitted to experimental density of pure ILs up to high pressures in a broad temperature range. Being provided with ion-specific and linearly molecular-weight-dependent parameters, ePC-SAFT allows reliably representing/predicting pure-IL and mixed-IL density up to high pressures. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2015.11.014
  • 2016 • 93 Nanoscale nonlinear effects in Erbium-implanted Yttrium Orthosilicate
    Kukharchyk, N. and Shvarkov, S. and Probst, S. and Xia, K. and Becker, H.-W. and Pal, S. and Markmann, S. and Kolesov, R. and Siyushev, P. and Wrachtrup, J. and Ludwig, Ar. and Ustinov, A.V. and Wieck, A.D. and Bushev, P.
    Journal of Luminescence 177 266-274 (2016)
    Doping of substrates at desired locations is a key technology for spin-based quantum memory devices. Focused ion beam implantation is well-suited for this task due to its high spacial resolution. In this work, we investigate ion-beam implanted Erbium ensembles in Yttrium Orthosilicate crystals by means of confocal photoluminescence spectroscopy. The sample temperature and the post-implantation annealing step strongly reverberate in the properties of the implanted ions. We find that hot implantation leads to a higher activation rate of the ions. At high enough fluences, the relation between the fluence and final concentration of ions becomes non-linear. Two models are developed explaining the observed behavior. © 2016 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jlumin.2016.05.010
  • 2016 • 92 Photoluminescence of gallium ion irradiated hexagonal and cubic GaN quantum dots
    Rothfuchs, C. and Kukharchyk, N. and Koppe, T. and Semond, F. and Blumenthal, S. and Becker, H.-W. and As, D.J. and Hofsäss, H.C. and Wieck, A.D. and Ludwig, Ar.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 383 1-5 (2016)
    We report on ion implantation into GaN QDs and investigate their radiation hardness. The experimental study is carried out by photoluminescence (PL) measurements on molecular beam epitaxy-grown GaN quantum dots after ion implantation. Both quantum dots grown in the hexagonal (H) and the cubic (C) crystal structure were subjected to gallium ions with an energy of 400 kV (H) and 75 kV (C) with fluences ranging from 5×1010 cm−2 to 1×1014 cm−2 (H) and to 1×1015 cm−2 (C), respectively. Low-temperature PL measurements reveal a PL quenching for which a quantitative model as a function of the ion fluence is developed. A high degradation resistance is concluded. A non-radiative trap with one main activation energy is found for all QD structures by temperature-dependent PL measurements. Further analysis of fluence-dependent PL energy shifts shows ion-induced intermixing and strain effects. Particular for the hexagonal quantum dots, a strong influence of the quantum confined Stark effect is present. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.nimb.2016.06.004
  • 2016 • 91 Positive and Negative Mixed Glass Former Effects in Sodium Borosilicate and Borophosphate Glasses Studied by 23Na NMR
    Storek, M. and Adjei-Acheamfour, M. and Christensen, R. and Martin, S.W. and Böhmer, R.
    Journal of Physical Chemistry B 120 4482-4495 (2016)
    Glasses with varying compositions of constituent network formers but constant mobile ion content can display minima or maxima in their ion transport which are known as the negative or the positive mixed glass former effect, MGFE, respectively. Various nuclear magnetic resonance (NMR) techniques are used to probe the ion hopping dynamics via the 23Na nucleus on the microscopic level, and the results are compared with those from conductivity spectroscopy, which are more sensitive to the macroscopic charge carrier mobility. In this way, the current work examines two series of sodium borosilicate and sodium borophosphate glasses that display positive and negative MGFEs, respectively, in the composition dependence of their Na+ ion conductivities at intermediate compositions of boron oxide substitution for silicon oxide and phosphorus oxide, respectively. A coherent theoretical analysis is performed for these glasses which jointly captures the results from measurements of spin relaxation and central-transition line shapes. On this basis and including new information from 11B magic-angle spinning NMR regarding the speciation in the sodium borosilicate glasses, a comparison is carried out with predictions from theoretical approaches, notably from the network unit trap model. This comparison yields detailed insights into how a variation of the boron oxide content and thus of either the population of silicon or phosphorus containing network-forming units with different charge-trapping capabilities leads to nonlinear changes of the microscopic transport properties. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcb.6b00482
  • 2016 • 90 Preparation of pulsed DC magnetron deposited Fe-doped SnO2 coatings
    Kormunda, M. and Fischer, D. and Hertwig, A. and Beck, U. and Sebik, M. and Esser, N.
    Physica Status Solidi (A) Applications and Materials Science 213 2303-2309 (2016)
    Iron-doped SnO2 coatings were deposited in a 50 kHz DC-pulsed magnetron sputtering discharge. The pulses had a duration of 4 μs in selected gas mixtures from pure argon up to 60% of oxygen at a constant total pressure of 0.2 Pa. A single target of SnO2 with Fe inset was used. The mass spectrometry study detected the gas-related ions Ar+, O2 + and O+, where the last one becomes the dominant positive ion at higher oxygen contents. Atomic oxygen ions had a higher energy as it resulted from the collision-caused dissociation on the target surface. The tin-related species were detected as Sn+ and SnO+. SnO2 + species were not detected. The deposition rate decreased by using gas mixtures with oxygen as well as the corresponding amount of Sn-related species in the plasma. The increase of oxygen also increased significantly the sheet resistance of the films. The XPS study showed that the iron concentration decreased by using additional oxygen. But the O/Sn ratio in the coatings was constant, contrary to the increased FeO/Fe ratio in the films. An additional analysis of the coatings by spectroscopic ellipsometry has shown a dependence of the polarizability and the permittivity on the amount of oxygen used during the deposition. In contrast, the study has found no such dependence for the absorption of the layers. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/pssa.201532882
  • 2016 • 89 Production yield of rare-earth ions implanted into an optical crystal
    Kornher, T. and Xia, K. and Kolesov, R. and Kukharchyk, N. and Reuter, R. and Siyushev, P. and Stöhr, R. and Schreck, M. and Becker, H.-W. and Villa, B. and Wieck, A.D. and Wrachtrup, J.
    Applied Physics Letters 108 (2016)
    Rare-earth (RE) ions doped into desired locations of optical crystals might enable a range of novel integrated photonic devices for quantum applications. With this aim, we have investigated the production yield of cerium and praseodymium by means of ion implantation. As a measure, the collected fluorescence intensity from both implanted samples and single centers was used. With a tailored annealing procedure for cerium, a yield up to 53% was estimated. Praseodymium yield amounts up to 91%. Such high implantation yield indicates a feasibility of creation of nanopatterned rare-earth doping and suggests strong potential of RE species for on-chip photonic devices. © 2016 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4941403
  • 2016 • 88 Relay-Like Exchange Mechanism through a Spin Radical between TbPc2 Molecules and Graphene/Ni(111) Substrates
    Marocchi, S. and Candini, A. and Klar, D. and Van Den Heuvel, W. and Huang, H. and Troiani, F. and Corradini, V. and Biagi, R. and De Renzi, V. and Klyatskaya, S. and Kummer, K. and Brookes, N.B. and Ruben, M. and Wende, H. and De...
    ACS Nano 10 9353-9360 (2016)
    We investigate the electronic and magnetic properties of TbPc2 single ion magnets adsorbed on a graphene/Ni(111) substrate, by density functional theory (DFT), ab initio complete active space self-consistent field calculations, and X-ray magnetic circular dichroism (XMCD) experiments. Despite the presence of the graphene decoupling layer, a sizable antiferromagnetic coupling between Tb and Ni is observed in the XMCD experiments. The molecule-surface interaction is rationalized by the DFT analysis and is found to follow a relay-like communication pathway, where the radical spin on the organic Pc ligands mediates the interaction between Tb ion and Ni substrate spins. A model Hamiltonian which explicitly takes into account the presence of the spin radical is then developed, and the different magnetic interactions at play are assessed by first-principle calculations and by comparing the calculated magnetization curves with XMCD data. The relay-like mechanism is at the heart of the process through which the spin information contained in the Tb ion is sensed and exploited in carbon-based molecular spintronics devices. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.6b04107
  • 2016 • 87 Revising secondary electron yields of ion-sputtered metal oxides
    Corbella, C. and Marcak, A. and de los Arcos, T. and von Keudell, A.
    Journal of Physics D-applied Physics 49 16LT01 (2016)
    The emission of secondary electrons (SE) during sputtering of Al and Ti foils by argon ions in an oxygen background has been measured in a particle beam reactor equipped with a SE-collector. This experiment mimics the process of reactive magnetron sputtering. Quantified beams of argon ions with energies between 500 eV and 2000 eV were employed, while simultaneously molecular oxygen fluxes impinged on the surface and caused oxidation. The measured secondary electron emission coefficients (gamma) ranged from approximately 0.1 (for clean aluminium and titanium) to 1.2 and 0.6 (in the case of aluminium oxide and titanium oxide, respectively). The increase of gamma is compared to SE measurements based on the modelling of magnetron plasmas. Moreover, the energy distributions of the emitted SE have been measured by varying the retarding potential of the SE-collector, which allows the monitoring of the oxidation state from the position of the Auger peaks. The origin of the observed SE yields based on the emission of low-and high-energy electrons generated on the oxide surface is discussed.
    view abstractdoi: 10.1088/0022-3727/49/16/16LT01
  • 2016 • 86 Salt influence on MIBK/water liquid-liquid equilibrium: Measuring and modeling with ePC-SAFT and COSMO-RS
    Mohammad, S. and Held, C. and Altuntepe, E. and Köse, T. and Gerlach, T. and Smirnova, I. and Sadowski, G.
    Fluid Phase Equilibria 416 83-93 (2016)
    In biotechnological processes, salts might be present during reaction steps and in downstream processes. Salts are known to have a strong impact on phase equilibria of aqueous systems.In this work, the liquid-liquid equilibria (LLE) of ternary salt/MIBK/water mixtures were measured at 298.15 K and 1 bar up to the salt solubility limit. The salts studied in this work were NaCl, LiCl, KCl, NaNO3, LiNO3, Na2SO4, CH3COONa, and CH3COOLi. From these LLE measurements it was found that a high amount of salt is dissolved in the aqueous phase whereas only a very small amount of salt was detected in the MIBK phase. Further, the salting-out behavior of MIBK from the aqueous phase upon addition of different salts was investigated to study ion-specific effects.Two ion-specific models, ePC-SAFT and an extended version of COSMO-RS for electrolytes were used for modeling the binary system MIBK/water and ternary salt/MIBK/water systems. In case of the COSMO-RS based approach, the modeling results were fully predictive. In contrast, ion-specific binary interaction parameters between MIBK and ions were fitted to experimental LLE data of the ternary systems salt/MIBK/water when using ePC-SAFT. The results show that the COSMO-RS based approach allows for predicting the salt influence on LLE with acceptable accuracy, whereas ePC-SAFT allows for almost quantitative correlations of experimental data. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2015.11.018
  • 2016 • 85 Structure and Stability of Long Rod-like Dodecyltrimethylammonium Chloride Micelles in Solutions of Hydroxybenzoates: A Molecular Dynamics Simulation Study
    Gujt, J. and Bešter-Rogač, M. and Spohr, E.
    Langmuir 32 8275-8286 (2016)
    The relative position of the hydroxylic and carboxylic groups in the isomeric hydroxybenzoate (HB) anions is experimentally known to have a large impact on the thermodynamics of micellization of cationic surfactants, such as dodecyltrimethylammonium chloride (DTAC), and on the structure of the resulting micelles. To understand the effect of the different isomers on the molecular level, we employed atomistic molecular dynamics simulations to study systems containing infinitely long cylindrical DTAC micelles in aqueous solutions of the sodium salts of all three isomers of HB at a temperature and a pressure of 298.15 K and 1 atm. In all studied systems, the number of DTAC unimers is identical to the number of HB anions. At this concentration, the initially cylindrical micelles remain stable, irrespective of the nature of the isomer, whereas micelles rapidly disintegrated in the absence of HB anions. The HB isomers decrease the line density of unimers along the micellar axis and its concomitant thickness in the order o-HB > m-HB > p-HB. It is further observed that o-HB anions penetrate more deeply into the micellar core, induce a more ordered internal structure of the micelle, and are oriented more strongly than the other two isomers. In addition, the ortho isomer shows two different preferential orientations with respect to the radial direction of the cylindrical micelle; it can either be incorporated almost completely into the micelle or it can be attached through hydrogen bonding to one of those o-HB anions that are already incorporated into the micelle, and thus stick out of the micellar surface. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.6b02076
  • 2016 • 84 The anodic emitter effect and its inversion demonstrated by temperature measurements at doped and undoped tungsten electrodes
    Hoebing, T. and Bergner, A. and Hermanns, P. and Mentel, J. and Awakowicz, P.
    Journal of Physics D: Applied Physics 49 (2016)
    The admixture of a small amount of emitter oxides, e.g. ThO2, La2O3 or Ce2O3 to tungsten generates the so-called emitter effect. t reduces the work function of tungsten cathodes that are applied in high intensity discharge (HID) lamps. After leaving the electrode ulk and moving to the surface, a monolayer of Th, La, or Ce atoms is formed on the surface which reduces the effective work function. Depending on the coverage of the electrode, the effective reduction in is subjected to the thermal desorption of the monolayer rom the hot electrode surface. The thermal desorption of emitter atoms from the cathode is compensated not only by the supply from he interior of the electrode and by surface diffusion of the emitter material to its tip, but also to a large extent by a repatriation f the emitter ions from the plasma by the strong electric field in front of the cathode. Yet, an emitter ion current from the arc ischarge to the anode may only be present, if the anode is cold enough to refrain from thermionic emission. Therefore, the ability of mitter oxides to reduce the temperature of tungsten anodes is only given for a moderate temperature so that the thermal desorption is ow and an additional ion current is present in front of the anode. A higher electrode temperature leads to their evaporation and to an nversion of the emitter effect, which increases the temperature of the respective anodes in comparison with pure tungsten anodes. ithin this article, the emitter effect of doped tungsten anodes and the transition to its inversion is investigated for thoriated, anthanated, and ceriated tungsten electrodes by measurements of the electrode temperature in dependence on the discharge current. It s shown for a lanthanated and a ceriated anode that the emitter effect is sustained by an ion current at anode temperatures at which he thermal evaporation of emitter material is completed. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/49/15/155504
  • 2016 • 83 Two-Component Self-Assembly: Hierarchical Formation of pH-Switchable Supramolecular Networks by π–π Induced Aggregation of Ion Pairs
    Samanta, K. and Ehlers, M. and Schmuck, C.
