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 • 248 A sustainable ultra-high strength Fe18Mn3Ti maraging steel through controlled solute segregation and α-Mn nanoprecipitation
    Kwiatkowski da Silva, A. and Souza Filho, I.R. and Lu, W. and Zilnyk, K.D. and Hupalo, M.F. and Alves, L.M. and Ponge, D. and Gault, B. and Raabe, D.
    Nature Communications 13 (2022)
    The enormous magnitude of 2 billion tons of alloys produced per year demands a change in design philosophy to make materials environmentally, economically, and socially more sustainable. This disqualifies the use of critical elements that are rare or have questionable origin. Amongst the major alloy strengthening mechanisms, a high-dispersion of second-phase precipitates with sizes in the nanometre range is particularly effective for achieving ultra-high strength. Here, we propose an alternative segregation-based strategy for sustainable steels, free of critical elements, which are rendered ultrastrong by second-phase nano-precipitation. We increase the Mn-content in a supersaturated, metastable Fe-Mn solid solution to trigger compositional fluctuations and nano-segregation in the bulk. These fluctuations act as precursors for the nucleation of an unexpected α-Mn phase, which impedes dislocation motion, thus enabling precipitation strengthening. Our steel outperforms most common commercial alloys, yet it is free of critical elements, making it a new platform for sustainable alloy design. © 2022, The Author(s).
    view abstractdoi: 10.1038/s41467-022-30019-x
  • 2022 • 247 Canted antiferromagnetic phases in the candidate layered Weyl material EuMnSb2
    Wilde, J.M. and Riberolles, S.X.M. and Das, A. and Liu, Y. and Heitmann, T.W. and Wang, X. and Straszheim, W.E. and Bud'Ko, S.L. and Canfield, P.C. and Kreyssig, A. and McQueeney, R.J. and Ryan, D.H. and Ueland, B.G.
    Physical Review B 106 (2022)
    EuMnSb2 is a candidate topological material which can be tuned towards a Weyl semimetal, but there are differing reports for its antiferromagnetic (AFM) phases. The coupling of bands dominated by pure Sb layers hosting topological fermions to Mn and Eu magnetic states provides a potential path to tune the topological properties. Here we present single-crystal neutron diffraction, magnetization, and heat-capacity data as well as polycrystalline Eu151 Mössbauer data which show that three AFM phases exist as a function of temperature, and we present a detailed analysis of the magnetic structure in each phase. The Mn magnetic sublattice orders into a C-type AFM structure below TNMn=323(1)K with the ordered Mn magnetic moment μMn lying perpendicular to the layers. AFM ordering of the Eu sublattice occurs below TNEu1=23(1)K with the ordered Eu magnetic moment μEu canted away from the layer normal and μMn retaining its higher temperature order. μEu is ferromagnetically aligned within each Eu layer but exhibits a complicated AFM layer stacking. Both of these higher-temperature phases are described by magnetic space group (MSG) Pn′m′a′ with the chemical and magnetic unit cells having the same dimensions. Cooling below TNEu2=9(1)K reveals a third AFM phase where μMn remains unchanged but μEu develops an additional substantial in-plane canting. This phase has MSG P1121a′. We also find some evidence of short-range magnetic correlations associated with the Eu between 12K T 30K. Using the determined magnetic structures, we postulate the signs of nearest-neighbor intralayer and interlayer exchange constants and the magnetic anisotropy within a general Heisenberg model. We then discuss implications of the various AFM states in EuMnSb2 and their potential for tuning topological properties. © 2022 American Physical Society. All rights reserved.
    view abstractdoi: 10.1103/PhysRevB.106.024420
  • 2022 • 246 Comparing London dispersion pnictogen-π interactions in naphthyl-substituted dipnictanes
    Gehlhaar, A. and Schiavo, E. and Wölper, C. and Schulte, Y. and Auer, A.A. and Schulz, S.
    Dalton Transactions 51 5016-5023 (2022)
    Using a combination of NMR, single crystal X-ray diffraction (sc-XRD) and quantum chemistry, the structure-directing role of London Dispersion (LD) is demonstrated for dibismuthane Bi2Naph2 (1). 1 shows intermolecular Bi⋯π contacts in the solid-state, while π⋯π interactions as observed in the lighter homologues are missing. Comparison of the whole series of dipnictanes revealed the influence of the pnictogen atom on the strength of London dispersion and highlights its importance in heavy main group element chemistry. © 2022 The Royal Society of Chemistry
    view abstractdoi: 10.1039/d2dt00477a
  • 2022 • 245 Coupling of electronic and structural degrees of freedom in vanadate superlattices
    Radhakrishnan, P. and Geisler, B. and Fürsich, K. and Putzky, D. and Wang, Y. and Christiani, G. and Logvenov, G. and Wochner, P. and Van Aken, P.A. and Pentcheva, R. and Benckiser, E.
    Physical Review B 105 (2022)
    Heterostructuring provides different ways to manipulate the orbital degrees of freedom and to tailor orbital occupations in transition-metal oxides. However, the reliable prediction of these modifications remains a challenge. Here we present a detailed investigation of the relationship between the crystal and electronic structure in YVO3-LaAlO3 superlattices by combining ab initio theory, scanning transmission electron microscopy, and x-ray diffraction. Density functional theory simulations including an on-site Coulomb repulsion term accurately predict the crystal structure and, in conjunction with x-ray diffraction, provide an explanation for the lifting of degeneracy of the vanadium dxz and dyz orbitals that was recently observed in this system. In addition, we unravel the combined effects of electronic confinement and octahedral connectivity by disentangling their impact from that of epitaxial strain. Our results demonstrate that the specific orientation of the substrate and the thickness of the YVO3 slabs in the multilayer can be utilized to reliably engineer orbital polarization. © 2022 authors. Published by the American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.165117
  • 2022 • 244 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 • 243 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 • 242 Fe(001) angle-resolved photoemission and intrinsic anomalous Hall conductivity in Fe seen by different ab initio approaches: LDA and GGA versus GW
    Młyńczak, E. and Aguilera, I. and Gospodarič, P. and Heider, T. and Jugovac, M. and Zamborlini, G. and Hanke, J.-P. and Friedrich, C. and Mokrousov, Y. and Tusche, C. and Suga, S. and Feyer, V. and Blügel, S. and Plucinski, L....
    Physical Review B 105 (2022)
    Many material properties such as the electronic transport characteristics depend on the details of the electronic band structure in the vicinity of the Fermi level. For an accurate ab initio description of the material properties, the electronic band structure must be known and theoretically reproduced with high fidelity. Here, we ask a question which of the ab initio methods compare the best to the experimental photoemission intensities from bcc Fe. We confront the photoemission data from Fe(001) thin film grown on Au(001) to the photoemission simulations based on different ab initio initial band structures: density functional theory (DFT) in the local density approximation (LDA) and the generalized gradient approximation (GGA) and GGA corrected with many-body perturbation theory in the GW approximation. We find the best comparison for the GW results. As a second step, we discuss how the calculated intrinsic anomalous Hall conductivity (AHC) in bcc Fe depends on the choice of the method that describes the electronic band structure and Fermi level position. We find very large differences in AHC between the three theoretical approaches and show that the AHC found for the experimental Fermi level location within the GW band structure is the closest to the literature results of transport experiments. This finding improves our understanding of not only the anomalous Hall effect itself, but also other related phenomena, such as the anomalous Nernst effect. © 2022 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.105.115135
  • 2022 • 241 Geminal C-Cl and Si-Cl bond activation of chloromethanes and chlorosilanes by gallanediyl LGa
    Helling, C. and Ganesamoorthy, C. and Wölper, C. and Schulz, S.
    Dalton Transactions 51 2050-2058 (2022)
    The activation of relatively inert E-X σ-bonds by low-valent main group metal complexes is receiving increasing interest. We here confirm the promising potential of gallanediyl LGa (L = HC[C(Me)N(Dip)]2, Dip = 2,6-i-Pr2C6H3) to activate E-Cl (E = C, Si) σ-bonds of group 14 element compounds. Equimolar reactions of LGa with chloromethanes and chlorosilanes EHxCl4-x (E = C, x = 0-2; E = Si, x = 0, 1) occurred with E-Cl bond insertion and formation of gallylmethanes and -silanes L(Cl)GaEHxCl3-x (E = C, x = 2 (1), 1 (2), 0 (3); E = Si, x = 1 (4)). In contrast, consecutive insertion into a geminal E-Cl bond was observed with two equivalents of LGa, yielding digallyl complexes [L(Cl)Ga]2EHxCl2-x (E = C, x = 2 (5); E = Si, x = 1 (6), 0 (7)). Compounds 1-7 were characterized by heteronuclear NMR (1H, 13C, 29Si (4, 6)), IR spectroscopy and elemental analysis, and their solid-state structures were determined by single-crystal X-ray diffraction (sc-XRD). © 2022 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d1dt04192d
  • 2022 • 240 Ion Implantation Enhanced Exfoliation Efficiency of V2AlC Single Crystals: Implications for Large V2CT zNanosheet Production
    Pazniak, H. and Hurand, S. and Guignard, N. and Célérier, S. and Wiedwald, U. and Ouisse, T. and David, M.-L. and Mauchamp, V.
    ACS Applied Nano Materials 5 8029-8037 (2022)
    MXenes are two-dimensional transition-metal carbides and nitrides with an attractive combination of physicochemical properties, gaining notable potential in many applications. Currently, MXene synthesis is mainly performed from powder precursors whose purity and grain size define the quality and flake size of 2D sheets, typically not exceeding 2-3 μm. In this work, we successfully synthesize macroscopic nanolayered V2CTzMXenes with lateral dimensions larger than 25 μm from a V2AlC single crystal by exploiting a new strategy based on ion implantation. Ne2+ion implantation of the single-crystal precursor is applied to introduce defects in the crystal structure of V2AlC, which facilitates chemical etching and drastically reduces the etching time down to 8 h (∼10 times lower as compared to conventional synthesis from powder precursors). The quality and morphology of exfoliated macroscopic MXene multilayers have been comprehensively studied by performing detailed analyses based on different kinds of microscopies and spectroscopies. The obtained macroscopic flakes are ideal objects to study the intrinsic physical properties of V2CTzMXenes and explore their potential application, in particular, as membranes. © 2022 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acsanm.2c01143
  • 2022 • 239 Synthesis and redox activity of carbene-coordinated group 13 metal radicals
    Li, B. and Geoghegan, B.L. and Weinert, H.M. and Wölper, C. and Cutsail, G.E. and Schulz, S.
    Chemical Communications 58 4372-4375 (2022)
    Carbenes are known to stabilize main group element compounds with unusual electronic properties. Herein, we report the synthesis of carbene-stabilized group 13 metal radicals (cAAC)MX2(IPr) (M = Al, X = Br 3; M = Ga, X = Cl 4) and the corresponding cations [(cAAC)MX2(IPr)][B(C6F5)4] (M = Al, X = Br 5; M = Ga, X = Cl 6), which were characterized spectroscopically and by sc-XRD. Quantum chemical calculation gave insights into their electronic structures. © 2022 The Royal Society of Chemistry
    view abstractdoi: 10.1039/d2cc00216g
  • 2021 • 238 A fully automated approach to calculate the melting temperature of elemental crystals
    Zhu, L.-F. and Janssen, J. and Ishibashi, S. and Körmann, F. and Grabowski, B. and Neugebauer, J.
    Computational Materials Science 187 (2021)
    The interface method is a well established approach for predicting melting points of materials using interatomic potentials. However, applying the interface method is tedious and involves significant human intervention. The whole procedure involves several successive tasks: estimate a rough melting point, set up the interface structure, run molecular dynamic calculations and analyze the data. Loop calculations are necessary if the predicted melting point is different from the estimated one by more than a certain convergence criterion, or if full melting/solidification occurs. In this case monitoring the solid–liquid phase transition in the interface structure becomes critical. As different initial random seeds for the molecular dynamic simulations within the interface method induce slightly different melting points, a few ten or hundred interface method calculations with different random seeds are necessary for performing a statistical analysis on these melting points. Considering all these technical details, the work load for manually executing and combining the various involved scripts and programs quickly becomes prohibitive. To simplify and automatize the whole procedure, we have implemented the interface method into pyiron ( Our fully automatized procedure allows to efficiently and precisely predict melting points of stable unaries represented by arbitrary potentials with only two user-specified parameters (interatomic potential file and element). For metastable or dynamically unstable unary phases, the crystal structure needs to be provided as an additional parameter. We have applied our automatized approach on fcc Al, Ni, dynamically unstable bcc Ti and hcp Mg and employed a large set of available interatomic potentials. Melting points for classical interatomic potentials of these metals have been obtained with a numerical precision well below 1 K. © 2020 The Authors
    view abstractdoi: 10.1016/j.commatsci.2020.110065
  • 2021 • 237 A Low-Temperature Structural Transition in Canfieldite, Ag8SnS6, Single Crystals
    Slade, T.J. and Gvozdetskyi, V. and Wilde, J.M. and Kreyssig, A. and Gati, E. and Wang, L.-L. and Mudryk, Y. and Ribeiro, R.A. and Pecharsky, V.K. and Zaikina, J.V. and Bud’ko, S.L. and Canfield, P.C.
    Inorganic Chemistry 60 19345-19355 (2021)
    Canfieldite, Ag8SnS6, is a semiconducting mineral notable for its high ionic conductivity, photosensitivity, and low thermal conductivity. We report the solution growth of large single crystals of Ag8SnS6 of mass up to 1 g from a ternary Ag–Sn–S melt. On cooling from high temperature, Ag8SnS6 undergoes a known cubic (F4̅3m) to orthorhombic (Pna21) phase transition at ≈460 K. By studying the magnetization and thermal expansion between 5–300 K, we discover a second structural transition at ≈120 K. Single crystal X-ray diffraction reveals the low-temperature phase adopts a different orthorhombic structure with space group Pmn21 (a = 7.662 9(5) Å, b = 7.539 6(5) Å, c = 10.630 0(5) Å, Z = 2 at 90 K) that is isostructural to the room-temperature forms of the related Se-based compounds Ag8SnSe6 and Ag8GeSe6. The 120 K transition is first-order and has a large thermal hysteresis. On the basis of the magnetization and thermal expansion data, the room-temperature polymorph can be kinetically arrested into a metastable state by rapidly cooling to temperatures below 40 K. We last compare the room- and low-temperature forms of Ag8SnS6 with its argyrodite analogues, Ag8TQ6 (T = Si, Ge, Sn; Q = S, Se), and identify a trend relating the preferred structures to the unit cell volume, suggesting smaller phase volume favors the Pna21 arrangement. We support this picture by showing that the transition to the Pmn21 phase is avoided in Ge alloyed Ag8Sn1–xGexS6 samples as well as in pure Ag8GeS6 © 2021 American Chemical Society
    view abstractdoi: 10.1021/acs.inorgchem.1c03158
  • 2021 • 236 A safety cap protects hydrogenase from oxygen attack
    Winkler, M. and Duan, J. and Rutz, A. and Felbek, C. and Scholtysek, L. and Lampret, O. and Jaenecke, J. and Apfel, U.-P. and Gilardi, G. and Valetti, F. and Fourmond, V. and Hofmann, E. and Léger, C. and Happe, T.
    Nature Communications 12 (2021)
    [FeFe]-hydrogenases are efficient H2-catalysts, yet upon contact with dioxygen their catalytic cofactor (H-cluster) is irreversibly inactivated. Here, we combine X-ray crystallography, rational protein design, direct electrochemistry, and Fourier-transform infrared spectroscopy to describe a protein morphing mechanism that controls the reversible transition between the catalytic Hox-state and the inactive but oxygen-resistant Hinact-state in [FeFe]-hydrogenase CbA5H of Clostridium beijerinckii. The X-ray structure of air-exposed CbA5H reveals that a conserved cysteine residue in the local environment of the active site (H-cluster) directly coordinates the substrate-binding site, providing a safety cap that prevents O2-binding and consequently, cofactor degradation. This protection mechanism depends on three non-conserved amino acids situated approximately 13 Å away from the H-cluster, demonstrating that the 1st coordination sphere chemistry of the H-cluster can be remote-controlled by distant residues. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41467-020-20861-2
  • 2021 • 235 Ab initio based models for temperature-dependent magnetochemical interplay in bcc Fe-Mn alloys
    Schneider, A. and Fu, C.-C. and Waseda, O. and Barreteau, C. and Hickel, T.
    Physical Review B 103 (2021)
    Body-centered cubic (bcc) Fe-Mn systems are known to exhibit a complex and atypical magnetic behavior from both experiments and 0 K electronic-structure calculations, which is due to the half-filled 3d band of Mn. We propose effective interaction models for these alloys, which contain both atomic-spin and chemical variables. They were parameterized on a set of key density functional theory (DFT) data, with the inclusion of noncollinear magnetic configurations being indispensable. Two distinct approaches, namely a knowledge-driven and a machine-learning approach have been employed for the fitting. Employing these models in atomic Monte Carlo simulations enables the prediction of magnetic and thermodynamic properties of the Fe-Mn alloys, and their coupling, as functions of temperature. This includes the decrease of Curie temperature with increasing Mn concentration, the temperature evolution of the mixing enthalpy, and its correlation with the alloy magnetization. Also, going beyond the defect-free systems, we determined the binding free energy between a vacancy and a Mn atom, which is a key parameter controlling the atomic transport in Fe-Mn alloys. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.024421
  • 2021 • 234 Analysis of the Fine Structure of the D-Exciton Shell in Cuprous Oxide
    Heckötter, J. and Rommel, P. and Main, J. and Aßmann, M. and Bayer, M.
    Physica Status Solidi - Rapid Research Letters 15 (2021)
    The exciton states in cuprous oxide show a pronounced fine structure splitting associated with the crystal environment and the resulting electronic band structure. High-resolution spectroscopy reveals an especially pronounced splitting of the yellow D excitons with one state pushed above any other state with the same principal quantum number. This large splitting offset is related to a strong mixing of these D states with the 1S exciton of the green series, as suggested by previously published calculations. Here, a detailed comparison of this theory with experimental data is given, which leads to a complete reassignment of the experimentally observed D exciton lines. The origin of different amounts of green admixture to D-envelope states is deduced by analyzing the different terms of the Hamiltonian. The yellow–green mixing leads to level repulsion and induces an exchange interaction splitting to D-envelope states, from which one of them becomes the highest state within each multiplet. Furthermore, the assignment of D exciton states according to their total angular momentum F is given and corrects an earlier description given in a former study. © 2021 The Authors. physica status solidi (RRL) Rapid Research Letters published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/pssr.202100335
  • 2021 • 233 Deep learning for visualization and novelty detection in large X-ray diffraction datasets
    Banko, L. and Maffettone, P.M. and Naujoks, D. and Olds, D. and Ludwig, Al.
    npj Computational Materials 7 (2021)
    We apply variational autoencoders (VAE) to X-ray diffraction (XRD) data analysis on both simulated and experimental thin-film data. We show that crystal structure representations learned by a VAE reveal latent information, such as the structural similarity of textured diffraction patterns. While other artificial intelligence (AI) agents are effective at classifying XRD data into known phases, a similarly conditioned VAE is uniquely effective at knowing what it doesn’t know: it can rapidly identify data outside the distribution it was trained on, such as novel phases and mixtures. These capabilities demonstrate that a VAE is a valuable AI agent for aiding materials discovery and understanding XRD measurements both ‘on-the-fly’ and during post hoc analysis. © 2021, The Author(s).
    view abstractdoi: 10.1038/s41524-021-00575-9
  • 2021 • 232 Dielectric and Piezoelectric Properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) Modified Ceramics
    Politova, E.D. and Kaleva, G.M. and Bel’kova, D.A. and Mosunov, A.V. and Sadovskaya, N.V. and Kiselev, D.A. and Il’ina, T.S. and Shvartsman, V.V.
    Inorganic Materials 57 942-949 (2021)
    Abstract—: We have studied the crystal structure and dielectric and local piezoelectric properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) modified sodium bismuth titanate-based ceramics and observed the formation of a pseudocubic phase with the perovskite structure. Its unit-cell volume first decreases and then, for x ≥ 0.05, increases. The ceramics undergo phase transitions, which show up as anomalies in their dielectric permittivity near ~450 K and peaks at a Curie temperature of ~600 K. As x increases to 0.04, their Curie temperature decreases by 40 K. The phase transitions near 450 K exhibit well-defined relaxor behavior due to the presence of polar regions in the nonpolar matrix. The samples with x < 0.05 have been shown to have an increased room-temperature dielectric permittivity, which correlates with the increased effective piezoelectric coefficient, suggesting that doping with manganese has an advantageous effect on the functional properties of sodium bismuth titanate ceramics. © 2021, Pleiades Publishing, Ltd.
    view abstractdoi: 10.1134/S0020168521090120
  • 2021 • 231 First-principles computational exploration of ferromagnetism in monolayer GaS via substitutional doping
    Khan, R. and Rahman, A.U. and Zhang, Q. and Kratzer, P. and Ramay, S.M.
    Journal of Physics Condensed Matter 33 (2021)
    Using first-principles calculations, functionalization of the monolayer-GaS crystal structure through N or Cr-doping at all possible lattice sites has been investigated. Our results show that pristine monolayer-GaS is an indirect-bandgap, non-magnetic semiconductor. The bandgap can be tuned and a magnetic moment (MM) can be induced by the introduction of N or Cr atomic anion/cation doping in monolayer GaS. For instance, the intrinsic character of monolayer GaS can be changed by substitution of N for the S-site to p-type, while substitution of Cr at the S-site or Ga-site induces half-metallicity at sufficiently high concentrations. The defect states are located in the electronic bandgap region of the GaS monolayer. These findings help to extend the application of monolayer-GaS structures in nano-electronics and spintronics. Since the S-sites at the surface are more easily accessible to doping in experiment, we chose the S-site for further investigations. Finally, we perform calculations with ferromagnetic (FM) and antiferromagnetic (AFM) alignment of the MMs at the dopants. For pairs of impurities of the same species at low concentrations we find Cr atoms to prefer the FM state, while N atoms prefer the AFM state, both for impurities on opposite surfaces of the GaS monolayer and for impurities sharing a common Ga neighbor sitting at the same surface. Extending our study to higher concentrations of Cr atoms, we find that clusters of four Cr atoms prefer AFM coupling, whereas the FM coupling is retained for Cr atoms at larger distance arranged on a honeycomb lattice. For the latter arrangement, we estimate the FM Curie temperature T C to be 241 K. We conclude that the Cr-doped monolayer-GaS crystal structure offers enhanced electronic and magnetic properties and is an appealing candidate for spintronic devices operating close to room temperature. © 2021 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/ac04ce
  • 2021 • 230 Large-Scale Production of Carbon-Supported Cobalt-Based Functional Nanoparticles for Oxygen Evolution Reaction
    Bähr, A. and Petersen, H. and Tüysüz, H.
    ChemCatChem (2021)
    A series of Co-based nanoparticles supported on activated carbon was synthesized by using waste tea leaves as a template as well as a sustainable carbon source. The crystal structure of the Co particles was adjusted by post-treatments with H2O2, ethanol vapor, and H2, which result in Co3O4, CoO, and metallic Co phases, respectively. After these different treatments, the composite materials consist of small Co-based nanoparticles with an average crystallite size of 6–14 nm supported on activated carbon with apparent specific surface areas up to 1065 m2 g−1. Correlations between the structure of the materials and their activity for the oxygen evolution reaction (OER) were established, whereby the post-treatment with ethanol vapor was found to yield the most effective electrocatalyst. The material shows good stability at 10 mA cm−2 over 10 h and reaches a mass activity of 2.9 A mgCo−1, which is even higher than pristine ordered mesoporous Co3O4. The superior electrocatalytic performance is ascribed to a high dispersion of Co-based nanoparticles and the conductivity of the activated carbon that facilitate the charge transport. © 2021 The Authors. ChemCatChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cctc.202100594
  • 2021 • 229 Link between Structural and Optical Properties of CoxFe3- xO4Nanoparticles and Thin Films with Different Co/Fe Ratios
    Kampermann, L. and Klein, J. and Korte, J. and Kowollik, O. and Pfingsten, O. and Smola, T. and Saddeler, S. and Piotrowiak, T.H. and Salamon, S. and Landers, J. and Wende, H. and Ludwig, A. and Schulz, S. and Bacher, G.
    Journal of Physical Chemistry C (2021)
    CoxFe3-xO4 nanoparticles (x = 0.4 to x = 2.5) and thin films (x = 0.9 to x = 2.2) are analyzed by Raman, absorption, and photoluminescence spectroscopy to link structural and optical properties to different cobalt to iron (Co/Fe) ratios. Raman spectroscopy shows that with decreasing Co content, the crystal structure changes from a predominantly normal cubic spinel phase to a mixed inverse spinel phase. This finding is supported by absorption spectroscopy that points out that inter valence charge transfer (IVCT) processes between octahedrally coordinated Co2+ and Fe3+ cations become more prominent with increasing Fe content. Independent of the Co/Fe ratio, CoxFe3-xO4 nanoparticles show a broad photoluminescence (PL) band with a maximum at around 510 nm. Time-resolved photoluminescence spectroscopy shows subnanosecond lifetimes and temperature-resolved photoluminescence experiments reveal that the green PL increases with decreasing temperature (300 to 10 K) while showing no temperature-dependent shift in energy. It is proposed that this green PL originates from OH-groups on the particles' surface. © 2021 The Authors. Published by American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.0c11277
  • 2021 • 228 Link between Structural and Optical Properties of CoxFe3-xO4Nanoparticles and Thin Films with Different Co/Fe Ratios
    Kampermann, L. and Klein, J. and Korte, J. and Kowollik, O. and Pfingsten, O. and Smola, T. and Saddeler, S. and Piotrowiak, T.H. and Salamon, S. and Landers, J. and Wende, H. and Ludwig, A. and Schulz, S. and Bacher, G.
    Journal of Physical Chemistry C 125 14356-14365 (2021)
    CoxFe3-xO4nanoparticles (x= 0.4 tox= 2.5) and thin films (x= 0.9 tox= 2.2) are analyzed by Raman, absorption, and photoluminescence spectroscopy to link structural and optical properties to different cobalt to iron (Co/Fe) ratios. Raman spectroscopy shows that with decreasing Co content, the crystal structure changes from a predominantly normal cubic spinel phase to a mixed inverse spinel phase. This finding is supported by absorption spectroscopy that points out that inter valence charge transfer (IVCT) processes between octahedrally coordinated Co2+and Fe3+cations become more prominent with increasing Fe content. Independent of the Co/Fe ratio, CoxFe3-xO4nanoparticles show a broad photoluminescence (PL) band with a maximum at around 510 nm. Time-resolved photoluminescence spectroscopy shows subnanosecond lifetimes and temperature-resolved photoluminescence experiments reveal that the green PL increases with decreasing temperature (300 to 10 K) while showing no temperature-dependent shift in energy. It is proposed that this green PL originates from OH-groups on the particles’ surface. © 2021 The Authors. Published by American Chemical Society
    view abstractdoi: 10.1021/acs.jpcc.0c11277
  • 2021 • 227 Mechanical milling to foster the solid solution formation and densification in Cr-W-Si for hot-pressing of PVD target materials
    Tillmann, W. and Fehr, A. and Heringhaus, M.
    Advanced Powder Technology 32 1927-1934 (2021)
    Based on the significantly different melting points and high oxygen affinities, the fabrication of chromium-based tungsten silicides is restricted to powder metallurgical production routes. To foster particle contacts and diffusion processes between chromium and tungsten, which are known to necessitate long sintering times, mechanical alloying or milling processes prior to sintering are established. Nonetheless, due to spinodal decomposition of Cr and W, the solid solution formation is complex and yet little understood. For this reason, the influence of the mechanical milling time (0–24 h) on the crystal structure and the microstructural properties of hot-pressed 60Cr30W10Si (wt.–%) is examined. In this context, two different powders containing a different tungsten particle size (0.8 and 3 µm) were mechanically alloyed to analyze the impact on the phase formation and the particle distribution in the microstructure. It was shown that mechanical milling supported the mechanical clamping between the particles. However, the increased milling times significantly decreased the crystallite sizes of the particles and fostered the tungsten solubility in the Cr-rich (Cr, W) solid solution formed during sintering, thus supporting the densification. © 2021 The Society of Powder Technology Japan
    view abstractdoi: 10.1016/j.apt.2021.04.001
  • 2021 • 226 Melting Properties of Peptides and Their Solubility in Water. Part 2: Di- And Tripeptides Based on Glycine, Alanine, Leucine, Proline, and Serine
    Do, H.T. and Chua, Y.Z. and Habicht, J. and Klinksiek, M. and Volpert, S. and Hallermann, M. and Thome, M. and Pabsch, D. and Zaitsau, D. and Schick, C. and Held, C.
    Industrial and Engineering Chemistry Research 60 4693-4704 (2021)
    In downstream processes for peptides, crystallization is still used as the state-of-the-art separation step for which the knowledge about the solubility of each single compound is mandatory. Since the determination of experimental temperature-dependent solubility data is time-consuming and expensive, modeling solubility based on physical properties such as melting properties is highly desired. Unfortunately, the direct determination of melting properties for biomolecules using conventional differential scanning calorimetry is not possible due to the decomposition of the peptides before their melting. In this work, fast scanning calorimetry (FSC) with heating rates up to 20,000 K s-1 was applied to measure the melting properties of 22 peptides with focus on isomeric dipeptides and tripeptides based on glycine, l-alanine, l-leucine, l-proline, and l-serine. The experimental determination of the aqueous solubility of these peptides was performed using the photometric method (UV/Vis spectrometer) and the gravimetric method of supersaturated solutions. Additionally, the pH value and the crystal structure of peptides were determined in order to ensure the neutral species in solution and to exclude crystal structure changes in the solid phase. The experimental FSC-measured melting properties were used as input data in the thermodynamic modeling framework PC-SAFT to model the peptide solubility in water. The PC-SAFT pure-component parameters of the peptides were determined following a weighted joint-parameter method introduced in this work. This approach allows determining the pure-component parameters of a peptide by joining the pure-component parameters of the parent amino acids. The binary interactions parameter between peptide and water was fitted to solubility-independent properties such as osmotic coefficients and mixture densities of aqueous peptide solutions. The modeled peptide solubility was in good agreement with the experimental solubility. © 2021 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.iecr.0c05652
  • 2021 • 225 On the relation of structural disorder and thermoelastic properties in ZnGa2O4 and Zn1−xMgxGa2O4 (x ≈ 0.33)
    Hirschle, C. and Schreuer, J. and Galazka, Z. and Ritter, C.
    Journal of Alloys and Compounds 886 (2021)
    The cation distribution at room temperature, as well as elastic properties and thermal expansion of single crystal ZnGa2O4 (ZGO) and Zn1−xMgxGa2O4 (x ≈ 0.33; ZMGO) with spinel-type structure were studied in a wide temperature range using single crystal X-ray diffraction, neutron powder diffraction, inductive gauge dilatometry and resonant ultrasound spectroscopy. ZGO adopts an almost normal spinel structure, whereas ZMGO is significantly disordered. At room temperature, the elastic properties of ZMGO mostly fall between those of ZGO and MgGa2O4 (MGO). The temperature dependences of the thermoelastic properties of ZGO and ZMGO, as well as thermal expansion of ZGO reveal distinct signatures of glass-like transitions, which separate states in which the cation dynamics are fast enough to relax the cation order in response to temperature change in laboratory timescales from those in which they are not. In equilibrium, thermal expansion is increased in ZMGO, whereas the thermoelastic coefficients are decreased in both ZGO and ZMGO. The temperature range of the transition is significantly larger in ZGO compared to ZMGO and MGO. Trends within the elastic properties, thermoelastic properties, thermal expansion and the glass-like transition in the (Zn,Mg)Ga2O4 solid solution series are discussed based on the impact of inversion, structural disorder, bond character and in comparison to other spinels. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.161214
  • 2021 • 224 Optical Probing of Crystal Lattice Configurations in Single CsPbBr3Nanoplatelets
    Schmitz, A. and Montanarella, F. and Schaberg, L.L. and Abdelbaky, M. and Kovalenko, M.V. and Bacher, G.
    Nano Letters (2021)
    Quantum-confined nanostructures of CsPbBr3 with luminescence quantum efficiencies approaching unity have shown tremendous potential for lighting and quantum light applications. In contrast to CsPbBr3 quantum dots, where the fine structure of the emissive exciton state has been intensely discussed, the relationship among lattice orientation, shape anisotropy, and exciton fine structure in lead halide nanoplatelets has not yet been established. In this work, we investigate the fine structure of the bright triplet exciton of individual CsPbBr3 nanoplatelets by polarization-resolved micro- and magnetophotoluminescence spectroscopy at liquid helium temperature and find a large zero-field splitting of up to 2.5 meV. A unique relation between the crystal structure and the photoluminescence emission confirms the existence of two distinct crystal configurations in such nanoplatelets with different alignments of the crystal axes with respect to the nanoplatelet facets. Polarization-resolved experiments eventually allow us to determine the absolute orientation of an individual nanoplatelet on the substrate purely by optical means. © 2021 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.1c02775
  • 2021 • 223 Phase behavior of ASDs based on hydroxypropyl cellulose
    Luebbert, C. and Stoyanov, E. and Sadowski, G.
    International Journal of Pharmaceutics: X 3 (2021)
    Novel polymeric carriers for amorphous solid dispersions (ASDs) are highly demanded in pharmaceutical industry to improve the bioavailability of poorly-soluble drug candidates. Besides established polymer candidates, hydroxypropyl celluloses (HPC) comes more and more into the focus of ASD production since they have the availability to stabilize drug molecules in aqueous media against crystallization. The thermodynamic long-term stability of HPC ASDs with itraconazole and fenofibrate was predicted in this work with PC-SAFT and compared to three-months enduring long-term stability studies. The glass-transition temperature is a crucial attribute of a polymer, but in case of HPC hardly detectable by differential scanning calorimetry. By investigating the glass transition of HPC blends with a miscible polymer, we were for the first time able to estimate the HPC glass transition. Although both, fenofibrate and itraconazole reveal a very low crystalline solubility in HPC regardless of the HPC molecular weight, we observed that low-molecular weight HPC grades such as HPC-UL prevent fenofibrate crystallization for a longer period than the higher molecular weight HPC grades. As predicted, the ASDs with higher drug load underwent amorphous phase separation according to the differential scanning calorimetry thermograms. This work thus showed that it is possible to predict critical drug loads above which amorphous phase separation and/or crystallization occurs in HPC ASDs. © 2020 The Authors
    view abstractdoi: 10.1016/j.ijpx.2020.100070
  • 2021 • 222 Phase decomposition in nanocrystalline Cr0.8Cu0.2 thin films
    Chakraborty, J. and Harzer, T.P. and Duarte, M.J. and Dehm, G.
    Journal of Alloys and Compounds 888 (2021)
    Metastable Cr0.8Cu0.2 alloy thin films with nominal thickness of 360 nm have been deposited on Si(100) substrate by co-evaporation of Cu and Cr using molecular beam epitaxy (MBE). Phase evolution, microstructure, stress development, and crystallographic texture in Cr0.8Cu0.2 thin films have been investigated by X-ray diffraction (XRD), atom probe tomography (APT) and transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDS) during annealing of the films in the temperature range 200–450 °C. X-ray diffraction of the as-deposited thin film shows single phase bcc crystal structure of the film whereas APT observation of fine precipitates in the film matrix due to inherent compositional fluctuation indicates onset of phase separation via spinodal decomposition regime. XRD (in-situ) and APT investigation of 300 °C annealed film reveals that the early stage of phase separation involves localized formation of metastable intermediate bcc precipitate phase having 60 at% Cr and 40 at% Cu approximately (~Cr0.6Cu0.4). For longer duration of annealing at temperature ≥350 °C, such metastable bcc precipitates act as heterogeneous nucleation sites for the onset of precipitation of Cu rich fcc Cu(Cr) phase which indicates a change of phase separation mechanism from ‘spinodal decomposition’ to ‘nucleation and growth’. Annealing of the film at temperature ≥400 °C for longer duration leads to the formation of a two phase structure with Cu rich fcc precipitate phase in a Cr rich bcc matrix. Observed phase decomposition is accompanied by significant changes in the microstructure, residual stress and crystallographic texture in the Cr rich bcc film matrix which leads to the minimization of both surface and strain energies and thereby a reduction of total Gibbs free energy of the thin film. Thermodynamic model calculation has been presented in order to understand the nucleation pathway of Cu rich stable fcc Cu(Cr) precipitates via non-classical nucleation of metastable intermediate bcc Cr0.6Cu0.4 phase. © 2021 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2021.161391
  • 2021 • 221 Spin-polarized quantized electronic structure of Fe(001) with symmetry breaking due to the magnetization direction
    Młyńczak, E. and Aguilera, I. and Gospodarič, P. and Heider, T. and Jugovac, M. and Zamborlini, G. and Tusche, C. and Suga, S. and Feyer, V. and Blügel, S. and Plucinski, L. and Schneider, C.M.
    Physical Review B 103 (2021)
    Quantum well states formed by d electrons in metallic thin films are responsible for many fundamental phenomena that oscillate with layer thickness, such as magnetic anisotropy or magnetoresistance. Using momentum microscopy and angle-resolved photoemission, we mapped in unprecedented detail the quantized electronic states of Fe(001) in a broad photon energy range starting from soft x-ray (160 eV) down to vacuum ultraviolet (8.4 eV). We show that it is possible to simulate the experimentally observed photoemission spectra with high accuracy by using the ab initio electronic bulk band structure as the initial state, taking into account that free electron final electronic states are intrinsically broadened along the wave vector direction perpendicular to the sample surface. To simulate the thin-film case, we take into account a subset of the initial electronic states, which results in the reproduction of the quantized electronic structure observed in the experiment. In addition, we present results of the spin-sensitive measurements, which are confronted with the photoemission simulation that takes into account the spin degree of freedom. We demonstrate electronic states that can be responsible for the oscillations of the magnetic anisotropy in Fe(001) thin films with periods of about 5 and 9 monolayers. We show that these quantum well states change position in reciprocal space depending on the magnetization direction. Our photoemission simulation reproduces this effect, which highlights its origin in the relativistic bulk electronic band structure of bcc Fe. We also observed magnetization-dependent spin-orbit gaps with the symmetry lower than the bulk symmetry. We believe that the same method of simulating photoemission spectra might facilitate interpretation of the photoemission intensities measured for other three-dimensional materials, especially when the spin-polarized quantized electronic states are considered. © 2021 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.103.035134
  • 2021 • 220 Synthesis, Structure, and Optical Properties of Large FAPbBr3 Perovskite Single Crystals
    Karabanov, A.D. and Salak, A.N. and Escobar C, M. and Shvartsman, V.V. and Lupascu, D.C.
    Integrated Ferroelectrics 220 46-55 (2021)
    The high power conversion efficiency of perovskite solar cells reaching 25.5% today [1], raises the question on the relation between the photovoltaic performance and physical nature of these materials. To get a better understanding of the properties, good quality single crystals are highly demanded. In this paper we report on large single crystals of formamidinium lead halide grown by a combination of inverse temperature crystallization and seed growth. Structure, phase transitions, dielectric and optical properties of the single crystals are shown. © 2021 Taylor & Francis Group, LLC.
    view abstractdoi: 10.1080/10584587.2021.1921534
  • 2021 • 219 Ultra-deep optical cooling of coupled nuclear spin-spin and quadrupole reservoirs in a GaAs/(Al,Ga)As quantum well
    Kotur, M. and Tolmachev, D.O. and Litvyak, V.M. and Kavokin, K.V. and Suter, D. and Yakovlev, D.R. and Bayer, M.
    Communications Physics 4 (2021)
    The physics of interacting nuclear spins in solids is well interpreted within the nuclear spin temperature concept. A common approach to cooling the nuclear spin system is adiabatic demagnetization of the initial, optically created, nuclear spin polarization. Here, the selective cooling of 75As spins by optical pumping followed by adiabatic demagnetization in the rotating frame is realized in a nominally undoped GaAs/(Al,Ga)As quantum well. The lowest nuclear spin temperature achieved is 0.54 μK. The rotation of 6 kG strong Overhauser field at the 75As Larmor frequency of 5.5 MHz is evidenced by the dynamic Hanle effect. Despite the presence of the quadrupole induced nuclear spin splitting, it is shown that the rotating 75As magnetization is uniquely determined by the spin temperature of coupled spin-spin and quadrupole reservoirs. The dependence of heat capacity of these reservoirs on the external magnetic field direction with respect to crystal and structure axes is investigated. © 2021, The Author(s).
    view abstractdoi: 10.1038/s42005-021-00681-6
  • 2020 • 218 A flexible and adaptive grid algorithm for global optimization utilizing basin hopping Monte Carlo
    Paleico, M.L. and Behler, J.
    Journal of Chemical Physics 152 (2020)
    Global optimization is an active area of research in atomistic simulations, and many algorithms have been proposed to date. A prominent example is basin hopping Monte Carlo, which performs a modified Metropolis Monte Carlo search to explore the potential energy surface of the system of interest. These simulations can be very demanding due to the high-dimensional configurational search space. The effective search space can be reduced by utilizing grids for the atomic positions, but at the cost of possibly biasing the results if fixed grids are employed. In this paper, we present a flexible grid algorithm for global optimization that allows us to exploit the efficiency of grids without biasing the simulation outcome. The method is general and applicable to very heterogeneous systems, such as interfaces between two materials of different crystal structures or large clusters supported at surfaces. As a benchmark case, we demonstrate its performance for the well-known global optimization problem of Lennard-Jones clusters containing up to 100 particles. Despite the simplicity of this model potential, Lennard-Jones clusters represent a challenging test case since the global minima for some "magic" numbers of particles exhibit geometries that are very different from those of clusters with only a slightly different size. © 2020 Author(s).
    view abstractdoi: 10.1063/1.5142363
  • 2020 • 217 Active Ga-catalysts for the ring opening homo- And copolymerization of cyclic esters, and copolymerization of epoxide and anhydrides
    Ghosh, S. and Glöckler, E. and Wölper, C. and Tjaberings, A. and Gröschel, A.H. and Schulz, S.
    Dalton Transactions 49 13475-13486 (2020)
    A series of gallium complexes L12Ga4Me8(1), L22Ga4Me8(2), and L32Ga4Me8(3) was synthesized by reaction of GaMe3with Schiff base ligands L1-3H2(L1H2= 2,4-di-tert-butyl-6-{[(3-hydroxypropyl)imino]methyl}phenol; L2H2= 2,4-dichloro-6-{[(3-hydroxypropyl)imino]methyl}phenol; L3H2= 4-tert-butyl-2-{[(3-hydroxypropyl)imino]methyl}phenol) and characterized by1H,13C NMR, IR spectroscopy, elemental analysis and single crystal X-ray analysis (1,2), proving their tetranuclear structure in the solid state. Complexes1-3showed good catalytic activity in the ring opening homopolymerization (ROP) and ring opening copolymerization (ROcoP) of lactide (LA) and ε-caprolactone (ε-CL) in the presence of benzyl alcohol (BnOH) in toluene at 100 °C, yielding polymers with the expected average molecular weights (Mn) and narrow molecular weight distributions (MWD), as well as a high isoselectivity for the ROP ofrac-lactide (rac-LA), yielding isotactic-enriched PLAs withPmvalues up to 0.78. Kinetic studies with complex1proved the first order dependence on monomer concentration, while mechanistic studies confirmed the coordination insertion mechanistic (CIM) pathway. Sequential addition of monomers gave well defined diblock copolymers of PCL-b-PLLA and PLLA-b-PCL, proving the living character of the polymerization reactions. The catalysts also showed perfect selectivity for the copolymerization of cyclohexene oxide (CHO) with both succinic anhydride (SA) and maleic anhydride (MA) in the presence of BnOH and produced >99% alternating block copolymers. © The Royal Society of Chemistry 2020.
    view abstractdoi: 10.1039/d0dt02831b
  • 2020 • 216 Additive-free spin coating of tin oxide thin films: Synthesis, characterization and evaluation of tin β-ketoiminates as a new precursor class for solution deposition processes
    Huster, N. and Zanders, D. and Karle, S. and Rogalla, D. and Devi, A.
    Dalton Transactions 49 10755-10764 (2020)
    The fabrication of SnOx in thin film form via chemical solution deposition (CSD) processes is favored over vacuum based techniques as it is cost effective and simpler. The precursor employed plays a central role in defining the process conditions for CSD. Particularly for processing SnO2 layers that are appealing for sensor or electronic applications, there are limited precursors available for CSD. Thus the focus of this work was to develop metalorganic precursors for tin, based on the ketoiminate ligand class. By systematic molecular engineering of the ligand periphery, a series of new homoleptic Sn(ii) β-ketoiminate complexes was synthesized, namely bis[4-(2-methoxyethylimino)-3-pentanonato] tin, [Sn(MEKI)2] (1), bis[4-(2-ethoxyethylimino)-2-pentanonato] tin, [Sn(EEKI)2] (2), bis[4-(3-methoxypropylimino)-2-pentanonato] tin, [Sn(MPKI)2] (3), bis[4-(3-ethoxypropylimino)-2-pentanonato] tin, [Sn(EPKI)2] (4) and bis[4-(3-isopropoxypropylimino)-2-pentanonato] tin, [Sn(iPPKI)2] (5). All these N-side-chain ether functionalized compounds were analyzed by nuclear magnetic resonance (NMR) spectroscopy, electron impact mass spectrometry (EI-MS), elemental analysis (EA) and thermogravimetric analysis (TGA). The solid state molecular structure of [Sn(MPKI)2] (3) was eludicated by means of single crystal X-ray diffraction (SCXRD). Interestingly, this class of compounds features excellent solubility and stability in common organic solvents alongside good reactivity towards H2O and low decomposition temperatures, thus fulfilling the desired requirements for CSD of tin oxides. With compound 3 as a representative example, we have demonstrated the possibility to directly deposit SnOx layers via hydrolysis upon exposure to air followed by heat treatment under oxygen at moderate temperatures and most importantly without the need for any additive that is generally used in CSD. A range of complementary analytical methods were employed, namely X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to analyse the structure, morphology and composition of the SnOx layers. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0dt01463j
  • 2020 • 215 An aminotetracyanocyclopentadienide system: Light-induced formation of a thermally stable cyclopentadienyl radical
    Nimax, P.R. and Zoller, F. and Blockhaus, T. and Küblböck, T. and Fattakhova-Rohlfing, D. and Sünkel, K.
    New Journal of Chemistry 44 72-78 (2020)
    Crystals of the aminotetracyanocyclopentadienyl radical were obtained from the reaction of CaCl2 with Ag[C5(CN)4(NH2)] and recrystallization in MeOH, performed in sunlight. The radical was characterized by X-ray diffraction, EPR and UV Vis spectroscopy as well as by cyclovoltammetry and DFT calculations. © 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
    view abstractdoi: 10.1039/c9nj04354c
  • 2020 • 214 BOPcat software package for the construction and testing of tight-binding models and bond-order potentials
    Ladines, A.N. and Hammerschmidt, T. and Drautz, R.
    Computational Materials Science 173 (2020)
    Atomistic models like tight-binding (TB), bond-order potentials (BOP) and classical potentials describe the interatomic interaction in terms of mathematical functions with parameters that need to be adjusted for a particular material. The procedures for constructing TB/BOP models differ from the ones for classical potentials. We developed the BOPcat software package as a modular python code for the construction and testing of TB/BOP parameterizations. It makes use of atomic energies, forces and stresses obtained by TB/BOP calculations with the BOPfox software package. It provides a graphical user interface and flexible control of raw reference data, of derived reference data like defect energies, of automated construction and testing protocols, and of parallel execution in queuing systems. We demonstrate the concepts and usage of the BOPcat software and illustrate its key capabilities by exemplary constructing and testing a parameterization of a magnetic BOP for Fe. We provide a parameterization protocol with a successively increasing set of reference data that leads to good transferability to a variety of properties of the ferromagnetic bcc groundstate and to crystal structures which were not part of the training set. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.commatsci.2019.109455
  • 2020 • 213 Composition and structure of magnetic high-temperature-phase, stable Fe-Au core-shell nanoparticles with zero-valent bcc Fe core
    Kamp, M. and Tymoczko, A. and Popescu, R. and Schürmann, U. and Nadarajah, R. and Gökce, B. and Rehbock, C. and Gerthsen, D. and Barcikowski, S. and Kienle, L.
    Nanoscale Advances 2 3912-3920 (2020)
    Advanced quantitative TEM/EDXS methods were used to characterize different ultrastructures of magnetic Fe-Au core-shell nanoparticles formed by laser ablation in liquids. The findings demonstrate the presence of Au-rich alloy shells with varying composition in all structures and elemental bcc Fe cores. The identified structures are metastable phases interpreted by analogy to the bulk phase diagram. Based on this, we propose a formation mechanism of these complex ultrastructures. To show the magnetic response of these magnetic core nanoparticles protected by a noble metal shell, we demonstrate the formation of nanostrands in the presence of an external magnetic field. We find that it is possible to control the lengths of these strands by the iron content within the alloy nanoparticles. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0na00514b
  • 2020 • 212 Crystal structure evolution of complex metal aluminum hydrides upon hydrogen release
    Weidenthaler, C.
    Journal of Energy Chemistry 42 133-143 (2020)
    Complex aluminum hydrides have been widely studied as potential hydrogen storage materials but also, for some time now, for electrochemical applications. This review summarizes the crystal structures of alkali and alkaline earth aluminum hydrides and correlates structure properties with physical and chemical properties of the hydride compounds. The crystal structures of the alkali metal aluminum hydrides change significantly during the stepwise dehydrogenation. The general pathway follows a transformation of structures built of isolated [AlH4]− tetrahedra to structures built of isolated [AlH6]3− octahedra. The crystal structure relations in the group of alkaline earth metal aluminum hydrides are much more complicated than those of the alkali metal aluminum hydrides. The structures of the alkaline earth metal aluminum hydrides consist of isolated tetrahedra but the intermediate structures exhibit chains of corner-shared octahedra. The coordination numbers within the alkali metal group increase with cation sizes which goes along with an increase of the decomposition temperatures of the primary hydrides. Alkaline earth metal hydrides have higher coordination numbers but decompose at slightly lower temperatures than their alkali metal counterparts. The decomposition pathways of alkaline metal aluminum hydrides have not been studied in all cases and require future research. © 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences
    view abstractdoi: 10.1016/j.jechem.2019.05.026
  • 2020 • 211 Design of Complex Solid-Solution Electrocatalysts by Correlating Configuration, Adsorption Energy Distribution Patterns, and Activity Curves
    Löffler, T. and Savan, A. and Meyer, H. and Meischein, M. and Strotkötter, V. and Ludwig, Al. and Schuhmann, W.
    Angewandte Chemie - International Edition 59 5844-5850 (2020)
    Complex solid-solution electrocatalysts (also referred to as high-entropy alloy) are gaining increasing interest owing to their promising properties which were only recently discovered. With the capability of forming complex single-phase solid solutions from five or more constituents, they offer unique capabilities of fine-tuning adsorption energies. However, the elemental complexity within the crystal structure and its effect on electrocatalytic properties is poorly understood. We discuss how addition or replacement of elements affect the adsorption energy distribution pattern and how this impacts the shape and activity of catalytic response curves. We highlight the implications of these conceptual findings on improved screening of new catalyst configurations and illustrate this strategy based on the discovery and experimental evaluation of several highly active complex solid solution nanoparticle catalysts for the oxygen reduction reaction in alkaline media. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201914666
  • 2020 • 210 Development of high entropy alloys for brazing applications
    Tillmann, W. and Ulitzka, T. and Wojarski, L. and Manka, M. and Ulitzka, H. and Wagstyl, D.
    Welding in the World 64 201-208 (2020)
    High entropy alloys are novel and innovative metallic materials, which have intensively moved into the focus of research over the last decade. The high entropy effect in those multi-component alloys promotes the formation of a characteristic crystal structure, the random solid solution, which features unique material properties, and reduces the number of possible brittle phases. In this publication, the influence of gallium as a melting point depressant on the melting range and the microstructure of the two-phased equimolar CoCrCoFeNi were determined. In order to integrate the vacuum brazing process into the solutioning heat treatment of the nickel-based super alloy Mar-M 247 between 1180 and 1270 °C, the liquidus temperature of CoCrCoFeNi was aimed to be below 1270 °C. The changes in the melting ranges due to the modified compositions were predicted by CALPHAD simulations and verified by differential thermal analysis measurements. The promising multi-component filler alloy CoCrCuFeNiGa was determined for further investigations. For this purpose, the microstructures of the filler metal itself and the brazement were conducted. A shear strength of 388 ± 73 MPa was achieved for a brazing gap of 200 μm. The crack, which led to joint failure propagated through high-entropic, fcc-structured phases in the brazing seam. © 2019, International Institute of Welding.
    view abstractdoi: 10.1007/s40194-019-00824-y
  • 2020 • 209 Exciton-driven change of phonon modes causes strong temperature dependent bandgap shift in nanoclusters
    Muckel, F. and Lorenz, S. and Yang, J. and Nugraha, T.A. and Scalise, E. and Hyeon, T. and Wippermann, S. and Bacher, G.
    Nature Communications 11 (2020)
    The fundamental bandgap Eg of a semiconductor—often determined by means of optical spectroscopy—represents its characteristic fingerprint and changes distinctively with temperature. Here, we demonstrate that in magic sized II-VI clusters containing only 26 atoms, a pronounced weakening of the bonds occurs upon optical excitation, which results in a strong exciton-driven shift of the phonon spectrum. As a consequence, a drastic increase of dEg/dT (up to a factor of 2) with respect to bulk material or nanocrystals of typical size is found. We are able to describe our experimental data with excellent quantitative agreement from first principles deriving the bandgap shift with temperature as the vibrational entropy contribution to the free energy difference between the ground and optically excited states. Our work demonstrates how in small nanoparticles, photons as the probe medium affect the bandgap—a fundamental semiconductor property. © 2020, The Author(s).
    view abstractdoi: 10.1038/s41467-020-17563-0
  • 2020 • 208 Factors Governing the Activity of α-MnO2 Catalysts in the Oxygen Evolution Reaction: Conductivity versus Exposed Surface Area of Cryptomelane
    Heese-Gärtlein, J. and Morales, D.M. and Rabe, A. and Bredow, T. and Schuhmann, W. and Behrens, M.
    Chemistry - A European Journal 26 12256-12267 (2020)
    Cryptomelane (α-(K)MnO2) powders were synthesized by different methods leading to only slight differences in their bulk crystal structure and chemical composition, while the BET surface area and the crystallite size differed significantly. Their performance in the oxygen evolution reaction (OER) covered a wide range and their sequence of increasing activity differed when electrocatalysis in alkaline electrolyte and chemical water oxidation using Ce4+ were compared. The decisive factors that explain this difference were identified in the catalysts’ microstructure. Chemical water oxidation activity is substantially governed by the exposed surface area, while the electrocatalytic activity is determined largely by the electric conductivity, which was found to correlate with the particle morphology in terms of needle length and aspect ratio in this sample series. This correlation is rather explained by an improved conductivity due to longer needles than by structure sensitivity as was supported by reference experiments using H2O2 decomposition and carbon black as additive. The most active catalyst R-cryptomelane reached a current density of 10 mA cm−2 at a potential 1.73 V without, and at 1.71 V in the presence of carbon black. The improvement was significantly higher for the catalyst with lower initial activity. However, the materials showed a disappointing catalytic stability during alkaline electrochemical OER, whereas the crystal structure was found to be stable at working conditions. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstractdoi: 10.1002/chem.201905090
  • 2020 • 207 Functional all-optical logic gates for true time-domain signal processing in nonlinear photonic crystal waveguides
    Jandieri, V. and Khomeriki, R. and Onoprishvili, T. and Werner, D.H. and Berakdar, J. and Erni, D.
    Optics Express 28 18317-18331 (2020)
    We present a conceptual study on the realization of functional and easily scalable all-optical NOT, AND and NAND logic gates using bandgap solitons in coupled photonic crystal waveguides. The underlying structure consists of a planar air-hole type photonic crystal with a hexagonal lattice of air holes in crystalline silicon (c-Si) as the nonlinear background material. The remaining logical operations can be performed using combinations of these three logic gates. A unique feature of the proposed working scheme is that it operates in the true time-domain, enabling temporal solitons to maintain a stable pulse envelope during each logical operation. Hence, multiple concatenated all-optical logic gates can be easily realized, paving the way to multiple-input all-optical logic gates for ultrafast full-optical digital signal processing. In the suggested setup, there is no need to amplify the output signal after each operation, which can be directly used as a new input signal for another logical operation. The feasibility and efficiency of the proposed logic gates as well as their scalability is demonstrated using our original rigorous theoretical formalism together with full-wave computational electromagnetics. © 2020 Optical Society of America.
    view abstractdoi: 10.1364/OE.395015
  • 2020 • 206 High entropy alloys: A focused review of mechanical properties and deformation mechanisms
    George, E.P. and Curtin, W.A. and Tasan, C.C.
    Acta Materialia 188 435-474 (2020)
    The high-entropy alloy (HEA) concept was based on the idea that high mixing entropy can promote formation of stable single-phase microstructures. During the past 15 years, various alloy systems have been explored to identify HEA systems with improved property combinations, leading to an extraordinary growth of this field. In the large pool of alloys with varying characteristics, the first single-phase HEA with good tensile properties, the equiatomic CrMnFeCoNi alloy has become the benchmark material, and it forms the basis of much of our current fundamental understanding of HEA mechanical behavior. As the field is evolving to the more broadly defined complex concentrated alloys (CCAs) and the available data in the literature increase exponentially, a fundamental question remains unchanged: how special are these new materials? In the first part of this review, select mechanical properties of HEAs and CCAs are compared with those of conventional engineering alloys. This task is difficult because of the limited tensile data available for HEAs and CCAs. Additionally, the wider suite of mechanical properties needed to assess structural materials is woefully lacking. Nonetheless, our evaluations have not revealed many HEAs or CCAs with properties far exceeding those of conventional engineering alloys, although specific alloys can show notable enhancements in specific properties. Consequently, it is reasonable to first approach the understanding of HEAs and CCAs through the assessment of how the well-established deformation mechanisms in conventional alloys operate or are modified in the presence of the high local complexity of the HEAs and CCAs. The second part of the paper provides a detailed review of the deformation mechanisms of HEAs with the FCC and BCC structures. For the former, we chose the CrMnFeCoNi (Cantor) alloy because it is the alloy on which the most rigorous and thorough investigations have been performed and, for the latter, we chose the TiZrHfNbTa (Senkov) alloy because this is one of the few refractory HEAs that exhibits any tensile ductility at room temperature. As expected, our review shows that the fundamental deformation mechanisms in these systems, and their dependence on basic physical properties, are broadly similar to those of conventional FCC and BCC metals. The third part of this review examines the theoretical and modeling efforts to date that seek to provide either qualitative or quantitative understanding of the mechanical performance of FCC and BCC HEAs. Since experiments reveal no fundamentally new mechanisms of deformation, this section starts with an overview of modeling perspectives and fundamental considerations. The review then turns to the evolution of modeling and predictions as compared to recent experiments, highlighting both successes and limitations. Finally, in spite of some significant successes, important directions for further theory development are discussed. Overall, while the individual deformation mechanisms or properties of the HEAs and CCAs are not, by and large, “special” relative to conventional alloys, the present HEA rush remains valuable because the compositional freedom that comes from the multi-element space will allow exploration of whether multiple mechanisms can operate sequentially or simultaneously, which may yet lead to the creation of new alloys with a spectrum of mechanical properties that are significantly superior to those of current engineering alloys. © 2019 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2019.12.015
  • 2020 • 205 Mg-containing multi-principal element alloys for hydrogen storage: A study of the MgTiNbCr0.5Mn0.5Ni0.5 and Mg0.68TiNbNi0.55 compositions
    Marques, F. and Pinto, H.C. and Figueroa, S.J.A. and Winkelmann, F. and Felderhoff, M. and Botta, W.J. and Zepon, G.
    International Journal of Hydrogen Energy 45 19539-19552 (2020)
    Recently, there has been growing interest in multi-principal element alloys for hydrogen storage. However, most of the papers published so far report compositions based only on transition metal elements, which limit the gravimetric storage capacities due to their densities. Since Mg is a low-density element promising for hydrogen storage, the study of Mg-containing multi-principal element compositions is opportune. In the present work, we report for the first time the structural characterization and hydrogen storage properties of the A2B type MgTiNbCr0.5Mn0.5Ni0.5 alloy and its derivative Mg0.68TiNbNi0.55 alloy. These Mg-containing multi-principal element alloys form major BCC phase (W-type, Im3¯m) and major FCC hydride (MH2 with CaF2-type structure) when synthesized by mechanical alloying (MA) and reactive milling (RM), respectively. Hydrogen is desorbed from both RM samples in two steps, with some overlap, from different hydrides formed during synthesis. The microstructure of the Mg0.68TiNbNi0.55 composition is more homogeneous (less secondary phases), but both alloys present a total gravimetric capacity of around 1.6 wt% H2. © 2020 Hydrogen Energy Publications LLC
    view abstractdoi: 10.1016/j.ijhydene.2020.05.069
  • 2020 • 204 Performance and Cost Assessment of Machine Learning Interatomic Potentials
    Zuo, Y. and Chen, C. and Li, X. and Deng, Z. and Chen, Y. and Behler, J. and Csányi, G. and Shapeev, A.V. and Thompson, A.P. and Wood, M.A. and Ong, S.P.
    Journal of Physical Chemistry A 124 731-745 (2020)
    Machine learning of the quantitative relationship between local environment descriptors and the potential energy surface of a system of atoms has emerged as a new frontier in the development of interatomic potentials (IAPs). Here, we present a comprehensive evaluation of machine learning IAPs (ML-IAPs) based on four local environment descriptors - atom-centered symmetry functions (ACSF), smooth overlap of atomic positions (SOAP), the spectral neighbor analysis potential (SNAP) bispectrum components, and moment tensors - using a diverse data set generated using high-throughput density functional theory (DFT) calculations. The data set comprising bcc (Li, Mo) and fcc (Cu, Ni) metals and diamond group IV semiconductors (Si, Ge) is chosen to span a range of crystal structures and bonding. All descriptors studied show excellent performance in predicting energies and forces far surpassing that of classical IAPs, as well as predicting properties such as elastic constants and phonon dispersion curves. We observe a general trade-off between accuracy and the degrees of freedom of each model and, consequently, computational cost. We will discuss these trade-offs in the context of model selection for molecular dynamics and other applications. © 2020 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpca.9b08723
  • 2020 • 203 Prismatic Slip in Magnesium
    Stricker, M. and Curtin, W.A.
    Journal of Physical Chemistry C 124 27230-27240 (2020)
    Magnesium is the lowest-density structural metal but has low ductility that limits applications. The low ductility is related to the hexagonally close-packed crystal structure where activation of nonbasal slip is required for general plasticity. Here, our recent neural network potential (NNP) for Mg, trained using Kohn-Sham density functional theory (DFT), is used to examine slip of a dislocations on the prismatic plane. The generalized stacking fault surface energies (GSFEs) for basal and prismatic slip are computed and agree better with Kohn-Sham density functional theory (KS-DFT) than orbital-free density functional theory (OF-DFT) and modified embedded atom method (MEAM), which predict spurious minima. Consistent with the generalized stacking fault energy (GSFE), direct simulations of the prismatic a»screw dislocation show it is unstable to dissociate into the a basal screw dislocation; this is mostly consistent with OF-DFT while MEAM predicts stability. Prismatic slip is thus achieved by a double-cross-slip process of the stable basal dislocations driven by a resolved shear stress on the orthogonal prismatic plane; this is consistent with the process deduced from experiments. The Nudged Elastic Band method is used with the NNP to examine the atomistic path and the stress-dependent enthalpy barrier for this mechanism; this requires many tens of thousands of atoms. The basal-prismatic cross-slip occurs in increments of c/2 via basal constriction, cross-slip on the prism plane, cross-slip back onto the basal plane, and lateral motion of the created jogs to extend the new basal dislocation. Comparisons with experimental deductions show some agreement and some notable disagreement. Resolution of the differences points toward further large-scale studies that require the accuracy and efficiency of KS-DFT-trained NNP, an approach that is also naturally extendable to the important domain of Mg alloys. © 2020 American Chemical Society. All rights reserved.
    view abstractdoi: 10.1021/acs.jpcc.0c09665
  • 2020 • 202 Role of inclination dependence of grain boundary energy on the microstructure evolution during grain growth
    Salama, H. and Kundin, J. and Shchyglo, O. and Mohles, V. and Marquardt, K. and Steinbach, I.
    Acta Materialia 188 641-651 (2020)
    The role of inclination dependence of grain boundary energy on the microstructure evolution and the orientation distribution of grain boundary planes during grain growth in polycrystalline materials is investigated by three-dimensional phase-field simulations. The anisotropic grain boundary energy model uses the description of the faceted surface structure of the individual crystals and constructs an anisotropic energy of solid-solid interface. The energy minimization occurs by the faceting of the grain boundary due to inclination dependence of the grain boundary energy. The simulation results for a single grain show the development of equilibrium shapes (faceted grain morphologies) with different families of facets which agrees well with the theoretical predictions. The results of grain growth simulations with isotropic and anisotropic grain boundary energy for cubic symmetry show that inclination dependence of grain boundary energy has a significant influence on the grain boundary migration, grain growth kinetics and the grain boundary plane distribution. It has been shown that the model essentially reproduces the experimental studies reported for NaCl and MgO polycrystalline systems where the anisotropic distribution of grain boundary planes has a peak for the low-index {100} type boundaries. © 2020 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2020.02.043
  • 2020 • 201 Structural evolution and magnetic properties of high-entropy CuCrFeTiNi alloys prepared by high-energy ball milling and spark plasma sintering
    Shkodich, N.F. and Spasova, M. and Farle, M. and Kovalev, D.Y. and Nepapushev, A.A. and Kuskov, K.V. and Vergunova, Y.S. and Scheck, Y.B. and Rogachev, A.S.
    Journal of Alloys and Compounds 816 (2020)
    A powder of equiatomic CuCrFeTiNi high-entropy alloy (HEA) was prepared by short-term (30 min) high-energy ball milling (HEBM). Our structural and chemical analysis showed that micron sized particles of bcc CuCrFeTiNi consisting of nanosized crystalline grains (∼6 nm) could be obtained after 30 min of HEBM. The influence of milling time (30 ÷ 240 min) on structural and magnetic transformations of CuCrFeTiNi powder mixture was investigated. The HEA powders were thermally stable up to 500°С based on DSC results. The HEA powder was subsequently consolidated by spark plasma sintering at 700 °C resulting in a consolidated bulk HEA with co-existing bcc and fcc phases. The as-milled CuCrFeTiNi powder blend contained a solid solution with bcc (Im3m) structure. Annealing at 600°С (t = 180 min) increased the crystallinity of the α-phase (bcc) and gave rise to formation of the γ-phase (fcc, Fm3m) whose amount grew with increasing dwell time. Between 800 and 1000°С, a tetragonal intermetallic σ-phase – most likely FeCr - appeared and subsequently vanished. At 1000°С, the final product was found to contain two solid solutions based on the γ-phase (fcc). The Vickers hardness HvHEBM = 7.7 GPa of the SPS consolidated CuCrFeTiNi alloy (milled for t = 180 min) was markedly higher than the one of SPS-produced ones without HEBM (Hv = 2.1 GPa). Paramagnetic behavior at room temperature with a small ferromagnetic contribution at low fields was observed for as-milled powder after 180 min of HEBM. A small magnetic hysteresis was observed at 5 K and 300 K with a coercive field of around 16 kA/m. Above 100 K, the inverse susceptibility of a HEA powder ball-milled for t = 240 min showed a clear paramagnetic response. The Curie temperature TC ∼50 K was found. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2019.152611
  • 2020 • 200 Structure Defines Function: Clinically Relevant Mutations in ErbB Kinases
    Niggenaber, J. and Hardick, J. and Lategahn, J. and Rauh, D.
    Journal of Medicinal Chemistry 63 40-51 (2020)
    The ErbB receptor tyrosine kinase family members EGFR (epidermal growth factor receptor) and Her2 are among the prominent mutated oncogenic drivers of non-small cell lung cancer (NSCLC). Their importance in proliferation, apoptosis, and cell death ultimately renders them hot targets in cancer therapy. Small-molecule tyrosine kinase inhibitors seem well suited to be tailor-made therapeutics for EGFR mutant NSCLC; however, drug resistance mutations limit their success. Against this background, the elucidation and visualization of the three-dimensional structure of cancer-related kinases provide valuable insights into their molecular functions. This field has undergone a revolution because X-ray crystal structure determinations aided structure-based drug design approaches and clarified the effect of activating and resistance-conferring mutations. Here, we present an overview of important mutations affecting EGFR and Her2 and highlight their influence on the kinase domain conformations and active site accessibility. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jmedchem.9b00964
  • 2019 • 199 3D printed alumina for low-loss millimeter wave components
    Jimenez-Saez, A. and Schubler, M. and Krause, C. and Pandel, D. and Rezer, K. and Bogel, G.V. and Benson, N. and Jakoby, R.
    IEEE Access 7 40719-40724 (2019)
    This paper compares the performance of three different materials and processing techniques suitable for low-loss mm-Wave components. The comparison is made by fabricating the same 2D photonic crystal structure in the W-band. Rogers RT/duroid® 6010.2LM and high resistive silicon are milled and etched, respectively. In addition, a novel technique consisting of 3D printed alumina is tested and its performance is compared with the technologies and materials above, which all have similar relative permittivities of around ten. The material characterization is carried out by means of high-Q resonator samples integrated into 2D photonic crystal structures. The results of these samples prove the high material purity and low loss of the 3D printed alumina structures, which opens up the use of this technology for high-permittivity low-loss mm-Wave components. © 2013 IEEE.
    view abstractdoi: 10.1109/ACCESS.2019.2906034
  • 2019 • 198 Alkylated Aromatic Thioethers with Aggregation-Induced Emission Properties—Assembly and Photophysics
    Riebe, S. and Saccone, M. and Stelzer, J. and Sowa, A. and Wölper, C. and Soloviova, K. and Strassert, C.A. and Giese, M. and Voskuhl, J.
    Chemistry - An Asian Journal 14 814-820 (2019)
    In this contribution, we present the synthesis and self-assembly of alkylated thioethers with interesting photophysical properties. To this end, the emission, absorption and excitation spectra in organic solvents and as aggregates in water were measured as well as the corresponding photoluminescence quantum yields and lifetimes. The aggregates in aqueous media were visualized and measured using transmission electron microscopy. Besides that, crystal structures of selected compounds allowed a detailed discussion of the structure–property relationship. Furthermore, the mesomorphic behavior was investigated using polarized optical microscopy (POM) as well as differential scanning calorimetry (DSC). © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/asia.201801564
  • 2019 • 197 Alkyloxy modified pyrene fluorophores with tunable photophysical and crystalline properties
    Kapf, A. and Eslahi, H. and Blanke, M. and Saccone, M. and Giese, M. and Albrecht, M.
    New Journal of Chemistry 43 6361-6371 (2019)
    Novel alkyloxy modified 2,7-di-tert-butyl-4,5,9,10-tetra(arylethynyl)pyrenes were prepared through a straightforward Sonogashira coupling approach. Optical properties such as quantum yields and absorption/emission spectra of the fluorophores were investigated by UV/Vis and fluorescence measurements. Aggregation induced excimer formation of the chromophores in polar solvents and in the solid state was proved by the presence of a characteristic bathochromically shifted emission band and a decrease of the emission capability. These results strongly indicate the unexpected observation that the excimer formation of adjacent pyrene rings is not prevented by the introduction of bulky tert-butyl substituents. Single-crystal X-ray and computational analyses reveal the co-planar alignment of adjacent molecules and the presence of π-π-stacking in the molecular packing of the pyrene polyaromatics. Furthermore, fluorescence, DSC and POM measurements indicate that the aggregation behaviour, the thermal characteristics and the crystalline properties are significantly influenced by changing structural features of the attached functional groups at the periphery of the pyrene core. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
    view abstractdoi: 10.1039/c9nj00652d
  • 2019 • 196 Co-crystal structure determination and cellular evaluation of 1,4-dihydropyrazolo[4,3-c] [1,2] benzothiazine 5,5-dioxide p38α MAPK inhibitors
    Bartolini, D. and Bührmann, M. and Barreca, M.L. and Manfroni, G. and Cecchetti, V. and Rauh, D. and Galli, F.
    Biochemical and Biophysical Research Communications 511 579-586 (2019)
    p38α mitogen-activated protein kinase (MAPK) is an attracting pharmacological target in inflammatory diseases and cancer. Searching for new and more efficient p38-MAPK inhibitors, two recently developed pyrazolobenzothiazine-based (COXP4M12 and COXH11) compounds were investigated in this study using a cellular model of p38 activation. This consisted of HT29 human colorectal adenocarcinoma cells exposed to H 2 O 2 or lipopolysaccharide (LPS). Immunoblot data confirmed the inhibitory effect of COXP4M12 and COXH11 on p38 substrate phosphorylation (MAPK-APK2 and ATF2 transcription factor). Compound cytotoxicity was very low and apparent efficacy of these inhibitors was comparable with that of SB203580, a commercially available type I inhibitor of p38. All these compounds also inhibit upstream kinases that promote p38-MAPK phosphorylation and co-activate the stress-activated protein kinase JNK, while ERK1/2 MAPK phosphorylation was unaffected. Compound-target kinase interaction was investigated by means of co-crystallization experiments that provided further structural and molecular insight on the inhibitory mechanism and optimization strategy of this new class of p38-MAPK inhibitors. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.bbrc.2019.02.063
  • 2019 • 195 Crystal growth, microstructure, and physical properties of SrMnSb2
    Liu, Y. and Ma, T. and Zhou, L. and Straszheim, W.E. and Islam, F. and Jensen, B.A. and Tian, W. and Heitmann, T. and Rosenberg, R.A. and Wilde, J.M. and Li, B. and Kreyssig, A. and Goldman, A.I. and Ueland, B.G. and McQueeney, R....
    Physical Review B 99 (2019)
    We report on the crystal and magnetic structures and magnetic and transport properties of SrMnSb2 single crystals grown by the self-flux method. Magnetic susceptibility measurements reveal an antiferromagnetic (AFM) transition at TN=295(3) K. Above TN, the susceptibility slightly increases and forms a broad peak at T∼420 K, which is a typical feature of two-dimensional magnetic systems. Neutron diffraction measurements on single crystals confirm the previously reported C-type AFM structure below TN. Both de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects are observed in SrMnSb2 single crystals. Analysis of the oscillatory component by a Fourier transform shows that the prominent frequencies obtained by the two different techniques are practically the same within error regardless of sample size or saturated magnetic moment. Transmission electron microscopy (TEM) reveals the existence of stacking faults in the crystals, which result from a horizontal shift of Sb atomic layers suggesting possible ordering of Sb vacancies in the crystals. Increase of temperature in susceptibility measurements leads to the formation of a strong peak at T∼570 K that upon cooling under magnetic field the susceptibility shows a ferromagnetic transition at TC∼580 K. Neutron powder diffraction on crushed single crystals does not support a ferromagnetic phase above TN. Furthermore, x-ray magnetic circular dichroism (XMCD) measurements of a single crystal at the L2,3 edge of Mn shows a signal due to induced canting of AFM moments by the applied magnetic field. All evidence strongly suggests that a chemical transformation at the surface of single crystals occurs above 500 K concurrently producing a minute amount of ferromagnetic impurity phase. © 2019 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.99.054435
  • 2019 • 194 Gas dependent hysteresis in MoS2 field effect transistors
    Urban, F. and Giubileo, F. and Grillo, A. and Iemmo, L. and Luongo, G. and Passacantando, M. and Foller, T. and Madauß, L. and Pollmann, E. and Geller, M.P. and Oing, D. and Schleberger, M. and Di Bartolomeo, A.