    Chemistry - A European Journal 22 15242-15247 (2016)
    Two-component self-assembly is a promising approach to construct functional nanomaterials. Interaction of a flexible guanidiniocarbonyl pyrrole tetra-cation (1) with naphthalene diimide dicarboxylic acid (NDIDC) in aqueous DMSO leads to the formation of supramolecular networks. First, the carboxylate groups of NDIDC bind to the guanidiniocarbonyl pyrrole cations of 1 in a 1:2 stoichiometry. Further π–π induced aggregation then leads to 3D networks, as established by dynamic light scattering studies (DLS), NMR, fluorescence titration, viscosity measurements, AFM, and TEM microscopy. Due to ion pairing, the resulting aggregates can be switched between the monomers and the aggregates reversibly using external stimuli like protonation or deprotonation. At high concentration, a stable colloidal solution is formed, which shows an extensive Tyndall effect. Increasing the concentrations even further leads to formation of a supramolecular gel. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201603944
  • 2015 • 82 A tailor-made specific anion-binding motif in the side chain transforms a tetrapeptide into an efficient vector for gene delivery
    Li, M. and Schlesiger, S. and Knauer, S.K. and Schmuck, C.
    Angewandte Chemie - International Edition 54 2941-2944 (2015)
    Arginine-rich cell-penetrating peptides are widely utilized as vectors for gene delivery. However, their transfection efficacy still needs to be optimized. To accomplish this, guanidinocarbonylpyrrole groups, which are tailor-made anion binding sites, were introduced into the side chains of tetralysine to obtain the peptide analogue 1. In contrast to the common strategy of adding a lipophilic tail to peptide vectors, this novel method most likely enhances transfection efficacy through more specific interactions between the binding motifs and DNA or the cell membrane. Tetrapeptide analogue 1 is thus the smallest peptidic transfection vector that has been reported to date. The transfection efficacy of 1, which on average has less than two positive charges under physiological conditions, is even better than that of polyethylenimine (PEI). Furthermore, 1 exhibits only negligible cytotoxicity, which makes it an interesting candidate for further development. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201410429
  • 2015 • 81 All-Optical Preparation of Coherent Dark States of a Single Rare Earth Ion Spin in a Crystal
    Xia, K. and Kolesov, R. and Wang, Y. and Siyushev, P. and Reuter, R. and Kornher, T. and Kukharchyk, N. and Wieck, A.D. and Villa, B. and Yang, S. and Wrachtrup, J.
    Physical Review Letters 115 (2015)
    All-optical addressing and coherent control of single solid-state based quantum bits is a key tool for fast and precise control of ground-state spin qubits. So far, all-optical addressing of qubits was demonstrated only in a very few systems, such as color centers and quantum dots. Here, we perform high-resolution spectroscopic of native and implanted single rare earth ions in solid, namely, a cerium ion in yttrium aluminum garnet (YAG) crystal. We find narrow and spectrally stable optical transitions between the spin sublevels of the ground and excited optical states. Utilizing these transitions we demonstrate the generation of a coherent dark state in electron spin sublevels of a single Ce3+ ion in YAG by coherent population trapping. © 2015 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.115.093602
  • 2015 • 80 Anion-π interactions with fluoroarenes
    Giese, M. and Albrecht, M. and Rissanen, K.
    Chemical Reviews 115 8867-8895 (2015)
    Recent findings in anion-π interactions of fluoroarenes were studied. The study clearly demonstrates that there is still a gap between theoretical studies and experimental evidence for those weak intermolecular interactions. Although computational studies, gas-phase experiments, and crystallographic results support the attractive nature of anion-π interactions, numerous investigations suggest that anion-π bonding very often is too weak to compete against other noncovalent interactions such as hydrogen bonding, electrostatic attraction, solvent effects, or dipole interactions in solution. Even halogen bonding seems to overrule the interaction between anions and the π-system of electron-deficient arenes. Nevertheless anion-π interactions gained considerable attention in anion-recognition and host-guest chemistry, and due to recent findings their participation in ion transport, stabilization of reactive anionic species, catalysis, templation, and sensing of fluoride ions motivates further detailed studies on the nature and relevance of this intriguing intermolecular interaction.
    view abstractdoi: 10.1021/acs.chemrev.5b00156
  • 2015 • 79 Biocompatible microgel-modified electrospun fibers for zinc ion release
    Wilke, P. and Coger, V. and Nachev, M. and Schachschal, S. and Million, N. and Barcikowski, S. and Sures, B. and Reimers, K. and Vogt, P.M. and Pich, A.
    Polymer (United Kingdom) 61 163-173 (2015)
    We present a novel and facile method for the design of biocompatible microgel-modified microfibers loaded with ZnO nanoparticles capable of zinc ion release under physiological conditions. The microfibers consist of three materials hierarchically assembled in a controlled and reproducible way. We synthesized poly(N-vinylcaprolactam-co-itaconic acid) aqueous microgels with carboxylic groups located in the microgel core. The obtained microgels can be loaded with various amounts of ZnO nanoparticles by in-situ growth of ZnO in microgels. As shown by electrophoretic mobility and TEM measurements, ZnO nanoparticles are selectively loaded in the microgel core and stabilized by itaconic acid groups bearing strong negative charges. ZnO-loaded microgels were used as functional additive to produce poly(ε-caprolactone) (PCL) microfibers using the electrospinning process. The resulting microfibers consist of a PCL core coated with the microgels located at the surface of the fibers. The variation of the ZnO amount loaded into microgels allows regulating the ZnO content in microfibers and gives the possibility to tune the released amount of zinc ions in aqueous medium at pH 7.5 and 37 °C. We demonstrate that the obtained functional microfibers are biocompatible and non-toxic, thus being good candidates for biomedical applications like scaffolds for tissue engineering, biointerface coatings or wound closing dressings. © 2015 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.polymer.2015.01.078
  • 2015 • 78 Combined AFM/SECM Investigation of the Solid Electrolyte Interphase in Li-Ion Batteries
    Zampardi, G. and Klink, S. and Kuznetsov, V. and Erichsen, T. and Maljusch, A. and LaMantia, F. and Schuhmann, W. and Ventosa, E.
    ChemElectroChem 2 1607-1611 (2015)
    The solid electrolyte interphase (SEI) is an electronically insulating film formed from the decomposition of the organic electrolyte at the surface of the negative electrodes in Li-ion batteries (LIBs). This film is of vital importance in the performance and safety of LIBs. Atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) are combined in one platform for the consecutive insitu investigation of surface reactions in LIBs inside an Ar-filled glovebox. As proof of concept, the formation and the electrochemical properties of the SEI formed on glassy carbon electrodes are investigated. Changes in topography during film formation of the SEI are studied via AFM. The AFM tip is then used to partially remove a small area (50×50μm2) of the SEI, which is subsequently probed using SECM in feedback mode. The AFM-scratched spot is clearly visualized in the SECM image, demonstrating the strength of the AFM/SECM combination for the investigation in the field of LIBs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201500085
  • 2015 • 77 Conformational Equilibria of Organic Adsorbates on Nanostructures in Aqueous Solution: MD Simulations
    Giri, A.K. and Spohr, E.
    Journal of Physical Chemistry C 119 25566-25575 (2015)
    We have performed atomistic molecular dynamics (MD) simulations of gold nanoparticles (GNPs) in aqueous NaCl solution. Alkanethiol chain-covered GNPs at grafting densities between approximately one-third and full coverage were studied with nonpolar CH3 and charged COO- and NH3 terminations. Special attention was given to the penetration depth of water and ions into the diffuse shell of the functionalized alkanethiol chains and its dependence on grafting density and functionalization. Solutions with polar terminations were neutralized by an excess of Na+ and Cl- ions. The penetration of water and ions into the hydration shell increases with decreasing grafting density irrespective of termination. High grafting densities lead to more extended hydrocarbon chains. Charged functionalized GNPs produce nonmonotonous counter charge distributions with reduced ion mobility. Partial replacement of first shell solvation water by the charged groups leads to a drastic increase in torsional relaxation times of the chain termini. Due to the large curvature of the GNPs with a diameter of 2 nm, gold cores remain accessible to both ions and water even at the highest studied grafting densities of about 5 chains/nm2. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b06249
  • 2015 • 76 Controllable Synthesis of Mesoporous Peapod-like Co3O4@Carbon Nanotube Arrays for High-Performance Lithium-Ion Batteries
    Gu, D. and Li, W. and Wang, F. and Bongard, H. and Spliethoff, B. and Schmidt, W. and Weidenthaler, C. and Xia, Y. and Zhao, D. and Schüth, F.
    Angewandte Chemie - International Edition 54 7060-7064 (2015)
    Abstract Transition metal oxides are regarded as promising anode materials for lithium-ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered by their large volume changes during the Li+ insertion and extraction process and their low electric conductivities. Herein, we report a specifically designed anode architecture to overcome such problems, that is, mesoporous peapod-like Co<inf>3</inf>O<inf>4</inf>@carbon nanotube arrays, which are constructed through a controllable nanocasting process. Co<inf>3</inf>O<inf>4</inf> nanoparticles are confined exclusively in the intratubular pores of the nanotube arrays. The pores between the nanotubes are open, and thus render the Co<inf>3</inf>O<inf>4</inf> nanoparticles accessible for effective electrolyte diffusion. Moreover, the carbon nanotubes act as a conductive network. As a result, the peapod-like Co<inf>3</inf>O<inf>4</inf>@carbon nanotube electrode shows a high specific capacity, excellent rate capacity, and very good cycling performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201501475
  • 2015 • 75 Direct photonic coupling of a semiconductor quantum dot and a trapped ion
    Meyer, H.M. and Stockill, R. and Steiner, M. and Le Gall, C. and Matthiesen, C. and Clarke, E. and Ludwig, Ar. and Reichel, J. and Atatüre, M. and Köhl, M.
    Physical Review Letters 114 (2015)
    Coupling individual quantum systems lies at the heart of building scalable quantum networks. Here, we report the first direct photonic coupling between a semiconductor quantum dot and a trapped ion and we demonstrate that single photons generated by a quantum dot controllably change the internal state of a Yb+ ion. We ameliorate the effect of the 60-fold mismatch of the radiative linewidths with coherent photon generation and a high-finesse fiber-based optical cavity enhancing the coupling between the single photon and the ion. The transfer of information presented here via the classical correlations between the σz projection of the quantum-dot spin and the internal state of the ion provides a promising step towards quantum-state transfer in a hybrid photonic network. © 2015 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.114.123001
  • 2015 • 74 Effect of the specific surface area on thermodynamic and kinetic properties of nanoparticle anatase TiO2 in lithium-ion batteries
    Madej, E. and Klink, S. and Schuhmann, W. and Ventosa, E. and La Mantia, F.
    Journal of Power Sources 297 140-148 (2015)
    Anatase TiO<inf>2</inf> nanoparticles with a specific surface area of 100 m2 g-1 and 300 m2 g-1 have been investigated as negative insertion electrode material for lithium-ion batteries. Galvanostatic intermittent titration (GITT) and electrochemical impedance spectroscopy (EIS) were used to investigate the effect of the specific surface area on the performance of the material. GITT was performed at C/10 rate, followed by an EIS measurement after each relaxation step. Separation of kinetic and thermodynamic contributions to the overpotential of the phase transformation on Li+ (de-)insertion allowed revealing a dependency of both terms on the specific surface area. The material with higher surface area undergoes intrinsic transformation during the initial cycles affecting the thermodynamics of (de-)insertion while the sample with lower surface area shows large and asymmetric kinetic hindrances. For the material with 15 nm particles, Li+ de-insertion appears to have a higher resistance than lithium insertion. © 2015, Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jpowsour.2015.07.079
  • 2015 • 73 Electrochemical strain microscopy time spectroscopy: Model and experiment on LiMn2O4
    Amanieu, H.-Y. and Thai, H.N.M. and Luchkin, S.Yu. and Rosato, D. and Lupascu, D.C. and Keip, M.-A. and Schröder, J. and Kholkin, A.L.
    Journal of Applied Physics 118 (2015)
    Electrochemical Strain Microscopy (ESM) can provide useful information on ionic diffusion in solids at the local scale. In this work, a finite element model of ESM measurements was developed and applied to commercial lithium manganese (III,IV) oxide (LiMn<inf>2</inf>O<inf>4</inf>) particles. ESM time spectroscopy was used, where a direct current (DC) voltage pulse locally disturbs the spatial distribution of mobile ions. After the pulse is off, the ions return to equilibrium at a rate which depends on the Li diffusivity in the material. At each stage, Li diffusivity is monitored by measuring the ESM response to a small alternative current (AC) voltage simultaneously applied to the tip. The model separates two different mechanisms, one linked to the response to DC bias and another one related to the AC excitation. It is argued that the second one is not diffusion-driven but is rather a contribution of the sum of several mechanisms with at least one depending on the lithium ion concentration explaining the relaxation process. With proper fitting of this decay, diffusion coefficients of lithium hosts could be extracted. Additionally, the effect of phase transition in LiMn<inf>2</inf>O<inf>4</inf> is taken into account, explaining some experimental observations. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4927747
  • 2015 • 72 Experimental investigations of electron heating dynamics and ion energy distributions in capacitive discharges driven by customized voltage waveforms
    Berger, B. and Brandt, S. and Franek, J. and Schüngel, E. and Koepke, M. and Mussenbrock, T. and Schulze, J.
    Journal of Applied Physics 118 (2015)
    Capacitively coupled radio frequency plasmas driven by customized voltage waveforms provide enhanced opportunities to control process-relevant energy distributions of different particle species. Here, we present an experimental investigation of the spatio-temporal electron heating dynamics probed by Phase-Resolved Optical Emission Spectroscopy (PROES) in an argon discharge driven by up to three consecutive harmonics of 13.56 MHz with individually adjustable harmonics' amplitudes and phases. PROES and voltage measurements are performed at fixed total voltage amplitudes as a function of the number of driving harmonics, their relative phases, and pressure to study the effects of changing the applied voltage waveform on the heating dynamics in collisionless and collisional regimes. Additionally, the ion energy distribution function (IEDF) is measured at low pressure. In this collisionless regime, the discharge is operated in the α-mode. The velocity of energetic electron beams generated by the expanding sheaths is found to be affected by the number of driving harmonics and their relative phases. This is understood based on the sheath dynamics obtained from a model that determines sheath voltage waveforms. The formation of the measured IEDFs is understood and found to be directly affected by the observed changes in the electron heating dynamics. It is demonstrated that the mean ion energy can be controlled by adjusting the harmonics' phases. In the collisional regime at higher pressures changing the number of harmonics and their phases at fixed voltage is found to induce heating mode transitions from the α- to the γ-mode. Finally, a method to use PROES as a non-invasive diagnostic to monitor and detect changes of the ion flux to the electrodes is developed. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4937403
  • 2015 • 71 Exploring the Structure of the Modified Top Layer of Polypropylene During Plasma Treatment
    Corbella, C. and Grosse-Kreul, S. and von Keudell, A.
    Plasma Processes and Polymers 12 564--573 (2015)
    Plasma modifications of polypropylene (PP) surfaces are analyzed by means of vacuum beam experiments. A plasma source provides Ar ion beams and a background of UV photons. Additionally, neutral oxygen beams are sent to perform reactive sputtering of PP. The etch rate and chemical state are monitored in real time by in situ Fourier transform infrared (FTIR) spectroscopy. At the onset of Ar bombardment, PP shows high sputter yields, which decrease down to a constant etch rate indicating the formation of a modified top layer. The stationary top layer is modeled as combination of a pristine fraction plus a crosslinked fraction of amorphous hydrocarbon. Photonand ion-dominated etch processes provide different cross-linking fractions, whereas the sputter efficiency is maximized at intermediate ion energies (200 eV).
    view abstractdoi: 10.1002/ppap.201400188
  • 2015 • 70 Fast and Accurate Measurement of Entropy Profiles of Commercial Lithium-Ion Cells
    Osswald, P.J. and Del Rosario, M. and Garche, J. and Jossen, A. and Hoster, H.E.
    Electrochimica Acta 177 270-276 (2015)
    We report on an effective approach to speed up the measurement of thermodynamic characterization curves (entropy of reaction ΔrS(x)) of rechargeable batteries, in particular commercial 18650 lithium ion cells. We propose and demonstrate a measurement and data processing protocol that reduces the time required to record entropy profiles from time scales of weeks to time scales of hours - without loss in accuracy. For time consuming studies such as investigations on ageing of battery cells, entropy profile measurements thus become as feasible as conventional electrochemical characterisation techniques like dV/dQ or cyclic voltammetry. We demonstrate this at the examples of two ageing protocols applied to a commercial high power and a commercial high energy cell, respectively: (i) accelerated calendric aging by storing cells at 100% state of charge at 60 °C and (ii) continuous cycling with a 1C current at 25 °C. © 2015 Published by Elsevier Ltd.
    view abstractdoi: 10.1016/j.electacta.2015.01.191
  • 2015 • 69 Ground and excited states of iron centers in ZnO: Pulse-EPR and magneto-optical spectroscopy
    Azamat, D.V. and Debus, J. and Yakovlev, D.R. and Ivanov, V.Yu. and Godlewski, M. and Fanciulli, M. and Bayer, M.
    Physical Review B - Condensed Matter and Materials Physics 92 (2015)
    We report on the ground- and excited-state properties of Fe3+ centers in hydrothermally and chemical-vapor-transport grown single ZnO crystals studied by continuous-wave electron-paramagnetic resonance (EPR) under dark and laser-illuminated conditions, pulsed-EPR and magneto-photoluminescence. By use of EPR experiments, the fine-structure parameters of the Fe3+ spin Hamiltonian are determined. Three types of charge-compensated Fe3+ centers are identified and the charge conversion from Fe2+ to Fe3+ is highlighted. The magneto-optical studies of the Zeeman components of the spin-forbidden electric-dipole transitions from excited T14(G) to ground A16(S6) states of the Fe3+ center indicate the trigonal symmetry of the fine structure of the lowest Γ8(T14) excited state. The energy positions of the Zeeman components are measured in the external magnetic field of 8 T rotated in (12¯10) and (0001) crystal planes. The angular variation of the Zeeman lines exhibits two magnetically nonequivalent Fe3+ centers. These features result from the contribution of high-rank Zeeman terms of dimension BJ3 in the spin Hamiltonian. For the electron spin S=5/2 system of the trigonal Fe3+ ion, we further demonstrate the tuning of one-photon Rabi oscillations by means of electron spin-echo measurements. ©2015 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.92.195202
  • 2015 • 68 Influence of Defects Introduced by Irradiation with 4-9 MeV Helium Ions on Impedance of Silicon Diodes
    Poklonski, N.A. and Gorbachuk, N.I. and Nha, V.Q. and Shpakovski, S.V. and Filipenya, V.A. and Skuratov, V.A. and Kotunowicz, T.N. and Kukharchyk, N. and Becker, H.-W. and Wieck, A.
    Acta Physica Polonica A 128 891-893 (2015)
    Silicon diodes irradiated with helium ions with energies of 4.1, 6.8 and 8.9 MeV are studied. It is shown that the mechanism determining the behaviour of frequency dependence of complex electric module and correspondingly the behavior of impedance of diodes irradiated with helium ions in the frequency region 3200 kHz is a recharging of vacancy complexes localized in the space charge region.
    view abstractdoi: 10.12693/APhysPolA.128.891
  • 2015 • 67 Influence of Post-Implantation Annealing Parameters on the Focused Ion Beam Directed Nucleation of InAs Quantum Dots
    Mehta, M. and Reuter, D. and Kamruddin, M. and Tyagi, A.K. and Wieck, A.D.
    Nano 10 (2015)
    We present the effect of post-implantation annealing conditions on the structural and optical quality of InAs quantum dots (QDs) grown by combination of focused ion beam (FIB) and molecular beam epitaxy (MBE) approach. A FIB of Ga+ ion was employed to pattern a homogeneously GaAs buffer layers and then, an in situ annealing step followed by InAs deposition was performed. Three different post-implantation annealing conditions were tested and under well-optimized conditions, a dislocation and defect-free InAs QDs growth on FIB patterned surface was successfully achieved. Furthermore, using photoluminescence (PL) study, we demonstrate that our best sample shows almost similar optical quality as MBE grown QDs on unimplanted GaAs surface. The patterning technique described here can presumably be applied to systems other than InAs/GaAs and highly interesting for site-controlled nucleation of QDs that finds its potential applications in nanooptoelectronic devices. © 2015 World Scientific Publishing Company.
    view abstractdoi: 10.1142/S1793292015500496
  • 2015 • 66 Mass spectrometry of atmospheric pressure plasmas
    Grosse-Kreul, S. and Hubner, S. and Schneider, S. and Ellerweg, D. and von Keudell, A. and Matejcik, S. and Benedikt, J.
    Plasma Sources Science & Technology 24 044008 (2015)
    Atmospheric pressure non-equilibrium plasmas (APPs) are effective source of radicals, metastables and a variety of ions and photons, ranging into the vacuum UV spectral region. A detailed study of these species is important to understand and tune desired effects during the interaction of APPs with solid or liquid materials in industrial or medical applications. In this contribution, the opportunities and challenges of mass spectrometry for detection of neutrals and ions from APPs, fundamental physical phenomena related to the sampling process and their impact on the measured densities of neutrals and fluxes of ions, will be discussed. It is shown that the measurement of stable neutrals and radicals requires a proper experimental design to reduce the beam-to-background ratio, to have little beam distortion during expansion into vacuum and to carefully set the electron energy in the ionizer to avoid radical formation through dissociative ionization. The measured ion composition depends sensitively on the degree of impurities present in the feed gas as well as on the setting of the ion optics used for extraction of ions from the expanding neutral-ion mixture. The determination of the ion energy is presented as a method to show that the analyzed ions are originating from the atmospheric pressure plasma.
    view abstractdoi: 10.1088/0963-0252/24/4/044008
  • 2015 • 65 On the mechanism of Zn4O-acetate precursors ripening to ZnO: How dimerization is promoted by hydroxide incorporation
    Milek, T. and Kirschbaum, R.W. and Gernler, M.S.V. and Lübbert, C. and Segets, D. and Drewello, T. and Peukert, W. and Zahn, D.
    Journal of Chemical Physics 143 (2015)
    We report on a combined experimental and molecular modelling study on Zn<inf>4</inf>O ion clusters stabilized by acetate molecules (OAc). In particular, ab initio calculations of acetate substitution by hydroxide ions are compared with mass spectrometry data. Though quantum calculations in the gas phase indicate strong energetic preference, no experimental evidence of stable Zn<inf>4</inf>O(OAc)<inf>6-x</inf>(OH)<inf>x</inf> clusters in ethanolic solutions could be observed. This apparent contradiction is rationalized by identifying the supportive role of hydroxide ions for the association of (OAc- → OH- substituted) Zn<inf>4</inf>O(OAc)<inf>6</inf> and Zn<inf>4</inf>O(OAc)<inf>5</inf>+ clusters. Mass spectrometry and quantum calculations hint at the stability of (Zn<inf>4</inf>O)<inf>2</inf>(OAc)<inf>12-x</inf>(OH)<inf>x</inf> dimers with x = 1, 2. Therein, the hydroxide ions establish salt-bridges that allow for the formation of additional Zn<inf>3</inf> motifs with the OH above the triangle center - a structural motif close to that of the ZnO-crystal. The association of Zn<inf>4</inf>O(OAc)<inf>6</inf> clusters is thus suggested to involve OAc- → OH- substitution as an activation step, quickly followed by dimerization and the subsequent agglomeration of oligomers. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4928190
  • 2015 • 64 One-Pot Synthesis of Carbon-Coated Nanostructured Iron Oxide on Few-Layer Graphene for Lithium-Ion Batteries
    Sun, Z. and Madej, E. and Wiktor, C. and Sinev, I. and Fischer, R.A. and Van Tendeloo, G. and Muhler, M. and Schuhmann, W. and Ventosa, E.
    Chemistry - A European Journal 21 16154-16161 (2015)
    Nanostructure engineering has been demonstrated to improve the electrochemical performance of iron oxide based electrodes in Li-ion batteries (LIBs). However, the synthesis of advanced functional materials often requires multiple steps. Herein, we present a facile one-pot synthesis of carbon-coated nanostructured iron oxide on few-layer graphene through high-pressure pyrolysis of ferrocene in the presence of pristine graphene. The ferrocene precursor supplies both iron and carbon to form the carbon-coated iron oxide, while the graphene acts as a high-surface-area anchor to achieve small metal oxide nanoparticles. When evaluated as a negative-electrode material for LIBs, our composite showed improved electrochemical performance compared to commercial iron oxide nanopowders, especially at fast charge/discharge rates. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201501935
  • 2015 • 63 Optical and microwave properties of focused ion beam implanted Erbium ions in Y2SiO5 crystals
    Kukharchyk, N. and Probst, S. and Pal, S. and Xia, K. and Kolesov, R. and Ludwig, Ar. and Ustinov, A.V. and Bushev, P. and Wieck, A.D.
    Conference on Lasers and Electro-Optics Europe - Technical Digest 2015-August (2015)
    We present focused ion beam implantation as a prospective tool for realizing a patterned rare-earth spin-ensemble in a solid-state substrate. We demonstrate a successful implantation with 20% of luminescent ion activation for Erbium ions in Y2SiO5 crystals. © 2015 OSA.
    view abstractdoi: 10.1364/CLEO_AT.2015.JW2A.21
  • 2015 • 62 Physics of the Advanced Plasma Source: A review of recent experimental and modeling approaches
    Brinkmann, R.P. and Harhausen, J. and Schröder, B. and Lapke, M. and Storch, R. and Styrnoll, T. and Awakowicz, P. and Foest, R. and Hannemann, M. and Loffhagen, D. and Ohl, A.
    Plasma Physics and Controlled Fusion 58 (2015)
    The Advanced Plasma Source (APS), a gridless hot cathode glow discharge capable of generating an ion beam with an energy of up to 150 eV and a flux of 1019s-1, is a standard industrial tool for the process of plasma ion-assisted deposition (PIAD). This manuscript details the results of recent experimental and modeling work aimed at a physical understanding of the APS. A three-zone model is proposed which consists of (i) the ionization zone (the source itself) where the plasma is very dense, hot, and has a high ionization rate, (ii) the acceleration zone (of ~20 cm extension) where a strong outward-directed electric field accelerates the primary ions to a high kinetic energy, and (iii) a drift zone (the rest of the process chamber) where the emerging plasma beam is further modified by resonant charge exchange collisions that neutralize some of the energetic ions and generate, at the same time, a flux of slow ions. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0741-3335/58/1/014033
  • 2015 • 61 Si-CNT/rGO Nanoheterostructures as High-Performance Lithium-Ion-Battery Anodes
    Xiao, L. and Sehlleier, Y.H. and Dobrowolny, S. and Orthner, H. and Mahlendorf, F. and Heinzel, A. and Schulz, C. and Wiggers, H.
    ChemElectroChem 2 1983-1990 (2015)
    A robust and electrochemically stable 3D nanoheterostructure consisting of Si nanoparticles (NPs), carbon nanotubes (CNTs) and reduced graphene oxide (rGO) is developed as an anode material (Si-CNT/rGO) for lithium-ion batteries (LIBs). It integrates the benefits from its three building blocks of Si NPs, CNTs, and rGO; Si NPs offer high capacity, CNTs act as a mechanical, electrically conductive support to connect Si NPs, and highly electrically conductive and flexible rGO provides a robust matrix with enough void space to accommodate the volume changes of Si NPs upon lithiation/delithiation and to simultaneously assure good electric contact. The composite material shows a high reversible capacity of 1665mAhg-1 with good capacity retention of 88.6% over 500 cycles when cycled at 0.5C, that is, a 0.02% capacity decay per cycle. The high-power capability is demonstrated at 10C (16.2Ag-1) where 755mAhg-1 are delivered, thus indicating promising characteristics of this material for high-performance LIBs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201500323
  • 2015 • 60 Silicon/carbon nano-composite based anodes for advanced lithium-ion batteries
    Dobrowolny, S. and Mahlendorf, F. and Heinzel, A.
    ECS Transactions 66 29-36 (2015)
    In this study, the investigation of high capacity and high efficiency graphene coated silicon composite (Si/C composite) based electrodes prepared by using a wet chemical manufacturing process is presented. The active material provides a capacity of >2000 mAh g-1 with a coulombic efficiency >99% for more than 500 cycles. The focus is set to the investigation of the electrode structure during cycling progression by using galvanostatic cycling, electrochemical impedance spectroscopy, scanning electron microscopy, confocal microscopy and the measurement of the coating adhesion strength. Results show the applicability of improved Si/C composite electrodes for future lithium-ion batteries, both in half cells as well as in full cells in combination with a commercially available cathode material. © The Electrochemical Society.
    view abstractdoi: 10.1149/06609.0029ecst
  • 2015 • 59 Ultrafiltration membranes with markedly different pH- and ion-responsivity by photografted zwitterionic polysulfobetain or polycarbobetain
    Birkner, M. and Ulbricht, M.