    2D Materials 6 (2019)
    We study the effect of electric stress, gas pressure and gas type on the hysteresis in the transfer characteristics of monolayer molybdenum disulfide (MoS2) field effect transistors. The presence of defects and point vacancies in the MoS2 crystal structure facilitates the adsorption of oxygen, nitrogen, hydrogen or methane, which strongly affect the transistor electrical characteristics. Although the gas adsorption does not modify the conduction type, we demonstrate a correlation between hysteresis width and adsorption energy onto the MoS2 surface. We show that hysteresis is controllable by pressure and/or gas type. Hysteresis features two well-separated current levels, especially when gases are stably adsorbed on the channel, which can be exploited in memory devices. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/2053-1583/ab4020
  • 2019 • 193 Improving the mesomorphic behaviour of supramolecular liquid crystals by resonance-assisted hydrogen bonding
    Saccone, M. and Pfletscher, M. and Kather, S. and Wölper, C. and Daniliuc, C. and Mezger, M. and Giese, M.
    Journal of Materials Chemistry C 7 8643-8648 (2019)
    A systematic structure-property relationship study on hydrogen-bonded liquid crystals was performed, revealing the impact of resonance-assisted hydrogen bonds (RAHBs) on the self-assembling behavior of the supramolecular architecture. The creation of a six-membered intramolecular hydrogen-bonded ring acts as a counterpart to the self-organization between hydrogen bond donators and acceptors and determines thus the suprastructure. Variation of the hydrogen-bonding pattern allowed us to significantly improve the temperature range of the reported liquid crystalline assemblies. © 2019 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9tc02787d
  • 2019 • 192 Influence of Calcium-Phosphate Coating on Wettability of Hybrid Piezoelectric Scaffolds
    Zviagin, A. and Chernozem, R. and Surmeneva, M. and Loza, K. and Prymak, O. and Ulbricht, M. and Epple, M. and Surmenev, R.
    IOP Conference Series: Materials Science and Engineering 597 (2019)
    Herein, electrospun biodegradable scaffolds based on polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB) and polyaniline (PANi) polymers were fabricated. A calcium-phosphate (CaP) coating was deposited on the surface of the scaffolds via an improved soaking process. Influence of the deposition cycles and ethanol concentration in the solution on the relative increase of the scaffolds weight and water contact angle (WCA) are determined. The characterization of the molecular and crystal structure confirmed the formation of CaP phase. Importantly, WCA results showed that the pristine scaffolds have the hydrophobic surface, while the deposition of CaP coating onto scaffolds allows to significantly improve the surface wetting behavior, and infiltration of the water droplets into the CaP-coated scaffolds was observed. Thus, the fabricated hybrid biodegradable piezoelectric scaffolds can be utilized for regenerative medicine. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/597/1/012061
  • 2019 • 191 Melting properties of peptides and their solubility in water. Part 1: Dipeptides based on glycine or alanine
    Do, H.T. and Chua, Y.Z. and Habicht, J. and Klinksiek, M. and Hallermann, M. and Zaitsau, D. and Schick, C. and Held, C.
    RSC Advances 9 32722-32734 (2019)
    Melting properties (melting temperature, melting enthalpy and heat capacity difference between liquid and solid phase) of biomolecules are indispensable for natural and engineering sciences. The direct determination of these melting properties by using conventional calorimeters for biological compounds is often not possible due to decomposition during slow heating. In the current study this drawback is overcome by using fast scanning calorimetry (FSC) to directly measure the melting properties of five dipeptides (glycyl-glycine, glycyl-l-alanine, l-alanyl-glycine, l-alanyl-l-alanine and cyclo(l-alanyl-glycine)). The experimental melting properties were used as inputs into a thermodynamic solid-liquid equilibrium relation to predict solubility of the dipeptides in water. The required activity coefficients were predicted with PC-SAFT using solubility-independent model parameters. PC-SAFT predicted different solubility profiles (solubility vs. temperature) of isomers. The predictions were validated by new experimental solubility data, and the crystal structure of the dipeptides in saturated solution was verified by X-ray diffraction. The different water solubility profiles of isomers (glycyl-l-alanine and l-alanyl-glycine) were found to be caused by the big difference in the melting enthalpy of the two dipeptides. To conclude, combining the PC-SAFT and FSC methods allows for accurate prediction of dipeptide solubility in water in a wide temperature range without the need to fit any model parameters to experimental solubility data. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9ra05730g
  • 2019 • 190 Microstructural and tribological properties of sputtered AlCrSiWN films deposited with segmented powder metallurgic target materials
    Tillmann, W. and Fehr, A. and Stangier, D.
    Thin Solid Films 687 (2019)
    When synthesizing magnetron sputtered films with a complex stoichiometry, integrating the desired coating constituents into one target material is favorable in order to avoid nanolaminar film depositions and to enable a homogenous film growth. In contrast to alloyed targets, segmented plug targets allow to merge elements with different physical properties in one target material. Two targets, amalgamating 20 and 48 hot-pressed 85.6Cr9.9Si4.5W (at. %) plugs, respectively, into a monolithic aluminum target were fabricated and employed in a direct current magnetron sputtering process to deposit AlCrSiWN films on high-speed steel (AISI M3:2, 1.3344). The cathode powers for the Al(CrSiW)20 and Al(CrSiW)48 targets were varied between 7.5 and 17.5 W/cm2 to analyze how differently composed targets and various cathode powers affect the microstructure and tribological properties of the sputtered films. The results revealed that the chemical composition as well as the thickness of the films strongly depend on the target setup. All AlCrSiWN films exhibited a Cr/Si/W ratio of approximately 84/11/6. The Cr and Al contents were dominant (19–29 at. %), while the Si and W contents varied between 2 and 3 at. %. Especially the Al/Cr ratio of the films is affected by the varying Al/CrSiW surface area ratio of the manufactured plug targets. Furthermore, the mechanical properties are significantly influenced by the Al/Cr ratio, which is responsible for a dense coating growth and the crystalline structure of the films. All AlCrSiWN films were (111) textured indicating a B1 (Al, Cr, W)N structure, which exhibited a finer crystalline growth with an increasing cathode power on the Al(CrSiW)20 target. Tribological analyses of the films against Al2O3 balls further revealed that thinner films resulted in a decreased wear coefficient. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2019.137465
  • 2019 • 189 Modeling of Thermal Conductivity for a CMOS-Compatible MEMS-ROIC Contact by TiN Nanotubes
    Michel, M. and Vogt, H.
    IEEE Transactions on Electron Devices 66 3485-3491 (2019)
    Size reduction in microelectromechanical systems (MEMS) leads to more complex behavior of physical parameters affected by quantum mechanical effects. Besides specific electrical resistance, thermal conductivity is a characteristic parameter for designing application-specific MEMS. Nanotubes are able to realize an electrical contact between a sensor element and a CMOS substrate while providing sufficient thermal isolation. A model for the prediction of thermal conductivity of nanotubes, compounded of alloys and demonstrated for titanium nitride, is presented here. The influence of the crystal structure on the mean free path is considered to limit electron and phonon mobility in thin layer geometries. A 3-D-2-D transition in the density of states of electrons and phonons is taken into account because feature sizes today are below the boundary scattering regime. We show that the dominating thermal conductance mechanism varies between phonons and electrons as a function of film thickness in TiN. © 1963-2012 IEEE.
    view abstractdoi: 10.1109/TED.2019.2919766
  • 2019 • 188 Polymorphism of hydrogen-bonded star mesogens-a combinatorial DFT-D and FT-IR spectroscopy study
    Pfletscher, M. and Wysoglad, J. and Gutmann, J.S. and Giese, M.
    RSC Advances 9 8444-8453 (2019)
    A comprehensive study combining detailed computational analyses with temperature-variable FT-IR experiments was performed in order to elucidate the structure of the hydrogen-bonded liquid crystals based on phloroglucinol and azopyridine in their mesophase. Conformational analysis revealed three relevant conformers: star, λ- and E-shape. The results demonstrate an entropy-driven unfolding mechanism of the assembly. The stability of the conformers is given by intermolecular π-π and dispersion interactions of the azopyridine side chains. Correlating the calculated vibrational frequency with experimental FT-IR spectra suggests a λ-folded conformation of the assemblies as the predominant species in the mesophase. © 2019 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8ra09458f
  • 2019 • 187 Profilin and formin constitute a pacemaker system for robust actin filament growth
    Funk, J. and Merino, F. and Venkova, L. and Heydenreich, L. and Kierfeld, J. and Vargas, P. and Raunser, S. and Piel, M. and Bieling, P.
    eLife 8 (2019)
    The actin cytoskeleton drives many essential biological processes, from cell morphogenesis to motility. Assembly of functional actin networks requires control over the speed at which actin filaments grow. How this can be achieved at the high and variable levels of soluble actin subunits found in cells is unclear. Here we reconstitute assembly of mammalian, non-muscle actin filaments from physiological concentrations of profilin-actin. We discover that under these conditions, filament growth is limited by profilin dissociating from the filament end and the speed of elongation becomes insensitive to the concentration of soluble subunits. Profilin release can be directly promoted by formin actin polymerases even at saturating profilin-actin concentrations. We demonstrate that mammalian cells indeed operate at the limit to actin filament growth imposed by profilin and formins. Our results reveal how synergy between profilin and formins generates robust filament growth rates that are resilient to changes in the soluble subunit concentration. © 2019, eLife Sciences Publications Ltd. All rights reserved.
    view abstractdoi: 10.7554/eLife.50963
  • 2019 • 186 Retrofitting metal-organic frameworks
    Schneider, C. and Bodesheim, D. and Keupp, J. and Schmid, R. and Kieslich, G.
    Nature Communications 10 (2019)
    The post-synthetic installation of linker molecules between open-metal sites (OMSs) and undercoordinated metal-nodes in a metal-organic framework (MOF) — retrofitting — has recently been discovered as a powerful tool to manipulate macroscopic properties such as the mechanical robustness and the thermal expansion behavior. So far, the choice of cross linkers (CLs) that are used in retrofitting experiments is based on qualitative considerations. Here, we present a low-cost computational framework that provides experimentalists with a tool for evaluating various CLs for retrofitting a given MOF system with OMSs. After applying our approach to the prototypical system CL@Cu3BTC2 (BTC = 1,3,5-benzentricarboxylate) the methodology was expanded to NOTT-100 and NOTT-101 MOFs, identifying several promising CLs for future CL@NOTT-100 and CL@NOTT-101 retrofitting experiments. The developed model is easily adaptable to other MOFs with OMSs and is set-up to be used by experimentalists, providing a guideline for the synthesis of new retrofitted MOFs with modified physicochemical properties. © 2019, The Author(s).
    view abstractdoi: 10.1038/s41467-019-12876-1
  • 2019 • 185 Site-specific quasi in situ investigation of primary static recrystallization in a low carbon steel
    Diehl, M. and Kertsch, L. and Traka, K. and Helm, D. and Raabe, D.
    Materials Science and Engineering A 755 295-306 (2019)
    Low-alloyed steels with body-centered cubic crystal structure are a material class that is widely used for sheet metal forming applications. When having an adequate crystallographic texture and microstructure, their mechanical behavior is characterized by an isotropic in-plane flow behavior in combination with a low yield strength. The decisive processing steps for obtaining these beneficial mechanical properties are cold rolling and subsequent annealing. While for the former the number of passes, the deformation rates, and the total thickness reduction are the main processing parameters, the latter is described mainly by the heating rate and the holding temperature and time. Primary static recrystallization during annealing subsequent to the cold rolling process alters mainly two aspects of the material state: It firstly replaces the elongated and heavily deformed grains of the cold rolled microstructure by small, globular grains with low dislocation density and secondly it changes the crystallographic texture insofar as it typically diminishes the α- and strengthens the γ-fiber texture components. In the present work, the recrystallization behavior of a commercial non-alloyed low carbon steel is studied. A quasi in situ setup that enables site-specific characterization is employed to gain a local picture of the nucleation and recrystallization process. From the Kernel Average Misorientation (KAM) values of the deformation structure, the tendency to be consumed by new grains can be predicted. Crystallographic analysis shows that the most deformed regions have either a γ-fiber orientation or belong to heavily fragmented regions. New grains nucleate especially in such highly deformed regions and inherit often the orientation from the deformation microstructure. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2019.02.032
  • 2019 • 184 Strain relaxation behaviour of vortices in a multiferroic superconductor
    Evans, D.M. and Schiemer, J.A. and Wolf, T. and Adelmann, P. and Böhmer, A.E. and Meingast, C. and Dutton, S.E. and Mukherjee, P. and Hsu, Y.-T. and Carpenter, M.A.
    Journal of Physics Condensed Matter 31 (2019)
    The elastic and anelastic properties of a single crystal of Co-doped pnictide Ba(Fe 0.957 Co 0.043 ) 2 As 2 have been determined by resonant ultrasound spectroscopy in the frequency range 10-500 kHz, both as a function of temperature through the normal-superconducting transition (T c ≈ 12.5 K) and as a function of applied magnetic field up to 12.5 T. Correlation with thermal expansion, electrical resistivity, heat capacity, DC and AC magnetic data from crystals taken from the same synthetic batch has revealed the permeating influence of strain on coupling between order parameters for the ferroelastic (Q E ) and superconducting (Q SC ) transitions and on the freezing/relaxation behaviour of vortices. Elastic softening through T c in zero field can be understood in terms of classical coupling of the order parameter with the shear strain e 6 , λe 6 , which means that there must be a common strain mechanism for coupling of the form λ Q E . At fields of ∼5 T and above, this softening is masked by Debye-like stiffening and acoustic loss processes due to vortex freezing. The first loss peak may be associated with the establishment of superconductivity on ferroelastic twin walls ahead of the matrix and the second is due to the vortex liquid-vortex glass transition. Strain contrast between vortex cores and the superconducting matrix will contribute significantly to interactions of vortices both with each other and with the underlying crystal structure. These interactions imply that iron-pnictides represent a class of multiferroic superconductors in which strain-mediated coupling occurs between the multiferroic properties (ferroelasticity, antiferromagnetism) and superconductivity. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-648X/aafbd7
  • 2019 • 183 Structural and chemical insights into the covalent-allosteric inhibition of the protein kinase Akt
    Uhlenbrock, N. and Smith, S. and Weisner, J. and Landel, I. and Lindemann, M. and Le, T.A. and Hardick, J. and Gontla, R. and Scheinpflug, R. and Czodrowski, P. and Janning, P. and Depta, L. and Quambusch, L. and Müller, M.P. and...
    Chemical Science 10 3573-3585 (2019)
    The Ser/Thr kinase Akt (Protein Kinase B/PKB) is a master switch in cellular signal transduction pathways. Its downstream signaling influences cell proliferation, cell growth, and apoptosis, rendering Akt a prominent drug target. The unique activation mechanism of Akt involves a change of the relative orientation of its N-terminal pleckstrin homology (PH) and the kinase domain and makes this kinase suitable for highly specific allosteric modulation. Here we present a unique set of crystal structures of covalent-allosteric interdomain inhibitors in complex with full-length Akt and report the structure-based design, synthesis, biological and pharmacological evaluation of a focused library of these innovative inhibitors. © 2019 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8sc05212c
  • 2019 • 182 Surface states in bulk single crystal of topological semimetal Co3Sn2S2 toward water oxidation
    Li, G. and Xu, Q. and Shi, W. and Fu, C. and Jiao, L. and Kamminga, M.E. and Yu, M. and Tüysüz, H. and Kumar, N. and Süß, V. and Saha, R. and Srivastava, A.K. and Wirth, S. and Auffermann, G. and Gooth, J. and Parkin, S. and S...
    Science Advances 5 (2019)
    The band inversion in topological phase matters bring exotic physical properties such as the topologically protected surface states (TSS). They strongly influence the surface electronic structures of the materials and could serve as a good platform to gain insight into the surface reactions. Here we synthesized high-quality bulk single crystals of Co3Sn2S2 that naturally hosts the band structure of a topological semimetal. This guarantees the existence of robust TSS from the Co atoms. Co3Sn2S2 crystals expose their Kagome lattice that constructed by Co atoms and have high electrical conductivity. They serves as catalytic centers for oxygen evolution process (OER), making bonding and electron transfer more efficient due to the partially filled orbital. The bulk single crystal exhibits outstanding OER catalytic performance, although the surface area is much smaller than that of Co-based nanostructured catalysts. Our findings emphasize the importance of tailoring TSS for the rational design of high-activity electrocatalysts. Copyright © 2019 The Authors.
    view abstractdoi: 10.1126/sciadv.aaw9867
  • 2019 • 181 The puzzling issue of silica toxicity: Are silanols bridging the gaps between surface states and pathogenicity?
    Pavan, C. and Delle Piane, M. and Gullo, M. and Filippi, F. and Fubini, B. and Hoet, P. and Horwell, C.J. and Huaux, F. and Lison, D. and Lo Giudice, C. and Martra, G. and Montfort, E. and Schins, R. and Sulpizi, M. and Wegner, K....
    Particle and Fibre Toxicology 16 (2019)
    Background: Silica continues to represent an intriguing topic of fundamental and applied research across various scientific fields, from geology to physics, chemistry, cell biology, and particle toxicology. The pathogenic activity of silica is variable, depending on the physico-chemical features of the particles. In the last 50 years, crystallinity and capacity to generate free radicals have been recognized as relevant features for silica toxicity. The 'surface' also plays an important role in silica toxicity, but this term has often been used in a very general way, without defining which properties of the surface are actually driving toxicity. How the chemical features (e.g., silanols and siloxanes) and configuration of the silica surface can trigger toxic responses remains incompletely understood. Main body: Recent developments in surface chemistry, cell biology and toxicology provide new avenues to improve our understanding of the molecular mechanisms of the adverse responses to silica particles. New physico-chemical methods can finely characterize and quantify silanols at the surface of silica particles. Advanced computational modelling and atomic force microscopy offer unique opportunities to explore the intimate interactions between silica surface and membrane models or cells. In recent years, interdisciplinary research, using these tools, has built increasing evidence that surface silanols are critical determinants of the interaction between silica particles and biomolecules, membranes, cell systems, or animal models. It also has become clear that silanol configuration, and eventually biological responses, can be affected by impurities within the crystal structure, or coatings covering the particle surface. The discovery of new molecular targets of crystalline as well as amorphous silica particles in the immune system and in epithelial lung cells represents new possible toxicity pathways. Cellular recognition systems that detect specific features of the surface of silica particles have been identified. Conclusions: Interdisciplinary research bridging surface chemistry to toxicology is progressively solving the puzzling issue of the variable toxicity of silica. Further interdisciplinary research is ongoing to elucidate the intimate mechanisms of silica pathogenicity, to possibly mitigate or reduce surface reactivity. © 2019 The Author(s).
    view abstractdoi: 10.1186/s12989-019-0315-3
  • 2018 • 180 A set-up for simultaneous measurement of second harmonic generation and streaming potential and some test applications
    Lützenkirchen, J. and Scharnweber, T. and Ho, T. and Striolo, A. and Sulpizi, M. and Abdelmonem, A.
    Journal of Colloid and Interface Science 529 294-305 (2018)
    We present a measurement cell that allows simultaneous measurement of second harmonic generation (SHG) and streaming potential (SP) at mineral-water interfaces with flat specimen that are suitable for non-linear optical (NLO) studies. The set-up directly yields SHG data for the interface of interest and can also be used to obtain information concerning the influence of flow on NLO signals from that interface. The streaming potential is at present measured against a reference substrate (PTFE). The properties of this inert reference can be independently determined for the same conditions. With the new cell, for the first time the SHG signal and the SP for flat surfaces have been simultaneously measured on the same surface. This can in turn be used to unambiguously relate the two observations for identical solution composition. The SHG test of the cell with a fluorite sample confirmed previously observed differences in NLO signal under flow vs. no flow conditions in sum frequency generation (SFG) investigations. As a second test surface, an inert (“hydrophobic”) OTS covered sapphire-c electrolyte interface was studied to verify the zeta-potential measurements with the new cell. For this system we obtained combined zeta-potential/SHG data in the vicinity of the point of zero charge, which were found to be proportional to each other as expected. Furthermore, on the accessible time scales of the SHG measurements no effects of flow, flow velocity and stopped flow occurred on the interfacial water structure. This insensitivity to flow for the inert surface was corroborated by concomitant molecular dynamics simulations. Finally, the set-up was used for simultaneous measurements of the two properties as a function of pH in automated titrations with an oxidic surface. Different polarization combinations obtained in two separate titrations, yielded clearly different SHG data, while under identical conditions zeta-potentials were exactly reproduced. The polarization combination that is characteristic for dipoles perpendicular to the surface scaled with the zeta-potentials over the pH-range studied, while the other did not. The work provides an advanced approach for investigating liquid/surface interactions which play a major role in our environment. The set-up can be upgraded for SFG studies, which will allow more detailed studies on the chemistry and the water structure at a given interface, but also the combined study of specific adsorption including kinetics in combination with electrokinetics. Such investigations are crucial for the basic understanding of many environmental processes from aquatic to atmospheric systems. © 2018 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2018.06.017
  • 2018 • 179 A TEM Investigation of Columnar-Structured Thermal Barrier Coatings Deposited by Plasma Spray-Physical Vapor Deposition (PS-PVD)
    Rezanka, S. and Somsen, C. and Eggeler, G. and Mauer, G. and Vaßen, R. and Guillon, O.
    Plasma Chemistry and Plasma Processing 38 791-802 (2018)
    The plasma spray-physical vapor deposition technique (PS-PVD) is used to deposit various types of ceramic coatings. Due to the low operating pressure and high enthalpy transfer to the feedstock, deposition from the vapor phase is very effective. The particular process conditions allow for the deposition of columnar microstructures when applying thermal barrier coatings (TBCs). These coatings show a high strain tolerance similar to those obtained by electron beam-physical vapor deposition (EB-PVD). But compared to EB-PVD, PS-PVD allows significantly reducing process time and costs. The application-related properties of PS-PVD TBCs have been investigated in earlier work, where the high potential of the process was described and where the good resistance to thermo-mechanical loading conditions was reported. But until now, the elementary mechanisms which govern the material deposition have not been fully understood and it is not clear, how the columnar structure is built up. Shadowing effects and diffusion processes are assumed to contribute to the formation of columnar microstructures in classical PVD processing routes. For such structures, crystallographic textures are characteristic. For PS-PVD, however, no crystallographic textures could initially be found using X-ray diffraction. In this work a more detailed TEM investigations and further XRD measurements of the columnar PS-PVD microstructure were performed. The smallest build units of the columnar TBC structure are referred to as sub-columns. The observed semi-single crystal structure of individual sub-columns was analyzed by means of diffraction experiments. The absence of texture in PS-PVD coatings is confirmed and elementary nucleation and growth mechanisms are discussed. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
    view abstractdoi: 10.1007/s11090-018-9898-y
  • 2018 • 178 Carbide types in an advanced microalloyed bainitic/ferritic Cr–Mo Steel – TEM observations and thermodynamic calculations [Karbide in einem mikrolegierten bainitisch-ferritischen Cr–Mo-Stahl – TEM Charakterisierung und thermodynamische Berechnungen]
    Wang, H. and Somsen, C. and Eggeler, G. and Detemple, E.
    Materialwissenschaft und Werkstofftechnik 49 726-740 (2018)
    The strength and toughness of low alloyed ferritic/bainitic steels depend on their microstructure, which evolves during thermo-mechanical treatments along the processing chain. Chromium-molybdenum steel microstructures are complex. Therefore, only a limited number of attempts have been made to fully characterize carbide populations in such steels. In the present work, analytical transmission electron microscopy is employed to study the microstructure of a low alloyed chromium-molybdenum steel, which features ferritic (F, mainly α-iron and niobium-carbides) and bainitic (B, α-phase, dislocation, grain/subgrain boundaries, various MxCy carbides) regions. The crystal structure and chemical nature of more than 200 carbides are determined and their distributions in the two microstructural regions are analyzed. The present work shows how particles can be identified in an effective manner and how the microstructural findings can be interpreted on the basis of thermodynamic calculations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/mawe.201700186
  • 2018 • 177 Chapter 7: NMR Studies of Ionic Dynamics in Solids
    Böhmer, R. and Storek, M. and Vogel, M.
    New Developments in NMR 2018-January 193-230 (2018)
    We outline NMR methods for studies of ionic dynamics in solids, including, but not limited to 7Li NMR approaches to lithium ion conductors. The covered techniques enable detailed characterization of ionic motions in wide ranges of time and length scales. © The Royal Society of Chemistry 2018.
    view abstractdoi: 10.1039/9781788010467-00193
  • 2018 • 176 Chemical modulation of transcription factors
    Wiedemann, B. and Weisner, J. and Rauh, D.
    MedChemComm 9 1249-1272 (2018)
    Transcription factors (TFs) constitute a diverse class of sequence-specific DNA-binding proteins, which are key to the modulation of gene expression. TFs have been associated with human diseases, including cancer, Alzheimer's and other neurodegenerative diseases, which makes this class of proteins attractive targets for chemical biology and medicinal chemistry research. Since TFs lack a common binding site or structural similarity, the development of small molecules to efficiently modulate TF biology in cells and in vivo is a challenging task. This review highlights various strategies that are currently being explored for the identification and development of modulators of Myc, p53, Stat, Nrf2, CREB, ER, AR, HIF, NF-κB, and BET proteins. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8md00273h
  • 2018 • 175 Coffee-Waste Templating of Metal Ion-Substituted Cobalt Oxides for the Oxygen Evolution Reaction
    Yu, M. and Chan, C.K. and Tüysüz, H.
    ChemSusChem 11 605-611 (2018)
    A facile and scalable method using coffee waste grounds as a hard template has been developed to fabricate nanostructured Co3O4 for the oxygen evolution reaction (OER). Co3O4 incorporating metals with different valences (M/Co=1:4; M=Cu, Ni, Fe, Cr, and W) were also prepared with similar sheet-like structures comprising nanosized crystallites. After detailed characterization by X-ray diffraction, electron microscopy, and nitrogen sorption, the oxides were employed as OER electrocatalysts. Substitution of octahedral and tetrahedral sites of the spinel structure with divalent and trivalent transition metals (Cu, Ni, Fe, and Cr) increased the activity of Co3O4 for the OER, whereas incorporation of hexavalent W led to formation of a second crystal phase and significantly higher electrocatalytic performance. Furthermore, this method is easily scaled up for mass production of Co3O4 with the same nanostructure, which is highly desirable for large-scale application. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cssc.201701877
  • 2018 • 174 Coherently strained [Fe-Co(C)/Au-Cu]n multilayers: A path to induce magnetic anisotropy in Fe-Co films over large thicknesses
    Giannopoulos, G. and Salikhov, R. and Varvaro, G. and Psycharis, V. and Testa, A.M. and Farle, M. and Niarchos, D.
    Journal of Physics D: Applied Physics 51 (2018)
    Among novel critical-element-free materials for permanent magnets, the nearly equiatomic Fe-Co alloy has recently attracted a great deal of attention as a large magneto-crystalline anisotropy can be induced by straining the Fe-Co unit cell. In thin film systems, the use of a suitable underlayer allows a tetragonal reconstruction of the Fe-Co to be triggered up to a critical thickness of few nanometers, above which the crystal structure relaxes to the magnetically soft cubic phase. Scaling-up the thickness of the metastable tetragonal Fe-Co phase is of crucial significance for different nanoscale applications, such as magnetic micro- and nano-electromechanical systems. To suppress the strain relaxation occurring at high thicknesses, we explored a novel approach based on Fe-Co(C)/Au-Cu multilayer films, where both Au-Cu interlayers and carbon (C) doping were used to stabilize the strained Fe-Co tetragonal phase over large thicknesses. Both doped and un-doped multilayer structures show a coherently strained regime, persisting up to a thickness of 60 nm, which leads, possibly in combination with the surface anisotropy induced at the Au-Cu interfaces, to the appearance of a large out-of-plane anisotropy (up to 0.4 MJ m-3), thus suggesting the potential of such an approach to develop critical-element-free thin film permanent magnets for a variety of nanoscale applications. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aaa41c
  • 2018 • 173 Crystallographic and spectroscopic assignment of the proton transfer pathway in [FeFe]-hydrogenases
    Duan, J. and Senger, M. and Esselborn, J. and Engelbrecht, V. and Wittkamp, F. and Apfel, U.-P. and Hofmann, E. and Stripp, S.T. and Happe, T. and Winkler, M.
    Nature Communications 9 (2018)
    The unmatched catalytic turnover rates of [FeFe]-hydrogenases require an exceptionally efficient proton-transfer (PT) pathway to shuttle protons as substrates or products between bulk water and catalytic center. For clostridial [FeFe]-hydrogenase CpI such a pathway has been proposed and analyzed, but mainly on a theoretical basis. Here, eleven enzyme variants of two different [FeFe]-hydrogenases (CpI and HydA1) with substitutions in the presumptive PT-pathway are examined kinetically, spectroscopically, and crystallographically to provide solid experimental proof for its role in hydrogen-turnover. Targeting key residues of the PT-pathway by site directed mutagenesis significantly alters the pH-activity profile of these variants and in presence of H2 their cofactor is trapped in an intermediate state indicative of precluded proton-transfer. Furthermore, crystal structures coherently explain the individual levels of residual activity, demonstrating e.g. how trapped H2O molecules rescue the interrupted PT-pathway. These features provide conclusive evidence that the targeted positions are indeed vital for catalytic proton-transfer. © 2018, The Author(s).
    view abstractdoi: 10.1038/s41467-018-07140-x
  • 2018 • 172 Direct monitoring of the conformational equilibria of the activation loop in the mitogen-activated protein kinase p38α
    Roser, P. and Weisner, J. and Simard, J.R. and Rauh, D. and Drescher, M.
    Chemical Communications 54 12057-12060 (2018)
    Conformational transitions in protein kinases are crucial for the biological function of these enzymes. Here, we characterize and assess conformational equilibria of the activation loop and the effect of small molecule inhibitors in the MAP kinase p38α. Our work experimentally revealed the existence of a two-state equilibrium for p38α while the addition of inhibitors shifts the equilibrium between these two states. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8cc06128a
  • 2018 • 171 Effect of substrate orientation on local magnetoelectric coupling in bi-layered multiferroic thin films
    Naveed-Ul-Haq, M. and Webers, S. and Trivedi, H. and Salamon, S. and Wende, H. and Usman, M. and Mumtaz, A. and Shvartsman, V.V. and Lupascu, D.C.
    Nanoscale 10 20618-20627 (2018)
    In this study we explore the prospect of strain-mediated magnetoelectric coupling in CoFe2O4-BaTiO3 bi-layers as a function of different interfacial boundary conditions. Pulsed laser deposition fabricated thin films on Nb:SrTiO3(100) and Nb:SrTiO3(111) single crystal substrates were characterized in terms of their peculiarities related to the structure-property relationship. Despite the homogeneous phase formation in both films, transmission electron microscopy showed that the bi-layers on Nb:SrTiO3(100) exhibit a higher number of crystallographic defects when compared to the films on Nb:SrTiO3(111). This signifies an intrinsic relationship of the defects and the substrate orientation. To analyze the consequences of these defects on the overall magnetoelectric coupling of the bi-layered films, piezoresponse force microscopy was performed in situ with an applied magnetic field. The local magnetic field dependence of the piezoresponse was obtained using principal component analysis. A detailed analysis of this dependence led to a conclusion that the bi-layers on Nb:SrTiO3(111) exhibit better strain-transfer characteristics between the magnetic and the piezoelectric layer than those which were deposited on Nb:SrTiO3(100). These strain transfer characteristics correlate well with the interface quality and the defect concentration. This study suggests that in terms of overall magnetoelectric coupling, the Nb:SrTiO3(111) grown bi-layers are expected to outperform their Nb:SrTiO3(100) grown counterparts. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8nr06041j
  • 2018 • 170 Experiments indicating a second hydrogen ordered phase of ice VI
    Gasser, T.M. and Thoeny, A.V. and Plaga, L.J. and Köster, K.W. and Etter, M. and Böhmer, R. and Loerting, T.
    Chemical Science 9 4224-4234 (2018)
    In the last twelve years five new ice phases were experimentally prepared. Two of them are empty clathrate hydrates and three of them represent hydrogen ordered counterparts of previously known disordered ice phases. Here, we report on hydrogen ordering in ice VI samples produced by cooling at pressures up to 2.00 GPa. Based on results from calorimetry, dielectric relaxation spectroscopy, Raman spectroscopy, and powder X-ray diffraction the existence of a second hydrogen ordered polymorph related to ice VI is suggested. Powder X-ray data show the oxygen network to be the one of ice VI. For the 1.80 GPa sample the activation energy from dielectric spectroscopy is 45 kJ mol-1, which is much larger than for the known hydrogen ordered proxy of ice VI, ice XV. Raman spectroscopy indicates the 1.80 GPa sample to be more ordered than ice XV. It is further distinct from ice XV in that it experiences hydrogen disordering above ≈103 K which is 26 K below the ice XV to ice VI disordering transition. Consequently, below 103 K it is thermodynamically more stable than ice XV, adding a stability region to the phase diagram of water. For the time being we suggest to call this new phase ice β-XV and to relabel it ice XVIII once its crystal structure is known. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8sc00135a
  • 2018 • 169 Fluoride doped γ-Fe2O3 nanoparticles with increased MRI relaxivity
    Jones, N.E. and Burnett, C.A. and Salamon, S. and Landers, J. and Wende, H. and Lazzarini, L. and Gibbs, P. and Pickles, M. and Johnson, B.R.G. and Evans, D.J. and Archibald, S.J. and Francesconi, M.G.
    Journal of Materials Chemistry B 6 3665-3673 (2018)
    Iron oxide nanoparticles (IONs) are being actively researched and experimented with as contrast agents for Magnetic Resonance Imaging (MRI), as well as image-directed delivery of therapeutics. The efficiency of an MRI contrast agent can be described by its longitudinal and transverse relaxivities, r1 and r2. γ-Fe2O3 nanoparticles-doped with fluoride in a controlled manner and functionalised with citric acid-showed a 3-fold increase in r1 and a 17-fold increase in r2 in a magnetic field of 3 T and almost 6-fold increase in r1 and a 14-fold increase in r2 at 11 T. Following fluorination, PXRD shows that the crystal structure of γ-Fe2O3 is maintained, Mössbauer spectroscopy shows that the oxidation state of the Fe cation is unchanged and HREM shows that the particle size does not vary. However, magnetisation curves show a large increase in the coercive field, pointing towards a large increase in the magnetic anisotropy for the fluorinated nanoparticles compared to the un-doped γ-Fe2O3 nanoparticles. Therefore, a chemically induced increase in magnetic anisotropy appears to be the most relevant parameter responsible for the large increase in relaxivity for γ-Fe2O3 nanoparticles. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8tb00360b
  • 2018 • 168 From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca-Au-Al: In Situ Variable-Temperature Transformation
    Pham, J. and Meng, F. and Lynn, M.J. and Ma, T. and Kreyssig, A. and Kramer, M.J. and Goldman, A.I. and Miller, G.J.
    Journal of the American Chemical Society 140 1337-1347 (2018)
    The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31(3)Al21.69 (CaAu4.33(1)Al1.67, Pa3 (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ∼570 °C and complete by ∼650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14□3.00] and an icosahedral shell of only Al [Al10.5□1.5]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au-Al nearest neighbor contacts over homoatomic Al-Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, "Ca24Au88Al64" (CaAu3.67Al2.67) is proposed. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/jacs.7b10358
  • 2018 • 167 Grain boundaries in bcc-Fe: A density-functional theory and tight-binding study
    Wang, J. and Madsen, G.K.H. and Drautz, R.
    Modelling and Simulation in Materials Science and Engineering 26 (2018)
    Grain boundaries (GBs) have a significant influence on material properties. In the present paper, we calculate the energies of eleven low-σ (σ > 13) symmetrical tilt GBs and two twist GBs in ferromagnetic bcc iron using firstprinciples density functional theory (DFT) calculations. The results demonstrate the importance of a sufficient sampling of initial rigid body translations in all three directions. We show that the relative GB energies can be xplained by the miscoordination of atoms at the GB region. While the main features of the studied GB structures were captured by previous empirical interatomic potential calculations, it is shown that the absolute values of GB energies calculated were substantially underestimated. Based on DFT-calculated GB structures and energies, we construct a new d-band orthogonal tight-binding (TB) model for bcc iron. The TB model is validated by its predictive power on all the studied GBs. We apply the TB model to block boundaries in lath martensite and demonstrate that the experimentally observed GB character distribution can be explained from the viewpoint of interface energy. © 2018 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-651X/aa9f81
  • 2018 • 166 Hedgehog Spin-Vortex Crystal Antiferromagnetic Quantum Criticality in CaK (Fe1-xNix)4As4 Revealed by NMR
    Ding, Q.-P. and Meier, W.R. and Cui, J. and Xu, M. and Böhmer, A.E. and Bud'Ko, S.L. and Canfield, P.C. and Furukawa, Y.
    Physical Review Letters 121 (2018)
    Two ordering states, antiferromagnetism and nematicity, have been observed in most iron-based superconductors (SCs). In contrast to those SCs, the newly discovered SC CaK(Fe1-xNix)4As4 exhibits an antiferromagnetic (AFM) state, called hedgehog spin-vortex crystal (SVC) structure, without nematic order, providing the opportunity for the investigation into the relationship between spin fluctuations and SC without any effects of nematic fluctuations. Our As75 nuclear magnetic resonance studies on CaK(Fe1-xNix)4As4 (0≤x≤0.049) revealed that CaKFe4As4 is located close to a hidden hedgehog SVC AFM quantum-critical point (QCP). The magnetic QCP without nematicity in CaK(Fe1-xNix)4As4 highlights the close connection of spin fluctuations and superconductivity in iron-based SCs. The advantage of stoichiometric composition also makes CaKFe4As4 an ideal platform for further detailed investigation of the relationship between magnetic QCP and superconductivity in iron-based SCs without disorder effects. © 2018 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.121.137204
  • 2018 • 165 High surface area black TiO2 templated from ordered mesoporous carbon for solar driven hydrogen evolution
    Xiong, Y. and Gu, D. and Deng, X. and Tüysüz, H. and van Gastel, M. and Schüth, F. and Marlow, F.