    Journal of Membrane Science 494 57-67 (2015)
    Stimuli-responsive ultrafiltration (UF) membranes were synthesized via photo-initiated "grafting from" of the zwitterionic monomers N-(3-sulfopropyl)-N-methacroyl-oxyethyl-N,N-dimethyl-ammonium betaine (sulfobetaine methacrylate, SPE) and 2-carboxy-N,N-dimethyl-N-(2'-(methacryl-oyloxy)ethyl)ethan-aminium inner salt (carbobetaine methacrylate, CBMA) onto commercial polyethersulfone UF membranes. The effects of kosmotropic and chaotropic potassium salts and pH on flux were determined in order to investigate the stimuli-responsive behavior of the polyzwitterion-grafted membranes. PolySPE showed the expected stimuli-responsiveness based on the "anti-polyelectrolyte" effect. The degree of swelling of grafted sulfobetaine polymer increased and water permeability decreased with increasing salt concentration; and the results can be related to the "Hofmeister series", i.e. the magnitude of the effect increased with increasing chaotropic character of the anion, in the order: SO<inf>4</inf>2-<H<inf>2</inf>PO<inf>4</inf>-<Cl-<ClO<inf>4</inf>-. However, the carbobetaine polymer (polyCBMA) did not show such anti-polyelectrolyte behavior at pH values in neutral and basic range. In contrast to the "strong-strong" type zwitterionic material polySPE, the swelling behavior of the "strong-weak" polyCBMA was significantly influenced by pH value because protonation of carboxylic acid side groups changes the grafted chains from net neutral zwitterionic into polycationic with ordinary polyelectrolyte properties. Hence, permeability of polyCBMA-grafted membranes increased with increasing salt concentration at pH=3. Furthermore, the rejection of dextrans as a function of electrolyte concentration and pH was determined and all results were in agreement with changes of water fluxes. For specific salt conditions, large and reversible changes of dextran rejection were found, confirming the possibilities of adjusting the sieving properties of the responsive zwitterionic membranes. Detailed studies by zetapotential measurements were also performed to investigate the specific effects of ion type, electrolyte concentration and pH onto the stimuli-responsive changes of surface charge of grafted membranes. All results support that the effects of the grafted zwitterionic polymers on the barrier properties of the UF membranes can be described with a pore-opening/-closing mechanism based on reversible deswelling/swelling of grafted chains on the pore walls in response to composition changes with respect to salt (for polySPE) or salt and pH value (polyCBMA). © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2015.07.046
  • 2015 • 58 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
  • 2014 • 57 Adhesion of thin CVD films on pulsed plasma pre-treated polypropylene
    Behm, H. and Bahroun, K. and Bahre, H. and Kirchheim, D. and Mitschker, F. and Bibinov, N. and Böke, M. and Dahlmann, R. and Awakowicz, P. and Hopmann, C. and Winter, J.
    Plasma Processes and Polymers 11 418-425 (2014)
    The adhesion of thin CVD films on polyolefins is often critical due to the low surface free energy of the polymers. In this study, injection moulded PP samples are produced and investigated. The samples are treated in very well-characterized pulsed plasmas before a HMDSO-based coating is applied. The resulting bond strength is analyzed using pull-off tests. The fractured interfaces are characterized with XPS. Oxygen and argon plasma pre-treatments of the PP samples result in a bond strength improvement by a factor of about 2. Comparing oxygen and argon pre-treatments at equal ion fluences to the surface, it can be shown that the bond strength between CVD-coating and polymer is similar. The influence of well-defined argon and oxygen pre-treatment plasmas on the adhesion of silicon organic CVD films (SiOCH) on polypropylene (PP) is investigated. Very short pre-treatment times result in an increase in bond strength by a factor of 2. Measurements show a dependency of the ion fluence on the surface on the bond strength between CVD film and PP in the region of best adhesion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppap.201300128
  • 2014 • 56 Bi-Zn bond formation in liquid ammonia solution: [Bi-Zn-Bi]4-, a linear polyanion that is Iso(valence)-electronic to CO2
    Benda, C.B. and Köchner, T. and Schäper, R. and Schulz, S. and Fässler, T.F.
    Angewandte Chemie - International Edition 53 8944-8948 (2014)
    Reactions of the zinc(I) complex [Zn2(Mesnacnac)2] (Mesnacnac=[(2,4,6-Me3C6H2)NC(Me)] 2CH) with solid K3Bi2 dissolved in liquid ammonia yield crystals of the compound K4[ZnBi2] ·(NH3)12 (1), which contains the molecular, linear heteroatomic [Bi-Zn-Bi]4- polyanion (1a). This anion represents the first example of a three-atomic molecular ion of metal atoms being iso(valence)-electronic to CO2 and being synthesized in solution. The analogy of the discrete [Bi-Zn-Bi]4- anion and the polymeric 1 ∞ [(ZnBi4/2)4-] unit to monomeric CO2 and polymeric SiS2 is rationalized. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201404343
  • 2014 • 55 Effect of silver nanoparticles on human mesenchymal stem cell differentiation
    Sengstock, C. and Diendorf, J. and Epple, M. and Schildhauer, T.A. and Köller, M.
    Beilstein Journal of Nanotechnology 5 2058-2069 (2014)
    Background: Silver nanoparticles (Ag-NP) are one of the fastest growing products in nano-medicine due to their enhanced antibacterial activity at the nanoscale level. In biomedicine, hundreds of products have been coated with Ag-NP. For example, various medical devices include silver, such as surgical instruments, bone implants and wound dressings. After the degradation of these materials, or depending on the coating technique, silver in nanoparticle or ion form can be released and may come into close contact with tissues and cells. Despite incorporation of Ag-NP as an antibacterial agent in different products, the toxicological and biological effects of silver in the human body after long-term and low-concentration exposure are not well understood. In the current study, we investigated the effects of both ionic and nanoparticulate silver on the differentiation of human mesenchymal stem cells (hMSCs) into adipogenic, osteogenic and chondrogenic lineages and on the secretion of the respective differentiation markers adiponectin, osteocalcin and aggrecan. Results: As shown through laser scanning microscopy, Ag-NP with a size of 80 nm (hydrodynamic diameter) were taken up into hMSCs as nanoparticulate material. After 24 h of incubation, these Ag-NP were mainly found in the endo-lysosomal cell compartment as agglomerated material. Cytotoxicity was observed for differentiated or undifferentiated hMSCs treated with high silver concentrations (≥20 μg·mL-1 Ag-NP; ≥1.5 μg·mL-1 Ag+ ions) but not with low-concentration treatments (≤10 μg·mL-1 Ag-NP; ≤1.0 μg·mL-1 Ag+ ions). Subtoxic concentrations of Ag-NP and Ag+ ions impaired the adipogenic and osteogenic differentiation of hMSCs in a concentration-dependent manner, whereas chondrogenic differentiation was unaffected after 21 d of incubation. In contrast to aggrecan, the inhibitory effect of adipogenic and osteogenic differentiation was confirmed by a decrease in the secretion of specific biomarkers, including adiponectin (adipocytes) and osteocalcin (osteoblasts). Conclusion: Aside from the well-studied antibacterial effect of silver, little is known about the influence of nano-silver on cell differentiation processes. Our results demonstrate that ionic or nanoparticulate silver attenuates the adipogenic and osteogenic differentiation of hMSCs even at non-toxic concentrations. Therefore, more studies are needed to investigate the effects of silver species on cells at low concentrations during long-term treatment. © 2014 Sengstock et al.
    view abstractdoi: 10.3762/bjnano.5.214
  • 2014 • 54 Enhancement of low-temperature activity over Cu-exchanged zeolite beta from organotemplate-free synthesis for the selective catalytic reduction of NOx with NH3 in exhaust gas streams
    Xu, L. and Shi, C. and Zhang, Z. and Gies, H. and Xiao, F.-S. and De Vos, D. and Yokoi, T. and Bao, X. and Feyen, M. and Maurer, S. and Yilmaz, B. and Müller, U. and Zhang, W.
    Microporous and Mesoporous Materials 200 304-310 (2014)
    A series of Cu-exchanged Al-rich Beta zeolites from organotemplate-free synthesis was prepared and investigated for selective catalytic reduction (SCR) of NO<inf>x</inf> with NH<inf>3</inf> in exhaust gas streams. In comparison to conventional Cu-Beta zeolite with Si/Al ratio of 19, Cu-Beta zeolite with Si/Al ratio of 4 is a superior low-temperature NH<inf>3</inf>-SCR catalyst. Very high NO conversion (>95%) can be achieved at temperatures as low as 150 to ∼400 °C. XRD, UV-Vis-NIR and NH<inf>3</inf>-TPD measurements show that more isolated Cu2+ ions are present at the exchange sites of Al-rich Beta zeolite. The combination of CO-FTIR and H<inf>2</inf>-TPR analysis demonstrates that Cu2+ ions could be reduced more readily on the Al-rich Beta than on the conventional Beta probably due to the proximity of the isolated Cu2+ ions. These can be correlated to the enhancement of NO conversion at lower temperatures over Cu-exchanged Al-rich Beta zeolite. © 2014 Elsevier Inc.
    view abstractdoi: 10.1016/j.micromeso.2014.04.034
  • 2014 • 53 Impact of the specific surface area on the memory effect in Li-ion batteries: The case of anatase TiO2
    Madej, E. and Mantia, F.L. and Schuhmann, W. and Ventosa, E.
    Advanced Energy Materials 4 (2014)
    Until recently, the memory effect was believed to be absent in Li-ion battery materials. Here, the memory effect is clearly observed in anatase TiO2 nanoparticles when they are used as the negative electrode material in Li-ion batteries. Additionally, the memory effect strongly decreases with increasing specific surface area of the TiO2 sample. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/aenm.201400829
  • 2014 • 52 In situ non-DLVO stabilization of surfactant-free, plasmonic gold nanoparticles: Effect of Hofmeister's anions
    Merk, V. and Rehbock, C. and Becker, F. and Hagemann, U. and Nienhaus, H. and Barcikowski, S.
    Langmuir 30 4213-4222 (2014)
    Specific ion effects ranking in the Hofmeister sequence are ubiquitous in biochemical, industrial, and atmospheric processes. In this experimental study specific ion effects inexplicable by the classical DLVO theory have been investigated at curved water-metal interfaces of gold nanoparticles synthesized by a laser ablation process in liquid in the absence of any organic stabilizers. Notably, ion-specific differences in colloidal stability occurred in the Hückel regime at extraordinarily low salinities below 50 μM, and indications of a direct influence of ion-specific effects on the nanoparticle formation process are found. UV-vis, zeta potential, and XPS measurements help to elucidate coagulation properties, electrokinetic potential, and the oxidation state of pristine gold nanoparticles. The results clearly demonstrate that stabilization of ligand-free gold nanoparticles scales proportionally with polarizability and antiproportionally with hydration of anions located at defined positions in a direct Hofmeister sequence of anions. These specific ion effects might be due to the adsorption of chaotropic anions (Br-, SCN-, or I-) at the gold/water interface, leading to repulsive interactions between the partially oxidized gold particles during the nanoparticle formation process. On the other hand, kosmotropic anions (F - or SO4 2-) seem to destabilize the gold colloid, whereas Cl- and NO3 - give rise to an intermediate stability. Quantification of surface charge density indicated that particle stabilization is dominated by ion adsorption and not by surface oxidation. Fundamental insights into specific ion effects on ligand-free aqueous gold nanoparticles beyond purely electrostatic interactions are of paramount importance in biomedical or catalytic applications, since colloidal stability appears to depend greatly on the type of salt rather than on the amount. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/la404556a
  • 2014 • 51 Interaction of charged amino-acid side chains with ions: An optimization strategy for classical force fields
    Kahlen, J. and Salimi, L. and Sulpizi, M. and Peter, C. and Donadio, D.
    Journal of Physical Chemistry B 118 3960-3972 (2014)
    Many well-established classical biomolecular force fields, fitted on the solvation properties of single ions, do not necessarily describe all the details of ion pairing accurately, especially for complex polyatomic ions. Depending on the target application, it might not be sufficient to reproduce the thermodynamics of ion pairing, but it may also be necessary to correctly capture structural details, such as the coordination mode. In this work, we analyzed how classical force fields can be optimized to yield a realistic description of these different aspects of ion pairing. Given the prominent role of the interactions of negatively charged amino-acid side chains and divalent cations in many biomolecular systems, we chose calcium acetate as a benchmark system to devise a general optimization strategy that we applied to two popular force fields, namely, GROMOS and OPLS-AA. Using experimental association constants and first-principles molecular dynamics simulations as a reference, we found that small modifications of the van der Waals ion-ion interaction parameters allow a systematic improvement of the essential thermodynamic and structural properties of ion pairing. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/jp412490c
  • 2014 • 50 Interaction of colloidal nanoparticles with their local environment: The (ionic) nanoenvironment around nanoparticles is different from bulk and determines the physico-chemical properties of the nanoparticles
    Pfeiffer, C. and Rehbock, C. and Hühn, D. and Carrillo-Carrion, C. and De Aberasturi, D.J. and Merk, V. and Barcikowski, S. and Parak, W.J.
    Journal of the Royal Society Interface 11 (2014)
    The physico-chemical properties of colloidal nanoparticles (NPs) are influenced by their local environment, as, in turn, the local environment influences the physico-chemical properties of the NPs. In other words, the local environment around NPs has a profound impact on the NPs, and it is different from bulk due to interaction with the NP surface. So far, this important effect has not been addressed in a comprehensive way in the literature. The vicinity of NPs can be sensitively influenced by local ions and ligands, with effects already occurring at extremely low concentrations. NPs in the Hückel regime are more sensitive to fluctuations in the ionic environment, because of a larger Debye length. The local ion concentration hereby affects the colloidal stability of the NPs, as it is different from bulk owing to Debye Hückel screening caused by the charge of the NPs. This can have subtle effects, now caused by the environment to the performance of the NP, such as for example a buffering effect caused by surface reaction on ultrapure ligandfree nanogold, a size quenching effect in the presence of specific ions and a significant impact on fluorophore-labelled NPs acting as ion sensors. Thus, the aim of this review is to clarify and give an unifying view of the complex interplay between the NP's surface with their nanoenvironment. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
    view abstractdoi: 10.1098/rsif.2013.0931
  • 2014 • 49 Magnetic separation of paramagnetic ions from initially homogeneous solutions
    Yang, X. and Tschulik, K. and Uhlemann, M. and Odenbach, S. and Eckert, K.