    Microporous and Mesoporous Materials 268 162-169 (2018)
    Hydrogen reduction of TiO2 to generate surface Ti3+ can significantly increase the photochemical activity under solar-light illumination. However, the low surface areas of commercial TiO2 limit their photocatalytic activities. Herein, we report a high surface area ordered mesoporous black TiO2, which exhibits an improved photocatalytic performance. The TiO2 material was prepared by using a highly ordered mesoporous carbon CMK-3 as a hard template, which possesses very high surface area, large pore volume and uniform mesopores. By using the advantage of pore confinement in the mesoporous carbon template, TiO2-carbon composites were annealed at different temperatures to investigate the influence of the crystallinity of TiO2 on the photocatalytic hydrogen production. TiO2 calcined at 500 °C, having a high surface area (up to 158 m2 g−1), large pore volume (up to 0.62 cm3 g−1), uniform pore size (5–6 nm), and anatase crystal structure, indicated the highest hydrogen generation rate. Since the TiO2 has been treated at a higher temperature in the confinement of the mesoporous carbon, the TiO2 can easily be reduced at 500 °C under hydrogen atmosphere to generate surface Ti3+ species without destruction of the mesostructure and exhibits a high solar-driven hydrogen evolution rate (188 μmol h−1), which is more than two times higher than that of commercial TiO2 (82 μmol h−1). © 2018 Elsevier Inc.
    view abstractdoi: 10.1016/j.micromeso.2018.04.018
  • 2018 • 164 Influence of composition and crystal structure on the fracture toughness of NbCo2 Laves phase studied by micro-cantilever bending tests
    Luo, W. and Kirchlechner, C. and Fang, X. and Brinckmann, S. and Dehm, G. and Stein, F.
    Materials and Design 145 116-121 (2018)
    Cubic and hexagonal NbCo2 Laves phases are known to have composition dependent hardness and yield strength. However, it is unknown whether this dependence is also reflected in their fracture toughness values. In order to elucidate the fracture behavior, single-crystalline micro-cantilevers of the cubic and hexagonal NbCo2 Laves phases having different compositions were fabricated in the diffusion layers grown by the diffusion couple technique. Micro-cantilever bending tests were performed to study the composition- and crystal-structure-dependence of the fracture toughness. To exclude the influence of micro-cantilever geometry, pentagonal and rectangular beams were tested and found to result in the same fracture toughness value. The present results reveal that neither a change of the crystal structure nor a change in chemical composition has a significant influence on the fracture toughness of NbCo2 Laves phase. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.matdes.2018.02.045
  • 2018 • 163 Inherent toughness and fracture mechanisms of refractory transition-metal nitrides via density-functional molecular dynamics
    Sangiovanni, D.G.
    Acta Materialia 151 11-20 (2018)
    Hard refractory transition-metal nitrides possess unique combinations of outstanding mechanical and physical properties, but are typically brittle. Recent experimental results demonstrated that single-crystal NaCl-structure (B1) V0.5Mo0.5N pseudobinary solid solutions are both hard (∼20 GPa) and ductile; that is, they exhibit toughness, which is unusual for ceramics. However, key atomic-scale mechanisms underlying this inherent toughness are unknown. Here, I carry out density-functional ab initio molecular dynamics (AIMD) simulations at room temperature to identify atomistic processes and associated changes in the electronic structure which control strength, plasticity, and fracture in V0.5Mo0.5N, as well as reference B1 TiN, subject to <001> and <110> tensile deformation. AIMD simulations reveal that V0.5Mo0.5N is considerably tougher than TiN owing to its ability to (i) isotropically redistribute mechanical stresses within the elastic regime, (ii) dissipate the accumulated strain energy by activating local structural transformations beyond the yield point. In direct contrast, TiN breaks in brittle manner when applied stresses reach its tensile strength. Charge transfer maps show that the adaptive mechanical response of V0.5Mo0.5N originates from highly populated d-d metallic-states, which allow for counterbalancing the destabilization induced via tensile deformation by enabling formation of new chemical bonds. The high ionic character and electron-localization in TiN precludes the possibility of modifying bonding geometries to accommodate the accumulated stresses, thus suddenly causing material's fracture for relatively low strain values. © 2018 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2018.03.038
  • 2018 • 162 Machine-learning-based atom probe crystallographic analysis
    Wei, Y. and Gault, B. and Varanasi, R.S. and Raabe, D. and Herbig, M. and Breen, A.J.
    Ultramicroscopy 194 15-24 (2018)
    Atom probe tomography is known for its accurate compositional analysis at the nanoscale. However, the patterns created by successive hits on the single particle detector during experiments often contain complementary information about the specimen's crystallography, including structure and orientation. This information remains in most cases unexploited because it is, up to now, retrieved predominantly manually. Here, we propose an approach combining image analysis techniques for feature selection and deep-learning to automatically interpret the patterns. Application of unsupervised machine learning techniques allows to build and train a deep neural network, based on a library generated from theoretically known crystallographic angular relationships. This approach enables direct interpretation of the detector hit maps, as shown here on the example of numerous pure-Al, and is robust enough to function under various conditions of base temperature, pulsing mode and pulse fraction. We benchmark our approach against recent attempts to automate the pattern identification via Hough-transform and discuss the current limitations of our approach. This new automated approach renders crystallographic atom probe tomography analysis more efficient, feature-sensitive, robust, user-independent and reliable. With that, deep-learning algorithms show a great potential to give access to combined atom probe crystallographic and compositional analysis to a large community of users. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2018.06.017
  • 2018 • 161 Microstructure and mechanical properties of Al0.7CoCrFeNi high-entropy-alloy prepared by directional solidification
    Liu, G. and Liu, L. and Liu, X. and Wang, Z. and Han, Z. and Zhang, G. and Kostka, A.
    Intermetallics 93 93-100 (2018)
    The high-entropy-alloy Al0.7CoCrFeNi (molar ratio) was prepared by vacuum arc melting followed by directional solidification (DS) with <001> oriented seed. The unique lamellar-dendrite microstructure was obtained over a wide cooling rate range. During solidification, Fe and Co are prone to segregate to the dendrite, while Cr and Al segregate to interdendrite. The solute pile-up of Cr and Al at the solid/liquid interface leads to the dendritic solidification. During the following cooling process, the BCC phase precipitates from the FCC dendrite to form the lamellar structure, while the ordered B2 phase precipitates from the interdendrite. Moreover, the lamellar spacing is significantly refined with increasing cooling rate, resulting in the higher hardness and compressive yield strength. Directional solidification is proved to be an efficient way to improve the mechanical properties of multi-phases high-entropy alloys. © 2017 Elsevier Ltd
    view abstractdoi: 10.1016/j.intermet.2017.11.019
  • 2018 • 160 On the growth mechanisms of polar (100) surfaces of ceria on copper (100)
    Hackl, J. and Duchoň, T. and Gottlob, D.M. and Cramm, S. and Veltruská, K. and Matolín, V. and Nemšák, S. and Schneider, C.M.
    Surface Science 671 1-5 (2018)
    We present a study of temperature dependent growth of nano-sized ceria islands on a Cu (100) substrate. Low-energy electron microscopy, micro-electron diffraction, X-ray absorption spectroscopy, and photoemission electron microscopy are used to determine the morphology, shape, chemical state, and crystal structure of the grown islands. Utilizing real-time observation capabilities, we reveal a three-way interaction between the ceria, substrate, and local oxygen chemical potential. The interaction manifests in the reorientation of terrace boundaries on the Cu (100) substrate, characteristic of the transition between oxidized and metallic surface. The reorientation is initiated at nucleation sites of ceria islands, whose growth direction is influenced by the proximity of the terrace boundaries. The grown ceria islands were identified as fully stoichiometric CeO2 (100) surfaces with a (2 × 2) reconstruction. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.susc.2018.01.008
  • 2018 • 159 Phase nucleation through confined spinodal fluctuations at crystal defects evidenced in Fe-Mn alloys
    Kwiatkowski Da Silva, A. and Ponge, D. and Peng, Z. and Inden, G. and Lu, Y. and Breen, A. and Gault, B. and Raabe, D.
    Nature Communications 9 (2018)
    Analysis and design of materials and fluids requires understanding of the fundamental relationships between structure, composition, and properties. Dislocations and grain boundaries influence microstructure evolution through the enhancement of diffusion and by facilitating heterogeneous nucleation, where atoms must overcome a potential barrier to enable the early stage of formation of a phase. Adsorption and spinodal decomposition are known precursor states to nucleation and phase transition; however, nucleation remains the less well-understood step in the complete thermodynamic sequence that shapes a microstructure. Here, we report near-atomic-scale observations of a phase transition mechanism that consists in solute adsorption to crystalline defects followed by linear and planar spinodal fluctuations in an Fe-Mn model alloy. These fluctuations provide a pathway for austenite nucleation due to the higher driving force for phase transition in the solute-rich regions. Our observations are supported by thermodynamic calculations, which predict the possibility of spinodal decomposition due to magnetic ordering. © 2018 The Author(s).
    view abstractdoi: 10.1038/s41467-018-03591-4
  • 2018 • 158 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 • 157 Synthesis of Furan-Annelated BINOL Derivatives: Acid-Catalyzed Cyclization Induces Partial Racemization
    Octa-Smolin, F. and Van Der Vight, F. and Yadav, R. and Bhangu, J. and Soloviova, K. and Wölper, C. and Daniliuc, C.G. and Strassert, C.A. and Somnitz, H. and Jansen, G. and Niemeyer, J.
    Journal of Organic Chemistry 83 14568-14587 (2018)
    In this account, we describe the synthesis of a series of BINOL-based bis- and trisphosphoric acids 11d/e/f, which commonly feature an unusual phosphoric acid monoester motif. This motif is generated by an acid-catalyzed 5-endo-dig cyclization of the 3-alkynyl-substituted BINOL precursors to give the corresponding Furan-annelated derivatives, followed by phosphorylation of the remaining phenolic alcohols. In the cyclization reaction, we observed an unexpected partial racemization in the bis- and tris-BINOL scaffolds, leading to mixtures of diastereomers that were separated and characterized spectroscopically and by X-ray crystal structure analyses. The cyclization and racemization processes were investigated both experimentally and by DFT-calculations, showing that although the cyclization proceeds faster, the barrier for the acid-catalyzed binaphthyl-racemization is only slightly higher. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.joc.8b02353
  • 2018 • 156 Thermal cycling testing of TBCs on Cr2AlC MAX phase substrates
    Gonzalez-Julian, J. and Go, T. and Mack, D.E. and Vaßen, R.
    Surface and Coatings Technology 340 17-24 (2018)
    Thermal barrier coatings (TBCs) based on yttria-stabilized zirconia (YSZ) were deposited by Atmospheric Plasma Spray (APS) on highly dense and pure Cr2AlC substrates. The Cr2AlC/YSZ systems were tested under thermal cycling conditions at temperatures between 1100 and 1300 °C testing up to 500 h. The response of the system was excellent due to the strong adhesion between the substrate and the coating, and the formation of an outer and protective layer based on α-Al2O3. The oxide scale is formed due to the diffusion of Al atoms from the crystal structure of the Cr2AlC, followed by the reaction with oxygen in the air. The thickness of the oxide scale was 8.9, 17.6 and 39.7 μm at 1100, 1200 and 1300 °C, respectively, which is rather thick in comparison with the classical superalloy/TBC systems. Cr2AlC/YSZ systems survived without any damage under the severe cycling conditions at 1100 and 1200 °C due to the protective oxide scale layer and the sufficient thermal expansion match between the Cr2AlC, YSZ and α-Al2O3. At 1300 °C and after 268 h of cycling conditions, the system failed due to the formation of a porous carbide layer underneath of the oxide scale. The results are rather promising and confirm the potential of the MAX phases to operate under long term applications of high temperature and oxidizing environments. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2018.02.035
  • 2018 • 155 Thermal stability of nanocomposite Mo2BC hard coatings deposited by magnetron sputtering
    Gleich, S. and Breitbach, B. and Peter, N.J. and Soler, R. and Bolvardi, H. and Schneider, J.M. and Dehm, G. and Scheu, C.
    Surface and Coatings Technology 349 378-383 (2018)
    The investigation of hard coatings under thermal load is crucial in order to obtain information on the thermal stability and possible changes of microstructure and mechanical properties. In addition, advanced heating studies may also provide feedback for the grain growth mechanism occurring during annealing and thus, help to predict optimum post-growth annealing conditions for producing high-performance hard coatings. Here, we investigate the thermal response of Mo2BC, deposited by bipolar pulsed direct current magnetron sputtering in an industrial chamber on a silicon substrate at a substrate temperature of 380 °C. Ex-situ and in-situ X-ray diffraction and transmission electron microscopy studies are performed at elevated temperatures to track changes in the structure. Whereas the as-deposited nanocomposite coating exhibits small spherical nanocrystals (1.2 nm in diameter) embedded in an amorphous matrix, a fully crystalline structure, mainly consisting of elongated and interconnected crystals with lengths of up to 1 μm, is obtained at elevated annealing temperatures. Hardness and Young's modulus increase by ~8% and ~47%, respectively, compared to the as-deposited coating. Delamination from the silicon substrate only occurs at temperatures above 840 °C. Thus, our detailed study of the micro- and nanostructure evolution upon thermal annealing suggests that heat treatments below 840 °C are a suitable method to improve the crystallinity and mechanical properties of nanocomposite Mo2BC coatings. © 2018
    view abstractdoi: 10.1016/j.surfcoat.2018.06.006
  • 2018 • 154 Thermodynamic properties of selenoether-functionalized ionic liquids and their use for the synthesis of zinc selenide nanoparticles
    Klauke, K. and Zaitsau, D.H. and Bülow, M. and He, L. and Klopotowski, M. and Knedel, T.-O. and Barthel, J. and Held, C. and Verevkin, S.P. and Janiak, C.
    Dalton Transactions 47 5083-5097 (2018)
    Three selenoether-functionalized ionic liquids (ILs) of N-[(phenylseleno)methylene]pyridinium (1), N-(methyl)- (2) and N-(butyl)-N'-[(phenylseleno)methylene]imidazolium (3) with bis(trifluoromethanesulfonyl)imide anions ([NTf2]) were prepared from pyridine, N-methylimidazole and N-butylimidazole with in situ obtained phenylselenomethyl chloride, followed by ion exchange to give the desired compounds. The crystal structures of the bromide and tetraphenylborate salts of the above cations (1-Br, 2-BPh4 and 3-BPh4) confirm the formation of the desired cations and indicate a multitude of different supramolecular interactions besides the dominating Coulomb interactions between the cations and anions. The vaporization enthalpies of the synthesized [NTf2]-containing ILs were determined by means of a quartz-crystal microbalance method (QCM) and their densities were measured with an oscillating U-tube. These thermodynamic data have been used to develop a method for assessment of miscibility of conventional solvents in the selenium-containing ILs by using Hildebrandt solubility parameters, as well as for modeling with the electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) method. Furthermore, structure-property relations between selenoether-functionalized and similarly shaped corresponding aryl-substituted imidazolium- and pyridinium-based ILs were analyzed and showed that the contribution of the selenium moiety to the enthalpy of vaporization of an IL is equal to the contribution of a methylene (CH2) group. An incremental approach to predict vaporization enthalpies of ILs by a group contribution method has been developed. The reaction of these ILs with zinc acetate dihydrate under microwave irradiation led to ZnSe nanoparticles of an average diameter between 4 and 10 nm, depending on the reaction conditions. © The Royal Society of Chemistry 2018.
    view abstractdoi: 10.1039/c8dt00233a
  • 2017 • 153 A Binary Bivalent Supramolecular Assembly Platform Based on Cucurbit[8]uril and Dimeric Adapter Protein 14-3-3
    de Vink, P.J. and Briels, J.M. and Schrader, T. and Milroy, L.-G. and Brunsveld, L. and Ottmann, C.
    Angewandte Chemie - International Edition 56 8998-9002 (2017)
    Interactions between proteins frequently involve recognition sequences based on multivalent binding events. Dimeric 14-3-3 adapter proteins are a prominent example and typically bind partner proteins in a phosphorylation-dependent mono- or bivalent manner. Herein we describe the development of a cucurbit[8]uril (Q8)-based supramolecular system, which in conjunction with the 14-3-3 protein dimer acts as a binary and bivalent protein assembly platform. We fused the phenylalanine–glycine–glycine (FGG) tripeptide motif to the N-terminus of the 14-3-3-binding epitope of the estrogen receptor α (ERα) for selective binding to Q8. Q8-induced dimerization of the ERα epitope augmented its affinity towards 14-3-3 through a binary bivalent binding mode. The crystal structure of the Q8-induced ternary complex revealed molecular insight into the multiple supramolecular interactions between the protein, the peptide, and Q8. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201701807
  • 2017 • 152 Ceramic Top Coats of Plasma-Sprayed Thermal Barrier Coatings: Materials, Processes, and Properties
    Bakan, E. and Vaßen, R.
    Journal of Thermal Spray Technology 26 992-1010 (2017)
    The ceramic top coat has a major influence on the performance of the thermal barrier coating systems (TBCs). Yttria-partially-stabilized zirconia (YSZ) is the top coat material frequently used, and the major deposition processes of the YSZ top coat are atmospheric plasma spraying and electron beam physical vapor deposition. Recently, also new thermal spray processes such as suspension plasma spraying or plasma spray-physical vapor deposition have been intensively investigated for TBC top coat deposition. These new processes and particularly the different coating microstructures that can be deposited with them will be reviewed in this article. Furthermore, the properties and the intrinsic–extrinsic degradation mechanisms of the YSZ will be discussed. Following the TBC deposition processes and standard YSZ material, alternative ceramic materials such as perovskites and hexaaluminates will be summarized, while properties of pyrochlores with regard to their crystal structure will be discussed more in detail. The merits of the pyrochlores such as good CMAS resistance as well as their weaknesses, e.g., low fracture toughness, processability issues, will be outlined. © 2017, ASM International.
    view abstractdoi: 10.1007/s11666-017-0597-7
  • 2017 • 151 Complexion-mediated martensitic phase transformation in Titanium
    Zhang, J. and Tasan, C.C. and Lai, M.J. and Dippel, A.-C. and Raabe, D.
    Nature Communications 8 (2017)
    The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α″ (orthorhombic) martensite bounded with planar complexions of athermal ω (a-ω hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a-ω is stable only at the hetero-interface. © The Author(s) 2017.
    view abstractdoi: 10.1038/ncomms14210
  • 2017 • 150 Correlative plasma-surface model for metastable Cr-Al-N: Frenkel pair formation and influence of the stress state on the elastic properties
    Music, D. and Banko, L. and Ruess, H. and Engels, M. and Hecimovic, A. and Grochla, D. and Rogalla, D. and Brögelmann, T. and Ludwig, Al. and Von Keudell, A. and Bobzin, K. and Schneider, J.M.
    Journal of Applied Physics 121 (2017)
    Correlatively employing density functional theory and experiments congregated around high power pulsed magnetron sputtering, a plasma-surface model for metastable Cr0.8Al0.2N (space group Fm 3 m) is developed. This plasma-surface model relates plasma energetics with film composition, crystal structure, mass density, stress state, and elastic properties. It is predicted that N Frenkel pairs form during Cr0.8Al0.2N growth due to high-energy ion irradiation, yielding a mass density of 5.69 g cm-3 at room temperature and Young's modulus of 358-130 GPa in the temperature range of 50-700 K for the stress-free state and about 150 GPa larger values for the compressive stress of 4 GPa. Our measurements are consistent with the quantum mechanical predictions within 5% for the mass density and 3% for Young's modulus. The hypothesis of a stress-induced Young's modulus change may at least in part explain the spread in the reported elasticity data ranging from 250 to 420 GPa. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4985172
  • 2017 • 149 Crystal Structure Induced Preferential Surface Alloying of Sb on Wurtzite/Zinc Blende GaAs Nanowires
    Hjort, M. and Kratzer, P. and Lehmann, S. and Patel, S.J. and Dick, K.A. and Palmstrøm, C.J. and Timm, R. and Mikkelsen, A.
    Nano Letters 17 3634-3640 (2017)
    We study the surface diffusion and alloying of Sb into GaAs nanowires (NWs) with controlled axial stacking of wurtzite (Wz) and zinc blende (Zb) crystal phases. Using atomically resolved scanning tunneling microscopy, we find that Sb preferentially incorporates into the surface layer of the {110}-terminated Zb segments rather than the {1120}-terminated Wz segments. Density functional theory calculations verify the higher surface incorporation rate into the Zb phase and find that it is related to differences in the energy barrier of the Sb-for-As exchange reaction on the two surfaces. These findings demonstrate a simple processing-free route to compositional engineering at the monolayer level along NWs. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.nanolett.7b00806
  • 2017 • 148 Crystal structures of Fe4C vs. Fe4N analysed by DFT calculations: Fcc-based interstitial superstructures explored
    Leineweber, A. and Hickel, T. and Azimi-Manavi, B. and Maisel, S.B.
    Acta Materialia 140 433-442 (2017)
    Knowledge of the thermodynamic and structural properties of iron carbide and nitride phases is crucial for understanding phase transformations and related microstructure formation in steels. While the existence and crystal structure of the primitive cubic fcc-based γ′-Fe4N1-z phase is experimentally well-established, there is no consensus in contemporary literature about an analogous γ′-Fe4C compound. Here, we present DFT calculations for all fcc-like Fe4C and Fe4N superstructures with up to two formula units per primitive unit cell, providing energy values and the relaxed atomic structures, which were analysed mathematically and by visual inspection of the atomic arrangement. Notably, all considered Fe4C and Fe4N superstructures are metastable with respect to α-Fe and cementite-Fe3C/ε-Fe3N. Unsurprisingly, we find the well-known γ′ compound's crystal structure to be most favourable among these metastable Fe4N superstructures. However, we find the equivalent superstructure to be quite unfavourable in Fe4C. The most favourable among these metastable Fe4C structures are stabilised by a partial Bain-like distortion into the direction of a body-centred cubic arrangement of Fe atoms. This makes the particular C-ordering interesting for comparison with the short-range order in Fe-C martensites. However, even the lowest-energy Fe4C structure releases about 0.056 eV/atom upon decomposition into α + Fe3C, much more than it is the case for Fe4N (0.019 eV/atom). That energy difference is difficult to overcome even at T > 0 K, in agreement with the lack of clear experimental evidence for existence of a Fe4C phase. © 2017 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2017.08.059
  • 2017 • 147 Design of Mg alloys: The effects of Li concentration on the structure and elastic properties in the Mg-Li binary system by first principles calculations
    Pavlic, O. and Ibarra-Hernandez, W. and Valencia-Jaime, I. and Singh, S. and Avendaño-Franco, G. and Raabe, D. and Romero, A.H.
    Journal of Alloys and Compounds 691 15-25 (2017)
    First principles calculations have been employed to search for energetically stable structures of the Mg-Li binary system over all possible Mg concentrations. Volume, space group, c/a and b/a ratios, vibrational contribution to the heat capacity, and Debye temperature are reported to investigate the effects of Li concentration on the Mg-Li binary system. Structures of high symmetry and those lying on or close to the convex hull are further explored to search for dynamic and elastic stability. Five ground state structures were found at Li1 Mg13, Li1 Mg2, Li1 Mg1, Li7 Mg2, and Li15 Mg1 compositions. Elastic constants and elastic properties of the selected low energy structures were calculated and analyzed. We also investigate the effect of the phonon band gap found in Li1 Mg1 and Li1 Mg2 on lattice thermal conductivity. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2016.08.217
  • 2017 • 146 Design, Synthesis, and Biological Evaluation of Novel Type I1/2 p38α MAP Kinase Inhibitors with Excellent Selectivity, High Potency, and Prolonged Target Residence Time by Interfering with the R-Spine
    Walter, N.M. and Wentsch, H.K. and Bührmann, M. and Bauer, S.M. and Döring, E. and Mayer-Wrangowski, S. and Sievers-Engler, A. and Willemsen-Seegers, N. and Zaman, G. and Buijsman, R. and Lämmerhofer, M. and Rauh, D. and Laufer, S.A.
    Journal of Medicinal Chemistry 60 8027-8054 (2017)
    We recently reported 1a (skepinone-L) as a type I p38α MAP kinase inhibitor with high potency and excellent selectivity in vitro and in vivo. However, as a type I inhibitor, it is entirely ATP-competitive and shows just a moderate residence time. Thus, the scope was to develop a new class of advanced compounds maintaining the structural binding features of skepinone-L scaffold like inducing a glycine flip at the hinge region and occupying both hydrophobic regions I and II. Extending this scaffold with suitable residues resulted in an interference with the kinase's R-Spine. By synthesizing 69 compounds, we could significantly prolong the target residence time with one example to 3663 s, along with an excellent selectivity score of 0.006 and an outstanding potency of 1.0 nM. This new binding mode was validated by cocrystallization, showing all binding interactions typifying type I1/2 binding. Moreover, microsomal studies showed convenient metabolic stability of the most potent, herein reported representatives. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jmedchem.7b00745
  • 2017 • 145 Electronic structure of metastable bcc Cu-Cr alloy thin films: Comparison of electron energy-loss spectroscopy and first-principles calculations
    Liebscher, C.H. and Freysoldt, C. and Dennenwaldt, T. and Harzer, T.P. and Dehm, G.
    Ultramicroscopy 178 96-104 (2017)
    Metastable Cu-Cr alloy thin films with nominal thickness of 300nm and composition of Cu67Cr33 (at%) are obtained by co-evaporation using molecular beam epitaxy. The microstructure, chemical phase separation and electronic structure are investigated by transmission electron microscopy (TEM). The thin film adopts the body-centered cubic crystal structure and consists of columnar grains with ~50nm diameter. Aberration-corrected scanning TEM in combination with energy dispersive X-ray spectroscopy confirms compositional fluctuations within the grains. Cu- and Cr-rich domains with composition of Cu85Cr15 (at%) and Cu42Cr58 (at%) and domain size of 1-5nm are observed. The alignment of the interface between the Cu- and Cr-rich domains shows a preference for (110)-type habit plane. The electronic structure of the Cu-Cr thin films is investigated by electron energy loss spectroscopy (EELS) and is contrasted to an fcc-Cu reference sample. The experimental EEL spectra are compared to spectra computed by density functional theory. The main differences between bcc-and fcc-Cu are related to differences in van Hove singularities in the electron density of states. In Cu-Cr solid solutions with bcc crystal structure a single peak after the L3-edge, corresponding to a van Hove singularity at the N-point of the first Brillouin zone is observed. Spectra computed for pure bcc-Cu and random Cu-Cr solid solutions with 10at% Cr confirm the experimental observations. The calculated spectrum for a perfect Cu50Cr50 (at%) random structure shows a shift in the van Hove singularity towards higher energy by developing a Cu-Cr d-band that lies between the delocalized d-bands of Cu and Cr. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2016.07.011
  • 2017 • 144 Fundamental study of an industrial reactive HPPMS (Cr,Al)N process
    Bobzin, K. and Brögelmann, T. and Kruppe, N.C. and Engels, M. and Von Keudell, A. and Hecimovic, A. and Ludwig, Al. and Grochla, D. and Banko, L.
    Journal of Applied Physics 122 (2017)
    In this work, a fundamental investigation of an industrial (Cr,Al)N reactive high power pulsed magnetron sputtering (HPPMS) process is presented. The results will be used to improve the coating development for the addressed application, which is the tool coating for plastics processing industry. Substrate-oriented plasma diagnostics and deposition of the (Cr,Al)N coatings were performed for a variation of the HPPMS pulse frequency with values from f = 300 Hz to f = 2000 Hz at constant average power P = 2.5 kW and pulse length ton = 40 μs. The plasma was investigated using an oscilloscope, an intensified charge coupled device camera, phase-resolved optical emission spectroscopy, and an energy-dispersive mass spectrometer. The coating properties were determined by means of scanning electron microscopy, glow discharge optical emission spectroscopy, cantilever stress sensors, nanoindentation, and synchrotron X-ray diffraction. Regarding the plasma properties, it was found that the average energy within the plasma is nearly constant for the frequency variation. In contrast, the metal to gas ion flux ratio is changed from JM/JG = 0.51 to JM/JG = 0.10 for increasing frequency. Regarding the coating properties, a structure refinement as well as lower residual stresses, higher universal hardness, and a changing crystal orientation from (111) to (200) were observed at higher frequencies. By correlating the plasma and coating properties, it can be concluded that the change in the gas ion to metal ion flux ratio results in a competitive crystal growth of the film, which results in changing coating properties. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4990997
  • 2017 • 143 Gradual modification of ITO particle's crystal structure and optical properties by pulsed UV laser irradiation in a free liquid jet
    Lau, M. and Straube, T. and Aggarwal, A.V. and Hagemann, U. and De Oliveira Viestel, B. and Hartmann, N. and Textor, T. and Lutz, H. and Gutmann, J.S. and Barcikowski, S.
    Dalton Transactions 46 6039-6048 (2017)
    Indium tin oxide (ITO) particle coatings are known for high transparency in the visible, good conductive properties and near-infrared absorption. These properties depend on ITO particle's stoichiometric composition, defects and size. Here we present a method to gradually change ITO particle's optical properties by a simple and controlled laser irradiation process. The defined irradiation process and controlled energy dose input allows one to engineer the absorption and transmission of coatings made from these particles. We investigate the role of the surrounding solvent, influence of laser fluence and the specific energy dose targeting modification of the ITO particle's morphology and chemistry by stepwise laser irradiation in a free liquid jet. TEM, SEM, EDX, XPS, XRD and Raman are used to elucidate the structural, morphological and chemical changes of the laser-induced ITO particles. On the basis of these results the observed modification of the optical properties is tentatively attributed to chemical changes, e.g. laser-induced defects or partial reduction. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7dt00010c
  • 2017 • 142 Halide Perovskite 3D Photonic Crystals for Distributed Feedback Lasers
    Schünemann, S. and Brittman, S. and Chen, K. and Garnett, E.C. and Tüysüz, H.
    ACS Photonics 4 2522-2528 (2017)
    Halide perovskites are under intense investigation for light harvesting applications in solar cells. Their outstanding optoelectronic properties such as long charge carrier diffusion lengths, high absorption coefficients, and defect tolerance also has triggered interest in laser and LED applications. Here, we report on the lasing properties of 3D distributed feedback halide perovskite nanostructures prepared via an all-solution process. A colloidal crystal templating approach was developed to precisely control the hybrid halide perovskite structure on the nanoscale. The prepared CH3NH3PbBr3 thin films with inverse opal morphology show narrow lasing emissions with a full width half-maximum as low as 0.15 nm and good long-term stability under pulsed laser excitation above the lasing threshold of 1.6 mJ cm-2 in ambient atmosphere. Furthermore, lasing emission was also observed for CH3NH3PbI3 inverse opals under excitation with a focused laser beam. Unlike other protocols for the fabrication of distributed feedback perovskite lasers, control of the nanostructure of hybrid halide perovskites is achieved without the use of expensive and elaborate lithography techniques or high temperatures. Therefore, the presented protocol opens a route to the low cost fabrication of hybrid halide perovskite lasers. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsphotonics.7b00780
  • 2017 • 141 Identifying Structure–Property Relationships Through DREAM.3D Representative Volume Elements and DAMASK Crystal Plasticity Simulations: An Integrated Computational Materials Engineering Approach
    Diehl, M. and Groeber, M. and Haase, C. and Molodov, D.A. and Roters, F. and Raabe, D.
    JOM 69 848-855 (2017)
    Predicting, understanding, and controlling the mechanical behavior is the most important task when designing structural materials. Modern alloy systems—in which multiple deformation mechanisms, phases, and defects are introduced to overcome the inverse strength–ductility relationship—give raise to multiple possibilities for modifying the deformation behavior, rendering traditional, exclusively experimentally-based alloy development workflows inappropriate. For fast and efficient alloy design, it is therefore desirable to predict the mechanical performance of candidate alloys by simulation studies to replace time- and resource-consuming mechanical tests. Simulation tools suitable for this task need to correctly predict the mechanical behavior in dependence of alloy composition, microstructure, texture, phase fractions, and processing history. Here, an integrated computational materials engineering approach based on the open source software packages DREAM.3D and DAMASK (Düsseldorf Advanced Materials Simulation Kit) that enables such virtual material development is presented. More specific, our approach consists of the following three steps: (1) acquire statistical quantities that describe a microstructure, (2) build a representative volume element based on these quantities employing DREAM.3D, and (3) evaluate the representative volume using a predictive crystal plasticity material model provided by DAMASK. Exemplarily, these steps are here conducted for a high-manganese steel. © 2017, The Author(s).
    view abstractdoi: 10.1007/s11837-017-2303-0
  • 2017 • 140 Investigating the crystallinity of Poly(butylene)terephthalate (PBT): Correlation between THz TDS measurements and X-ray scattering data
    Sommer, S. and Raidt, T. and Engel, A. and Balzer, J.C. and Fischer, B.M. and Katzenberg, F. and Tiller, J.C. and Koch, M.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz (2017)
    We present angle-resolved terahertz time-domain spectroscopy (THz TDS) measurements of poly(butylene) terephthalate (PBT) and compare the results to x-ray scattering measurements. This comparison confirms that the THz TDS measurements can be correlated to the crystal structure. Further, the THz TDS measurements give insights into the binding energies of the crystal bounds. © 2017 IEEE.
    view abstractdoi: 10.1109/IRMMW-THz.2017.8066927
  • 2017 • 139 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 • 138 Mössbauer spectroscopy evidence of intrinsic non-stoichiometry in iron telluride single crystals
    Kiiamov, A.G. and Lysogorskiy, Y.V. and Vagizov, F.G. and Tagirov, L.R. and Tayurskii, D.A. and Croitori, D. and Tsurkan, V. and Loidl, A.
    Annalen der Physik 529 (2017)
    The FeTe parent compound for iron-superconductor chalcogenides was studied applying Mössbauer spectroscopy accompanied by ab initio calculations of electric field gradients at the iron nuclei. Room-temperature (RT) Mössbauer spectra of single crystals have shown asymmetric doublet structure commonly ascribed to contributions of over-stoichiometric iron or impurity phases. Low-temperature Mössbauer spectra of the magnetically ordered compound could be well described by four hyperfine-split sextets, although no other foreign phases different from Fe1.05Te were detected by XRD and microanalysis within the sensitivity limits of the equipment. Density functional ab initio calculations have shown that over-stoichiometric iron atoms significantly affect electron charge and spin density up to the second coordination sphere of the iron sub-lattice, and, as a result, four non-equivalent groups of iron atoms are formed by their local environment. The resulting four-group model consistently describes the angular dependence of the single crystals Mössbauer spectra as well as intensity asymmetry of the doublet absorption lines in powdered samples at RT. We suppose that our approach could be extended to the entire class of Fe1+ySe1-xTex compounds, which contain excess iron atoms. (Figure presented.). © 2016 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/andp.201600241
  • 2017 • 137 Nano-sized metal organic framework to improve the structural properties and desalination performance of thin film composite forward osmosis membrane
    Zirehpour, A. and Rahimpour, A. and Ulbricht, M.
    Journal of Membrane Science 531 59-67 (2017)
    In the present study, nano-sized metal-organic framework (MOF) particles consisting of silver (I) and 1,3,5-benzene tricarboxylic acid were synthesized and applied to improve the structural properties as well as desalination performance of thin-film composite (TFC) forward osmosis (FO) membranes. The MOF nanocrystals were incorporated into the polyamide layer of membranes through interfacial polymerization. Characterizations by Field emission scanning electron microscopy and X-ray photoelectron spectroscopy enabled the detection of MOF nanocrystals within the selective layer of the resultant membranes. The MOF incorporation led to changes of the membrane active layer in terms of hydrophilicity and transport properties, without detrimental effects on the layer selectivity. These features enhanced pure water permeability of the membranes to 129%, which was provided through 0.04% MOF loading of the organic phase during interfacial polymerization. As a result, the modified membrane exhibited an enhanced FO seawater desalination performance in comparison with the control membrane. The performance stability of TFC membrane was also improved by presence of MOF in active layer (as seen by a water flux decline of about 7% for modified membrane against about 18% for unmodified membrane when tested with real seawater). This study demonstrates the potential of MOF particles to enhance desalination performance of TFC membranes in FO systems. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2017.02.049
  • 2017 • 136 New amidinate complexes of indium(III): Promising CVD precursors for transparent and conductive In2O3 thin films
    Gebhard, M. and Hellwig, M. and Kroll, A. and Rogalla, D. and Winter, M. and Mallick, B. and Ludwig, Ar. and Wiesing, M. and Wieck, A.D. and Grundmeier, G. and Devi, A.
    Dalton Transactions 46 10220-10231 (2017)
    For the first time, synthesis of two new amidinate-ligand comprising heteroleptic indium complexes, namely [InCl(amd)2] (1) and [InMe(amd)2] (2), via salt-metathesis and their detailed characterization is reported. For comparison, the earlier reported homoleptic tris-amidinate [In(amd)3] (3) was also synthesized and analyzed in detail especially with respect to the thermal properties and molecular crystal structure analysis which are reported here for the first time. From nuclear magnetic resonance spectroscopy (NMR) and single-crystal X-ray diffraction (XRD), all three compounds were found to be monomeric with C2 (compound 1 and 2) and C3 symmetry (compound 3). Both halide-free compounds 2 and 3 were evaluated regarding their thermal properties using temperature-dependent 1H-NMR, thermogravimetric analysis (TGA) and iso-TGA, revealing suitable volatility and thermal stability for their application as potential precursors for chemical vapor phase thin film deposition methods. Indeed, metalorganic chemical vapor deposition (MOCVD) experiments over a broad temperature range (400 °C-700 °C) revealed the suitability of these two compounds to fabricate In2O3 thin films in the presence of oxygen on Si, thermally grown SiO2 and fused silica substrates. The as-deposited thin films were characterized in terms of their crystallinity via X-ray diffraction (XRD), morphology by scanning electron microscopy (SEM) and composition through complementary techniques such as Rutherford-backscattering spectrometry (RBS) in combination with nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS). From UV/Vis spectroscopy, the deposited In2O3 thin films on fused silica substrates were found to be highly transparent (T > 95% at 560 nm, compound 3). In addition, Hall measurements revealed high charge carrier densities of 1.8 × 1020 cm-3 (2) and 6.5 × 1019 cm-3 (3) with a Hall-mobility of 48 cm2 V-1 s-1 (2) and 74 cm2 V-1 s-1 (3) for the respective thin films, rendering the obtained thin films applicable as a transparent conducting oxide that could be suitable for optoelectronic applications. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7dt01280b
  • 2017 • 135 Operando Phonon Studies of the Protonation Mechanism in Highly Active Hydrogen Evolution Reaction Pentlandite Catalysts
    Zegkinoglou, I. and Zendegani, A. and Sinev, I. and Kunze, S. and Mistry, H. and Jeon, H.S. and Zhao, J. and Hu, M.Y. and Alp, E.E. and Piontek, S. and Smialkowski, M. and Apfel, U.-P. and Körmann, F. and Neugebauer, J. and Hicke...