    IEEE Transactions on Magnetics 50 (2014)
    The concentration change in an initially homogeneous paramagnetic solution is studied interferometrically upon applying sufficiently strong inhomogeneous magnetic fields. For this purpose, five different magnetic field configurations are analyzed. Clear evidence is provided that an enrichment of paramagnetic ions occurs in the field gradient. In particular, we show that the shape of this enrichment layer maps the spatial distribution of the magnetic field gradient force. © 1965-2012 IEEE.
    view abstractdoi: 10.1109/TMAG.2014.2324284
  • 2014 • 48 Modeling imidazolium-based ionic liquids with ePC-SAFT. Part II. Application to H2S and synthesis-gas components
    Ji, X. and Held, C. and Sadowski, G.
    Fluid Phase Equilibria 363 59-65 (2014)
    ePC-SAFT was used to model the gas solubility in ionic liquids (ILs). The gases under consideration were CO, H2, H2S and O2, and the imidazolium-based ILs studied were [Cnmim][Tf2N], [Cnmim][PF6] and [Cnmim][BF4] (n=2, 4, 6 and 8). For the ePC-SAFT modeling, each IL was considered to be completely dissociated into a cation and an anion. Each ion was modeled as a non-spherical species exerting repulsive, dispersive and Coulomb forces. CO, H2 and O2 were modeled as non-spherical molecules exerting repulsive and dispersive forces, and H2S was modeled as a non-spherical, associating molecule. ePC-SAFT reasonably predicts the gas solubility in the considered gas/IL mixtures. In order to describe the experimental gas solubilities quantitatively in a broad temperature and pressure range, one ion-specific binary interaction parameter between the IL-anion and the gas was applied, which was allowed to depend linearly on temperature. © 2013.
    view abstractdoi: 10.1016/j.fluid.2013.11.019
  • 2014 • 47 Photoluminescence of focused ion beam implanted Er3+: Y2SiO5 crystals
    Kukharchyk, N. and Pal, S. and Rödiger, J. and Ludwig, Ar. and Probst, S. and Ustinov, A.V. and Bushev, P. and Wieck, A.D.
    Physica Status Solidi - Rapid Research Letters 8 880-884 (2014)
    Erbium-doped low symmetry Y<inf>2</inf>SiO<inf>5</inf> crystals attract a lot of attention in perspective of quantum information applications. However, only doping of the samples during growth is available up to now, which yields a quite homogeneous doping density. In the present work, we deposit Er3+-ions by the focused ion beam technique at yttrium sites with several fluences in one sample. With a photoluminescence study of these locally doped Er3+:Y<inf>2</inf>SiO<inf>5</inf> crystals, we are able to evaluate the efficiency of the implantation process and develop it for the highest efficiency possible. We observe the dependence of ion activation after the post-implantation annealing on the fluence value. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssr.201409304
  • 2014 • 46 Position of Cu atoms at the Pt(111) electrode surfaces controls electrosorption of (H)SO4 (2)- from H2SO4 electrolytes
    Tymoczko, J. and Schuhmann, W. and Bandarenka, A.S.
    ChemElectroChem 1 (2014)
    Selective positioning of monolayer amounts of foreign atoms at the surface and subsurface regions of metal electrodes is a promising way to fine-tune the properties of the electrode/ electrolyte interface. The latter is critical as it largely governs the adsorption of electrolyte components and reaction intermediates and, therefore, controls many key electrocatalytic processes. Using model Pt(111) single-crystal electrodes, we demonstrate how the relative position of Cu atoms at the surface drastically changes the adsorption energies for (bi)sulfate anions. Our measurements involve pseudomorphic overlayers of Cu on Pt(111) as well as Cu-Pt(111) surface and sub-surface alloys, where Cu atoms were located either in the first or in the second atomic layers of Pt, respectively. In the case of Cu- Pt(111) surface alloys, specific adsorption of the anions starts earlier compared to the unmodified Pt(111) surface. In contrast, placing Cu atoms into the second atomic layer weakens the binding between the surface and the anions. Surprisingly, Cu pseudomorphic overlayers do not reveal any specific adsorption of (bi)sulfates (within the region of the overlayer stability). Taking into account that electrified interfaces between Pt(111) electrodes and sulfate-containing electrolytes often play the role of benchmark systems in fundamental physico-chemical and, particularly, electrocatalytic studies, our findings demonstrate a promising and relatively easy route of tuning the properties of these interfaces. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201300107
  • 2014 • 45 Retarding the corrosion of iron by inhomogeneous magnetic fields
    Sueptitz, R. and Tschulik, K. and Uhlemann, M. and Eckert, J. and Gebert, A.
    Materials and Corrosion 65 803-808 (2014)
    The influence of a magnetic field yielding high magnetic flux densities and high flux density gradients on the free corrosion behavior of iron in a low concentrated acidic solution with and without chloride ions is studied by long time exposure experiments and electrochemical impedance spectroscopy (EIS). A decrease of the corrosion rate in electrode surface regions of high magnetic flux density is detected. This decrease of the dissolution rate is significantly stronger in the presence of chloride ions. The observed effects are discussed on the basis of the magnetically induced forces acting on the ions present in the solution, the surface coverage fraction of adsorbed species, and the stability of these adsorbed species. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/maco.201206890
  • 2014 • 44 Symmetry-adapted perturbation theory based on density functional theory for noncovalent interactions
    Jansen, G.
    Wiley Interdisciplinary Reviews: Computational Molecular Science 4 127-144 (2014)
    The combination of symmetry-adapted perturbation theory (SAPT) of intermolecular interactions with a density functional theory (DFT) description of the underlying molecular properties, known as DFT-SAPT or SAPT(DFT), is reviewed, with a focus on methodology. A theoretical formalism avoiding an overlap expansion and the single-exchange approximation for the second-order exchange contributions is presented, and ways to include higher order contributions are discussed. The influence of the exchange-correlation potential and kernel underlying any DFT-SAPT calculation will be explicated. Enhancements of the computational efficiency through density fitting are described and comparisons to coupled cluster theory and experiment benchmark the performance of the method. © 2013 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/wcms.1164
  • 2014 • 43 Thermodynamic model for polyelectrolyte hydrogels
    Arndt, M.C. and Sadowski, G.
    Journal of Physical Chemistry B 118 10534-10542 (2014)
    The composition and swelling behavior of hydrogels may be dramatically influenced by external stimuli. Polyelectrolyte hydrogels consisting of charged polymers are particularly well-known for a high sensitivity to the presence of ionic species. For a thermodynamic description of such systems, the polyelectrolyte Perturbed-Chain Statistical Association Fluid Theory (pePC-SAFT) equation of state was augmented and merged with an extension of the modeling of hydrogels. This combined approach allowed for two effects to be taken into account: first, charges along the polymer chain and their interaction with mobile ions of the same or opposite charge in aqueous solutions and, second, the elastic interactions of swellable networks and their effect on Helmholtz energy and pressure. Thus, predictions of the degree of counterion condensation on the polymer chains could be made both for vapor-liquid equilibria of aqueous polyelectrolyte solutions and for polyelectrolyte hydrogels in aqueous salt solutions. The influence of temperature and molecular weight thereon was predicted successfully, and the impact of the degree of neutralization and the effect of additional salts were examined in comparison to literature data. With the inclusion of the influence of the Donnan potential, our model gave good predictions of swellable polyelectrolyte hydrogel systems in salt solutions. Poly(acrylic acid) and poly(methacrylic acid) gels were studied along with their corresponding sodium salts. Their swelling behavior in aqueous NaCl and NaNO3 solutions was examined. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/jp501798x
  • 2013 • 42 A study of electrode temperature lowering in Dy-containing ceramic metal halide lamps: I. the effect of mixtures of Dy, Tl and Na compared with pure Dy
    Westermeier, M. and Ruhrmann, C. and Bergner, A. and Denissen, C. and Suijker, J. and Awakowicz, P. and Mentel, J.
    Journal of Physics D: Applied Physics 46 (2013)
    The reduction in the electrode temperature by the gas phase emitter effect of dysprosium in ceramic metal halide lamps is investigated within special research lamps in dependence on the operating frequency of switched-dc lamp currents. The lamp tubes are made of transparent YAG material. They are filled with a fixed amount of Hg, which produces a buffer gas during lamp operation at a pressure of 2 MPa, with different amounts of DyI3 and in part with different amounts of NaI plus TlI. The Dy atomic ground state density is measured phase resolved both in the middle of the discharge and in front of the upper electrode by broad band absorption spectroscopy. The Dy ion density in front of the electrode is evaluated from line intensities being measured in absolute units by emission spectroscopy. The electrode tip temperature is determined by a 1λ - 2D pyrometric measuring method. It is found that a high Dy ion density in front of the electrode is correlated with a strong reduction in the electrode tip temperature relating to a pure mercury lamp. At low operating frequencies (f 100 Hz) the Dy ion density and the temperature reduction is high within the cathodic phase and low within the anodic phase, at higher operating frequencies an increased Dy ion density and a reduction in the electrode tip temperature overlaps onto the anodic phase. The Dy ion density is reduced and with it the tip temperature drop by an addition of Na and Tl vapour to the lamp plasma. The effect of Tl and Na is investigated in more detail in a successive paper. © 2013 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/46/18/185201
  • 2013 • 41 A study of electrode temperature lowering in Dy-containing ceramic metal halide lamps: II. An investigation of the converse effect of Tl and/or Na additives
    Westermeier, M. and Ruhrmann, C. and Bergner, A. and Denissen, C. and Suijker, J. and Awakowicz, P. and Mentel, J.
    Journal of Physics D: Applied Physics 46 (2013)
    The lowering of the gas phase emitter effect of Dy in ceramic metal halide lamps by the admixture of TlI and NaI to the rare earth iodide salt DyI 3 is investigated at lamps with different additives. The arcs are operated in an Hg buffer gas atmosphere of 2 MPa between rod-shaped pure tungsten electrodes within transparent YAG lamp tubes with a switched-dc current at operating frequencies from 1 Hz to 1 kHz. The atomic ground state density of Dy is measured phase resolved half way between the electrodes and in front of an electrode by broad band absorption spectroscopy, the Dy ion density in front of an electrode by emission spectroscopy and the electrode tip temperature pyrometrically within lamps seeded with differently composed fillings. The measurements confirm that a strong reduction in the electrode tip temperature is correlated with a high Dy ion density in front of the electrode within the cathodic half period. The Dy ion density is depressed predominantly and with it the reduction in the electrode tip temperature by a competing ionization of Tl, and in addition by a lowering of the Dy vapour pressure above the pool of molten salt by TlI. The influence of Na is of minor importance. © 2013 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/46/18/185202
  • 2013 • 40 CO adsorption on a mixed-valence ruthenium metal-organic framework studied by UHV-FTIR spectroscopy and DFT calculations
    Noei, H. and Kozachuk, O. and Amirjalayer, S. and Bureekaew, S. and Kauer, M. and Schmid, R. and Marler, B. and Muhler, M. and Fischer, R.A. and Wang, Y.
    Journal of Physical Chemistry C 117 5658-5666 (2013)
    The mixed-valence metal-organic framework [Ru3 II,III(btc)2Cl1.5] (Ru-MOF) was synthesized by the controlled SBU approach and characterized by combined powder XRD, XPS, and FTIR methods. The interaction of CO molecules with Ru-MOF was studied by a novel instrumentation for ultra-high-vacuum (UHV) FTIR spectroscopy. The high-quality IR data demonstrate the presence of two different CO species within the framework: a strongly bonded CO showing a low-lying band at 2137 cm-1 and a second CO species at 2171 cm-1 with a lower binding energy. It was found that these IR bands cannot be assigned in a straightforward manner to CO molecules adsorbed on the coordinatively unsaturated RuII site (CUS) and RuIII site connected to an additional Cl- ion for charge compensation. The accurate DFT calculations reveal that the structural and electronic properties of the mixed-valence Ru-MOF are much more complex than expected. One of the Cl- counterions could be transferred to a neighboring paddle-wheel, forming an anionic SBU blocked by two Cl- counterions, whereas the other positively charged paddle-wheel with a Ru2 II,III dimer exposes two "free" CUS, which can bind two CO molecules with different frequencies and binding energies. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/jp3056366
  • 2013 • 39 Correlation of electronic and magnetic properties of thin polymer layers with cobalt nanoparticles
    Kharchenko, A. and Lukashevich, M. and Popok, V. and Khaibullin, R. and Valeev, V. and Bazarov, V. and Petracic, O. and Wieck, A. and Odzhaev, V.
    Particle and Particle Systems Characterization 30 180-184 (2013)
    Nanoparticles (NPs) of cobalt are synthesized in shallow layers of polyimide using 40 keV implantation of Co+ ions with a few different fluences at various ion current densities. Nucleation of individual NPs at low fluencies and their percolation at high fluencies are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites that can be controlled by the implantation regimes. In particular, one can tune the magnetoresistance between negative and positive through appropriate choice of ion fluence and current density. The found non-monotonous dependence of the magnetoresistance on the applied magnetic field allows suggestion of spin-dependent domain wall scattering affecting the electron transport. The samples implanted with low fluencies demonstrate superparamagnetic behavior down to very low blocking temperatures. For high fluence (1.25 × 1017 cm-2) the transition to ferromagnetic ordering is observed that is related to the increased magnetic interaction of NPs. Nanoparticles of cobalt are synthesized in shallow layers of polyimide using low-energy implantation of cobalt ions. Nucleation of individual particles and their percolation are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites. By tuning the implantation regimes magnetoresistance and transitions between the superparamagnetic and ferromagnenic behavior can be controlled. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppsc.201200042
  • 2013 • 38 Counterion-mediated hierarchical self-assembly of an ABC miktoarm star terpolymer
    Hanisch, A. and Gröschel, A.H. and Förtsch, M. and Drechsler, M. and Jinnai, H. and Ruhland, T.M. and Schacher, F.H. and Müller, A.H.E.