    Journal of the American Chemical Society 139 14360-14363 (2017)
    Synthetic pentlandite (Fe4.5Ni4.5S8) is a promising electrocatalyst for hydrogen evolution, demonstrating high current densities, low overpotential, and remarkable stability in bulk form. The depletion of sulfur from the surface of this catalyst during the electrochemical reaction has been proposed to be beneficial for its catalytic performance, but the role of sulfur vacancies and the mechanism determining the reaction kinetics are still unknown. We have performed electrochemical operando studies of the vibrational dynamics of pentlandite under hydrogen evolution reaction conditions using 57Fe nuclear resonant inelastic X-ray scattering. Comparing the measured Fe partial vibrational density of states with density functional theory calculations, we have demonstrated that hydrogen atoms preferentially occupy substitutional positions replacing pre-existing sulfur vacancies. Once all vacancies are filled, the protonation proceeds interstitially, which slows down the reaction. Our results highlight the beneficial role of sulfur vacancies in the electrocatalytic performance of pentlandite and give insights into the hydrogen adsorption mechanism during the reaction. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/jacs.7b07902
  • 2017 • 134 Preparation, catalytical activity and crystal structure of a heptanuclear zinc acetate cluster
    Dittrich, D. and Tewes, H. and Wölper, C. and Bläser, D. and Schulz, S. and Roll, J.
    Transition Metal Chemistry 42 237-241 (2017)
    Reaction of [Zn4(µ4-O)(O2CCH3)6] with one equivalent of 4-tertiary-butylpyridine leads to a nearly quantitative formation of the heptanuclear cluster [Zn7O2(O2CCH3)10(tbupy)2] (1). Here, we present the crystal structure of 1 and first results of the examination of its catalytic activity in transesterification reactions and polymerization of lactide compared to the activity of [Zn4(µ4-O)(O2CCH3)6] in the presence of 4-tertiary-butylpyridine. © 2017, Springer International Publishing Switzerland.
    view abstractdoi: 10.1007/s11243-017-0127-y
  • 2017 • 133 Redox Activity of Oxo-Bridged Iridium Dimers in an N,O-Donor Environment: Characterization of Remarkably Stable Ir(IV,V) Complexes
    Sinha, S.B. and Shopov, D.Y. and Sharninghausen, L.S. and Stein, C.J. and Mercado, B.Q. and Balcells, D. and Pedersen, T.B. and Reiher, M. and Brudvig, G.W. and Crabtree, R.H.
    Journal of the American Chemical Society 139 9672-9683 (2017)
    Chemical and electrochemical oxidation or reduction of our recently reported Ir(IV,IV) mono-μ-oxo dimers results in the formation of fully characterized Ir(IV,V) and Ir(III,III) complexes. The Ir(IV,V) dimers are unprecedented and exhibit remarkable stability under ambient conditions. This stability and modest reduction potential of 0.99 V vs NHE is in part attributed to complete charge delocalization across both Ir centers. Trends in crystallographic bond lengths and angles shed light on the structural changes accompanying oxidation and reduction. The similarity of these mono-μ-oxo dimers to our Ir "blue solution" water-oxidation catalyst gives insight into potential reactive intermediates of this structurally elusive catalyst. Additionally, a highly reactive material, proposed to be a Ir(V,V) μ-oxo species, is formed on electrochemical oxidation of the Ir(IV,V) complex in organic solvents at 1.9 V vs NHE. Spectroelectrochemistry shows reversible conversion between the Ir(IV,V) and proposed Ir(V,V) species without any degradation, highlighting the exceptional oxidation resistance of the 2-(2-pyridinyl)-2-propanolate (pyalk) ligand and robustness of these dimers. The Ir(III,III), Ir(IV,IV) and Ir(IV,V) redox states have been computationally studied both with DFT and multiconfigurational calculations. The calculations support the stability of these complexes and provide further insight into their electronic structures. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/jacs.7b04874
  • 2017 • 132 Stability, phase separation and oxidation of a supersaturated nanocrystalline Cu-33 at.% Cr thin film alloy
    Harzer, T.P. and Dehm, G.
    Thin Solid Films 623 48-58 (2017)
    A binary nanocrystalline Cu67Cr33 thin film alloy consisting of columnar grains was synthesized via co-evaporation of the constituent elements under non-equilibrium ultra-high vacuum conditions using molecular beam epitaxy. In the as-deposited state, the alloy film is a supersaturated solid solution with a single-phase body-centered cubic structure. In order to study the thermal stability of the microstructure and phase separation behavior towards the two phase equilibrium structure, isothermal annealing experiments in a temperature range of 150 °C – 500 °C were conducted inside a transmission electron microscope and compared to data obtained by X-ray diffraction under protective N2 atmosphere. It is shown that the single-phase nature of the alloy film is maintained for annealing temperatures of ≤ 300 °C, whereas heat treatment at temperatures of ≥ 400 °C results in the formation of a second phase, i.e. the equilibrium face-centered cubic phase of Cu. Phase separation proceeds predominantly by a spinodal-type decomposition process but a simultaneous diffusion of Cr along the columnar grain boundaries to the surface of the alloy film is observed as well. Temperature dependent diffusion coefficients for volume and grain boundary diffusion along with the activation energy for volume diffusion of Cr within the crystal lattice of the alloy film in a temperature range between 400 °C – 500 °C are determined from analytical in situ transmission electron microscopy experiments. Moreover, grain boundary diffusion of Cr leads to the growth of an external Cr-rich oxide scale. It is found that the growth kinetics of this oxide scale exhibits a transition from a linear to a nearly parabolic growth rate. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2016.12.048
  • 2017 • 131 Structure-Guided Development of Covalent and Mutant-Selective Pyrazolopyrimidines to Target T790M Drug Resistance in Epidermal Growth Factor Receptor
    Engel, J. and Smith, S. and Lategahn, J. and Tumbrink, H.L. and Goebel, L. and Becker, C. and Hennes, E. and Keul, M. and Unger, A. and Müller, H. and Baumann, M. and Schultz-Fademrecht, C. and Günther, G. and Hengstler, J.G. and Rauh, D.
    Journal of Medicinal Chemistry 60 7725-7744 (2017)
    Reversible epidermal growth factor receptor (EGFR) inhibitors prompt a beneficial clinical response in non-small cell lung cancer patients who harbor activating mutations in EGFR. However, resistance mutations, particularly the gatekeeper mutation T790M, limit this efficacy. Here, we describe a structure-guided development of a series of covalent and mutant-selective EGFR inhibitors that effectively target the T790M mutant. The pyrazolopyrimidine-based core differs structurally from that of aminopyrimidine-based third-generation EGFR inhibitors and therefore constitutes a new set of inhibitors that target this mechanism of drug resistance. These inhibitors exhibited strong inhibitory effects toward EGFR kinase activity and excellent inhibition of cell growth in the drug-resistant cell line H1975, without significantly affecting EGFR wild-type cell lines. Additionally, we present the in vitro ADME/DMPK parameters for a subset of the inhibitors as well as in vivo pharmacokinetics in mice for a candidate with promising activity profile. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jmedchem.7b00515
  • 2017 • 130 Structure-property relationships in hydrogen-bonded liquid crystals
    Pfletscher, M. and Hölscher, S. and Wölper, C. and Mezger, M. and Giese, M.
    Chemistry of Materials 29 8462-8471 (2017)
    The structural impact of hydrogen-donating moieties on the liquid crystalline behavior of hydrogen-bonded assemblies (HBAs) is comprehensively investigated. Therefore, a series of phenol derivatives such as phenol, catechol (CA), resorcinol (RE), hydroquinone (HQ), pyrogallol, hydroxyhydroquinone, and phloroglucinol (PHG) were combined with alkoxyazopyridines (Ap-N) yielding 49 new HBAs, which were studied with respect to their mesomorphic properties. The present study revealed significant differences in the liquid crystalline behavior of the structurally diverse assemblies, ranging from the absence of a mesophase to smectic or nematic phases. In contrast to previous studies a comprehensive crystallographic analysis provides insight into the structure-property relationships of the assemblies and proves a correlation between the supramolecular architecture and the macroscopic properties (=liquid crystallinity). More specifically, comparison of the single crystal data with the 2D X-ray diffraction patterns indicates that linear assemblies tend to form crystalline or smectic phases (for the HQ and RE, respectively), while a bent-shaped assembly yields nematic phases (for CA and PHG). Furthermore, our results suggest that segregation of aliphatic and aromatic segments, as observed in the solid state structures, supports the formation of stable mesophases. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.7b03182
  • 2017 • 129 Synthesis and characterization of germanosilicate molecular sieves: GeO2/SiO2 ratio, H2O/TO2 ratio and temperature
    Jiao, K. and Zhang, Z. and Xu, X. and Lv, Z. and Song, J. and Lin, C. and Sun, J. and He, M. and Gies, H.
    Dalton Transactions 46 2270-2280 (2017)
    Many synthesis parameters can influence zeolite crystallization, which include the molar ratio of reagents, water content, temperature, the selection of extraframework cations (organic or inorganic template) and so on. In this paper, two new materials, BUCT-1 with cuboid morphology and BUCT-2 with plate-like morphology were obtained based on the synthesis conditions of ITQ-17 by adjusting the GeO2/SiO2 ratio, H2O/TO2 ratio and temperature. The influence of the three factors on crystal size, crystallinity and phase selection and transformation was carefully discussed. Therein, phase selection and transformation is determined by their synergistic effects; while the influence on crystal size and crystallinity is different for different materials, which is caused by the differences in their structure, or in other words, the building unit, and chemical composition. In addition, the structure of BUCT-2 has already been solved as the stacking of sti layers, and it was identified as pure germanate molecular sieves. Meanwhile, through the characterization of XRD, ICP-AES, IR and STA, some topological information on BUCT-1, such as unit cell parameters, pore size and connectivity, was predicted and the work to present its final structure is still going on. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6dt04688f
  • 2017 • 128 Synthesis, Solid-State Structure, and Bonding Analysis of a Homoleptic Beryllium Azide
    Naglav, D. and Tobey, B. and Lyhs, B. and Römer, B. and Bläser, D. and Wölper, C. and Jansen, G. and Schulz, S.
    Angewandte Chemie - International Edition 56 8559-8563 (2017)
    [Ph4P]2[Be(N3)4] (1) and [PNP]2[Be(N3)4] (2; PNP=Ph3PNPPh3) were synthesized by reacting Be(N3)2 with [Ph4P]N3 and [PNP]N3. Compound 1 represents the first structurally characterized homoleptic beryllium azide. The electronic structure and bonding situation in the tetraazidoberyllate dianion [Be(N3)4]2− were investigated by quantum-chemical calculations (NPA, ELF, LOL). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201703147
  • 2017 • 127 The Molecular Tweezer CLR01 Stabilizes a Disordered Protein-Protein Interface
    Bier, D. and Mittal, S. and Bravo-Rodriguez, K. and Sowislok, A. and Guillory, X. and Briels, J. and Heid, C. and Bartel, M. and Wettig, B. and Brunsveld, L. and Sanchez-Garcia, E. and Schrader, T. and Ottmann, C.
    Journal of the American Chemical Society 139 16256-16263 (2017)
    Protein regions that are involved in protein-protein interactions (PPIs) very often display a high degree of intrinsic disorder, which is reduced during the recognition process. A prime example is binding of the rigid 14-3-3 adapter proteins to their numerous partner proteins, whose recognition motifs undergo an extensive disorder-to-order transition. In this context, it is highly desirable to control this entropy-costly process using tailored stabilizing agents. This study reveals how the molecular tweezer CLR01 tunes the 14-3-3/Cdc25CpS216 protein-protein interaction. Protein crystallography, biophysical affinity determination and biomolecular simulations unanimously deliver a remarkable finding: a supramolecular "Janus" ligand can bind simultaneously to a flexible peptidic PPI recognition motif and to a well-structured adapter protein. This binding fills a gap in the protein-protein interface, "freezes" one of the conformational states of the intrinsically disordered Cdc25C protein partner and enhances the apparent affinity of the interaction. This is the first structural and functional proof of a supramolecular ligand targeting a PPI interface and stabilizing the binding of an intrinsically disordered recognition motif to a rigid partner protein. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/jacs.7b07939
  • 2017 • 126 Tracing the coupled atomic shear and shuffle for a cubic to a hexagonal crystal transition
    Wang, H.L. and Hao, Y.L. and He, S.Y. and Du, K. and Li, T. and Obbard, E.G. and Hudspeth, J. and Wang, J.G. and Wang, Y.D. and Wang, Y. and Prima, F. and Lu, N. and Kim, M.J. and Cairney, J.M. and Li, S.J. and Yang, R.
    Scripta Materialia 133 70-74 (2017)
    Tracing the rearranged atoms in the first-order phase transformation is unrealistic due to the discrete structure change. Here we report that, by tuning a nano-scale decomposition in a titanium alloy, the bcc crystal distorts successively toward the hcp crystal by keeping an orthorhombic symmetry. Thus, the shear-shuffle relationship is traced experimentally to enrich the well-known Burgers mechanism. Our results reveal also that the successive tuning on crystal structure at the atomic level leads to some novel properties which are unexpected from the discrete phase transformations. © 2017 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2017.02.024
  • 2016 • 125 A structural view of synthetic cofactor integration into [FeFe]-hydrogenases
    Esselborn, J. and Muraki, N. and Klein, K. and Engelbrecht, V. and Metzler-Nolte, N. and Apfel, U.-P. and Hofmann, E. and Kurisu, G. and Happe, T.
    Chemical Science 7 959-968 (2016)
    [FeFe]-hydrogenases are nature's fastest catalysts for the evolution or oxidation of hydrogen. Numerous synthetic model complexes for the [2Fe] subcluster (2FeH) of their active site are known, but so far none of these could compete with the enzymes. The complex Fe2[μ-(SCH2)2X](CN)2(CO)4 2- with X = NH was shown to integrate into the apo-form of [FeFe]-hydrogenases to yield a fully active enzyme. Here we report the first crystal structures of the apo-form of the bacterial [FeFe]-hydrogenase CpI from Clostridium pasteurianum at 1.60 Å and the active semisynthetic enzyme, CpIADT, at 1.63 Å. The structures illustrate the significant changes in ligand coordination upon integration and activation of the [2Fe] complex. These changes are induced by a rigid 2FeH cavity as revealed by the structure of apoCpI, which is remarkably similar to CpIADT. Additionally we present the high resolution crystal structures of the semisynthetic bacterial [FeFe]-hydrogenases CpIPDT (X = CH2), CpIODT (X = O) and CpISDT (X = S) with changes in the headgroup of the dithiolate bridge in the 2FeH cofactor. The structures of these inactive enzymes demonstrate that the 2FeH-subcluster and its protein environment remain largely unchanged when compared to the active enzyme CpIADT. As the active site shows an open coordination site in all structures, the absence of catalytic activity is probably not caused by steric obstruction. This demonstrates that the chemical properties of the dithiolate bridge are essential for enzyme activity. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5sc03397g
  • 2016 • 124 Amorphous Cobalt Boride (Co2B) as a Highly Efficient Nonprecious Catalyst for Electrochemical Water Splitting: Oxygen and Hydrogen Evolution
    Masa, J. and Weide, P. and Peeters, D. and Sinev, I. and Xia, W. and Sun, Z. Y. and Somsen, C. and Muhler, M. and Schuhmann, W.
    Advanced Energy Materials 6 1502313 (2016)
    It is demonstrated that amorphous cobalt boride (Co2B) prepared by the chemical reduction of CoCl2 using NaBH4 is an exceptionally efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline electrolytes and is simultaneously active for catalyzing the hydrogen evolution reaction (HER). The catalyst achieves a current density of 10 mA cm(-2) at 1.61 V on an inert support and at 1.59 V when impregnated with nitrogen-doped graphene. Stable performance is maintained at 10 mA cm(-2) for at least 60 h. The optimized catalyst, Co2B annealed at 500 degrees C (Co2B-500) evolves oxygen more efficiently than RuO2 and IrO2, and its performance matches the best cobalt-based catalysts reported to date. Co2B is irreversibly oxidized at OER conditions to form a CoOOH surface layer. The active form of the catalyst is therefore represented as CoOOH/Co2B. EXAFS observations indicate that boron induces lattice strain in the crystal structure of the metal, which potentially diminishes the thermodynamic and kinetic barrier of the hydroxylation reaction, formation of the OOH* intermediate, a key limiting step in the OER.
    view abstractdoi: 10.1002/aenm.201502313
  • 2016 • 123 Coupled molecular and cantilever dynamics model for frequency-modulated atomic force microscopy
    Klocke, M. and Wolf, D.E.
    Beilstein Journal of Nanotechnology 7 708-720 (2016)
    A molecular dynamics model is presented, which adds harmonic potentials to the atomic interactions to mimic the elastic properties of an AFM cantilever. It gives new insight into the correlation between the experimentally monitored frequency shift and cantilever damping due to the interaction between tip atoms and scanned surface. Applying the model to ionic crystals with rock salt structure two damping mechanisms are investigated, which occur separately or simultaneously depending on the tip position. These mechanisms are adhesion hysteresis on the one hand and lateral excitations of the cantilever on the other. We find that the short range Lennard-Jones part of the atomic interaction alone is sufficient for changing the predominant mechanism. When the long range ionic interaction is switched off, the two damping mechanisms occur with a completely different pattern, which is explained by the energy landscape for the apex atom of the tip. In this case the adhesion hysteresis is always associated with a distinct lateral displacement of the tip. It is shown how this may lead to a systematic shift between the periodic patterns obtained from the frequency and from the damping signal, respectively. © 2016 Klocke and Wolf.
    view abstractdoi: 10.3762/bjnano.7.63
  • 2016 • 122 Crystal plasticity study of monocrystalline stochastic honeycombs under in-plane compression
    Ma, D. and Eisenlohr, P. and Epler, E. and Volkert, C.A. and Shanthraj, P. and Diehl, M. and Roters, F. and Raabe, D.
    Acta Materialia 103 796-808 (2016)
    We present a study on the plastic deformation of single crystalline stochastic honeycombs under in-plane compression using a crystal plasticity constitutive description for face-centered cubic (fcc) materials, focusing on the very early stage of plastic deformation, and identifying the interplay between the crystallographic orientation and the cellular structure during plastic deformation. We observe that despite the stochastic structure, surprisingly, the slip system activations in the honeycombs are almost identical to their corresponding bulk single crystals at the early stage of the plastic deformation. On the other hand, however, the yield stresses of the honeycombs are nearly independent of their crystallographic orientations. Similar mechanical response is found in compression testing of nanoporous gold micro-pillars aligned with various crystallographic orientations. The macroscopic stress tensors of the honeycombs show the same anisotropy as their respective bulk single crystals. Locally, however, there is an appreciable fluctuation in the local stresses, which are even larger than for polycrystals. This explains why the Taylor/Schmid factor associated with the crystallographic orientation is less useful to estimate the yield stresses of the honeycombs than the bulk single crystals and polycrystals, and why the plastic deformation occurs at smaller strains in the honeycombs than their corresponding bulk single crystals. Besides these findings, the observations of the crystallographic reorientation suggest that conventional orientation analysis tools, such as inverse pole figure and related tools, would in general fail to study the plastic deformation mechanism of monocrystalline cellular materials. © 2015 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2015.11.016
  • 2016 • 121 Enhancement of the Superconducting Gap by Nesting in CaKFe4As4: A New High Temperature Superconductor
    Mou, D. and Kong, T. and Meier, W.R. and Lochner, F. and Wang, L.-L. and Lin, Q. and Wu, Y. and Bud'Ko, S.L. and Eremin, I. and Johnson, D.D. and Canfield, P.C. and Kaminski, A.
    Physical Review Letters 117 (2016)
    We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe4As4. In contrast to the related CaFe2As2 compounds, CaKFe4As4 has a high Tc of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos(kx)cos(ky) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. These results provide strong support for the multiband character of superconductivity in CaKFe4As4, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting. © 2016 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.117.277001
  • 2016 • 120 Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures
    Gludovatz, B. and Hohenwarter, A. and Thurston, K.V.S. and Bei, H. and Wu, Z. and George, E.P. and Ritchie, R.O.
    Nature Communications 7 (2016)
    High-entropy alloys are an intriguing new class of metallic materials that derive their properties from being multi-element systems that can crystallize as a single phase, despite containing high concentrations of five or more elements with different crystal structures. Here we examine an equiatomic medium-entropy alloy containing only three elements, CrCoNi, as a single-phase face-centred cubic solid solution, which displays strength-toughness properties that exceed those of all high-entropy alloys and most multi-phase alloys. At room temperature, the alloy shows tensile strengths of almost 1 GPa, failure strains of ∼70% and KJIc fracture-toughness values above 200 MPa m1/2; at cryogenic temperatures strength, ductility and toughness of the CrCoNi alloy improve to strength levels above 1.3 GPa, failure strains up to 90% and KJIc values of 275 MPa m1/2. Such properties appear to result from continuous steady strain hardening, which acts to suppress plastic instability, resulting from pronounced dislocation activity and deformation-induced nano-twinning. © 2016, Nature Publishing Group. All rights reserved.
    view abstractdoi: 10.1038/ncomms10602
  • 2016 • 119 Experimental and modelling characterisation of residual stresses in cylindrical samples of rapidly cooled bulk metallic glass
    Korsunsky, A.M. and Sui, T. and Salvati, E. and George, E.P. and Sebastiani, M.
    Materials and Design 104 235-241 (2016)
    Quench processing is widely used in industry to impart the desired structural and mechanical properties by controlling microstructure and compositional gradients, e.g. to obtain supersaturated solid solutions in aluminium alloys, or to achieve martensitic hardening in steels. Rapid cooling, also referred to as quenching or tempering, is also the principal production route for bulk metallic glasses that exhibit high hardness and strength due to their amorphous structure that precludes plastic deformation by easy crystal slip. Importantly, rapid cooling is accompanied by the creation of residual stresses that also have a strong effect on the deformation behaviour. The present study aims to obtain insight into the residual stresses in cylindrical samples of Zr-based bulk metallic glass (BMG) by combining analytical modelling of thermal and mechanical problems with experimental measurements using Focused Ion Beam–Digital Image Correlation (FIB-DIC) ring-core milling. The results show good agreement between the two approaches, providing improved confidence in the validity of the two approaches considered here. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.matdes.2016.05.017
  • 2016 • 118 Heat-Induced Phase Transformation of Three-Dimensional Nb3O7(OH) Superstructures: Effect of Atmosphere and Electron Beam
    Betzler, S.B. and Harzer, T. and Ciston, J. and Dahmen, U. and Dehm, G. and Scheu, C.
    Crystal Growth and Design 16 4309-4317 (2016)
    Nanostructured niobium oxides and hydroxides are potential candidates for photochemical applications due to their excellent optical and electronic properties. In the present work the thermal stability of Nb3O7(OH) superstructures prepared by a simple hydrothermal approach is investigated at the atomic scale. Transmission electron microscopy and electron energy-loss spectroscopy provide insights into the phase transformation occurring at elevated temperatures and probe the effect of the atmospheric conditions. In the presence of oxygen, H2O is released from the crystal at temperatures above 500 °C, and the crystallographic structure changes to H-Nb2O5. In addition to the high thermal stability of Nb3O7(OH), the morphology was found to be stable, and first changes in the form of a merging of nanowires are not observed until 850 °C. Under reducing conditions in a transmission electron microscope and during electron beam bombardment, an oxygen-deficient phase is formed at temperatures above 750 °C. This transformation starts with the formation of defects in the crystal lattice at 450 °C and goes along with the formation of pores in the nanowires which accommodate the volume differences of the two crystal phases. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.cgd.6b00386
  • 2016 • 117 Importance of inclusion of the effect of s electrons into bond-order potentials for transition bcc metals with d-band mediated bonding
    Lin, Y.-S. and Mrovec, M. and Vitek, V.
    Modelling and Simulation in Materials Science and Engineering 24 (2016)
    In bond-order potentials (BOPs) for transition metals only the bonding mediated by the d electrons is included explicitly and the covalent part of the cohesive energy is evaluated using Slater-Koster dd bond integrals. However, the effect of s electrons with orbitals centered on atoms neighboring the corresponding dd bond is not necessarily negligible. As shown in Nguyen-Manh et al (2000 Phys. Rev. Lett. 85 4136) this can be taken into account via screening of the dd bond integrals. In a recent paper (Lin et al 2014 Model. Simul. Mater. Sci. Eng. 22 034002) the dd bond integrals were determined using a projection scheme utilizing atomic orbitals that give the best representation of the electronic wave functions in the calculations based on the density functional theory (DFT) (Madsen et al 2011 Phys. Rev. B 83 4119) and it was inferred that in this case the effect of s electrons was already included. In this paper we analyze this hypothesis by comparing studies employing BOPs with both unscreened and screened dd bond integrals. In all cases results are compared with calculations based on DFT and/or experiments. Studies of structures alternate to the bcc lattice, transformation paths that connect the bcc structure with fcc, simple cubic (sc), body centered tetragonal (bct) and hcp structures via continuously distorted configurations and calculations of γ-surfaces were all found to be insensitive to the screening of bond integrals. On the other hand, when the bond integrals are screened, formation energies of vacancies are improved and calculated phonon dispersion spectra reproduce the experimentally observed ones much better. Most importantly, dislocation core structure and dislocation glide are significantly different without and with screening of dd bond integrals. The latter lead to a much better agreement with available experiments. These findings suggest that the effect of s electrons on dd bonds, emulated by the screening of corresponding bond integrals, is the least significant when the lattice is distorted away from the ideal bcc structure homogeneously even if such distortion is large. On the other hand, when the distortion is local and inhomogeneous the impact of screening of the dd bond integrals is significant. In the studies presented in this paper such local inhomogeneities occur when phonons propagate through the lattice, at point defects and in the cores of dislocations. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0965-0393/24/8/085001
  • 2016 • 116 In-situ metal matrix composite steels: Effect of alloying and annealing on morphology, structure and mechanical properties of TiB2 particle containing high modulus steels
    Aparicio-Fernández, R. and Springer, H. and Szczepaniak, A. and Zhang, H. and Raabe, D.
    Acta Materialia 107 38-48 (2016)
    We systematically study the morphology, size and dispersion of TiB2 particles formed in-situ from Fe-Ti-B based melts, as well as their chemical composition, crystal structure and mechanical properties. The effects of 5 wt.% additions of Cr, Ni, Co, Mo, W, Mn, Al, Si, V, Ta, Nb and Zr, respectively, as well as additional annealing treatments, were investigated in order to derive guidelines for the knowledge based alloy design of steels with an increased stiffness/density ratio and sufficiently high ductility. All alloying elements were found to increase the size of the coarse primary TiB2 particles, while Co led to the most homogeneous size distribution. The size of the eutectic TiB2 constituents was decreased by all alloying additions except Ni, while their aspect ratio was little affected. No clear relation between chemical composition, crystal structure and mechanical properties of the particles could be observed. Annealing of the as-cast alloys slightly increased the size of the primary particles, but at the same time strongly spheroidised the eutectics. Additions of Co and Cr appear thus as the best starting point for designing novel in-situ high modulus metal matrix composite steels, while using Mn in concert with thermo-mechanical processing is most suited to adapt the matrix' microstructure and optimise the particle/matrix co-deformation processes. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2016.01.048
  • 2016 • 115 Interactions between metal species and nitrogen-functionalized carbon nanotubes
    Xia, W.
    Catalysis Science and Technology 6 630-644 (2016)
    Nitrogen-functionalized carbon nanotubes are promising materials in catalysis due to their versatile surface properties involving nitrogen groups, oxygen groups, surface defects and metal impurities. These factors can be used to tune the dispersion, morphology, crystal structure, electronic structure, mobility/stability and finally the catalytic performance of supported metal nanoparticles. This review focuses on selected examples aiming at understanding the interactions between surface groups, defects, and metal species and their impact on the catalytic properties in electrocatalysis and gas-phase redox catalysis. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5cy01694k
  • 2016 • 114 Low cycle fatigue in aluminum single and bi-crystals: On the influence of crystal orientation
    Nellessen, J. and Sandlöbes, S. and Raabe, D.
    Materials Science and Engineering A 668 166-179 (2016)
    Aluminum single crystals with three different double-slip orientations and two aluminum bi-crystals - one with a high-angle grain boundary and one with a low-angle grain boundary - were cyclically deformed up to 100 cycles under constant displacement control. The distribution of the local strain and the local strain amplitudes was captured by in-situ digital image correlation (DIC). Dislocation structure analysis was performed by electron channeling contrast imaging (ECCI) and the evolution of local misorientations was recorded by high resolution electron backscatter diffraction (EBSD). The DIC results show a homogeneous strain amplitude distribution in the single crystals while the measured strain amplitude in the low-angle grain boundary bi-crystal sample differs significantly. ECCI observations reveal the presence of dislocation cells elongated along the trace of the primary {111} slip plane in all investigated crystals and the formation of deformation bands parallel to the trace of {110} planes. Deformation bands (DB) were observed in all samples but their frequency and misorientation with respect to the matrix was found to sensitively depend on the crystal orientation and the local strain amplitude. Our results on the bi-crystals show that the grain orientation mainly determines the local stresses and therefore also the formation of the associated dislocation structures rather than the grain boundary character. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2016.05.054
  • 2016 • 113 Molecular structure of diethylaminoalane in the solid state: An X-ray powder diffraction, DFT calculation and Raman spectroscopy study
    Bernert, T. and Ley, M.B. and Ruiz-Fuertes, J. and Fischer, M. and Felderhoff, M. and Weidenthaler, C.
    Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 72 232-240 (2016)
    The crystal structure of diethylaminoalane, [H2Al - N(C2H5)2]2, was determined by X-ray powder diffraction in conjunction with DFT calculations. Diethylaminoalane crystallizes in the monoclinic space group P21/c with a = 7.4020 (2), b = 12.9663 (3), c = 7.2878 (2) Å and β = 90.660 (2)° at 293 K. The crystal structure was confirmed by DFT calculations and Raman spectroscopy. The molecular structure of diethylaminoalane consists of dimers of [H2Al - N(CH2CH3)2] in which an Al2N2 four-membered ring is formed by a center of inversion. Such an arrangement of the aminoalane moieties in the crystal structure is well known for this class of compound, as shown by the comparison with ethylmethylaminoalane and diisopropylaminoalane.The crystal structure of diethylaminoalane, [H2Al - N(C2H5)2]2, was determined by X-ray powder diffraction, geometry optimization by density functional theory (DFT) and Raman spectroscopy. The DFT calculations were validated by calculating the ground state structures of two known aminoalanes while the Raman spectrum of diethylaminoalane was measured and compared to the simulated ones. Furthermore, the crystal structure of diethylaminoalane is compared with chemically and structurally similar compounds. © International Union of Crystallography, 2016.
    view abstractdoi: 10.1107/S2052520616000093
  • 2016 • 112 Monitoring Conformational Changes in the Receptor Tyrosine Kinase EGFR
    Becker, C. and Öcal, S. and Nguyen, H.D. and Phan, T. and Keul, M. and Simard, J.R. and Rauh, D.
    ChemBioChem 17 990-994 (2016)
    The receptor tyrosine kinase EGFR is regulated by complex conformational changes, and this conformational control is disturbed in certain types of cancer. Many ligands are known to bind EGFR in its active conformation, thereby preventing ATP from binding. Only a few ligands are known to stabilize EGFR in its inactive conformation, thus providing novel strategies for perturbing EGFR activity. We report a direct binding assay that enables the identification of novel ligands that bind to and stabilize the inactive conformation of EGFR. Too active? Stabilize the inactive conformation. EGFR is a target for tumor therapy, with many small molecules known to bind its kinase domain in the active conformation. A binding assay was developed to search for ligands stabilizing its inactive conformation, thus providing a tool for new approaches to target its dynamic regulatory mechanisms. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cbic.201600115
  • 2016 • 111 Nanostructured Ti-Ta thin films synthesized by combinatorial glancing angle sputter deposition
    Motemani, Y. and Khare, C. and Savan, A. and Hans, M. and Paulsen, A. and Frenzel, J. and Somsen, C. and Mücklich, F. and Eggeler, G. and Ludwig, Al.
    Nanotechnology 27 (2016)
    Ti-Ta alloys are attractive materials for applications in actuators as well as biomedical implants. When fabricated as thin films, these alloys can potentially be employed as microactuators, components for micro-implantable devices and coatings on surgical implants. In this study, Ti100-xTa x (x = 21, 30) nanocolumnar thin films are fabricated by glancing angle deposition (GLAD) at room temperature using Ti73Ta27 and Ta sputter targets. Crystal structure, morphology and microstructure of the nanostructured thin films are systematically investigated by XRD, SEM and TEM, respectively. Nanocolumns of ∼150-160 nm in width are oriented perpendicular to the substrate for both Ti79Ta21 and Ti70Ta30 compositions. The disordered α″ martensite phase with orthorhombic structure is formed in room temperature as-deposited thin films. The columns are found to be elongated small single crystals which are aligned perpendicular to the and planes of α″ martensite, indicating that the films' growth orientation is mainly dominated by these crystallographic planes. Laser pre-patterned substrates are utilized to obtain periodic nanocolumnar arrays. The differences in seed pattern, and inter-seed distances lead to growth of multi-level porous nanostructures. Using a unique sputter deposition geometry consisting of Ti73Ta27 and Ta sputter sources, a nanocolumnar Ti-Ta materials library was fabricated on a static substrate by a co-deposition process (combinatorial-GLAD approach). In this library, a composition spread developed between Ti72.8Ta27.2 and Ti64.4Ta35.6, as confirmed by high-throughput EDX analysis. The morphology over the materials library varies from well-isolated nanocolumns to fan-like nanocolumnar structures. The influence of two sputter sources is investigated by studying the resulting column angle on the materials library. The presented nanostructuring methods including the use of the GLAD technique along with pre-patterning and a combinatorial materials library fabrication strategy offer a promising technological approach for investigating Ti-Ta thin films for a range of applications. The proposed approaches can be similarly implemented for other materials systems which can benefit from the formation of a nanocolumnar morphology. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/49/495604
  • 2016 • 110 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 • 109 PKU-20: A new silicogermanate constructed from sti and asv layers
    Chen, Y. and Su, J. and Huang, S. and Liang, J. and Lin, X. and Liao, F. and Sun, J. and Wang, Y. and Lin, J. and Gies, H.
    Microporous and Mesoporous Materials 224 384-391 (2016)
    A new silicogermanate (PKU-20) was hydrothermally synthesized using triethylisopropylammonium cation as the structure directing agent in the presence of fluoride. Its structure was determined from a combination of synchrotron single crystal X-ray diffraction and powder X-ray diffraction data. PKU-20 crystallizes in the monoclinic space group C2/m, with the lattice parameters of a = 18.5901(6) Å, b = 13.9118 (4) Å, c = 22.2614 (7) Å and β = 100.1514 (12)°. The framework of PKU-20 is constructed from an alternate stacking of sti and asv layers. The sti layer is exactly the same as that in the STI framework,while the asv layer is a new layer sliced off from the ASV framework parallel to the (112) plane. The take-out scheme of the layer is discussed on the basis of a composite building unit "D4R-lau-D4R". PKU-20 possesses a two-dimensional channel system, where the 10-ring channels parallel to the [010] direction are intercrossed by 12-ring pockets along the [101] direction. © 2016 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.micromeso.2015.12.052
  • 2016 • 108 Preparation of Organometal Halide Perovskite Photonic Crystal Films for Potential Optoelectronic Applications
    Schünemann, S. and Chen, K. and Brittman, S. and Garnett, E. and Tüysüz, H.
    ACS Applied Materials and Interfaces 8 25489-25495 (2016)
    Herein, a facile method for the preparation of organometal halide perovskite (OHP) thin films in photonic crystal morphology is presented. The OHP photonic crystal thin films with controllable porosity and thicknesses between 2 μm and 6 μm were prepared on glass, fluorine-doped tin oxide (FTO), and TiO2 substrates by using a colloidal crystal of polystyrene microspheres as a template to form an inverse opal structure. The composition of OHP could be straightforwardly tuned by varying the halide anions. The obtained OHP inverse opal films possess large ordered domains with a periodic change of the refractive index, which results in pronounced photonic stop bands in the visible light range. By changing the diameter of the polystyrene microspheres, the position of the photonic stop band can be tuned through the visible spectrum. This developed methodology can be used as blueprint for the synthesis of various OHP films that could eventually be used as more effective light harvesting materials for diverse applications. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b09227
  • 2016 • 107 Size and orientation dependent mechanical behavior of body-centered tetragonal Sn at 0.6 of the melting temperature
    Philippi, B. and Kirchlechner, C. and Micha, J.S. and Dehm, G.
    Acta Materialia 115 76-82 (2016)
    Although, tin is one of the most prominent metals in soldering, very little is known about its mechanical behavior. In addition, possible size-effects of tin can become restricting for the ongoing miniaturization of microelectronic devices. Due to the low melting temperature of 505.15 K and the body-centered tetragonal crystal structure, differences in the mechanical behavior compared to face-centered cubic and body-centered cubic metals can be expected. Since Tin is especially interesting because of its multiple different slip systems, post mortem slip step analysis allowed to determine the activated slip systems and thus, to calculate size dependent critical resolved shear stresses. The measured size scaling exponent (-1.07 ± 0.06) is close to model-predictions of -1, irrespective of the activated families of slip systems in different orientations. Furthermore, an exceptional low scatter of the flow stress in various samples and no apparent hardening is found. It is concluded, that the activation of dislocation sources instead of dislocation-dislocation interactions are responsible for the observed behavior. This is in line with complementary μLaue diffraction experiments which indicate an unresolvable low density of geometrical necessary dislocations. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2016.05.055
  • 2016 • 106 Structure and properties of ITQ-8: A hydrous layer silicate with microporous silicate layers
    Marler, B. and Müller, M. and Gies, H.
    Dalton Transactions 45 10155-10164 (2016)
    ITQ-8 is a new hydrous layer silicate (HLS) with a chemical composition of [C4H8(C7H13N)2]8 [Si64O128(OH)16]·48H2O per unit cell. The synthesis of ITQ-8 was first described in 2002 by Díaz-Cabañas et al., the structure of this material, however, remained unsolved at that time. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and FTIR spectroscopy confirmed that ITQ-8 is a layer silicate. The XRD powder pattern was indexed in the monoclinic system with lattice parameters of a0 = 35.5168(5) Å, b0 = 13.3989(2) Å, c0 = 16.0351(2) Å, β = 106.74(2)°. The crystal structure was solved by simulated annealing. Rietveld refinement of the structure in space group C2/c converged to residual values of RBragg = 0.023, RF = 0.022 and chi2 = 2.3 confirming the structure model. The structure of ITQ-8 contains silicate layers with a topology that resembles a (11-1) section of the framework of zeolite levyne. So far, this layer topology is unique among layer silicates. The layer can be regarded as made up of 4-, 6-, double-six and 8-rings which are interconnected to form cup-like "half-cages". Unlike other HLSs, which possess impermeable silicate layers, ITQ-8 contains 8-rings pores with a free diameter of 3.5 Å × 3.4 Å and can be regarded as a "small-pore layer silicate". In the crystal structure, the organic cations, 1,4-diquiniclidiniumbutane, used as structure directing agents during synthesis are intercalated between the silicate layers. Clusters (bands) of water molecules which are hydrogen bonded to each other and to the terminal Si-OH/Si-O- groups are located between the organic cations and interconnect the silicate layers. ITQ-8 is a very interesting material as precursor for the synthesis of microporous framework silicates by topotactic condensation or interlayer expansion reactions leading to 3D micro-pore systems which may be useful in applications as e.g. catalysts, catalyst supports and adsorbents of for separation. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c6dt00713a
  • 2016 • 105 Superelasticity and Tunable Thermal Expansion across a Wide Temperature Range
    Hao, Y. L. and Wang, H. L. and Li, T. and Cairney, J. M. and Ceguerra, A. V. and Wang, Y. D. and Wang, Y. and Wang, D. and Obbard, E. G. and Li, S. J. and Yang, R.
    Journal of Materials Science & Technology 32 705--709 (2016)
    Materials that undergo a reversible change of crystal structure through martensitic transformation (MT) possess unusual functionalities including shape memory, superelasticity, and low/negative thermal expansion. These properties have many advanced applications, such as actuators, sensors, and energy conversion, but are limited typically in a narrow temperature range of tens of Kelvin. Here we report that, by creating a nano-scale concentration modulation via phase separation, the MT can be rendered continuous by an in-situ elastic confinement mechanism. Through a model titanium alloy, we demonstrate that the elastically confined continuous MT has unprecedented properties, such as superelasticity from below 4.2 K to 500 K, fully tunable and stable thermal expansion, from positive, through zero, to negative, from below 4.2 K to 573 K, and high strength-to-modulus ratio across a wide temperature range. The elastic tuning on the MT, together with a significant extension of the crystal stability limit, provides new opportunities to explore advanced materials. Copyright (C) 2016, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited.
    view abstractdoi: 10.1016/j.jmst.2016.06.017
  • 2016 • 104 Surface analysis of the Heusler Ni49.7Mn29.1Ga21.2 Alloy: The composition, phase transition, and twinned microstructure of martensite
    Horáková, K. and Cháb, V. and Heczko, O. and Drchal, V. and Fekete, L. and Honolka, J. and Kopeček, J. and Kudrnovský, J. and Polyak, Y. and Sajdl, P. and Vondráček, M. and Lančok, J. and Feyer, V. and Wiemann, C. and Schn...
    Journal of Applied Physics 120 (2016)
    Surface analysis was used to study the dynamics of the martensitic transformation on macro- and mesoscopic scales. The chemical state, morphology, and magnetic and surface structure were monitored at particular stages of the phase transition. At room temperature, the martensitic phase of the Ni49.7Mn29.1Ga21.2 (100) single crystal exhibited macroscopic a/c twinning and a corresponding magnetic domain structure characterized by magnetization vector in and out of the surface plane. Induced by radiation heating, the transformation from martensite to austenite takes place separately at the surface and in the bulk. Its dynamics depend on the history of the sample treatment which affects the crystallographic orientation of twins and minor changes of the surface stoichiometry. The interfaces (twin planes) between twin variants in the martensitic phase were noticeable also in the austenitic phase, thanks to the shape memory effect of this material. © 2016 Author(s).
    view abstractdoi: 10.1063/1.4962648
  • 2016 • 103 Synthesis of Bi2Te3 and (Bi: XSb1- x)2Te3 nanoparticles using the novel IL [C4mim]3[Bi3I12]
    Loor, M. and Bendt, G. and Hagemann, U. and Wölper, C. and Assenmacher, W. and Schulz, S.
    Dalton Transactions 45 15326-15335 (2016)
    The novel Bi-containing reactive ionic liquid [C4mim]3[Bi3I12], which was synthesized in quantitative yield by equimolar reaction of BiI3 and [C4mim]I, was used as a novel Bi-source for the ionothermal synthesis of Bi2Te3 nanoparticles by reaction with (Et3Si)2Te in the ionic liquid [C4mim]I. The solid state structure of [C4mim]3[Bi3I12] was determined by single crystal X-ray diffraction. In addition, the ionothermal synthesis of the single source precursor (Et2Sb)2Te and [C4mim]3[Bi3I12] yielded the ternary (BixSb1-x)2Te3 (x = 0.25, 0.5, 0.75) nanoparticles. The chemical composition and phase purity of the tetradymite-type materials were determined by EDX and XRD and the surface composition of the nanoparticles was further investigated by IR and XPS. In addition, the morphology of the nanoparticles was investigated by SEM and TEM. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6dt02361d
  • 2016 • 102 Synthesis of nanosized Silicalite-1 in F-media
    Jiao, K. and Xu, X. and Lv, Z. and Song, J. and He, M. and Gies, H.
    Microporous and Mesoporous Materials 225 98-104 (2016)
    This paper reports on the successful crystallization of monodisperse, highly crystalline, nanosized zeolite Silicalite-1 crystals in fluoride media by using an active silica gel as silica source and tetrapropylammonium fluoride as structure directing agent. The synthesis procedure is hydrothermal dynamic crystallization. The silica/water ratio and synthesis temperature were reduced to optimize the number of crystal nuclei and control the rate of crystallization for obtaining nanosized zeolite crystals. Meanwhile, F- ions were used to partly replace OH- ions in the synthesis system to obtain zeolite products with high crystallinity. Analytical results of XRD-, SEM-, Dynamic Light Scanning- (DLS) IR-, Simultaneous Thermal Analysis- (STA) and N2 adsorption and desorption experiments show that the average particle size of zeolite Silicalite-1 product is about 45 nm and shows high crystallinity. The F- containing Silicalite-1 zeolite sample was compared with an industrial ZSM-5 zeolite sample and it shows obvious advantages in both reduced particle size and enhanced crystallinity. © 2015 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.micromeso.2015.11.043
  • 2016 • 101 Three-Parameter Crystal-Structure Prediction for sp-d-Valent Compounds
    Bialon, A.F. and Hammerschmidt, T. and Drautz, R.
    Chemistry of Materials 28 2550-2556 (2016)
    We present a three-dimensional structure-map based on experimental data for compounds that contain sp-block elements and transition metals. The map predicts the correct crystal structure with a probability of 86% and has a confidence of better than 98% that the correct crystal structure is among three predicted crystal structures. The three descriptors of the structure map are physically intuitive functions of the number of valence electrons, atomic volume, and electronegativity of the constituent elements. We test the structure map against standard density-functional theory calculations for 1:1 sp-d-valent compounds and show that our three-parameter model has a comparable predictive power. We demonstrate the application of the structure map in conjunction with density-functional theory calculations. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.5b04299
  • 2016 • 100 X-Ray diffraction on large single crystals using a powder diffractometer
    Jesche, A. and Fix, M. and Kreyssig, A. and Meier, W.R. and Canfield, P.C.
    Philosophical Magazine 96 2115-2124 (2016)
    Information on the lattice parameter of single crystals with known crystallographic structure allows for estimations of sample quality and composition. In many cases, it is sufficient to determine one lattice parameter or the lattice spacing along a certain, high-symmetry direction, e.g. in order to determine the composition in a substitution series by taking advantage of Vegard’s rule. Here we present a guide to accurate measurements of single crystals with dimensions ranging from 200 μm up to several millimetres using a standard powder diffractometer in Bragg–Brentano geometry. The correction of the error introduced by the sample height and the optimisation of the alignment are discussed in detail. In particular for single crystals with a plate-like habit, the described procedure allows for measurement of the lattice spacings normal to the plates with high accuracy on a timescale of minutes. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/14786435.2016.1192725
  • 2015 • 99 A study on the geometry of dislocation patterns in the surrounding of nanoindents in a TWIP steel using electron channeling contrast imaging and discrete dislocation dynamics simulations
    Zhang, J.-L. and Zaefferer, S. and Raabe, D.
    Materials Science and Engineering A 636 231-242 (2015)
    Electron channeling contrast imaging under controlled diffraction conditions (cECCI) enables observation of crystal defects, especially dislocations, stacking faults and nano-twins, close to the surface of bulk samples. In this work cECCI has been employed to observe defects around nanoindents into the surface of {100}-, {110}-, {111}-oriented grains in a Fe-22Mn-0.65C (wt%) TWIP steel sample (fcc crystal structure, stacking fault energy ~20. mJ/m) using a cone-spherical indenter. The dislocation patterns show four- and two-fold symmetries for the {100}- and {110}-orientation, and a three-fold symmetry for the {111}-orientation which is, however, difficult to observe. Discrete dislocation dynamics (DDD) simulations of the indentation were carried out to complement the static experimental investigations. The simulations were carried out with both, cross-slip disabled and enabled conditions, where the former were found to match to the experimental results better, as may be expected for an fcc material with low stacking fault energy. The 3-dimensional geometry of the dislocation patterns of the different indents was analysed and discussed with respect to pattern formation mechanisms. The force-displacement curves obtained during indentation showed a stronger strain hardening for the {111} oriented crystal than that for the other orientations. This is in contrast to the behaviour of, for example, copper and is interpreted to be due to planar slip. Irrespective of orientation and indentation depth the radius of the plastically deformed area was found to be approximately 4 times larger than that of the indenter contact area. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2015.03.078
  • 2015 • 98 Ab initio simulations on N and S co-doped titania nanotubes for photocatalytic applications
    Chesnokov, A. and Lisovski, O. and Bocharov, D. and Piskunov, S. and Zhukovskii, Y.F. and Wessel, M. and Spohr, E.
    Physica Scripta 90 (2015)
    In this paper we present the results of quantum chemical modeling for energetically stable anatase (001) TiO<inf>2</inf> nanotubes, undoped, doped, and codoped with N<inf>O</inf> and S<inf>O</inf> atoms. We calculate the electronic structure of one-dimensional (1D) nanotubes and zero-dimensional (0D) atomic fragments cut out from these nanotubes, employing hybrid density functional theory with a partial incorporation of an exact, nonlocal Hartree-Fock exchange within the formalism of the linear combination of atomic orbitals, as implemented in both CRYSTAL and NWChem total energy codes. Structural optimization of 1D nanotubes has been performed using CRYSTAL09 code, while the cut-out 0D fragments have been modelled using the NWChem code. The electronic properties of the studied systems prove that the band structure of the pristine TiO<inf>2</inf> nanotube can be substantially modified by introducing substitutional impurity defects. The N-doped nanotube creates a midgap state that largely has a nitrogen 2p character. The S-doped nanotube has a defect state that almost coincides with the top of the valence bond for the pristine material. For nanotubes codoped with both S and N, we observe a downward shift of the gap state of nitrogen relative to the purely N-doped state by about 0.3 eV. This results in a system with a filled gap state about 0.3 eV below the O<inf>2</inf>/H<inf>2</inf>O oxidation level, making it a very promising candidate for photocatalytic hydrogen generation under visible light, because due to the presence of sulfur, the bottom of the conduction band is only about 2.2 eV above the occupied midgap state, and also, clearly above the standard hydrogen electrode level. © 2015 The Royal Swedish Academy of Sciences.
    view abstractdoi: 10.1088/0031-8949/90/9/094013
  • 2015 • 97 Ab initio thermodynamics of the CoCrFeMnNi high entropy alloy: Importance of entropy contributions beyond the configurational one
    Ma, D. and Grabowski, B. and Körmann, F. and Neugebauer, J. and Raabe, D.
    Acta Materialia 100 90-97 (2015)
    We investigate the thermodynamic properties of the prototype equi-atomic high entropy alloy (HEA) CoCrFeMnNi by using finite-temperature ab initio methods. All relevant free energy contributions are considered for the hcp, fcc, and bcc structures, including electronic, vibrational, and magnetic excitations. We predict the paramagnetic fcc phase to be most stable above room temperature in agreement with experiment. The corresponding thermal expansion and bulk modulus agree likewise well with experimental measurements. A careful analysis of the underlying entropy contributions allows us to identify that the originally postulated dominance of the configurational entropy is questionable. We show that vibrational, electronic, and magnetic entropy contributions must be considered on an equal footing to reliably predict phase stabilities in HEA systems. © 2015 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2015.08.050
  • 2015 • 96 Combining X-ray crystallography and molecular modeling toward the optimization of pyrazolo[3,4-d ]pyrimidines as potent c-Src inhibitors active in vivo against neuroblastoma
    Tintori, C. and Fallacara, A.L. and Radi, M. and Zamperini, C. and Dreassi, E. and Crespan, E. and Maga, G. and Schenone, S. and Musumeci, F. and Brullo, C. and Richters, A. and Gasparrini, F. and Angelucci, A. and Festuccia, C. a...
    Journal of Medicinal Chemistry 58 347-361 (2015)
    c-Src is a tyrosine kinase belonging to the Src-family kinases. It is overexpressed and/or hyperactivated in a variety of cancer cells, thus its inhibition has been predicted to have therapeutic effects in solid tumors. Recently, the pyrazolo[3,4-d]pyrimidine 3 was reported as a dual c-Src/Abl inhibitor. Herein we describe a multidisciplinary drug discovery approach for the optimization of the lead 3 against c-Src. Starting from the X-ray crystal structure of c-Src in complex with 3, Monte Carlo free energy perturbation calculations were applied to guide the design of c-Src inhibitors with improved activities. As a result, the introduction of a meta hydroxyl group on the C4 anilino ring was computed to be particularly favorable. The potency of the synthesized inhibitors was increased with respect to the starting lead 3. The best identified compounds were also found active in the inhibition of neuroblastoma cell proliferation. Furthermore, compound 29 also showed in vivo activity in xenograft model using SH-SY5Y cells. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/jm5013159
  • 2015 • 95 Correlation between structure and magnetic properties in CoxFe100-x nanowires: The roles of composition and wire diameter
    Bran, C. and Palmero, E.M. and Li, Z.-A. and Del Real, R.P. and Spasova, M. and Farle, M. and Vázquez, M.
    Journal of Physics D: Applied Physics 48 (2015)
    The structural and magnetic characteristics of CoxFe100-x (0 ≤ x ≤ 100) cylindrical nanowire arrays are investigated for two series of nanowires with diameters of 20 and 40 nm, respectively. The crystalline structure evolves with Co content from bcc Fe through a mixed bcc-fcc phase to a final polycrystalline fcc or hcp phase for 40 and 20 nm diameter Co nanowires, respectively. A monocrystalline structure is found only in a few nanowires with a 40 nm diameter. The magnetic characterization under axial magnetic field reveals an increase in coercivity and remanence for increasing Co content as the crystalline structure evolves from bcc Fe to fcc Co. These parameters decrease when hcp Co with a stronger magnetocrystalline anisotropy and nearly perpendicular 'c' axis is formed. Overall higher values are observed in nanowires when the nanowire diameter decreases from 40 to 20 nm. An increase of the total magnetic anisotropy energy density is found with decreasing temperature, especially for Co wires where the strong magnetocrystalline anisotropy plays the most significant role. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/48/14/145304
  • 2015 • 94 Detection of Cu2Zn5SnSe8 and Cu2Zn6SnSe9 phases in co-evaporated Cu2ZnSnSe4 thin-films
    Schwarz, T. and Marques, M.A.L. and Botti, S. and Mousel, M. and Redinger, A. and Siebentritt, S. and Cojocaru-Mirédin, O. and Raabe, D. and Choi, P.-P.
    Applied Physics Letters 107 (2015)
    Cu2ZnSnSe4 thin-films for photovoltaic applications are investigated using combined atom probe tomography and ab initio density functional theory. The atom probe studies reveal nano-sized grains of Cu2Zn5SnSe8 and Cu2Zn6SnSe9 composition, which cannot be assigned to any known phase reported in the literature. Both phases are considered to be metastable, as density functional theory calculations yield positive energy differences with respect to the decomposition into Cu2ZnSnSe4 and ZnSe. Among the conceivable crystal structures for both phases, a distorted zinc-blende structure shows the lowest energy, which is a few tens of meV below the energy of a wurtzite structure. A band gap of 1.1 eV is calculated for both the Cu2Zn5SnSe8 and Cu2Zn6SnSe9 phases. Possible effects of these phases on solar cell performance are discussed. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4934847
  • 2015 • 93 Dustiness and deagglomeration testing: Interlaboratory comparison of systems for nanoparticle powders
    Ding, Y. and Stahlmecke, B. and Jiménez, A.S. and Tuinman, I.L. and Kaminski, H. and Kuhlbusch, T.A.J. and Van Tongeren, M. and Riediker, M.
    Aerosol Science and Technology 49 1222-1231 (2015)
    Different types of aerosolization and deagglomeration testing systems exist for studying the properties of nanomaterial powders and their aerosols. However, results are dependent on the specific methods used. In order to have well-characterized aerosols, we require a better understanding of how system parameters and testing conditions influence the properties of the aerosols generated. In the present study, four experimental setups delivering different aerosolization energies were used to test the resultant aerosols of two distinct nanomaterials (hydrophobic and hydrophilic TiO2). The reproducibility of results within each system was good. However, the number concentrations and size distributions of the aerosols created varied across the four systems; for number concentrations, e.g., from 103 to 106 #/cm3. Moreover, distinct differences were also observed between the two materials with different surface coatings. The article discusses how system characteristics and other pertinent conditions modify the test results. We propose using air velocity as a suitable proxy for estimating energy input levels in aerosolization systems. The information derived from this work will be especially useful for establishing standard operating procedures for testing nanopowders, as well as for estimating their release rates under different energy input conditions, which is relevant for occupational exposure. © 2015 American Association for Aerosol Research.
    view abstractdoi: 10.1080/02786826.2015.1114999
  • 2015 • 92 Dynamics enhanced by HCl doping triggers full Pauling entropy release at the ice XII-XIV transition
    Köster, K.W. and Fuentes-Landete, V. and Raidt, A. and Seidl, M. and Gainaru, C. and Loerting, T. and Böhmer, R.
    Nature Communications 6 (2015)
    The pressure-temperature phase diagram of ice displays a perplexing variety of structurally distinct phases. In the century-long history of scientific research on ice, the proton-ordered ice phases numbered XIII through XV were discovered only recently. Despite considerable effort, none of the transitions leading from the low-temperature ordered ices VIII, IX, XI, XIII, XIV and XV to their high-temperature disordered counterparts were experimentally found to display the full Pauling entropy. Here we report calorimetric measurements on suitably high-pressure-treated, hydrogen chloride-doped ice XIV that demonstrate just this at the transition to ice XII. Dielectric spectroscopy on undoped and on variously doped ice XII crystals reveals that addition of hydrogen chloride, the agent triggering complete proton order in ice XIV, enhances the precursor dynamics strongest. These discoveries provide new insights into the puzzling observation that different dopants trigger the formation of different proton-ordered ice phases. © 2015 Macmillan Publishers Limited.
    view abstractdoi: 10.1038/ncomms8349
  • 2015 • 91 Highly Ordered Mesoporous Cobalt-Containing Oxides: Structure, Catalytic Properties, and Active Sites in Oxidation of Carbon Monoxide
    Gu, D. and Jia, C.-J. and Weidenthaler, C. and Bongard, H.-J. and Spliethoff, B. and Schmidt, W. and Schüth, F.
    Journal of the American Chemical Society 137 11407-11418 (2015)
    Co<inf>3</inf>O<inf>4</inf> with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co3+ is considered to be the active site, while tetrahedrally coordinated Co2+ is assumed to be basically inactive. In this study, a highly ordered mesoporous CoO has been prepared by H<inf>2</inf> reduction of nanocast Co<inf>3</inf>O<inf>4</inf> at low temperature (250 °C). The as-prepared CoO material, which has a rock-salt structure with a single Co2+ octahedrally coordinated by lattice oxygen in Fm3¯m symmetry, exhibited unexpectedly high activity for CO oxidation. Careful investigation of the catalytic behavior of mesoporous CoO catalyst led to the conclusion that the oxidation of surface Co2+ to Co3+ causes the high activity. Other mesoporous spinels (CuCo<inf>2</inf>O<inf>4</inf>, CoCr<inf>2</inf>O<inf>4</inf>, and CoFe<inf>2</inf>O<inf>4</inf>) with different Co species substituted with non/low-active metal ions were also synthesized to investigate the catalytically active site of cobalt-based catalysts. The results show that not only is the octahedrally coordinated Co3+ highly active but also the octahedrally coordinated Co2+ species in CoFe<inf>2</inf>O<inf>4</inf> with an inverse spinel structure shows some activity. These results suggest that the octahedrally coordinated Co2+ species is easily oxidized and shows high catalytic activity for CO oxidation. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/jacs.5b06336
  • 2015 • 90 Hydrogen diffusion and segregation in α iron ∑ 3 (111) grain boundaries
    Hamza, M. and Hatem, T.M. and Raabe, D. and El-Awady, J.A.
    ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) 9-2015 (2015)
    Polycrystalline material generally exhibits degradation in its mechanical properties and shows more tendency for intergranular fracture due to segregation and diffusion of hydrogen on the grain boundaries (GBs). Understanding the parameters affecting the diffusion and binding of hydrogen within GBs will allow enhancing the mechanical properties of the commercial engineering materials and developing interface dominant materials. In practice during forming processes, the coincidence site lattice (CSL) GBs are experiencing deviations from their ideal configurations. Consequently, this will change the atomic structural integrity by superposition of sub-boundary dislocation networks on the ideal CSL interfaces. For this study, the ideal ∑ 3 111 [11 0] GB structure and its angular deviations in BCC iron within the range of Brandon criterion will be studied comprehensively using molecular statics (MS) simulations. The clean GB energy will be quantified, followed by the GB and free surface segregation energies calculations for hydrogen atoms. Rice-Wang model will be used to assess the embrittlement impact variation over the deviation angles. The results showed that the ideal GB structure is having the greatest resistance to embrittlement prior GB hydrogen saturation, while the 3° deviated GB is showing the highest susceptibility to embrittlement. Upon saturation, the 5° deviated GB appears to have the highest resistance instead due to the lowest stability of hydrogen atoms observed in the free surfaces of its simulation cell. Molecular dynamics (MD) simulations are then applied to calculate hydrogen diffusivity within the ideal and deviated GB structure. It is shown that hydrogen diffusivity decreases significantly in the deviated GB models. In addition, the 5° deviated GB is representing the local minimum for diffusivity results suggesting the existence of the highest atomic disorder and excessive secondary dislocation accommodation within this interface. Copyright © 2015 by ASME.
    view abstractdoi: 10.1115/IMECE2015-53118
  • 2015 • 89 Impact of ambient pressure on titania nanoparticle formation during spray-flame synthesis
    Hardt, S. and Wlokas, I. and Schulz, C. and Wiggers, H.
    Journal of Nanoscience and Nanotechnology 15 9449-9456 (2015)
    Nanocrystalline titania was synthesized via liquid-fed spray-flame synthesis in a hermetically closed system at various pressures. Titanium tetraisopropoxide dissolved in isopropanol was used as precursor. The size, crystal structure, degree of agglomeration, morphology and the band gap of the as-prepared particles were investigated ex situ by nitrogen adsorption, transmission electron microscopy, X-ray diffraction, and UV-VIS absorption spectroscopy. In comparison to synthesis at atmospheric pressure it was found that decreasing pressure has a significant influence on the particle size distribution leading to smaller particles with reduced geometric standard deviation while particle morphology and crystal structure are not affected. Computational fluid dynamics simulations support the experimental findings also indicating a significant decrease in particle size at reduced pressure. Although it is well known that decreasing pressure leads to smaller particle sizes, it is (to our knowledge) the first time that this relation was investigated for spray-flame synthesis. Copyright © 2015 American Scientific Publishers All rights reserved.
    view abstractdoi: 10.1166/jnn.2015.10607
  • 2015 • 88 Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds
    Steil, D. and Schmitt, O. and Fetzer, R. and Kubota, T. and Naganuma, H. and Oogane, M. and Ando, Y. and Rodan, S. and Blum, C.G.F. and Balke, B. and Wurmehl, S. and Aeschlimann, M. and Cinchetti, M.
    48 (2015)
    Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demagnetization studies can, thus, help to understand the impact of stoichiometry and order on ultrafast spin dynamics. Here, we present a comparative study of the structural ordering and magnetization dynamics for thin films and bulk single crystals of the family of Heusler alloys with composition Co2Fe1 - xMnxSi. The local ordering is studied by 59Co nuclear magnetic resonance (NMR) spectroscopy, while the time-resolved magneto-optical Kerr effect gives access to the ultrafast magnetization dynamics. In the NMR studies we find significant differences between bulk single crystals and thin films, both regarding local ordering and stoichiometry. The ultrafast magnetization dynamics, on the other hand, turns out to be mostly unaffected by the observed structural differences, especially on the time scale of some hundreds of femtoseconds. These results confirm hole-mediated spin-flip processes as the main mechanism for ultrafast demagnetization and the robustness of this demagnetization channel against defect states in the minority band gap as well as against the energetic position of the band gap with respect to the Fermi energy. The very small differences observed in the magnetization dynamics on the picosecond time-scale, on the other hand, can be explained by considering the differences in the electronic structure at the Fermi energy and in the heat diffusion of thin films and bulk crystals. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/48/16/164016
  • 2015 • 87 Manganese tetraboride, MnB4: High-temperature crystal structure, p-n transition, 55Mn NMR spectroscopy, solid solutions, and mechanical properties
    Knappschneider, A. and Litterscheid, C. and Brgoch, J. and George, N.C. and Henke, S.c and Cheetham, A.K. and Hu, J.G. and Seshadri, R. and Albert, B.
    Chemistry - A European Journal 21 8177-8181 (2015)
    The structural and electronic properties of MnB<inf>4</inf> were studied by high-temperature powder X-ray diffraction and measurements of the conductivity and Seebeck coefficient on spark-plasma-sintered samples. A transition from the room-temperature monoclinic structure (space group P2<inf>1</inf>/c) to a high-temperature orthorhombic structure (space group Pnnm) was observed at about 650K. The material remained semiconducting after the transition, but its behavior changed from p-type to n-type. 55Mn NMR measurements revealed an isotropic chemical shift of -1315ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr<inf>1-x</inf>Mn<inf>x</inf>B<inf>4</inf> (two phases in space groups Pnnm and P2<inf>1</inf>/c) were synthesized for the first time. In addition, nanoindentation studies yielded values of (496±26) and (25.3±1.7)GPa for the Young's modulus and hardness, respectively, compared to values of 530 and 37GPa obtained by DFT calculations. Phase transition: Monoclinic manganese tetraboride can be transformed into an orthorhombic phase thermally or by forming solid solutions with chromium tetraboride. The structural phase transition of semiconducting MnB<inf>4</inf> is accompanied by a p-n transition. 55Mn NMR spectroscopy confirmed the oxidation state I of the metal atom, and nanoindentation experiments resulted in hardness values that are in accordance with DFT calculations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201406631
  • 2015 • 86 Mullite: Crystal Structure and Related Properties
    Schneider, H. and Fischer, R.X. and Schreuer, J.
    Journal of the American Ceramic Society 98 2948-2967 (2015)
    Mullite is certainly one of the most important oxide materials for both conventional and advanced ceramics. Mullite belongs to the compositional series of orthorhombic aluminosilicates with the general composition Al2(Al2+2xSi2-2x)O10-x. Main members are sillimanite (x = 0), stoichiometric 3/2-mullite (x = 0.25), 2/1-mullite (x = 0.40), and the SiO2-free phase ι-alumina (x = 1, crystal structure not known). This study gives an overview on the present state of research regarding single crystal mullite. Following a short introduction, the second part of the review focuses on the crystal structure of mullite. In particular, the characteristic mullite-type structural backbone of parallel chains consisting of edge-sharing MO6 octahedra and their specific cross-linkage by TO4 tetrahedra is explained in detail, the role of cation disorder and structural oxygen vacancies is addressed, and the possibility of cation substitution on different sites is discussed. The third part of the study deals with physical properties being relevant for technical applications of mullite and includes mechanical properties (e.g., elasticity, compressibility, strength, toughness, creep), thermal properties (e.g., thermal expansion, heat capacity, atomic diffusion, thermal conductivity), electrical conductivity, and optical properties. Special emphasis is put on structure-property relationships which allow for interpretation of corresponding experimental data and offer in turn the possibility to tailor new mullite materials with improved properties. Finally, the reported anomalies and discontinuities in the evolution of certain physical properties with temperature are summarized and critically discussed. © 2015 The American Ceramic Society.
    view abstractdoi: 10.1111/jace.13817
  • 2015 • 85 Neuritogenic Militarinone-Inspired 4-Hydroxypyridones Target the Stress Pathway Kinase MAP4K4
    Schröder, P. and Förster, T. and Kleine, S. and Becker, C. and Richters, A. and Ziegler, S. and Rauh, D. and Kumar, K. and Waldmann, H.
    Angewandte Chemie - International Edition 54 12398-12403 (2015)
    Progressive loss and impaired restoration of neuronal activity are hallmarks of neurological diseases, and new small molecules with neurotrophic activity are in high demand. The militarinone alkaloids and structurally simplified analogues with 4-hydroxy-2-pyridone core structure induce pronounced neurite outgrowth, but their protein target has not been identified. Reported herein is the synthesis of a militarinone-inspired 4-hydroxy-2-pyridone collection, its investigation for enhancement of neurite outgrowth, and the discovery of the stress pathway kinase MAP4K4 as a target of the discovered neuritogenic pyridones. The most potent 4-hydroxy-2-pyridone is a selective ATP-competitive inhibitor of MAP4K4 but not of the other stress pathway related kinases, as proven by biochemical analysis and by a crystal structure of the inhibitor in complex with MAP4K4. The findings support the notion that MAP4K4 may be a new target for the treatment of neurodegenerative diseases. No stress: Reported herein is the synthesis of a militarinone-inspired 4-hydroxy-2-pyridone collection, its investigation for enhancement of neurite outgrowth, and the discovery of the stress pathway kinase MAP4K4 as a target of the discovered neuritogenic pyridones. The findings support the notion that MAP4K4 may be a new target for the treatment of neurodegenerative diseases. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201501515
  • 2015 • 84 Predicting the Solubility Advantage of Amorphous Pharmaceuticals: A Novel Thermodynamic Approach
    Paus, R. and Ji, Y. and Vahle, L. and Sadowski, G.
    Molecular Pharmaceutics 12 2823-2833 (2015)
    For the solubility and bioavailability of poorly soluble active pharmaceutical ingredients (APIs) to be improved, the transformation of crystalline APIs to the amorphous state has often been shown to be advantageous. As it is often difficult to measure the solubility of amorphous APIs, the application of thermodynamic models is the method of choice for determining the solubility advantage. In this work, the temperature-dependent solubility advantage of an amorphous API versus its crystalline form was predicted for five poorly soluble APIs in water (glibenclamide, griseofulvin, hydrochlorothiazide, indomethacin, and itraconazole) based on modeling the API/solvent phase diagrams using the perturbed-chain statistical associating fluid theory (PC-SAFT). Evaluation of the performance of this approach was performed by comparing the predicted solubility advantage to experimental data and to the solubility advantage calculated by the commonly applied Gibbs-energy-difference method. For all of the systems considered, PC-SAFT predictions of the solubility advantage are significantly more accurate than the results obtained from the Gibbs-energy-difference method. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/mp500824d
  • 2015 • 83 Synthesis and X-ray Crystal Structure of Diimidosulfinate Transition Metal Complexes
    Bayram, M. and Bläser, D. and Wölper, C. and Schulz, S.
    Organometallics 34 3421-3427 (2015)
    Bis(trimethylsilyl)sulfurdiimide S(NSiMe3)2 reacts with equimolar amounts of Me2Zn and Cp∗2Zn either with insertion into the metal-carbon bond and formation of the expected S-methyl diimidosulfinate complex [MeZnN(SiMe3)S(Me)NSiMe3]2 1 or the unexpected complex {Me3SiNS[N(SiMe3)SNSiMe3]N(SiMe3)Zn}2 2. Insertion reactions were also observed with Cp∗MMe3 (M = Ti, Zr, Hf), yielding Cp∗(Me)2M[Me3SiNS(Me)NSiMe3] (M = Ti 3, Zr 4, Hf 5), whereas the corresponding Cl-substituted derivatives Cp∗(Cl)2M[(Me3SiNS(Me)NSiMe3] (M = Ti 6, Zr 7, Hf 8) were obtained from salt elimination reactions of Li S-methyl diimidosulfinate (Me3SiN)2S(Me)Li(thf)]2 9 with Cp∗MCl3. Compounds 1-8 were characterized by heteronuclear NMR (1H and 13C) and IR spectroscopy, and the solid state structures of 1-5 and 9 were determined by single crystal X-ray diffraction. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.organomet.5b00407
  • 2015 • 82 Synthesis, morphology and structure of the dense (Y1-xEux)2O3 spherical shape particles
    Bezkrovnyi, O.S. and Matveevskaya, N.A. and Yermolayeva, Y.V. and Tolmachev, A.V. and Prymak, O. and Epple, M. and Baumer, V.N.
    Crystal Research and Technology 50 621-625 (2015)
    The method to decrease of the porosity (densification) of crystalline spherical particles of the solid substitution solution, obtained by the method of precipitation from aqueous solution followed by low temperature crystallization of the amorphous intermediate product was proposed. The comparative analysis of morphology and structure of the particles before and after densification have been carried. It has been established that porosity of (Y<inf>1-x</inf>Eu<inf>x</inf>)<inf>2</inf>O<inf>3</inf> particles has decreased 5 times compared to their initial state. It has been shown that densification process of the (Y<inf>1-x</inf>Eu<inf>x</inf>)<inf>2</inf>O<inf>3</inf> spherical particles changes their morphology and structure: the size of the crystals doubles, the number and area of crystalline boundaries decrease, the intercrystalline spaces, which forming pores, are almost absent. The dense (Y<inf>1-x</inf>Eu<inf>x</inf>)<inf>2</inf>O<inf>3</inf>(x=0-0,1) isolated spherical particles of 120-300 nm in diameter and dispersion less than 15 % by size, with the porosity 5 times lower, compared to the initial spherical particles of (Y<inf>1-x</inf>Eu<inf>x</inf>)<inf>2</inf>O<inf>3</inf>, were obtained for the first time. It was established that in the process of the densification of porous spherical particles their morphology and structure state are improved: intercrystalline spaces are almost absent, the size of the crystals doubles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/crat.201500026
  • 2015 • 81 Targeting Drug Resistance in EGFR with Covalent Inhibitors: A Structure-Based Design Approach
    Engel, J. and Richters, A. and Getlik, M. and Tomassi, S. and Keul, M. and Termathe, M. and Lategahn, J. and Becker, C. and Mayer-Wrangowski, S. and Grütter, C. and Uhlenbrock, N. and Krüll, J. and Schaumann, N. and Eppmann, S. ...
    Journal of Medicinal Chemistry 58 6844-6863 (2015)
    Receptor tyrosine kinases represent one of the prime targets in cancer therapy, as the dysregulation of these elementary transducers of extracellular signals, like the epidermal growth factor receptor (EGFR), contributes to the onset of cancer, such as non-small cell lung cancer (NSCLC). Strong efforts were directed to the development of irreversible inhibitors and led to compound CO-1686, which takes advantage of increased residence time at EGFR by alkylating Cys797 and thereby preventing toxic effects. Here, we present a structure-based approach, rationalized by subsequent computational analysis of conformational ligand ensembles in solution, to design novel and irreversible EGFR inhibitors based on a screening hit that was identified in a phenotype screen of 80 NSCLC cell lines against approximately 1500 compounds. Using protein X-ray crystallography, we deciphered the binding mode in engineered cSrc (T338M/S345C), a validated model system for EGFR-T790M, which constituted the basis for further rational design approaches. Chemical synthesis led to further compound collections that revealed increased biochemical potency and, in part, selectivity toward mutated (L858R and L858R/T790M) vs nonmutated EGFR. Further cell-based and kinetic studies were performed to substantiate our initial findings. Utilizing proteolytic digestion and nano-LC-MS/MS analysis, we confirmed the alkylation of Cys797. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jmedchem.5b01082
  • 2015 • 80 Thermal dissolution mechanisms of AlN/CrN hard coating superlattices studied by atom probe tomography and transmission electron microscopy
    Tytko, D. and Choi, P.-P. and Raabe, D.