    ACS Nano 7 4030-4041 (2013)
    Directed self-assembly processes of polymeric systems represent a powerful approach for the generation of structural hierarchy in analogy to biological systems. Herein, we utilize triiodide as a strongly polarizable counterion to induce hierarchical self-assembly of an ABC miktoarm star terpolymer comprising a polybutadiene (PB), a poly(tert-butyl methacrylate) (PtBMA), and a poly(N-methyl-2-vinylpyridinium) (P2VPq) segment. Hereby, the miktoarm architecture in conjunction with an increasing ratio of triiodide versus iodide counterions allows for a stepwise assembly of spherical micelles as initial building blocks into cylindrical structures and superstructures thereof. Finally, micrometer-sized multicompartment particles with a periodic lamellar fine structure are observed, for which we introduce the term "woodlouse". The counterion-mediated decrease in hydrophilicity of the corona-forming P2VPq block is the underlying trigger to induce this hierarchical structure formation. All individual steps and the corresponding intermediates toward these well-defined superstructures were intensively studied by scattering and electron microscopic techniques, including transmission electron microtomography. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/nn400031u
  • 2013 • 37 Cu doped V2O5 flowers as cathode material for high-performance lithium ion batteries
    Yu, H. and Rui, X. and Tan, H. and Chen, J. and Huang, X. and Xu, C. and Liu, W. and Yu, D.Y.W. and Hng, H.H. and Hoster, H.E. and Yan, Q.
    Nanoscale 5 4937-4943 (2013)
    Hierarchical Cu doped vanadium pentoxide (V2O5) flowers were prepared via a simple hydrothermal approach followed by an annealing process. The flower precursors are self-assembled with 1D nanobelts surrounding a central core. The morphological evolution is investigated and a plausible mechanism is proposed. As the cathode material for lithium ion batteries, the Cu doped V2O5 samples exhibit improved electrochemical performance compared to the un-doped ones. Among them Cu 0.02V1.98O5 delivered higher reversible specific capacities, better cycling stabilities and excellent rate capabilities, e.g. 97 mA h g-1 at 20.0 C. © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3nr00548h
  • 2013 • 36 Current-voltage characteristic features of diodes irradiated with 170 MeV xenon ions
    Poklonski, N.A. and Gorbachuk, N.I. and Nha, V.Q. and Tarasik, M.I. and Shpakovski, S.V. and Filipenia, V.A. and Skuratov, V.A. and Wieck, A. and Kołtunowicz, T.N.
    Acta Physica Polonica A 123 926-928 (2013)
    Diodes manufactured on the wafers of single-crystalline silicon uniformly doped with phosphorus are studied. The wafer resistivity was 90 cm. Xenon ions were implanted into the diodes from the side of the p+-region (implantation energy 170 MeV, fluence ψ from 5×107 to 109 cm-2). It is shown that the formation of a continuous irradiation damaged layer with the thickness of the order of magnitude of the average projective range creates prerequisites for the negative differential resistance in the current-voltage characteristics of the irradiated diodes.
    view abstractdoi: 10.12693/APhysPolA.123.926
  • 2013 • 35 Dynamic of the growth flux at the substrate during high-power pulsed magnetron sputtering (HiPIMS) of titanium
    Breilmann, W. and Maszl, C. and Benedikt, J. and von Keudell, A.
    Journal of Physics D-applied Physics 46 485204 (2013)
    The temporal distribution of the incident fluxes of argon and titanium ions on the substrate during an argon HiPIMS pulse to sputter titanium with pulse lengths between 50 to 400 mu s and peak powers up to 6 kW are measured by energy-resolved ion mass spectrometry with a temporal resolution of 2 mu s. The data are correlated with time-resolved growth rates and with phase-resolved optical emission spectra. Four ion contributions impinging on the substrate at different times and energies are identified: (i) an initial argon ion burst after ignition, (ii) a titanium and argon ion flux in phase with the plasma current due to ionized neutrals in front of the target, (iii) a small energetic burst of ions after plasma shut off, and (iv) cold ions impinging on the substrate in the late afterglow showing a pronounced maximum in current. The last contribution originates from ions generated during the plasma current maximum at 50 mu s after ignition in the magnetic trap in front of the target. They require long transport times of a few 100 mu s to reach the substrate. All energy distributions can be very well fitted with a shifted Maxwellian indicating an efficient thermalization of the energetic species on their travel from target to substrate. The energy of titanium is higher than that of argon, because they originate from energetic neutrals of the sputter process. The determination of the temporal sequence of species, energies and fluxes in HiPIMS may lead to design rules for the targeted generation of these discharges and for synchronized biasing concepts to further improve the capabilities of high-power impulse magnetron sputtering (HiPIMS) processes.
    view abstractdoi: 10.1088/0022-3727/46/48/485204
  • 2013 • 34 Eu-doped ZnO nanowire arrays grown by electrodeposition
    Lupan, O. and Pauporté, T. and Viana, B. and Aschehoug, P. and Ahmadi, M. and Cuenya, B.R. and Rudzevich, Y. and Lin, Y. and Chow, L.
    Applied Surface Science 282 782-788 (2013)
    The preparation of efficient light emitting diodes requires active optical layers working at low voltage for light emission. Trivalent lanthanide doped wide-bandgap semiconducting oxide nanostructures are promising active materials in opto-electronic devices. In this work we report on the electrochemical deposition (ECD) of Eu-doped ZnO (ZnO:Eu) nanowire arrays on glass substrates coated with F-doped polycrystalline SnO2. The structural, chemical and optical properties of ZnO:Eu nanowires have been systematically characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and photoluminescence. XRD results suggest the substitution of Zn2+ by Eu ions in the crystalline lattice. High-resolution TEM and associated electron diffraction studies indicate an interplanar spacing of 0.52 nm which corresponds to the (0 0 0 1) crystal plane of the hexagonal ZnO, and a growth along the c-direction. The ZnO:Eu nanowires have a single crystal structure, without noticeable defects. According to EDX, SIMS and XPS studies, cationic Eu species are detected in these samples showing the incorporation of Eu into the ZnO matrix. The oxidation states of europium ions in the nanowires are determined as +3 (74%) and +2 (26%). Photoluminescence studies demonstrated red emission from the Eu-doped ZnO nanowire arrays. When Eu was incorporated during the nanowire growth, the sharp 5D0-7F 2 transition of the Eu3+ ion at around 612 nm was observed. These results suggest that Eu doped ZnO nanowires could pave the way for efficient, multispectral LEDs and optical devices. © 2013 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2013.06.053
  • 2013 • 33 Formation of crystalline gamma-Al2O3 induced by variable substrate biasing during reactive magnetron sputtering
    Prenzel, M. and Kortmann, A. and von Keudell, A. and Nahif, F. and Schneider, J. M. and Shihab, M. and Brinkmann, R. P.
    Journal of Physics D-applied Physics 46 084004 (2013)
    Reactive magnetron sputtering is a widely used technique to deposit various materials such as oxides and nitrides with a superior control of morphology and stoichiometry. The adjustment of the film properties at a given substrate temperature is believed to be affected by the average energy < E > per incorporated atom during film growth, which is controlled by the ion-to-neutral ratio in the film forming growth flux and the energy of the incident ions. This concept is tested for alumina growth in an rf-magnetron discharge by keeping < E >, the average energy of the incident ions E-ions, and the ion-to-neutral flux ratio constant, but varying only the energy distribution of the incident ions (ion energy distribution-IED). The influence of the IED on film growth is monitored by observing the transition of the films between x-ray amorphous Al2O3 to gamma-Al2O3. The results reveal that the substrate temperature necessary for the transition to gamma-crystalline films can be lowered by almost 100 degrees C, when the maximum energy of the incident ions is kept at 100 eV, while maintaining the energy per incorporated atom at 11 eV. This result is compared with TRIM calculations for the collision cascades of impacting ions.
    view abstractdoi: 10.1088/0022-3727/46/8/084004
  • 2013 • 32 Low-temperature oxidation of alkali overlayers: Ionic species and reaction kinetics
    Krix, D. and Nienhaus, H.
    Applied Surface Science 270 231-237 (2013)
    Clean and oxidized alkali metal films have been studied using X-ray photoelectron spectroscopy (XPS). Thin films, typically 10 nm thick, of lithium, sodium, potassium, rubidium and cesium have been deposited on silicon substrates and oxidized at 120 K. Plasmon losses were found to dress the primary photo emission structures of the metals' core lines which confirms the metallic, bulk like nature of the films. The emission from the O 1s core levels was used to determine the chemical composition and the reaction kinetics during the exposure to molecular oxygen at low pressures. Molecular oxide ions O2- and O22- as well as atomic oxygen ions O2- were detected in varying amounts depending on the alkali metal used. Diffusive transport of material in the film is shown to greatly determine the composition of the oxides. Especially, the growth of potassium superoxide is explained by the diffusion of potassium atoms to the surface and growth at the surface in a Deal-Grove like model.
    view abstractdoi: 10.1016/j.apsusc.2013.01.008
  • 2013 • 31 Measurement of the silver ion concentration in wound fluids after implantation of silver-coated megaprostheses: Correlation with the clinical outcome
    Hussmann, B. and Johann, I. and Kauther, M.D. and Landgraeber, S. and Jäger, M. and Lendemans, S.
    BioMed Research International 2013 (2013)
    Background. Tumor patients and patients after traumas are endangered by a reduced immune defense, and a silver coating on their megaprostheses may reduce their risks of infection. The aim of this study was to determine the silver ion concentration directly measured from the periprosthetic tissue and the influence on the clinical outcome. Material and Methods. Silver ions were evaluated in 5 mL wound fluids two days postoperatively and in blood patients 7 and 14 days after surgery using inductively coupled plasma emission spectrometry in 18 patients who underwent total joint replacement with a silver-coated megaendoprosthesis. Results. The concentration of silver ions averaged 0.08 parts per million. Patients who showed an increased silver concentration in the blood postoperatively presented a lower silver concentration in the wound fluids and a delayed decrease in C-reactive protein levels. There were significantly fewer reinfections and shorter hospitalization in comparison with a group that did not receive a silver-coated megaprosthesis. Conclusion. An increased concentration of silver in the immediate surroundings of silver-coated prostheses was demonstrated for the first time in cohorts of patients with trauma or tumors. An elevated concentration of silver ions in the direct periprosthetic tissue may have reduced the infection rate. © 2013 B. Hussmann et al.
    view abstractdoi: 10.1155/2013/763096
  • 2013 • 30 Silver as antibacterial agent: Ion, nanoparticle, and metal
    Chernousova, S. and Epple, M.
    Angewandte Chemie - International Edition 52 1636-1653 (2013)
    The antibacterial action of silver is utilized in numerous consumer products and medical devices. Metallic silver, silver salts, and also silver nanoparticles are used for this purpose. The state of research on the effect of silver on bacteria, cells, and higher organisms is summarized. It can be concluded that the therapeutic window for silver is narrower than often assumed. However, the risks for humans and the environment are probably limited. Silver shield: Silver is used in different forms as an antibacterial agent. Earlier, sparingly soluble silver salts were predominantly used, but today, silver nanoparticles (see picture for an SEM image of cubic silver nanoparticles) are gaining increasing importance. As silver is also toxic towards mammalian cells, there is the question of the therapeutic window in the cases of consumer products and medical devices. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201205923
  • 2013 • 29 Ultra-thin MoS2 irradiated with highly charged ions
    Hopster, J. and Kozubek, R. and Krämer, J. and Sokolovsky, V. and Schleberger, M.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 317 165-169 (2013)
    Single MoS2 layers exfoliated on KBr have been irradiated with highly charged Xe ions, i.e. with Xe35+ and Xe40+. By atomic force microscopy (AFM) we identified pits and hillocks induced by single ion impacts. The latter ones appear on single layer and bulk-like MoS 2 after both irradiations, whereas their diameter and height apparently depend on the charge state q and layer number. By comparison of contact mode and tapping mode AFM measurements we deduce that these ion induced defects are topographical hillocks accompanied by an enhanced friction. In contrast to this, pit-like structures were only observed on single layer MoS2 irradiated with q = 40. Taking into account the well known ion induced pit formation on KBr due to defect mediated sputtering, we deduce that pit formation takes place in the substrate and not in the MoS2 layer. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.nimb.2013.02.038
  • 2012 • 28 Cytotoxicity and ion release of alloy nanoparticles
    Hahn, A. and Fuhlrott, J. and Loos, A. and Barcikowski, S.
    Journal of Nanoparticle Research 14 (2012)
    It is well-known that nanoparticles could cause toxic effects in cells. Alloy nanoparticles with yet unknown health risk may be released from cardiovascular implants made of Nickel-Titanium or Cobalt-Chromium due to abrasion or production failure. We show the bio-response of human primary endothelial and smooth muscle cells exposed to different concentrations of metal and alloy nanoparticles. Nanoparticles having primary particle sizes in the range of 5-250 nm were generated using laser ablation in three different solutions avoiding artificial chemical additives, and giving access to formulations containing nanoparticles only stabilized by biological ligands. Endothelial cells are found to be more sensitive to nanoparticle exposure than smooth muscle cells. Cobalt and Nickel nanoparticles caused the highest cytotoxicity. In contrast, Titanium, Nickel- Iron, and Nickel-Titanium nanoparticles had almost no influence on cells below a nanoparticle concentration of 10 lM. Nanoparticles in cysteine dissolved almost completely, whereas less ions are released when nanoparticles were stabilized in water or citrate solution. Nanoparticles stabilized by cysteine caused less inhibitory effects on cells suggesting cysteine to form metal complexes with bioactive ions in media. © Springer Science+Business Media B.V. 2012.
    view abstractdoi: 10.1007/s11051-011-0686-3
  • 2012 • 27 Enrichment of paramagnetic ions from homogeneous solutions in inhomogeneous magnetic fields
    Yang, X. and Tschulik, K. and Uhlemann, M. and Odenbach, S. and Eckert, K.
    Journal of Physical Chemistry Letters 3 3559-3564 (2012)
    Applying interferometry to an aqueous solution of paramagnetic manganese ions, subjected to an inhomogeneous magnetic field, we observe an unexpected but highly reproducible change in the refractive index. This change occurs in the top layer of the solution, closest to the magnet. The shape of the layer is in accord with the spatial distribution of the largest component of the magnetic field gradient force. It turns out that this layer is heavier than the underlying solution because it undergoes a Rayleigh-Taylor instability upon removal of the magnet. The very good agreement between the magnitudes of buoyancy, associated with this layer, and the field gradient force at steady state provides conclusive evidence that the layer formation results from an enrichment of paramagnetic manganese ions in regions of high magnetic field gradient. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/jz301561q
  • 2012 • 26 Measuring and modeling alcohol/salt systems
    Held, C. and Prinz, A. and Wallmeyer, V. and Sadowski, G.