    Acta Materialia 85 32-41 (2015)
    AlN/CrN superlattices with a B1 cubic crystal structure and a bilayer period of 4 nm were deposited by reactive radiofrequency magnetron sputtering. The coatings were investigated with respect to their thermal stability and changes in microstructure and chemical composition at 900 °C. The AlN layers show high chemical stability but undergo dissolution by pinching off at grain boundaries. A transformation from cubic to hexagonal AlN with subsequent coarsening at grain boundary triple junctions is observed. In contrast to AlN, the CrN layers show poor chemical stability and their compositions are shifted towards Cr2N upon annealing in a protective argon atmosphere due to nitrogen loss. However, even after establishing Cr2N stoichiometry the crystal structure of the layers remains cubic. © 2014 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2014.11.004
  • 2015 • 79 Vanadium-based polyoxometalate as new material for sodium-ion battery anodes
    Hartung, S. and Bucher, N. and Chen, H.-Y. and Al-Oweini, R. and Sreejith, S. and Borah, P. and Yanli, Z. and Kortz, U. and Stimming, U. and Hoster, H.E. and Srinivasan, M.
    Journal of Power Sources 288 270-277 (2015)
    Affordable energy storage is crucial for a variety of technologies. One option is sodium-ion batteries (NIBs) for which, however, suitable anode materials are still a problem. We report on the application of a promising new class of materials, polyoxometalates (POMs), as an anode in NIBs. Specifically, Na6[V10O28]·16H2O is being synthesized and characterized. Galvanostatic tests reveal a reversible capacity of approximately 276 mA h g-1 with an average discharge potential of 0.4 V vs. Na/Na+, as well as a high cycling stability. The underlying mechanism is rationalized to be an insertion of Na+ in between the [V10O28]6- anions rather than an intercalation into a crystal structure; the accompanying reduction of V+V to V+IV is confirmed by X-ray Photoelectron Spectroscopy. Finally, a working full-cell set-up is presented with the POM as the anode, substantiating the claim that Na6[V10O28]·16H2O is a promising option for future high-performing sodium-ion batteries. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jpowsour.2015.04.009
  • 2015 • 78 Visualization of nanocrystal breathing modes at extreme strains
    Szilagyi, E. and Wittenberg, J.S. and Miller, T.A. and Lutker, K. and Quirin, F. and Lemke, H. and Zhu, D. and Chollet, M. and Robinson, J. and Wen, H. and Sokolowski-Tinten, K. and Lindenberg, A.M.
    Nature Communications 6 (2015)
    Nanoscale dimensions in materials lead to unique electronic and structural properties with applications ranging from site-specific drug delivery to anodes for lithium-ion batteries. These functional properties often involve large-amplitude strains and structural modifications, and thus require an understanding of the dynamics of these processes. Here we use femtosecond X-ray scattering techniques to visualize, in real time and with atomic-scale resolution, light-induced anisotropic strains in nanocrystal spheres and rods. Strains at the percent level are observed in CdS and CdSe samples, associated with a rapid expansion followed by contraction along the nanosphere or nanorod radial direction driven by a transient carrier-induced stress. These morphological changes occur simultaneously with the first steps in the melting transition on hundreds of femtosecond timescales. This work represents the first direct real-time probe of the dynamics of these large-amplitude strains and shape changes in few-nanometre-scale particles. © 2015 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/ncomms7577
  • 2014 • 77 A molecular iron catalyst for the acceptorless dehydrogenation and hydrogenation of N-heterocycles
    Chakraborty, S. and Brennessel, W.W. and Jones, W.D.
    Journal of the American Chemical Society 136 8564-8567 (2014)
    A well-defined iron complex (3) supported by a bis(phosphino)amine pincer ligand efficiently catalyzes both acceptorless dehydrogenation and hydrogenation of N-heterocycles. The products from these reactions are isolated in good yields. Complex 3, the active catalytic species in the dehydrogenation reaction, is independently synthesized and characterized, and its structure is confirmed by X-ray crystallography. A trans-dihydride intermediate (4) is proposed to be involved in the hydrogenation reaction, and its existence is verified by NMR and trapping experiments. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/ja504523b
  • 2014 • 76 A new method for development of bond-order potentials for transition bcc metals
    Lin, Y.-S. and Mrovec, M. and Vitek, V.
    Modelling and Simulation in Materials Science and Engineering 22 (2014)
    A new development of numerical bond-order potentials (BOPs) for the non-magnetic transition metals V, Nb, Ta, Cr, Mo and W is presented. The principles on which the BOPs have been set up are the same as in earlier developments (Aoki et al 2007 Prog. Mater. Sci. 52 154). However, the bond integrals are based on the recently advanced method of parametrization of tight-binding from DFT calculations (Madsen et al 2011 Phys. Rev. B 83 4119, Urban et al 2011 Phys. Rev. B 84 155119) and do not require any screening. At the same time, the functional form of the environmentally dependent repulsion is identified with the functional form of the repulsion arising from the overlap of s and p electrons in argon as proposed in Aoki and Kurokawa (2007 J. Phys.: Condens. Matter 19 136228). This is justified by the same physical origin of the environment dependent repulsion, which in transition metals arises from the overlap of s electrons that are being squeezed into the ion core regions under the influence of the strong covalent d bonds. The testing of the developed BOPs involves investigation of alternative higher energy structures, transformation paths connecting the bcc structure with other structures via continuously distorted configurations, evaluation of the vacancy formation energy and calculation of phonon spectra. In all cases, the BOP calculations are in more than satisfactory agreement with either DFT calculations and/or available experimental data. The calculated γ-surfaces for {1 0 1} planes all suggest that the core of 1/21 1 1 screw dislocations is non-degenerate in the transition metals. This is also in full agreement with available calculations that account fully for the quantum-mechanical nature of the d electrons that provide the bulk of the bonding in transition metals. The testing of developed BOPs clearly demonstrates that they are transferable to structures well outside the regime of the ideal bcc lattice and are suitable for investigating the atomic structure and behaviour of extended crystal defects. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0965-0393/22/3/034002
  • 2014 • 75 Aluminum-doped ZnO nanoparticles: Gas-phase synthesis and dopant location
    Schilling, C. and Zähres, M. and Mayer, C. and Winterer, M.
    Journal of Nanoparticle Research 16 (2014)
    Aluminum-doped ZnO (AZO) nanoparticles are studied widely as transparent conducting alternatives for indium tin oxide. However, the properties of AZO vary in different investigations not only with the amount of dopant and the particle size, but also with other parameters such as synthesis method and conditions. Hence, AZO nanoparticles, synthesized in the gas phase, were investigated to study the influence of the synthesis parameters dopant level, reactor temperature and residence time in the reaction zone on the particle characteristics. The local structure of the dopant in semiconductors determines whether the doping is functional, i.e., whether mobile charge carriers are generated. Therefore, information obtained from 27Al solid-state NMR spectroscopy, X-ray diffraction, photoluminescence and UV-Vis spectroscopy was used to understand how the local structure influences particles characteristics and how the local structure itself can be influenced by the synthesis parameters. In addition to AZO particles of different Al content, pure ZnO, Al2O3, ZnAl2O4 and core-shell particles of ZnO and Al2O3 were synthesized for comparison and aid to a deeper understanding of the formation of AZO nanoparticles in the gas phase. © 2014 Springer Science+Business Media.
    view abstractdoi: 10.1007/s11051-014-2506-z
  • 2014 • 74 Amine-based solvents for exfoliating graphite to graphene outperform the dispersing capacity of N-methyl-pyrrolidone and surfactants
    Sun, Z. and Huang, X. and Liu, F. and Yang, X. and Rösler, C. and Fischer, R.A. and Muhler, M. and Schuhmann, W.
    Chemical Communications 50 10382-10385 (2014)
    Four organic amine-based solvents were discovered which enable direct exfoliation of graphite to produce high-quality and oxygen-free graphene nanosheets. These solvents outperform previously used solvents and additives such as N-methyl-pyrrolidone and surfactants in terms of their dispersing capacity. The resulting dispersions allow the facile fabrication of zeolitic imidazolate framework (ZIF)-graphene nanocomposites with remarkable CO 2 storage capability. This journal is © the Partner Organisations 2014.
    view abstractdoi: 10.1039/c4cc03923h
  • 2014 • 73 Analytic bond-order potentials for the bcc refractory metals Nb, Ta, Mo and W
    Čák, M. and Hammerschmidt, T. and Rogal, J. and Vitek, V. and Drautz, R.
    Journal of Physics Condensed Matter 26 (2014)
    Bond-order potentials (BOPs) are based on the tight-binding approximation for determining the energy of a system of interacting atoms. The bond energy and forces are computed analytically within the formalism of the analytic BOPs. Here we present parametrizations of the analytic BOPs for the bcc refractory metals Nb, Ta, Mo and W. The parametrizations are optimized for the equilibrium bcc structure and tested for atomic environments far from equilibrium that had not been included in the fitting procedure. These tests include structural energy differences for competing crystal structures; tetragonal, trigonal, hexagonal and orthorhombic deformation paths; formation energies of point defects as well as phonon dispersion relations. Our tests show good agreement with available experimental and theoretical data. In practice, we obtain the energetic ordering of vacancy, [1 1 1], [1 1 0], and [1 0 0] self-interstitial atom in agreement with density functional theory calculations. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/26/19/195501
  • 2014 • 72 Anisotropy of electromigration-induced void and island drift
    Latz, A. and Sindermann, S.P. and Brendel, L. and Dumpich, G. and Meyer zu Heringdorf, F.-J. and Wolf, D.E.
    Journal of Physics Condensed Matter 26 (2014)
    By means of our novel self-learning kinetic Monte Carlo model (Latz et al 2012 J. Phys.: Condens. Matter 24 485005) we study the electromigration-induced drift of monolayer voids and islands on unpassivated surfaces of single crystalline Ag(111) and Ag(001) films at the atomic scale. Regarding the drift velocity, we find a non-monotonic size dependence for small voids. The drift direction is aligned with the electromigration force only along high symmetry directions, while halfway between, the angle enclosed by them is maximal. The magnitude of these directional deviations strongly depends on the system parameter, which are investigated in detail. The simulation results are in accordance with void motion observed in experiments performed on Ag(111). © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/26/5/055005
  • 2014 • 71 Charge order and its connection with fermi-liquid charge transport in a pristine high-Tc cuprate
    Tabis, W. and Li, Y. and Le Tacon, M. and Braicovich, L. and Kreyssig, A. and Minola, M. and Dellea, G. and Weschke, E. and Veit, M.J. and Ramazanoglu, M. and Goldman, A.I. and Schmitt, T. and Ghiringhelli, G. and Barišić, N. an...
    Nature Communications 5 (2014)
    Electronic inhomogeneity appears to be an inherent characteristic of the enigmatic cuprate superconductors. Here we report the observation of charge–density–wave correlations in the model cuprate superconductor HgBa2CuO4 + d (Tc = 72 K) via bulk Cu L3-edge-resonant X-ray scattering. At the measured hole-doping level, both the short-range charge modulations and Fermi-liquid transport appear below the same temperature of about 200 K. Our result points to a unifying picture in which these two phenomena are preceded at the higher pseudogap temperature by q = 0 magnetic order and the build-up of significant dynamic antiferromagnetic correlations. The magnitude of the charge modulation wave vector is consistent with the size of the electron pocket implied by quantum oscillation and Hall effect measurements for HgBa2CuO4 + d and with corresponding results for YBa2Cu3O6 + d, which indicates that charge–density–wave correlations are universally responsible for the low-temperature quantum oscillation phenomenon. © 2014 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/ncomms6875
  • 2014 • 70 Correlating structure and ligand affinity in drug discovery: A cautionary tale involving second shell residues
    Tziridis, A. and Rauh, D. and Neumann, P. and Kolenko, P. and Menzel, A. and Bräuer, U. and Ursel, C. and Steinmetzer, P. and Stürzebecher, J. and Schweinitz, A. and Steinmetzer, T. and Stubbs, M.T.
    Biological Chemistry 395 891-903 (2014)
    A high-resolution crystallographic structure determination of a protein-ligand complex is generally accepted as the 'gold standard' for structure-based drug design, yet the relationship between structure and affinity is neither obvious nor straightforward. Here we analyze the interactions of a series of serine proteinase inhibitors with trypsin variants onto which the ligand-binding site of factor Xa has been grafted. Despite conservative mutations of only two residues not immediately in contact with ligands (second shell residues), significant differences in the affinity profiles of the variants are observed. Structural analyses demonstrate that these are due to multiple effects, including differences in the structure of the binding site, differences in target flexibility and differences in inhibitor binding modes. The data presented here highlight the myriad competing microscopic processes that contribute to protein-ligand interactions and emphasize the difficulties in predicting affinity from structure.
    view abstractdoi: 10.1515/hsz-2014-0158
  • 2014 • 69 Electrical conductivity of synthetic mullite single crystals
    Malki, M. and Schreuer, J. and Schneider, H.
    American Mineralogist 99 1104-1108 (2014)
    The electrical conductivity of 2/1-mullite (approximate composition 2Al2O3 •SiO2) was measured using plane parallel, polished plates cut perpendicular to [100], [010], and [001] from a large single crystal grown by the Czochralski method. Impedance spectra were recorded in the 1 Hz to 1 MHz frequency range at temperatures from 550 to 1400 °C in air. The conductivity vs. temperature curves display changes of their slope between 850 and 950 °C depending on the crystallographical direction. The low-temperature region (T < 850 °C) of conductivity is characterized by low-electrical conductivities (σav ≈ 5.4 × 10 -9 Ω-1cm-1, average conductivity at 550 °C) with σ[010] &gt; σ[100] &gt; σ[001] and low-activation energies (≈0.66 eV, average value). In the high-temperature region (T &gt; 950 °C) the electrical conductivity is significantly higher (σav ≈ 1.1 × 10-5 Ω-1cm-1, average conductivity at 1400 °C) with σ[001] &gt; σ[100] ≈ σ[010], and with higher activation energies (≈1.6 eV). While the conductivity in the low-temperature region essentially is electronic, ion conductivity dominates the conductivity in the high-temperature region. We believe that the ionic conductivity is essentially due to hopping of O atoms from structural sites linking the tetrahedral double chains in mullite toward adjacent oxygen vacancies especially in c-axis direction. These oxygen hoppings are associated with complex structural re-arrangements, which control and slow down the velocity of the processes. Thus the electrical conductivity of mullite at high temperature is much lower than, e.g., that of Y-doped zirconia, but is significantly higher than that of a-alumina.
    view abstractdoi: 10.2138/am.2014.4442
  • 2014 • 68 Fetuin-A and albumin alter cytotoxic effects of calcium phosphate nanoparticles on human vascular smooth muscle cells
    Dautova, Y. and Kozlova, D. and Skepper, J.N. and Epple, M. and Bootman, M.D. and Proudfoot, D.
    PLoS ONE 9 (2014)
    Calcification is a detrimental process in vascular ageing and in diseases such as atherosclerosis and arthritis. In particular, small calcium phosphate (CaP) crystal deposits are associated with inflammation and atherosclerotic plaque de-stabilisation. We previously reported that CaP particles caused human vascular smooth muscle cell (VSMC) death and that serum reduced the toxic effects of the particles. Here, we found that the serum proteins fetuin-A and albumin (≥1 μM) reduced intracellular Ca2+ elevations and cell death in VSMCs in response to CaP particles. In addition, CaP particles functionalised with fetuin-A, but not albumin, were less toxic than naked CaP particles. Electron microscopic studies revealed that CaP particles were internalised in different ways; via macropinocytosis, membrane invagination or plasma membrane damage, which occurred within 10 minutes of exposure to particles. However, cell death did not occur until approximately 30 minutes, suggesting that plasma membrane repair and survival mechanisms were activated. In the presence of fetuin-A, CaP particle-induced damage was inhibited and CaP/plasma membrane interactions and particle uptake were delayed. Fetuin-A also reduced dissolution of CaP particles under acidic conditions, which may contribute to its cytoprotective effects after CaP particle exposure to VSMCs. These studies are particularly relevant to the calcification observed in blood vessels in patients with kidney disease, where circulating levels of fetuin-A and albumin are low, and in pathological situations where CaP crystal formation outweighs calcification-inhibitory mechanisms. © 2014 Dautova et al.
    view abstractdoi: 10.1371/journal.pone.0097565
  • 2014 • 67 Giant magnetic anisotropy and tunnelling of the magnetization in Li 2(Li1-xFex)N
    Jesche, A. and McCallum, R.W. and Thimmaiah, S. and Jacobs, J.L. and Taufour, V. and Kreyssig, A. and Houk, R.S. and Bud'Ko, S.L. and Canfield, P.C.
    Nature Communications 5 (2014)
    Large magnetic anisotropy and coercivity are key properties of functional magnetic materials and are generally associated with rare earth elements. Here we show an extreme, uniaxial magnetic anisotropy and the emergence of magnetic hysteresis in Li2(Li1-xFex)N. An extrapolated, magnetic anisotropy field of 220 T and a coercivity field of over 11 T at 2 K outperform all known hard ferromagnets and single-molecular magnets. Steps in the hysteresis loops and relaxation phenomena in striking similarity to single-molecular magnets are particularly pronounced for x 1 and indicate the presence of nanoscale magnetic centres. Quantum tunnelling, in the form of temperature-independent relaxation and coercivity, deviation from Arrhenius behaviour and blocking of the relaxation, dominates the magnetic properties up to 10 K. The simple crystal structure, the availability of large single crystals and the ability to vary the Fe concentration make Li2(Li 1-xFex)N an ideal model system to study macroscopic quantum effects at elevated temperatures and also a basis for novel functional magnetic materials. © 2014 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/ncomms4333
  • 2014 • 66 Local determination of the amount of integration of an atom into a crystal surface
    Volgmann, K. and Gawronski, H. and Zaum, C. and Rusina, G.G. and Borisova, S.D. and Chulkov, E.V. and Morgenstern, K.
    Nature Communications 5 (2014)
    Collective vibrational modes of crystal lattices, called phonons, determine fundamental material properties, such as their thermal and electrical conductivities. Bulk phonon spectra are influenced by point defects. More recently, the importance of phonons on nanostructures has come into the focus of attention. Here we show a spatially resolved phonon spectra of point defects that reveal distinctly different signatures for a cavity alone and an impurity atom fully integrated into the surface as opposed to one placed into a cavity. The spectra are indicative for delocalized phonons and localized vibrations, respectively, as confirmed by theory. © 2014 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/ncomms6089
  • 2014 • 65 Nanocrystalline barium strontium titanate ceramics synthesized via the "organosol" route and spark plasma sintering
    Gao, Y. and Shvartsman, V.V. and Gautam, D. and Winterer, M. and Lupascu, D.C.
    Journal of the American Ceramic Society 97 2139-2146 (2014)
    Dense nanocrystalline barium strontium titanate Ba0.6Sr 0.4TiO3 (BST) ceramics with an average grain size around 40 nm and very small dispersion were obtained by spark plasma sintering at 950°C and 1050°C starting from nonagglomerated nanopowders (~20 nm). The powders were synthesized by a modified "Organosol" process. X-ray diffraction (XRD) and dielectric measurements in the temperature range 173-313 K were used to investigate the evolution of crystal structure and the ferroelectric to paraelectric phase transformation behavior for the sintered BST ceramics with different grain sizes. The Curie temperature TC decreases, whereas the phase transition becomes diffuse for the particle size decreasing from about 190 to 40 nm with matching XRD and permittivity data. Even the ceramics with an average grain size as small as 40 nm show the transition into the ferroelectric state. The dielectric permittivity ε shows relatively good thermal stability over a wide temperature range. The dielectric losses are smaller than 2%-4% in the frequency range of 100 Hz-1 MHz and temperature interval 160-320 K. A decrease in the dielectric permittivity in nanocrystalline ceramics was observed compared to submicrometer-sized ceramics. © 2014 The American Ceramic Society.
    view abstractdoi: 10.1111/jace.12933
  • 2014 • 64 Synthesis of 7-pentafluorophenyl-1 H -indole: An anion receptor for anion-π interactions
    Sun, Z.-H. and Albrecht, M. and Giese, M. and Pan, F. and Rissanen, K.
    Synlett 25 2075-2077 (2014)
    7-Pentafluorophenyl-1H-indole has the potential to be a key compound for the investigation of anion-π interactions in solution. Unfortunately, it was not possible to obtain it by aryl-aryl coupling reaction. Finally, it has been prepared by Bartoli indole synthesis. The key compound as well as analogues were submitted to preliminary studies of anion binding. Single crystals of two key receptors were obtained. © Georg Thieme Verlag Stuttgart New York.
    view abstractdoi: 10.1055/s-0034-1378449
  • 2014 • 63 Synthesis, characterization, and nanoindentation response of single crystal Fe-Cr-Ni alloys with FCC and BCC structures
    Xia, Y.Z. and Bei, H. and Gao, Y.F. and Catoor, D. and George, E.P.
    Materials Science and Engineering A 611 177-187 (2014)
    Fe-based alloys are used extensively in many structural applications including under irradiation conditions in the nuclear industry. In this study, model Fe-Cr, Fe-Ni and Fe-Cr-Ni alloys that are the basis of many structural steels were synthesized as single crystals and characterized. The compositions investigated were Fe-15Cr, Fe-30Cr, Fe-30Ni and Fe-15Cr-15Ni (at%). Several key mechanical properties were determined which will be useful in further studies of irradiation/deformation-induced defects. Incipient plasticity and slip characteristics were investigated by nanoindentation on (001) and (1-10) surfaces, and hardness, modulus, pop-in behavior and theoretical strength were determined. The slip trace patterns after microindentation were imaged in a microscope. A novel slip trace analysis was developed and the underlying deformation mechanisms identified. The analysis shows that under both (001) and (1-10) indentations, the activated slip system for the BCC alloys is {112} for the FCC alloys the activated slip plane is {111}. These results were confirmed with finite element simulations using a slip-based crystal-plasticity model. Finally, the effects of heterogeneous pop-in mechanisms are discussed in the context of incipient plasticity in the four different alloys. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2014.05.079
  • 2013 • 62 A Z′ = 6 crystal structure of (E)-N,N′-dicyclohexylacetamidine
    Krasnopolski, M. and Seidel, R.W. and Goddard, R. and Breidung, J. and Winter, M.V. and Devi, A. and Fischer, R.A.
    Journal of Molecular Structure 1031 239-245 (2013)
    The crystal and molecular structure of (E)-N,N′- dicyclohexylacetamidine (1) is described. Crystalline material of 1 was obtained by sublimation. Single-crystal X-ray analysis revealed a centrosymmetric triclinic structure (space group P1̄) with six molecules in the asymmetric unit (Z′ = 6). The six crystallographically distinct molecules all exhibit an E-syn structure, but differ in the orientation of the cyclohexyl groups about the central acetamidine moiety. In the crystal, the molecules form polymeric helices via NH⋯N hydrogen bonds. The crystal structure comprises two crystallographically distinct helices of opposite handedness (P and M form). The characterisation of 1 in the solid-state is augmented by powder X-ray diffraction, infrared spectroscopy and thermal analysis. Density functional theory (DFT) structure optimisation and frequency calculation were performed at the B3LYP/cc-pVTZ level. The DFT results for the isolated molecule are compared with the experimental results for the solid-state. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.molstruc.2012.10.003
  • 2013 • 61 Ab Initio Based conformational study of the crystalline α-chitin
    Petrov, M. and Lymperakis, L. and Friák, M. and Neugebauer, J.
    Biopolymers 99 22-34 (2013)
    The equilibrium structure including the network of hydrogen bonds of an α-chitin crystal is determined combining density-functional theory (DFT), self-consistent DFT-based tight-binding (SCC-DFTB), and empirical forcefield molecular dynamics (MD) simulations. Based on the equilibrium geometry several possible crystal conformations (local energy minima) have been identified and related to hydrogen bond patterns. Our results provide new insight and allow to resolve the contradicting α-chitin structural models proposed by various experiments. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/bip.22131
  • 2013 • 60 Anion-π interaction: An influential force in solid state molecular microstructures
    Giese, M. and Albrecht, M. and Valkonen, A. and Rissanen, K.
    European Journal of Organic Chemistry 3247-3253 (2013)
    The crystal structures of simple triphenyl(pentafluorobenzyl)phosphonium salts provide crucial data on the influence of anion size on the molecular structure of bis(pentafluorobenzyl)phosphonium cations containing two adjacent electron-deficient moieties. Whereas the bromide anions interact by anion-π interaction in a 1:1 mode with the pentafluorobenzene unit Z-configured, the bulkier anions iodide, tetrafluoroborate, and hexafluorophosphate result in a 1:2 tweezer-like anti-configuration in which one anion interacts simultaneously with two pentafluorobenzene units. When spatial separation of the two electron-deficient rings match the size of the anion, anion-π interactions induce a conformational change from the anti-form observed for the smaller anion to the tweezer-like syn-form. The solid-state structures of a series of bis(pentafluorobenzyl)phosphonium salts reveal the crucial relevance of anion size in anion-π interactions, leading to conformational control. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ejoc.201201704
  • 2013 • 59 Composition-dependent crystal structure and martensitic transformation in Heusler Ni-Mn-Sn alloys
    Zheng, H. and Wang, W. and Xue, S. and Zhai, Q. and Frenzel, J. and Luo, Z.
    Acta Materialia 61 4648-4656 (2013)
    In the present work, modulated four- and five-layered orthorhombic, seven-layered monoclinic (4O, 10M and 14M) and unmodulated double tetragonal (L10) martensites are characterized in Heusler Ni-Mn-Sn alloys using X-ray diffraction, high-resolution transmission electron microscopy, electron diffraction techniques and thermal analysis. All modulated layered martensites exhibit twins and stacking faults, while the L10 martensite shows fewer structural defects. The substitution of Sn with Mn in Ni 50Mn37+xSn13-x (x = 0, 2, 4) enhances the martensitic transition temperatures, while the transition temperatures decrease with increasing Mn content for constant Sn levels in Ni50-yMn37+ySn13 (y = 0, 2, 4). The compositional dependence of the martensitic transition temperatures is mainly attributed to the valence electron concentration (e/a) and the unit-cell volume of the high-temperature phase. With increasing transition temperatures (or e/a), the resultant martensitic crystal structure evolves in a sequence of 4O → 10M → 14M → L10 in bulk Ni-Mn-Sn alloys. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2013.04.035
  • 2013 • 58 CsNaC2, CsKC2, CsRbC2 -syntheses and crystal structures of three new acetylides
    Liebig, S. and Paulus, M. and Sternemann, C. and Ruschewitz, U.
    Zeitschrift fur Anorganische und Allgemeine Chemie 639 2804-2808 (2013)
    Three new alkali metal acetylides CsNaC2, CsKC2, and CsRbC2 have been synthesized and characterized by means of synchrotron powder diffraction studies. As a new synthetic approach, the binary alkali metal acetylides were reacted at relatively low temperatures (200 °C). DSC measurements were performed to prove the general usability of this reaction. CsKC2 and CsRbC2 crystallize in a variant of the anti-PbCl2-type structure (Pnma, Z = 4), while for CsNaC2 a new structure type (Pbcm, Z = 4) is found. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/zaac.201300147
  • 2013 • 57 Direct gas-phase synthesis of single-phase β-FeSi2 nanoparticles
    Bywalez, R. and Orthner, H. and Mehmedovic, E. and Imlau, R. and Kovacs, A. and Luysberg, M. and Wiggers, H.
    Journal of Nanoparticle Research 15 (2013)
    For the first time, phase-pure β-FeSi2 nanoparticles were successfully produced by gas-phase synthesis. We present a method to fabricate larger quantities of semiconducting β-FeSi2 nanoparticles, with crystallite sizes between 10 and 30 nm, for solar and thermoelectric applications utilizing a hot-wall reactor. A general outline for the production of those particles by thermal decomposition of silane and iron pentacarbonyl is provided based on kinetic data. The synthesized particles are investigated by X-ray diffraction and transmission electron microscopy, providing evidence that the as-prepared materials are indeed β-FeSi2, while revealing morphological characteristics inherent to the nanoparticles created. © 2013 Springer Science+Business Media.
    view abstractdoi: 10.1007/s11051-013-1878-9
  • 2013 • 56 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 • 55 Metabolically stable dibenzo[ b, e ]oxepin-11(6 H)-ones as highly selective p38 MAP kinase inhibitors: Optimizing anti-cytokine activity in human whole blood
    Baur, B. and Storch, K. and Martz, K.E. and Goettert, M.I. and Richters, A. and Rauh, D. and Laufer, S.A.
    Journal of Medicinal Chemistry 56 8561-8578 (2013)
    Five series of metabolically stable disubstituted dibenzo[b,e]oxepin-11(6H) -ones were synthesized and tested in a p38α enzyme assay for their inhibition of tumor necrosis factor-α (TNF-α) release in human whole blood. Compared to the monosubstituted dibenzo[b,e]oxepin-11(6H)-one derivatives, it has been shown that the additional introduction of hydrophilic residues at position 9 leads to a substantial improvement of the inhibitory potency and metabolic stability. Using protein X-ray crystallography, the binding mode of the disubstituted dibenzoxepinones and the induction of a glyince flip in the hinge region were confirmed. The most potent compound of this series, 32e, shows an outstanding biological activity on isolated p38α, with an IC50 value of 1.6 nM, extraordinary selectivity (by a factor &gt;1000, Kinase WholePanelProfiler), and low ATP competitiveness. The ability to inhibit the release of TNF-α from human whole blood was optimized down to an IC50 value of 125 nM. With the promising dibenzoxepinone inhibitor 3i, a pharmacokinetic study in mice was conducted. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/jm401276h
  • 2013 • 54 Solid dispersions prepared by continuous cogrinding in an air jet mill
    Muehlenfeld, C. and Kann, B. and Windbergs, M. and Thommes, M.
    Journal of Pharmaceutical Sciences 102 4132-4139 (2013)
    Embedding a poorly water-soluble drug as a solid dispersion in a hydrophilic carrier by cogrinding is a possible strategy for enhancing the drug dissolution rate. Although general interest in continuous processes for manufacturing drug formulations has increased, many publications still focus on batch processes. The jet mill used in this study is a promising tool for continuous cogrinding. Investigation of different drug-to-carrier ratios (griseofulvin/mannitol) demonstrated that a drug load of 10% is best suited to investigate the enhanced dissolution behavior. To gain deeper insight into the underlying mechanisms, the coground dispersion is compared with different physical mixtures in terms of physicochemical properties and dissolution behavior. Differential scanning calorimetry and X-ray powder diffraction were used to verify the crystalline structure of the coground formulation. On the basis of the Hixson-Crowell model, particle size reduction was ruled out as the main reason for dissolution enhancement. An increase of surface free energies because of grinding is shown with contact angle measurements. Confocal Raman microscopy investigations revealed the drug's bulk dispersity in the coground formulation as an additional factor for the increased dissolution rate. In conclusion, the continuous cogrinding approach is a promising technique to prepare the drug in a rapidly dissolving, yet crystalline, form. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association.
    view abstractdoi: 10.1002/jps.23731
  • 2013 • 53 Structural characterization of the RLCK family member BSK8: A pseudokinase with an unprecedented architecture
    Grütter, C. and Sreeramulu, S. and Sessa, G. and Rauh, D.
    Journal of Molecular Biology 425 4455-4467 (2013)
    Brassinosteroid signaling kinases (BSKs) are plant-specific receptor-like cytoplasmic protein kinases involved in the brassinosteroid signaling pathway. Unlike common protein kinases, they possess a naturally occurring alanine residue at the "gatekeeper" position, as well as other sequence variations. How BSKs activate downstream proteins such as BSU1, as well as the structural consequences of their unusual sequential features, was unclear. We crystallized the catalytic domain of BSK8 and solved its structure by multiple-wavelength anomalous dispersion phasing methods to a resolution of 1.5 Å. In addition, a co-crystal structure of BSK8 with 5-adenylyl imidodiphosphate (AMP-PNP) revealed unusual conformational arrangements of the nucleotide phosphate groups and catalytic key motifs, typically not observed for active protein kinases. Sequential analysis and comparisons with known pseudokinase structures suggest that BSKs represent constitutively inactive protein kinases that regulate brassinosteroid signal transfer through an allosteric mechanism. © 2013. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.jmb.2013.07.034
  • 2013 • 52 Synthesis and crystal structure of a salt containing ∞ 1{Zn[trans-μ2(η3: η3-Ge9)]}2- anions: A polymer with Ge 9 zintl clusters bridged by Zn atoms
    Benda, C.B. and Schäper, R. and Schulz, S. and Fässler, T.F.
    European Journal of Inorganic Chemistry 5964-5968 (2013)
    The reaction of an ethylenediamine (en) solution of K4Ge 9 with Zn2(Mesnacnac)2 {Mesnacnac = [(2,4,6-Me3C6H2)NC(Me)]2CH} in the presence of 18-crown-6 (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) leads to the formation of the new compound [K(18-crown-6)]2{Zn[trans- μ2(η3:η3-Ge9)]}(en). A crystallographic structure determination revealed that the salt contains ∞ 1[Zn(Ge9)]2- polyanions in which each Zn atom bridges two Ge9 clusters by coordinating to opposite triangular faces of the Ge9 deltahedra. The polymeric chain can be formally described as consisting of a trans ZnII complex with two [η3:η3-Ge9]4- ligands. 1H NMR spectroscopic investigations indicated that the protonation of the Mesnacnac- ligand by the solvent ethylenediamine plays a crucial role in the disproportionation of the ZnI starting material and thus in the formation of the polymeric ZnII complex. In contrast, the reaction of ZnPh2 instead of Zn2(Mesnacnac)2 under the same conditions leads to the known complex [PhZn(η4- Ge9)]3-. Crystals of the compound [K(18-crown-6)] 2{Zn[trans-μ2(η3:η3- Ge9)]}(en), containing strands of ∞ 1{Zn[trans-μ2(η3:η3- Ge9)]}2- units in which Zn atoms connect Ge9 clusters in an η3-fashion, were obtained by the reaction of the binary Zintl phase K4Ge9 with Zn2(Mesnacnac) 2 (Mesnacnac = [(2,4,6-Me3C6H 2)NC(Me)]2CH) in ethylenediamine (en). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ejic.201301122
  • 2013 • 51 To tilt or not to tilt: Correction of the distortion caused by inclined sample surfaces in low-energy electron diffraction
    Sojka, F. and Meissner, M. and Zwick, C. and Forker, R. and Vyshnepolsky, M. and Klein, C. and Horn-von Hoegen, M. and Fritz, T.
    Ultramicroscopy 133 35-40 (2013)
    Low-energy electron diffraction (LEED) is a widely employed technique for the structural characterization of crystalline surfaces and epitaxial adsorbates. For technical reasons the accessible reciprocal space is limited at a given primary electron energy E. This limitation may be overcome by sweeping E to observe higher diffraction orders decisively enhancing the quantitative examination. Yet, in many cases, such as molecular films with rather large unit cells, the adsorbate reflexes become less pronounced at energies high enough to observe substrate reflexes. One possibility to overcome this problem is an intentional inclination of the sample surface during the measurement at the expense of the quantitative interpretability of then severely distorted diffraction patterns. Here, we introduce a correction method for the axially symmetric distortion in LEED images of tilted samples. We provide experimental confirmation for micro-channel plate LEED and spot-profile analysis LEED instruments using the (7×7) reconstructed surface of a Si(111) single crystal as a reference sample. Finally, we demonstrate that the correction of this distortion considerably improves the quantitative analysis of diffraction patterns of adsorbates since substrate and adsorbate reflexes can be evaluated simultaneously. As an illustrative example we have chosen an epitaxial monolayer of 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111) that is known to form a commensurate superstructure. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2013.04.005
  • 2012 • 50 A comparison of the solid-state structures of halogen azides XN3 (X=Cl, Br, I)
    Lyhs, B. and Bläser, D. and Wölper, C. and Schulz, S. and Jansen, G.
    Angewandte Chemie - International Edition 51 12859-12863 (2012)
    Delicate crystals: ClN3 adopts a polymeric structure in the solid state (see picture; N blue, Cl green) with short intermolecular Cl×××Cl distances, as was observed for the elemental halogen. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201206028
  • 2012 • 49 Basic properties of magnetic shape-memory materials from first-principles calculations
    Entel, P. and Dannenberg, A. and Siewert, M. and Herper, H.C. and Gruner, M.E. and Comtesse, D. and Elmers, H.-J. and Kallmayer, M.
    Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 43 2891-2900 (2012)
    The mutual influence of phase transformations, magnetism, and electronic properties of magnetic-shape memory Heusler materials is a basic issue of electronic structure calculations based on density functional theory. In this article, we show that these calculations can be pursued to finite temperatures, which allows to derive on a first-principles basis the temperature versus composition phase diagram of the pseudo-binary Ni-Mn-(Ga, In, Sn, Sb) system. The free energy calculations show that the phonon contribution stabilizes the body-centered-cubic (bcc)-like austenite structure at elevated temperatures, whereas magnetism favors the lowtemperature martensite phase with body-centered-tetragonal (bct) or rather face-centeredtetragonal (fct) structure. The calculations also allow to make predictions of magnetostructural and magnetic field induced properties of other (new) magnetic Heusler alloys not based on NiMn such as Co-Ni-(Ga-Zn) and Fe-Co-Ni-(Ga-Zn) intermetallic compounds. © The Minerals, Metals & Materials Society and ASM International 2011.
    view abstractdoi: 10.1007/s11661-011-0832-7
  • 2012 • 48 Comparison of InAs nanowire conductivity: Influence of growth method and structure
    Sladek, K. and Winden, A. and Wirths, S. and Weis, K. and Blömers, C. and Gül, Ö. and Grap, T. and Lenk, S. and von der Ahe, M. and Weirich, T.E. and Hardtdegen, H. and Lepsa, M.I. and Lysov, A. and Li, Z.-A. and Prost, W. and ...