    Chemical Engineering Science 68 328-339 (2012)
    Liquid densities, osmotic coefficients, and mean ionic activity coefficients (MIAC) at 25. °C of single-salt alcohol (methanol and ethanol) solutions containing univalent ions were measured and modeled with the ePC-SAFT equation of state. In accordance with our previous work [Held, C., Cameretti, L.F., Sadowski, G., Fluid Phase Equlilib. 270 (2008) 87-96], only two solvent-specific ion parameters were adjusted to experimental solution densities and osmotic coefficients: the solvated ion diameter and the dispersion-energy parameter. ePC-SAFT was able to reproduce experimental data of the respective alcohol/salt systems with reasonable accuracy. Based on the solvent-specific ion-parameter sets, it is possible to predict densities and MIACs in ternary and quaternary water/alcohol(s)/salt solutions by introducing appropriate mixing rules that do not contain any additional fitting parameters. © 2011 Elsevier Ltd.
    view abstractdoi: 10.1016/j.ces.2011.09.040
  • 2011 • 25 Effects of specific versus nonspecific ionic interactions on the structure and lateral organization of lipopolysaccharides
    Jeworrek, C. and Evers, F. and Howe, J. and Brandenburg, K. and Tolan, M. and Winter, R.
    Biophysical Journal 100 2169-2177 (2011)
    We report x-ray reflectivity and grazing incidence x-ray diffraction measurements of lipopolysaccharide (LPS) monolayers at the water-air interface. Our investigations reveal that the structure and lateral ordering of the LPS molecules is very different from phospholipid systems and can be modulated by the ionic strength of the aqueous subphase in an ion-dependent manner. Our findings also indicate differential effects of monovalent and divalent ions on the two-dimensional ordering of lipid domains. Na+ ions interact unspecifically with LPS molecules based on their ability to efficiently screen the negative charges of the LPS molecules, whereas Ca2+ ions interact specifically by cross-linking adjacent molecules in the monolayer. At low lateral pressures, Na+ ions present in the subphase lead to a LPS monolayer structure ordered over large areas with high compressibility, nearly hexagonal packing of the hydrocarbon chains, and high density in the LPS headgroup region. At higher film pressures, the LPS monolayer becomes more rigid and results in a less perfect, oblique packing of the LPS hydrocarbon chains as well as a smaller lateral size of highly ordered domains on the monolayer. Furthermore, associated with the increased surface pressure, a conformational change of the sugar headgroups occurs, leading to a thickening of the entire LPS monolayer structure. The effect of Ca2+ ions in the subphase is to increase the rigidity of the LPS monolayer, leading to an oblique packing of the hydrocarbon chains already at low film pressures, an upright orientation of the sugar moieties, and much smaller sizes of ordered domains in the plane of the monolayer. In the presence of both Na+-and Ca2+ ions in the subphase, the screening effect of Na+ is predominant at low film pressures, whereas, at higher film pressures, the structure and lateral organization of LPS molecules is governed by the influence of Ca2+ ions. The unspecific charge-screening effect of the Na+ ions on the conformation of the sugar moiety becomes less dominant at biologically relevant lateral pressures. © 2011 by the Biophysical Society.
    view abstractdoi: 10.1016/j.bpj.2011.03.019
  • 2011 • 24 Growth of GaN based structures on focused ion beam patterned templates
    Cordier, Y. and Tottereau, O. and Nguyen, L. and Ramdani, M. and Soltani, A. and Boucherit, M. and Troadec, D. and Lo, F.-Y. and Hu, Y.Y. and Ludwig, Ar. and Wieck, A.D.
    Physica Status Solidi (C) Current Topics in Solid State Physics 8 1516-1519 (2011)
    Focused ion beam technique is a powerful tool for defining patterns within a semiconductor film. In this paper, we show that it is possible to realize patterns such as disks and columns within thick GaN templates and that it is compatible with the regrowth of GaN based heterostructures. We study the effect of the pattern size and shape on the regrowth by molecular beam epitaxy. We show that the growth using ammonia as the nitrogen source with flux at temperature optimized for 2-dimensional growth leads to the apparition of well defined growth planes. We show that the development of these planes is dependent with the initial pattern size and shape. These results confirm the difficulty for realizing micro or nano-columns with axial heterostructures. At the opposite, these growth conditions seem favourable for core-shell heterostructures column with well defined m-plane and eventually a-plane lateral facets. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssc.201000882
  • 2011 • 23 Hawking radiation on an ion ring in the quantum regime
    Horstmann, B. and Schützhold, R. and Reznik, B. and Fagnocchi, S. and Cirac, J.I.
    New Journal of Physics 13 (2011)
    This paper discusses a recent proposal for the simulation of acoustic black holes with ions (Horstmann et al 2010 Phys. Rev. Lett. 104 250403). Ions are rotating on a ring with an inhomogeneous but stationary velocity profile. Phonons cannot leave a region in which the ion velocity exceeds the group velocity of the phonons, because light cannot escape from a black hole. The system is described by a discrete field theory with a nonlinear dispersion relation. Hawking radiation is emitted by this acoustic black hole, generating entanglement between the inside and the outside of the black hole. We study schemes for detecting the Hawking effect in this setup. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
    view abstractdoi: 10.1088/1367-2630/13/4/045008
  • 2011 • 22 Hierarchical micro- and mesoporous carbide-derived carbon as a high-performance electrode material in supercapacitors
    Rose, M. and Korenblit, Y. and Kockrick, E. and Borchardt, L. and Oschatz, M. and Kaskel, S. and Yushin, G.
    Small 7 1108-1117 (2011)
    Ordered mesoporous carbide-derived carbon (OM-CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of micropores. The micropores result in outstanding adsorption capacities and the well-defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temperature on the electrochemical performance of these materials in supercapacitors based on a 1 M aqueous solution of sulfuric acid and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are reported. Cyclic voltammetry shows the specific capacitance of the OM-CDC materials exceeds 200 F g-1 in the aqueous electrolyte and 185 F g-1 in the ionic liquid, when measured in a symmetric configuration in voltage ranges of up to 0.6 and 2 V, respectively. The ordered mesoporous channels in the produced OM-CDC materials serve as ion-highways and allow for very fast ionic transport into the bulk of the OM-CDC particles. At room temperature the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of ∼10 A g-1 in ionic liquid and aqueous electrolytes, respectively. The supercapacitors based on 250-300 μm OM-CDC electrodes demonstrate an operating frequency of up to 7 Hz in aqueous electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM-CDC materials is unmatched by state-of-the art activated carbons and strictly microporous CDC materials. © 2011 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201001898
  • 2011 • 21 How to obtain structured metal deposits from diamagnetic ions in magnetic gradient fields?
    Tschulik, K. and Yang, X. and Mutschke, G. and Uhlemann, M. and Eckert, K. and Sueptitz, R. and Schultz, L. and Gebert, A.
    Electrochemistry Communications 13 946-950 (2011)
    Electrodeposition of Bi in magnetic gradient fields was performed from two different electrolytes. The first electrolyte contained only diamagnetic Bi 3+-ions; the second one additionally contained electrochemically inert paramagnetic Mn2+-ions. While homogeneous Bi deposits were obtained from the former, structured Bi layers were derived from the latter. The structured deposits show an inverse correlation between deposit thickness and superimposed magnetic field gradient. Minima of film thickness are observed in regions of maximum magnetic gradients. This demonstration of magneto-electrochemical structuring by deposition of diamagnetic ions is discussed considering the acting magnetic forces. Several possibilities explaining the structuring mechanism are presented. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.elecom.2011.06.007
  • 2011 • 20 Influence of individual ionic components on the agglomeration kinetics of silver nanoparticles
    Gebauer, J.S. and Treuel, L.
    Journal of Colloid and Interface Science 354 546-554 (2011)
    The precise characteristic of the agglomeration behavior of colloidal suspensions is of paramount interest to many current studies in nanoscience. This work seeks to elucidate the influence that differently charged salts have on the agglomeration state of a Lee-Meisel-type silver colloid. Moreover, we investigate the influence of the chemical nature of individual ions on their potential to induce agglomeration. Raman spectroscopy and surface-enhanced Raman spectroscopy are used to give insights into mechanistic aspects of the agglomeration process and to assess the differences in the influence of different salts on the agglomeration behavior. Finally, we demonstrate the potential of the measurement procedure used in this work to determine the elementary charge on colloidal NPs. © 2010 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2010.11.016
  • 2011 • 19 Influence of Na on the structure of Bi4Ti3O 12 films deposited by liquid-delivery spin MOCVD
    Schwarzkopf, J. and Dirsyte, R. and Devi, A. and Kwasniewski, A. and Schmidbauer, M. and Wagner, G. and Michling, M. and Schmeisser, D. and Fornari, R.
    Thin Solid Films 519 5754-5759 (2011)
    Thin Na-substituted Bi4Ti3O12 films were grown by the liquid-delivery spin metal-organic chemical vapor deposition (MOCVD) method with different concentrations of sodium bis(trimethylsilyl)amide [Na(TMSA)] as Na precursor. At a substrate temperature of 600 °C the original Aurivillius structure was preserved, however high resolution x-ray diffraction (HRXRD) studies indicate that the Na-substituted phase exhibits a slightly smaller lattice parameter compared to the pure Bi4Ti 3O12 phase. From additional x-ray photoemission spectroscopy (XPS) results, we have concluded that monovalent Na+ ions have been incorporated on Bi3+ sites in the perovskite units. The proposed charge compensation for this aliovalent substitution is explained by a shift of the valence state of Bi3+ ions in the vicinity of the incorporated Na+ ions from 3+ to 5+. Due to the small ionic radius of the Bi5+ ions, the incorporation efficiency amounts to a few atomic percent only. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2010.12.206
  • 2011 • 18 Interface failure and adhesion measured by focused ion beam cutting of metal-polymer interfaces
    Cordill, M.J. and Schmidegg, K. and Dehm, G.
    Philosophical Magazine Letters 91 530-536 (2011)
    New developments in flexible electronics require metal films to adhere to polymer substrates. Measuring the interfacial adhesion of these systems is challenging, requiring the formulation of new techniques and models. A strategy to measure the adhesion of Cr-polyethylene terephthalate (PET) interfaces using tensile straining and buckle formation is presented in this article. Focused ion beam cross-sectioning of the buckles reveals that the polymer substrate can locally fail, which may lead to an overestimate of adhesion. Cr-PET adhesion energy of 9.4±1.6 J/m2 is determined with the present approach. © 2011 Taylor &Francis.
    view abstractdoi: 10.1080/09500839.2011.593575
  • 2011 • 17 Investigating the influence of the operating frequency on the gas phase emitter effect of dysprosium in ceramic metal halide lamps
    Reinelt, J. and Westermeier, M. and Ruhrmann, C. and Bergner, A. and Luijks, G.M.J.F. and Awakowicz, P. and Mentel, J.
    Journal of Physics D: Applied Physics 44 (2011)
    The dependence of the gas phase emitter effect of Dy on a variation of the operating frequency between a few Hz and 2 kHz is investigated in a high intensity discharge lamp. The buffer gas of the lamp consisting of Ar, Kr and predominantly Hg is seeded with DyI3, its burner vessel is formed from transparent yttrium-alumina-garnet material. Phase and spatial resolved emission spectroscopy in front of the lamp electrode and pyrometric temperature measurements along the tungsten electrode are performed with a spectroscopic setup. Dy atom and ion densities in front of the electrode are deduced from absolute intensities of optically thin Dy lines and a plasma temperature, derived from the absolute intensity of mercury lines. Phase resolved values of the electrode tip temperature Ttip and input power Pin are obtained from temperature distributions along the electrode. Distinctly higher Dy ion and atom densities are measured in front of the electrode within the cathodic phase. With increasing operating frequency a reduction in both atoms and ions is observed in front of the cathode. In contrast, an increase in the ion density in front of the anode is seen. Moreover, the Dy ion density is drastically reduced by an additional seeding of the lamp with TlI. It is found that an up rating of the Dy ion density is correlated with a decline of T tip and Pin. At higher frequencies this effect takes place not only within the cathodic phase but also within the anodic phase. The reduction of the average electrode tip temperature of the order of several hundred kelvin compared with a YAG lamp with a pure mercury filling is explained by a Dy monolayer on the electrode surface which is sustained by a Dy ion current. © 2011 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/44/22/224006
  • 2011 • 16 iTRAQ protein quantification: A quality-controlled workflow
    Burkhart, J.M. and Vaudel, M. and Zahedi, R.P. and Martens, L. and Sickmann, A.
    Proteomics 11 1125-1134 (2011)
    Reporter ion-based methods are among the major techniques to quantify peptides and proteins. Two main labels, tandem mass tag (TMT) and iTRAQ, are widely used by the proteomics community. They are, however, often applied as out-of-the-box methods, without thorough quality control. Thus, due to undiscovered limitations of the technique, irrelevant results might be trusted. To address this issue, we here propose a step-by-step quality control of the iTRAQ workflow. From sample preparation to final ratio calculation we provide metrics and techniques assessing the actual effectiveness of iTRAQ quantification as well as a novel method for more reliable protein ratio estimation. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pmic.201000711
  • 2011 • 15 Metal ion release kinetics from nanoparticle silicone composites
    Hahn, A. and Brandes, G. and Wagener, P. and Barcikowski, S.
    Journal of Controlled Release 154 164-170 (2011)
    Metal ion release kinetics from silver and copper nanoparticle silicone composites generated by laser ablation in liquids are investigated. The metal ion transport mechanism is studied by using different model equations and their fit to experimental data. Results indicate that during the first 30 days of immersion, Fickian diffusion is the dominant transport mechanism. After this time period, the oxidation and dissolution of nanoparticles from the bulk determine the ion release. This second mechanism is very slow since the dissolution of the nanoparticle is found to be anisotropic. Silver ion release profile is best described by pseudo-first order exponential equation. Copper ion release profile is best described by a second order exponential equation. For practical purposes, the in vitro release characteristics of the bioactive metal ions are evaluated as a function of nanoparticle loading density, the chemistry and the texture of the silicone. Based on the proposed two-step release model, a prediction of the release characteristics over a time course of 84 days is possible and a long-term ion release could be demonstrated. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jconrel.2011.05.023
  • 2011 • 14 Optical orientation of Mn2+ ions in GaAs in weak longitudinal magnetic fields
    Akimov, I.A. and Dzhioev, R.I. and Korenev, V.L. and Kusrayev, Yu.G. and Sapega, V.F. and Yakovlev, D.R. and Bayer, M.
    Physical Review Letters 106 (2011)
    We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins. © 2011 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.106.147402
  • 2011 • 13 Simultaneous correlation of hydrophobic interactions in HIC and protein solubility in aqueous salt solutions and mixed solvents
    Mollerup, J.M. and Breil, M.P. and Vogelpohl, C. and Sadowski, G.
    Fluid Phase Equilibria 301 163-170 (2011)
    The chromatographic retention in hydrophobic and reversed phase chromatography and the solubility of proteins display some common features. The chromatographic retention, as well as the solubility, is modulated by the thermodynamic properties of the solute in the fluid phase. The retention measurements at linear conditions provide information of the solution properties of the protein at infinite dilution, and the solubility measurements produce the supplementary information about the solution properties at the saturation limit. This provides a useful approach to simultaneous correlation of the chromatographic retention and the solubility.The experimental data, used for the correlation, comprise retention measurements of lysozyme on different HIC adsorbents using an aqueous ammonium sulphate eluant, an aqueous ammonium sulphate eluant with an admixture of ethanol, as well as published solubility data.The chromatographic retention data and the corresponding solubility data have been correlated using a chemical potential model derived from Kirkwood's theory of solutions of charged macro-ions and zwitterions in electrolyte solutions. The model correlated the chromatographic retention factor and the solubility data within the precision of the measurements. The model was applied in a pH range from 4 to 11. It was demonstrated experimentally, as well as theoretically, that an admixture of ethanol to the aqueous eluant changes the thermodynamic retention factor on various adsorbents identically when compared to the thermodynamic retention factor in an ethanol free eluant. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.fluid.2010.11.028
  • 2011 • 12 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
  • 2010 • 11 Analysis of the ion distribution at a charged solid-liquid interface using X-ray standing waves
    Brücher, M. and Jacob, P. and Von Bohlen, A. and Franzke, J. and Sternemann, C. and Paulus, M. and Hergenröder, R.
    Langmuir 26 959-966 (2010)
    Functionalized solid-liquid interfaces were analyzed by X-ray standing waves (XSW) combined with, streaming current measurements to study surface charges, interfacial potential, and ion distributions. Thin films of aqueous solution containing Br- anions and Fe3+ cations at a concentration of 10 mg/L were prepared on functionalized silicon wafers. Functionalization of Si surfaces was accomplished by aminosilane groups shifting the interfacial potential, toward, positive values. The ion distribution was measured with nanometer resolution, which allows distinguishing between absorbed and mobile ions at the surface and in the diffusive layer, respectively. For Br-, different degrees of ion attraction were measured for the pH values 5.7 and 2.8. The ion Debye length values of the diffuse layer were 4 and 2 nm, respectively. © 2009 American Chemical Society.
    view abstractdoi: 10.1021/la902385d
  • 2010 • 10 Calibration of a miniaturized retarding field analyzer for low-temperature plasmas: geometrical transparency and collisional effects
    Baloniak, T. and Reuter, R. and Flotgen, C. and von Keudell, A.
    Journal of Physics D-applied Physics 43 055203 (2010)
    Retarding field analyzers (RFAs) are important diagnostics to measure fluxes and energies of ions impinging onto the wall of a plasma reactor. Any quantitative use of the data requires a proper calibration, which is here performed for a miniaturized RFA. The calibration accounts for the transparencies of the RFA grids as well as for collisions inside the RFA. An analytical model is derived which covers both geometrical and collisional effects. The model is calibrated and experimentally verified using a Langmuir probe. We find that the transparency of an RFA is a random variable which depends on the individual alignment of the RFA grids. Collisions inside the RFA limit the ion current transfer through the RFA at higher pressures. A simple method is presented which allows one to remove these artefacts from the RFA data and to obtain quantitative ion velocity distributions.
    view abstractdoi: 10.1088/0022-3727/43/5/055203
  • 2010 • 9 Effects of focused ion beam milling and pre-straining on the microstructure of directionally solidified molybdenum pillars: A Laue diffraction analysis
    Zimmermann, J. and Van Petegem, S. and Bei, H. and Grolimund, D. and George, E.P. and Van Swygenhoven, H.
    Scripta Materialia 62 746-749 (2010)
    White beam Laue micro-diffraction was performed on directionally solidified, single-crystal Mo pillars in the as-grown state, after focused ion beam (FIB) milling and after pre-straining. The Laue diffraction peaks from the as-grown pillars are very sharp and show no broadening, similar to those from single-crystal Si wafers. Significant broadening and streaking of the peaks occurred after FIB milling and pre-straining, indicative of the damage these treatments induce in the nearly perfect crystal structure of the directionally solidified Mo pillars. © 2010 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2010.02.013
  • 2010 • 8 Electrostatics plus O-π interactions rather than "Directed" hydrogen bonding keep so42- in a triangular Pt 3Pd3-tris(2,2′-bipyrazine) host
    Galstyan, A. and Sanz Miguel, P.J. and Lippert, B.
    Chemistry - A European Journal 16 5577-5580 (2010)
    (Figure Presented) Not just hydrogen bonds can trap SO4 2- in a host cavity! Rather, a combination of electrostatic attraction, incomplete anion dehydration, and π interactions between the oxygen atoms and N-heterocyclic ligands of the host will do it as well (see picture). © 2010 Wiley-VCH Verlag GmbH &amp; Co. KGaA.
    view abstractdoi: 10.1002/chem.201000500
  • 2010 • 7 Fundamental aspects of substrate biasing: ion velocity distributions and nonlinear effects
    Baloniak, T. and Reuter, R. and von Keudell, A.
    Journal of Physics D-applied Physics 43 335201 (2010)
    Ion bombardment of the substrate is a significant parameter in plasma processing such as dry etching or thin film deposition. The ion bombardment is described by ion velocity distribution functions (IVDFs), which were here measured quantitatively at a sinusoidally and non-sinusoidally biased electrode. The electrode voltage was monitored and controlled in the frequency domain using fast Fourier transformation. IVDF measurements were performed by a floating retarding field analyzer. A full modulation of the IVDF by arbitrary bias waveforms is only achieved if sufficiently high sheath voltages are used. If the applied sheath voltages become too low, the IVDFs are only partly determined by the RF bias waveforms and the system response becomes nonlinear. An analytical sheath model is derived from the experimental data, which accounts for arbitrary bias waveforms as well as for collisional and nonlinear effects in the sheath. It is shown that a combined DC and RF biasing of the electrode is required to gain full control over the ion bombardment of the substrate.
    view abstractdoi: 10.1088/0022-3727/43/33/335201
  • 2010 • 6 Inactivation of bacteria and biomolecules by low-pressure plasma discharges
    Von Keudell, A. and Awakowicz, P. and Benedikt, J. and Raballand, V. and Yanguas-Gil, A. and Opretzka, J. and Flötgen, C. and Reuter, R. and Byelykh, L. and Halfmann, H. and Stapelmann, K. and Denis, B. and Wunderlich, J. and Mur...
    Plasma Processes and Polymers 7 327-352 (2010)
    (Figure Presented) The inactivation of bacteria and biomolecules using plasma discharges were investigated within the European project BIODECON. The goal of the project was to identify and isolate inactivation mechanisms by combining dedicated beam experiments with especially designed plasma reactors. The plasma reactors are based on a fully computer-controlled, low-pressure inductively-coupled plasma (ICP). Four of these reactors were built and distributed among the consortium, thereby ensuring comparability of the results between the teams. Based on this combined effort, the role of UV light, of chemical sputtering (i.e. the combined impact of neutrals and ions), and of thermal effects on bacteria such as Bacillus atrophaeus, Aspergillus niger, as well as on biomolecules such as LPS, Lipid A, BSA and prions have been evaluated. The particle fluxes emerging from the plasmas are quantified by using mass spectrometry, Langmuir probe measurements, retarding field measurements and optical emission spectroscopy. The effects of the plasma on the biological systems are evaluated using atomic force microscopy, ellipsometry, electrophoresis, specially-designed western blot tests, and animal models. A quantitative analysis of the plasma discharges and the thorough study of their effect on biological systems led to the identification of the different mechanisms operating during the decontamination process. Our results confirm the role of UV in the 200-2 50 nm range for the inactivation of microorganisms and a large variability of results observed between different strains of the same species. Moreover, we also demonstrate the role of chemical sputtering corresponding to the synergism between ion bombardment of a surface with the simultaneous reaction of active species such as O, O2 or H. Finally, we show that plasma processes can be efficient against different micro-organisms, bacteria and fungi, pyrogens, model proteins and prions. The effect of matrices is described, and consequences for any future industrial implementation are discussed. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/ppap.200900121
  • 2010 • 5 Intentionally positioned self-assembled InAs quantum dots in an electroluminescent pin junction diode
    Mehta, M. and Reuter, D. and Melnikov, A. and Wieck, A.D. and Michaelis De Vasconcellos, S. and Baumgarten, T. and Zrenner, A. and Meier, C.
    Physica E: Low-Dimensional Systems and Nanostructures 42 2749-2752 (2010)
    An intentional positioning of optically active quantum dots using site-selective growth by a combination of molecular beam epitaxy (MBE) and focused ion beam (FIB) implantation in an all-ultra-high-vacuum (UHV) setup has been successfully demonstrated. A square array of periodic holes on GaAs substrate was fabricated with FIB of 30 keV Ga ions followed by an in situ annealing step. Subsequently, the patterned holes were overgrown with an optimized amount of InAs in order to achieve site-selective growth of the QDs on the patterned holes. Under well-optimized conditions, a selectivity of single quantum dot growth in the patterned holes of 52% was achieved. Thereafter, carrier injection and subsequent radiative recombination from the positioned InAs/GaAs self-assembled QDs was investigated by embedding the QDs in the intrinsic part of a GaAs-based pin junction device. Electroluminescence spectra taken at 77 K show interband transitions up to the fifth excited state from the QDs. © 2009 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.physe.2009.12.053
  • 2010 • 4 Ion-enhanced oxidation of aluminum as a fundamental surface process during target poisoning in reactive magnetron sputtering
    Kuschel, T. and von Keudell, A.
    Journal of Applied Physics 107 103302 (2010)
    Plasma deposition of aluminum oxide by reactive magnetron sputtering (RMS) using an aluminum target and argon and oxygen as working gases is an important technological process. The undesired oxidation of the target itself, however, causes the so-called target poisoning, which leads to strong hysteresis effects during RMS operation. The oxidation occurs by chemisorption of oxygen atoms and molecules with a simultaneous ion bombardment being present. This heterogenous surface reaction is studied in a quantified particle beam experiment employing beams of oxygen molecules and argon ions impinging onto an aluminum-coated quartz microbalance. The oxidation and/or sputtering rates are measured with this microbalance and the resulting oxide layers are analyzed by x-ray photoelectron spectroscopy. The sticking coefficient of oxygen molecules is determined to 0.015 in the zero coverage limit. The sputtering yields of pure aluminum by argon ions are determined to 0.4, 0.62, and 0.8 at 200, 300, and 400 eV. The variation in the effective sticking coefficient and sputtering yield during the combined impact of argon ions and oxygen molecules is modeled with a set of rate equations. A good agreement is achieved if one postulates an ion-induced surface activation process, which facilitates oxygen chemisorption. This process may be identified with knock-on implantation of surface-bonded oxygen, with an electric-field-driven in-diffusion of oxygen or with an ion-enhanced surface activation process. Based on these fundamental processes, a robust set of balance equations is proposed to describe target poisoning effects in RMS. (C) 2010 American Institute of Physics. [doi:10.1063/1.3415531]
    view abstractdoi: 10.1063/1.3415531
  • 2010 • 3 Magnetic coupling mechanisms in particle/thin film composite systems
    Confalonieri, G.A.B. and Szary, P. and Mishra, D. and Benitez, M.J. and Feyen, M. and Lu, A.H. and Agudo, L. and Eggeler, G. and Petracic, O. and Zabel, H.
    Beilstein Journal of Nanotechnology 1 101-107 (2010)
    Magnetic Γ-Fe 2O 3 nanoparticles with a mean diameter of 20 nm and size distribution of 7% were chemically synthesized and spin-coated on top of a Si-substrate. As a result, the particles self-assembled into a mono layer with hexagonal close-packed order. Subsequently, the nanoparticle array was coated with a Co layer of 20 nm thickness. The magnetic properties of this composite nanopar-ticle/thin film system were investigated by magnetometry and related to high-resolution transmission electron microscopy studies. Herein three systems were compared: i.e. a reference sample with only the particle monolayer, a composite system where the particle array was ion-milled prior to the deposition of a thin Co film on top, and a similar composite system but without ion-milling. The nanoparticle array showed a collective super-spin behavior due to dipolar interparticle coupling. In the composite system, we observed a decoupling into two nanoparticle subsystems. In the ion-milled system, the nanoparticle layer served as a magnetic flux guide as observed by magnetic force microscopy. Moreover, an exchange bias effect was found, which is likely to be due to oxygen exchange between the iron oxide and the Co layer, and thus forming of an antiferromagnetic CoO layer at the Γ-Fe 2O 3/Co interface. © 2010 Confalonieri et al.
    view abstractdoi: 10.3762/bjnano.1.12
  • 2010 • 2 Nanoscale engineering and optical addressing of single spins in diamond
    Pezzagna, S. and Wildanger, D. and Mazarov, P. and Wieck, A.D. and Sarov, Y. and Rangelow, I. and Naydenov, B. and Jelezko, F. and Hell, S.W. and Meijer, J.
    Small 6 2117-2121 (2010)
    The artificial creation of shallow nitrogen-vacancy (NV) centres in diamond with 25 nm lateral resolution is performed by collimated implantation of low-energy nitrogen ions. The electron spin associated to this defect is the most promising qubit for a scalable quantum computer working at room temperature. Individual optical addressing of two single centres separated by only 16 nm is demonstrated with stimulated emission depletion (STED) microscopy.
    view abstractdoi: 10.1002/smll.201000902
  • 2010 • 1 PH-Switchable vesicles from a serine-derived guanidiniocarbonyl pyrrole carboxylate zwitterion in DMSO
    Rodler, F. and Linders, J. and Fenske, T. and Rehm, T. and Mayer, C. and Schmuck, C.
    Angewandte Chemie - International Edition 49 8747-8750 (2010)
    Tightly closed: Zwitterion 1 forms vesicles that have an approximate size of 50nm in DMSO solution. The vesicles can be opened and closed by the addition of either acid or base, as vesicle formation depends on the protonation state of zwitterion 1 (see picture). The membrane permeability of the vesicles is surprisingly low: the encapsulated solvent does not exchange with the surrounding solution, even on a time scale of a few hundred milliseconds. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201003405