    Physica Status Solidi (C) Current Topics in Solid State Physics 9 230-234 (2012)
    The conductivity and crystal structure of nominally undoped InAs nanowires deposited by three different methods - 1. selective area metal organic vapor phase epitaxy (SA MOVPE), 2. gold assisted vapor liquid solid (VLS) MOVPE and 3. extrinsic catalyst free VLS molecular beam epitaxy (MBE) - is investigated. The influence on conductivity by stacking faults and different growth conditions is analyzed to determine the main impact. It is found that in terms of crystal structure, nanowires deposited by VLS MOVPE and VLS MBE behave similarly showing a zinc blende (ZB) phase while nanowires deposited by SA MOVPE feature a high density of stacking faults and a tendency to higher amounts of wurtzite (WZ) when grown with a decreased growth rate. However, the conductivity of wires deposited by VLS MOVPE is found to be much higher and statistically less dispersive compared to the other two wire types. An electrical similarity between nominally undoped wires in VLS MOVPE and previously reported intentionally doped wires in SA MOVPE is observed and discussed. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssc.201100282
  • 2012 • 47 Cooperativity of H-bonding and anion-π interaction in the binding of anions with neutral π-acceptors
    Giese, M. and Albrecht, M. and Krappitz, T. and Peters, M. and Gossen, V. and Raabe, G. and Valkonen, A. and Rissanen, K.
    Chemical Communications 48 9983-9985 (2012)
    A rare anion-π complex between bromide and a neutral receptor is reported and related receptor systems are studied with a series of anions. The interaction is observed in the solid state and in solution, and further evidence for it is obtained by a computational study. © The Royal Society of Chemistry 2012.
    view abstractdoi: 10.1039/c2cc34748b
  • 2012 • 46 Design, Synthesis, and biological evaluation of novel disubstituted dibenzosuberones as highly potent and selective inhibitors of p38 mitogen activated protein kinase
    Koeberle, S.C. and Fischer, S. and Schollmeyer, D. and Schattel, V. and Grütter, C. and Rauh, D. and Laufer, S.A.
    Journal of Medicinal Chemistry 55 5868-5877 (2012)
    Synthesis, biological testing, structure-activity relationships (SARs), and selectivity of novel disubstituted dibenzosuberone derivatives as p38 MAP kinase inhibitors are described. Hydrophilic moieties were introduced at the 7-, 8-, and 9-position of the 2-phenylamino-dibenzosuberones, improving physicochemical properties as well as potency. Extremely potent inhibitors were obtained, with half-maximal inhibitory concentration (IC 50) values in the low nM range in a whole blood assay measuring the inhibition of cytokine release. The high potency of the target compounds together with the outstanding selectivity of this novel class of compounds toward p38 mitogen activated protein (MAP) kinase as compared to other kinases indicate them to be most applicable as tools in pharmacological research and eventually they may foster a new generation of anti-inflammatory drugs. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/jm300327h
  • 2012 • 45 Direct binding assay for the detection of type IV allosteric inhibitors of Abl
    Schneider, R. and Becker, C. and Simard, J.R. and Getlik, M. and Bohlke, N. and Janning, P. and Rauh, D.
    Journal of the American Chemical Society 134 9138-9141 (2012)
    Abelson (Abl) tyrosine kinase is an important cellular enzyme that is rendered constitutively active in the breakpoint cluster region (BCR)-Abl fusion protein, contributing to several forms of leukemia. Although inhibiting BCR-Abl activity with imatinib shows great clinical success, many patients acquire secondary mutations that result in resistance to imatinib. Second-generation inhibitors such as dasatinib and nilotinib can overcome the majority of these mutations but fail to treat patients with an especially prevalent T315I mutation at the gatekeeper position of the kinase domain. However, a combination of nilotinib with an allosteric type IV inhibitor was recently shown to overcome this clinically relevant point mutation. In this study, we present the development of a direct binding assay that enables the straightforward detection of allosteric inhibitors which bind within the myristate pocket of Abl. The assay is amenable to high-throughput screening and exclusively detects the binding of ligands to this unique allosteric site. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/ja303858w
  • 2012 • 44 Fluorophore labeled kinase detects ligands that bind within the MAPK insert of p38α kinase
    Getlik, M. and Simard, J.R. and Termathe, M. and Grütter, C. and Rabiller, M. and van Otterlo, W.A.L. and Rauh, D.
    PLoS ONE 7 (2012)
    The vast majority of small molecules known to modulate kinase activity, target the highly conserved ATP-pocket. Consequently, such ligands are often less specific and in case of inhibitors, this leads to the inhibition of multiple kinases. Thus, selective modulation of kinase function remains a major hurdle. One of the next great challenges in kinase research is the identification of ligands which bind to less conserved sites and target the non-catalytic functions of protein kinases. However, approaches that allow for the unambiguous identification of molecules that bind to these less conserved sites are few in number. We have previously reported the use of fluorescent labels in kinases (FLiK) to develop direct kinase binding assays that exclusively detect ligands which stabilize inactive (DFG-out) kinase conformations. Here, we present the successful application of the FLiK approach to develop a high-throughput binding assay capable of directly monitoring ligand binding to a remote site within the MAPK insert of p38α mitogen-activated protein kinase (MAPK). Guided by the crystal structure of an initially identified hit molecule in complex with p38α, we developed a tight binding ligand which may serve as an ideal starting point for further investigations of the biological function of the MAPK insert in regulating the p38α signaling pathway. © 2012 Getlik et al.
    view abstractdoi: 10.1371/journal.pone.0039713
  • 2012 • 43 Hydrous layer silicates as precursors for zeolites obtained through topotactic condensation: A review
    Marler, B. and Gies, H.
    European Journal of Mineralogy 24 405-428 (2012)
    In the search for new synthesis routes of zeolites, the topotactic condensation of hydrous layer silicates shows promising results in generating novel zeolite materials with distinct framework types which might have new, interesting properties as, e.g., molecular sieves or form-selective catalysts. In order to manipulate and optimise the condensation process detailed knowledge of the crystal structures is essential. The layer silicates considered here are of a special type and can be designated as high-silica hydrous layer silicates, HLSs. The structures consist of a tetrahedral layer of interconnected [SiO 4]-units containing equal numbers of terminal silanol/siloxy groups on either side of the layer and of an inter-layer region where cations of low charge density (predominantly organic cations) and water molecules are located. A topotactic condensation of the layers performed at temperatures of around 500°C with simultaneous expulsion of the inter-layer constituents is able to form fully condensed, uninterrupted framework silicates. The topotactic conversion has so far been described rarely in comparison to the classical hydrothermal synthesis of zeolites. Nevertheless, several hydrous layer silicates with different layer topologies were successfully converted into zeolites of different framework types using this synthesis route: CAS (type material: EU-20, EU-20b), CDO (type material: CDS-1), FER (type material: siliceous ferrierite), MWW (type material: MCM-22), NSI (type material: NU-6(2)), RRO (type material: RUB-41), RWR (type material: RUB-24), SOD (type material: guest-free silica sodalite). Thereby, four new zeolite framework types were obtained which have not been synthesized, so far, by direct hydrothermal synthesis (CDO, NSI, RRO, RWR). This review gives an overview on the hydrous layer silicates being structurally characterized in detail, on the condensation process and on some properties of the resulting zeolite materials. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung.
    view abstractdoi: 10.1127/0935-1221/2012/0024-2187
  • 2012 • 42 Interlayer expansion of the hydrous layer silicate rub-36 to a functionalized, microporous framework silicate: Crystal structure analysis and physical and chemical characterization
    Gies, H. and Müller, U. and Yilmaz, B. and Feyen, M. and Tatsumi, T. and Imai, H. and Zhang, H. and Xie, B. and Xiao, F.-S. and Bao, X. and Zhang, W. and Baerdemaeker, T.D. and De Vos, D.
    Chemistry of Materials 24 1536-1545 (2012)
    The hydrous layer silicate RUB-36, (C 6H 16N) 4 [H 4Si 36O 76], has been used for an interlayer expansion reaction with dichlorodimethylsilane to interconnect neighboring ferrierite-type layers to a three-dimensional framework silicate. The linker group (-O-Si(CH 3) 2-O-) still has the two methyl groups in the as-synthesized form (material name COE-3 [Si 20O 38(CH 3) 4] for the silicate framework) rendering hydrophobic properties. The interlayer expanded zeolite, IEZ, is thermally stable and can be calcined at 550 °C to yield a hydrophilic material COE-4 [Si 20O 38(OH) 4]. 29Si solid state MAS NMR experiments confirm the insertion of the linker group and the methyl and hydroxyl substitution in the as-made and calcined form, respectively. The BET surface area is 238 m 2/g for COE-3 and 350 m 2/g for COE-4. COE-3 and COE-4 crystallize in space group Pm with a = 12.2503(3) Å b = 13.9752(2) Å c = 7.3850(1) Å and β = 107.33(1)° and a = 12.16985(4) Å, b = 13.95066(3) Å c = 7.37058(2) Å, and β = 107.30(1)°, respectively. Rietveld crystal structure refinement of the PXRD pattern of COE-3 and COE-4 reveal the expanded, two-dimensional 10-ring pore system including the linker group as homogeneous structural property of the materials. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/cm300525u
  • 2012 • 41 Lanthanide(III) complexes of bis-semicarbazone and bis-imine-substituted phenanthroline ligands: Solid-state structures, photophysical properties, and anion sensing
    Nadella, S. and Selvakumar, P.M. and Suresh, E. and Subramanian, P.S. and Albrecht, M. and Giese, M. and Fröhlich, R.
    Chemistry - A European Journal 18 16784-16792 (2012)
    Phenanthroline-based hexadentate ligands L1 and L2 bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as LaIII, EuIII, TbIII, LuIII, and YIII metal ions, were synthesized, and the crystal structures of [ML1Cl3] (M=LaIII, EuIII, Tb III, LuIII, or YIII) complexes were determined. Solvent or water molecules act as coligands for the rare-earth metals in addition to halide anions. The big LnIII ion exhibits a coordination number (CN) of 10, whereas the corresponding EuIII, TbIII, LuIII, and YIII centers with smaller ionic radii show CN=9. Complexes of L2, namely [ML2Cl3] (M=EuIII, TbIII, LuIII, or YIII) ions could also be prepared. Only the complex of EuIII showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine-5′-triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine-5′-diphosphate (ADP) and adenosine-5′-monophosphate (AMP) was found. 31P NMR spectroscopic studies revealed the formation of a [EuL2(ATP)] coordination species. Illuminating the ion: Hexadentate bis-semicarbazone-based achiral and bis-imine chiral ligands of phenathroline together with their respective lanthanide complexes were synthesized. The crystal structures obtained for bis- semicarbazone-based LnIII complexes reveal coordination numbers of 9 and 10. Among the bis-imine chiral complexes, a luminescent EuIII complex was investigated for sensing various anions, and selectivity towards adenosine-5′-triphosphate (ATP) was achieved in an aqueous medium (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201201705
  • 2012 • 40 On the structural relations of malachite. I. the rosasite and ludwigite structure families
    Girgsdies, F. and Behrens, M.
    Acta Crystallographica Section B: Structural Science 68 107-117 (2012)
    The crystal structures of malachite Cu 2(OH) 2CO 3 and rosasite (Cu,Zn)2(OH)2CO 3, though not isotypic, are closely related. A previously proposed approach explaining this relation via a common hypothetical parent structure is elaborated upon on the basis of group-subgroup considerations, leading to the conclusion that the aristotype of malachite and rosasite should crystallize in the space group Pbam (No. 55). An ICSD database search for actual representatives of this aristotype leads to the interesting observation that the structure type of ludwigite (Mg,Fe) 2FeO 2BO 3, which is adopted by several natural and synthetic oxide orthoborates M 3O 2BO 3, is closely related to the proposed malachite-rosasite aristotype and thus to the malachite-rosasite family of hydroxide carbonates M 2(OH) 2CO 3 in general. Relations within both structure families and their analogies are summarized in a joint simplified Bärnighausen tree. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.
    view abstractdoi: 10.1107/S0108768112005125
  • 2012 • 39 Pentafluorophenyl salicylamine receptors in anion-π interaction studies
    Giese, M. and Albrecht, M. and Plum, C. and Hintzen, D. and Valkonen, A. and Rissanen, K.
    Supramolecular Chemistry 24 755-761 (2012)
    A crystal structure analysis confirms the appropriateness of pentafluorophenyl salicylamine (1a) as a-acceptor for anion-interactions. Crystals of 1aHCl show that the OH-group fixes the anion in a η 2-type binding motif above the electron-deficient arene. Attempts to find some relevance for this weak intermolecular force in solution failed. Stronger CH-, NH-and OH-anion interactions are dominant over the weak anion-interactions. Due to the hydrogen bonding, the non-fluorinated receptor exhibits the highest binding constants within this series. © 2012 Taylor and Francis Group, LLC.
    view abstractdoi: 10.1080/10610278.2012.715648
  • 2012 • 38 Single crystal growth and characterization of mullite-type Bi 2Mn 4O 10
    Burianek, M. and Krenzel, T.F. and Schmittner, M. and Schreuer, J. and Fischer, R.X. and Mühlberg, M. and Nénertd, G. and Schneider, H. and Gesing, T.M.
    International Journal of Materials Research 103 449-455 (2012)
    A part of the pseudo-binary join Bi 2O 3-Bi 2Mn 4O 10 of the ternary system Bi 2O 3 -MnO-MnO 2 was examined using thermo-analytical methods. Because Bi 2Mn 4O 10 melts incongruently single crystals of up to 20 mm in diameter were grown by the top seeded solution growth method in the temperature range from about 1223 K to 1173 K. Single crystal neutron diffraction confirmed the principles of the crystal structure of Bi 2Mn 4O 10 but revealed much smaller distortions of the cation coordination polyhedra. In contrast to the anisotropy observed in other mullite-type Bi containing compounds, the linear thermal expansion of Bi 2Mn 4O 10, as studied by means of dilatometry and X-ray powder diffraction techniques, is characterized by α 11 &gt; α;33 &gt; α22 at room temperature. The relatively large expansion along the a-axis can be attributed to the two oxygen atoms bridging two corner shared MnO 5 tetrahedral pyramids which alternate with the structural void between two adjacent Bi 3+ cations. © 2012 Carl Hanser Verlag.
    view abstractdoi: 10.3139/146.110714
  • 2012 • 37 Solid-state structure of bromine azide
    Lyhs, B. and Bläser, D. and Wölper, C. and Schulz, S. and Jansen, G.
    Angewandte Chemie - International Edition 51 1970-1974 (2012)
    A new twist: The single-crystal structural analysis of BrN 3 is described. In contrast to IN 3, which forms chains, BrN 3 forms a helical structure in the solid state (see picture). Such a structural feature has not been previously observed in covalent p-block azide chemistry. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201108092
  • 2012 • 36 Structure-based design, synthesis and biological evaluation of N-pyrazole, N′-thiazole urea inhibitors of MAP kinase p38α
    Getlik, M. and Grütter, C. and Simard, J.R. and Nguyen, H.D. and Robubi, A. and Aust, B. and Van Otterlo, W.A.L. and Rauh, D.
    European Journal of Medicinal Chemistry 48 1-15 (2012)
    In this paper, we present the structure-based design, synthesis and biological activity of N-pyrazole, N′-thiazole-ureas as potent inhibitors of p38α mitogen-activated protein kinase (p38α MAPK). Guided by complex crystal structures, we employed the initially identified N-aryl, N′-thiazole urea scaffold and introduced key structural elements that allowed the formation of novel hydrogen bonding interactions within the allosteric site of p38α, resulting in potent type III inhibitors. [4-(3-tert-Butyl-5-{[(1,3-thiazol-2-ylamino)carbonyl]amino}-1H-pyrazol-1-yl) -phenyl]acetic acid 18c was found to be the most potent compound within this series and inhibited p38α activity with an IC 50 of 135 ± 21 nM. Its closest analog, ethyl [4-(3-tert-butyl-5-{[(1,3-thiazol-2-ylamino) carbonyl]amino}-1H-pyrazol-1-yl)phenyl]acetate 18b, effectively inhibited p38α mediated phosphorylation of the mitogen activated protein kinase activated protein kinase 2 (MK2) in HeLa cells. © 2011 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ejmech.2011.11.019
  • 2012 • 35 Synthesis and X-ray crystal structures of heteroleptic zinc amidinate complexes
    Schmidt, S. and Schulz, S. and Bläser, D. and Wölper, C.
    Main Group Metal Chemistry 35 35-40 (2012)
    The synthesis of heteroleptic zinc amidinate complexes is reported. Reactions of LZnI [L=t-BuC(NDipp) 2; Dipp=2,6-i-Pr 2-C 6H 3] with diisopropylcarbodiimide (i-PrN) 2C yielded the Lewis acid-base adduct LZn(I)-N(i-Pr)CN(i-Pr) 1. In addition, the synthesis of LZnN(SiMe 3) 2 2 and its reaction with (i-PrN) 2C, which occurred with formation of the heteroleptic amidinate-guanidinate complex LZnL′ 3 [L′=(Me 3Si) 2NC(Ni-Pr) 2], is reported. Compounds 1-3 were characterized by nuclear magnetic resonance ( 1H, 13C) and infrared spectro\xadscopy, elemental analysis, and single crystal X-ray diffraction (1 and 2), respectively. © 2012 by Walter de Gruyter Berlin Boston.
    view abstractdoi: 10.1515/mgmc-2012-0004
  • 2012 • 34 Toward highly stable electrocatalysts via nanoparticle pore confinement
    Galeano, C. and Meier, J.C. and Peinecke, V. and Bongard, H. and Katsounaros, I. and Topalov, A.A. and Lu, A. and Mayrhofer, K.J.J. and Schüth, F.
    Journal of the American Chemical Society 134 20457-20465 (2012)
    The durability of electrode materials is a limiting parameter for many electrochemical energy conversion systems. In particular, electrocatalysts for the essential oxygen reduction reaction (ORR) present some of the most challenging instability issues shortening their practical lifetime. Here, we report a mesostructured graphitic carbon support, Hollow Graphitic Spheres (HGS) with a specific surface area exceeding 1000 m2 g-1 and precisely controlled pore structure, that was specifically developed to overcome the long-term catalyst degradation, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles of approximately 3 to 4 nm size encapsulated in the HGS pore structure that are stable at 850 C and, more importantly, during simulated accelerated electrochemical aging. Moreover, the high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochemical cycling the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degradation mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/ja308570c
  • 2011 • 33 Determining the activation energies and slip systems for dislocation nucleation in body-centered cubic Mo and face-centered cubic Ni single crystals
    Wang, L. and Bei, H. and Li, T.L. and Gao, Y.F. and George, E.P. and Nieh, T.G.
    Scripta Materialia 65 179-182 (2011)
    Nanoindentation tests were performed on single crystals of Mo and Ni. The critical shear stress for the first pop-in was ∼1/7 of the shear modulus in both crystals. The dependence of pop-in probability on load was understood in terms of a thermally activated dislocation nucleation process. Comparison of the activation energies suggests nucleation of full dislocations in Mo and partial dislocations in Ni. The activation energy analysis also offers information on the specific slip system on which dislocations are nucleated. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.scriptamat.2011.03.036
  • 2011 • 32 Dislocation-vacancy interactions in tungsten
    Chen, Z.M. and Mrovec, M. and Gumbsch, P.
    Modelling and Simulation in Materials Science and Engineering 19 (2011)
    We systematically investigate the interaction between a monovacancy and various lattice dislocations in body-centered cubic (bcc) metal tungsten by means of atomistic simulations. Two models with a different level of sophistication have been employed for the description of interatomic interactions - the empirical Finnis-Sinclair potential, which is a central-force scheme, and the bond-order potential, which is able to describe correctly unsaturated directional covalent bonds that are crucial for the cohesion and structure of bcc transition metals. Our simulation results show that the vacancy-dislocation interaction depends sensitively on the separation distance and orientation of the two defects. A comparison of the simulation results with the predictions of elasticity theory shows excellent agreement between the two approaches when the separation between the vacancy and the dislocation core is above 0.5 nm. Large deviations from the elastic limit are found at close distances, when the vacancy enters the dislocation core. © 2011 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0965-0393/19/7/074002
  • 2011 • 31 Element-specific magnetic hysteresis of individual 18 nm Fe nanocubes
    Kronast, F. and Friedenberger, N. and Ollefs, K. and Gliga, S. and Tati-Bismaths, L. and Thies, R. and Ney, A. and Weber, R. and Hassel, C. and Römer, F.M. and Trunova, A.V. and Wirtz, C. and Hertel, R. and Dürr, H.A. and Farle, M.
    Nano Letters 11 1710-1715 (2011)
    Correlating the electronic structure and magnetic response with the morphology and crystal structure of the same single ferromagnetic nanoparticle has been up to now an unresolved challenge. Here, we present measurements of the element-specific electronic structure and magnetic response as a function of magnetic field amplitude and orientation for chemically synthesized single Fe nanocubes with 18 nm edge length. Magnetic states and interactions of monomers, dimers, and trimers are analyzed by X-ray photoemission electron microscopy for different particle arrangements. The element-specific electronic structure can be probed and correlated with the changes of magnetic properties. This approach opens new possibilities for a deeper understanding of the collective response of magnetic nanohybrids in multifunctional materials and in nanomagnetic colloidal suspensions used in biomedical and engineering technologies. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/nl200242c
  • 2011 • 30 From attraction to repulsion: Anion-π interactions between bromide and fluorinated phenyl groups
    Giese, M. and Albrecht, M. and Bannwarth, C. and Raabe, G. and Valkonen, A. and Rissanen, K.
    Chemical Communications 47 8542-8544 (2011)
    Anion-π interactions in crystals of fluorobenzyl ammonium salts depend on the degree of fluorination at the aromatics. © The Royal Society of Chemistry 2011.
    view abstractdoi: 10.1039/c1cc12667a
  • 2011 • 29 Gated channels in a honeycomb-like zinc-dicarboxylate-bipyridine framework with flexible alkyl ether side chains
    Henke, S. and Fischer, R.A.
    Journal of the American Chemical Society 133 2064-2067 (2011)
    Covalent functionalization of 1,4-benzenedicarboxylate (bdc) with methoxyethoxy groups induces conformational freedom in this molecule. Applying these 2,5-disubstituted bdc derivatives in metal-organic framework synthesis together with 4,4′-bipyridine as coligand yields novel honeycomb-like structures. The cylindrical channels of these materials are populated with flexible groups, which act as molecular gates for guest molecules. This allows highly selective sorption of CO2 over N2 and CH 4. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ja109317e
  • 2011 • 28 Interlayer expansion of the layered zeolite precursor RUB-39: A universal method to synthesize functionalized microporous silicates
    Gies, H. and Müller, U. and Yilmaz, B. and Tatsumi, T. and Xie, B. and Xiao, F.-S. and Xinhe Bao and Zhang, W. and De Vos, D.
    Chemistry of Materials 23 2545-2554 (2011)
    Interlayer expansion reaction leads to a new family of microporous framework silicates using hydrous layer silicates as precursors. Using silylating agents such as dichlor-dimethylsilane (DCDMS), neighboring layers connect. In addition to the topotactic condensation of hydrous silicates, this leads to expanded silicate frameworks, with the number of pore openings increased by two Si-units. The hydrous layer silicate RUB-39 has been subjected to interlayer expansion reaction, using DCDMS at 180-C, yielding new, crystalline microporous frameworks (COE-1 and COE-2), varying in their methyl function carrying as-made and oxidized calcined forms, respectively. An intersecting two-dimensional (2D) channel system with 10- and 12-membered rings is accessible for probemolecules, leading to a surface area of 540m2/g and a pore volume of 0.169 cm3/g. The powder diagram was indexed in space group P2 with a = 15.609(3) Å, b = 11.163(1) Å, c = 7.301(1) Å, and β = 91.2(1)° for COE-1 and a = 15.594(4) Å, b = 11.039(2) Å, c = 7.276(1) Å, and β = 91.2(1)- for calcined COE-2. Rietveld refinement of the powder X-ray diffractometry (PXRD) diagram confirmed the framework topology for COE-1 and COE-2 (?2 = 8.0 and 9.9, respectively) and showed that the silicate framework suffers from stacking disorder after interlayer expansion reaction. DIFFaX simulations allowed for the modeling of the stacking disorder, showing that RRO- and HEU-type stacking occurs. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/cm103506q
  • 2011 • 27 Knowledge-based development of a nitrate-free synthesis route for Cu/ZnO methanol synthesis catalysts via formate precursors
    Behrens, M. and Kißner, S. and Girsgdies, F. and Kasatkin, I. and Hermerschmidt, F. and Mette, K. and Ruland, H. and Muhler, M. and Schlögl, R.
    Chemical Communications 47 1701-1703 (2011)
    High-performance Cu/ZnO/(Al2O3) methanol synthesis catalysts are conventionally prepared by co-precipitation from nitrate solutions and subsequent thermal treatment. A new synthesis route is presented, which is based on similar preparation steps and leads to active catalysts, but avoids nitrate contaminated waste water. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0cc04933f
  • 2011 • 26 Methylated [(arene)(1,3-cyclohexadiene)Ru(0)] complexes as low-melting MOCVD precursor complexes with a controlled follow-up chemistry of the ligands
    Jipa, I. and Danova, K. and Popovska, N. and Siddiqi, M.A. and Siddiqui, R.A. and Atakan, B. and Cremer, T. and Maier, F. and Marbach, H. and Steinrück, H.-P. and Heinemann, F.W. and Zenneck, U.
    Journal of Materials Chemistry 21 3014-3024 (2011)
    [(Benzene)(2-methyl-1,3-cyclohexadiene)Ru(0)] (1), [(1,3-cyclohexadiene) (toluene)Ru(0)] (2), and [(methyl-cyclohexadiene)(toluene)Ru(0)] (3, mixture of isomers) have been prepared and tested as new metal organic ruthenium precursor complexes for chemical vapor deposition (MOCVD) with favorable properties. 1 is a low-melting precursor complex (mp = 29 °C) and the isomeric mixture 3 forms a liquid at room temperature. X-ray diffraction studies of single crystals of complexes 1 and 2 are characteristic for true Ru(0) π-complexes without molecular structure peculiarities or significant intermolecular interactions in the solid state, which could hinder undecomposed evaporation. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and vapor pressure data qualify the compounds as almost ideal MOCVD precursors. Thin ruthenium films have been deposited successfully on silicon wafers and substrate temperatures between 200 and 450 °C in inert gas atmospheres. Film growth and properties were evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and four-point probe conductivity measurements. All films consist of polycrystalline metallic ruthenium with a low surface roughness. © The Royal Society of Chemistry 2011.
    view abstractdoi: 10.1039/c0jm02652b
  • 2011 • 25 Radiaxial-fibrous calcites: A new look at an old problem
    Richter, D.K. and Neuser, R.D. and Schreuer, J. and Gies, H. and Immenhauser, A.
    Sedimentary Geology 239 23-36 (2011)
    Marine radiaxial-fibrous and fascicular-optic calcites are very common but poorly understood pore-filling cements in Paleozoic and Mesozoic marine neritic and upper bathyal limestones. The main diagnostic feature of these cements is their converging or diverging crystal c-axis, respectively. The reasons for this anomalous texture are at present unknown. Another controversy is due to the relative lack of occurrences in Cenozoic strata and their apparent absence in Quaternary marine limestones. Despite these uncertainties, marine fibrous cements are thought by some to be amongst the best proxies for the geochemistry of ancient oceans because of the absence of metabolic effects during their precipitation. Applying electron backscatter diffraction analysis, we here for the first time document radiaxial-fibrous and subordinate fascicular-optic fibrous biominerals from well-preserved Jurassic and Cretaceous low-Mg calcite belemnite rostra. The finding of fibrous biogenic calcites in combination with the recent description of Holocene and modern fibrous calcites in stalagmites represents-in the view of the authors-a significant advance in carbonate research. Here, these findings are placed in their wider, processes-oriented context and the significance of biogenic and speloan fibrous calcite for their marine counterparts is assessed. Comparing the physico-chemical and organomineralic properties of different precipitation sites indicates that the diagnostic variations in the crystal c-axis orientation are not related to a specific nucleation environment or substratum. In contrast, preliminary crystallographic analyses suggest that kinetic factors during nucleation or subtle gradients in the statistical replacements of Ca2+ by Mg2+ in the crystal structure may lead to local strain resulting in converging or diverging crystal c-axes. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.sedgeo.2011.06.003
  • 2011 • 24 Shape transformation mechanism of silver nanorods in aqueous solution
    Damm, C. and Segets, D. and Yang, G. and Vieweg, B.F. and Spiecker, E. and Peukert, W.
    Small 7 147-156 (2011)
    The spontaneous shape transformation of silver nanorods with an initial length of several hundred nanometers towards spherical particle shapes in aqueous solution is investigated by means of scanning electron microscopy, UV-vis absorption spectroscopy, anodic stripping voltammetry, and high-resolution transmission electron microscopy (HRTEM). The consolidation of the results reveals an increase in the particle number density with time. Moreover, HRTEM image analysis along the cross section of the rods evidences the presence of fivefold twinning defects which extend along the whole rod length. According to the analytical model of Monk et al. this kind of rod structure is only thermodynamically stable if the rod length is below a critical value at a given diameter. The rods investigated in the present work do not fulfill the stability criterion as they exceed the critical length. Thus, the rods decay into smaller "nanobuns" and defective as well as defect-free spheres. A mechanism based on findings from the literature, HRTEM image analysis of former rods, transition states, and the final particle structures is proposed. The defects along the surface are seen as starting points for the dissolution of material, which is reintegrated into the solid phase by homogeneous as well as heterogeneous nucleation and growth. The decay process of silver nanorods in aqueous suspension is investigated. During ageing the aspect ratio decreases with time whereas the absolute particle number increases. Defects play a decisive role in rod decay and underline how crystal structure influences particle shape. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201001600
  • 2011 • 23 Silicon and magnesium diffusion in a single crystal of MgSiO3 perovskite
    Xu, J. and Yamazaki, D. and Katsura, T. and Wu, X. and Remmert, P. and Yurimoto, H. and Chakraborty, S.
    Journal of Geophysical Research: Solid Earth 116 (2011)
    Si and Mg self-diffusion coefficients were measured simultaneously in single crystals of MgSiO<inf>3</inf> perovskite under lower mantle conditions. There is little difference in Si volume diffusivity measured directly using single crystals (this study) and those retrieved from experiments with polycrystals (earlier studies). This agreement between studies establishes the reliability of Si diffusion coefficients measured in perovskite. Within the uncertainties of our measurements, no anisotropy in the diffusion of either Si or Mg could be resolved. Diffusion of Si and Mg in perovskite are described by an Arrhenius equation, D=D<inf>0</inf> exp (-H/RT) at 25GPa, with D <inf>0</inf>=5.10×10-11m2/s for Si and 4.99×10-11m2/s for Mg, H=308kJ/mol for Si, and 305kJ/mol for Mg. Mg diffusivity in MgSiO<inf>3</inf> perovskite is distinctly lower than those measured in olivine, wadsleyite, and ringwoodite. We find that Mg has very similar diffusivity to Si in perovskite. As a consequence, the rheological properties of the lower mantle may be controlled by the coupled motion of Si and Mg. A point defect-based model is discussed that may account for the diffusion behavior of Si and Mg in MgSiO<inf>3</inf> perovskite. Our data indicate that, within realistic ranges of temperature, grain size, and state of stress, both diffusion creep as well as dislocation creep may be observed in the lower mantle. Copyright 2011 by the American Geophysical Union.
    view abstractdoi: 10.1029/2011JB008444
  • 2011 • 22 Structural, ferroelectric and magnetic properties of Bi 0.85Sm0.15FeO3 perovskite
    Khomchenko, V.A. and Paixão, J.A. and Costa, B.F.O. and Karpinsky, D.V. and Kholkin, A.L. and Troyanchuk, I.O. and Shvartsman, V.V. and Borisov, P. and Kleemann, W.
    Crystal Research and Technology 46 238-242 (2011)
    Room temperature crystal structure, ferroelectric and magnetic properties of polycrystalline Bi0.85Sm0.15FeO3 samples were investigated. X-ray diffraction study shows that the compound possesses a dominant PbZrO3-like orthorhombic structure with √2a× 2√2a × √2a superlattice (a is the parameter of the cubic perovskite subcell). In contrast to piezoresponse force microscopy data demonstrating some features characteristic of ferroelectrics, polarization vs. electric field measurements reveal the behavior expected for nonpolar materials. Investigation of magnetic properties confirms that 15% samarium substitution suppresses the spin modulation typical of BiFeO3 and induces the appearance of spontaneous magnetization. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/crat.201100040
  • 2011 • 21 Syntheses and structures of triazides of heavy group 15 elements
    Schulz, S. and Lyhs, B. and Jansen, G. and Bläser, D. and Wölper, C.
    Chemical Communications 47 3401-3403 (2011)
    Synthesis of group 15-triazides E(N3)3 (E = Sb 1, Bi 2) and Py2-Bi(N3)33 (Py = pyridine). Single crystals of 1 were in situ grown by an IR-laser-assisted technique on the diffractometer. The structure of 3, which represents the first structurally characterized neutral Bi-triazide, is influenced by crystal packing effects according to DFT calculations. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c1cc10237k
  • 2011 • 20 Synthesis and microwave absorbing properties of highly ordered mesoporous crystalline NiFe2O4
    Gu, X. and Zhu, W. and Jia, C. and Zhao, R. and Schmidt, W. and Wang, Y.
    Chemical Communications 47 5337-5339 (2011)
    Highly ordered mesoporous NiFe2O4 with excellent microwave absorption properties has been synthesized by using mesoporous silica (KIT-6) as a hard template. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0cc05800a
  • 2011 • 19 Synthesis, structural properties, and catalytic behavior of Cu-BTC and mixed-linker Cu-BTC-PyDC in the oxidation of benzene derivatives
    Marx, S. and Kleist, W. and Baiker, A.
    Journal of Catalysis 281 76-87 (2011)
    Mixed-linker metal-organic frameworks based on the Cu-BTC structure have been synthesized in which the benzene-1,3,5-tricarboxylate (BTC) linkers have been partially replaced by pyridine-3,5-dicarboxylate (PyDC). X-ray-based techniques (powder XRD and XAS), thermal analysis, and infrared spectroscopy proved that a desired amount of PyDC (up to 50%) can be incorporated without changing significantly the crystal structure. The pyridine unit can be seen as a defect site in the local coordination environment of the dimeric copper units, which is significantly altering their electronic structure and the catalytic properties. Both Cu-BTC and the mixed Cu-BTC-PyDCs catalyze the demanding direct hydroxylation of toluene both in acetonitrile and in neat substrate. Different selectivity toward the desired ortho- and para-cresol and other oxidation products (benzaldehyde, benzyl alcohol, methylbenzoquinone) was observed for Cu-BTC and the Cu-BTC-PyDCs, respectively. Leaching tests and comparison with homogeneously dissolved Cu catalysts indicate mainly a heterogeneous reaction pathway. © 2011 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.jcat.2011.04.004
  • 2010 • 18 Detection of Yb impurities in the VUV spectral range of NdGaO3 crystals
    Piasecki, M.M. and Andriyevsky, B.B. and Cobet, C.C. and Esser, N.N. and Kityk, I.V. and Świrkowicz, M.M. and Majchrowski, A.A.
    Optics Communications 283 3998-4003 (2010)
    Substantial influence of the 1 at.% Yb doping of NdGaO3 single crystals on the optical functions ε1(E) and ε 2(E) in the spectral range of electronic excitations is established. The corresponding differences of the optical functions for pure and doped NdGaO3 have been monitored using spectroscopic ellipsometry method and synchrotron radiation light source. This opens an opportunity for the spectroscopic diagnostics of the rare earth dopants in crystals using the spectroscopic information concerning the electronic inter-band optical transitions. To understand better the experimental results obtained, the ab-initio calculations of band structure and optical spectra of the centrosymmetric single crystal NdGaO3 have been performed using the VASP code (Vienna Ab-initio Simulation Package). The calculated dielectric functions ε1(E) and ε2(E) agree satisfactorily with our experimental results obtained with using the spectroscopic ellipsometry method and synchrotron radiation. It was demonstrated that differences of the optical functions for pure and doped crystals using stable synchrotron source may serve as a powerful tool for spectroscopic diagnostic of localised rare earth ions with respect to the strong inter-band transitions. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.optcom.2010.06.004
  • 2010 • 17 Diffusion of Li in olivine. Part I: Experimental observations and a multi species diffusion model
    Dohmen, R. and Kasemann, S.A. and Coogan, L. and Chakraborty, S.
    Geochimica et Cosmochimica Acta 74 274-292 (2010)
    There are an increasing number of studies that focus on the systematics of the distribution of Li and its isotopes among different geochemical reservoirs. These studies have found that Li is relatively mobile compared to many other elements (e.g., Fe, Mg), and diffusion has been considered as a mechanism to generate large isotopic fractionations even at high temperatures. In order to quantify some of these aspects, we have measured Li diffusion rates experimentally along [0 0 1] of single crystals of olivines from San Carlos, Arizona and Pakistan, at 800-1200 °C at a total pressure of 100 kPa and fO2 ≈ WM buffer. A complex diffusion behavior of Li is observed, indicating that two mechanisms of diffusion (a fast and a slower one) operate simultaneously. The behavior is well described by a model that partitions Li between two different sites in olivine - an octahedral site (LiMe) and an interstitial site (Lii). Transport of Li is a combination of hopping within and between each of these kinds of sites involving also vacancies on the octahedral site (VMe). It is assumed that the homogeneous reaction (LiMe = VMe + Lii) that maintains equilibrium distribution of Li between the sites is instantaneous compared to the timescales of all other processes associated with diffusive transport. One consequence of this mode of transport of Li in olivine is that the shape and length of diffusion profiles depend on the boundary conditions imposed at the surface of a crystal; i.e., the chemical environment (e.g., fO2, aLi4SiO4), in addition to temperature and pressure. Our model describes the variable experimentally determined Li-profile shapes produced at different temperatures and with different boundary conditions, as well as their time evolution, quantitatively. Modeling the observed isotopic fractionation shows that 6Li diffuses about 5% faster than 7Li on the interstitial site. Inspection of published data on Li distribution in natural olivines that are available until now indicates that the fast (interstitial) mechanism of Li diffusion is unlikely to be dominant in most natural systems; Li rich, oxidizing environments (e.g., fluids?) may be exceptions. However, when it operates it can decouple the equilibration of Li isotopic gradients from the time scale of equilibration of overall Li concentrations. Diffusion dominated by the slower mechanism will occur on the average at a rate that is about an order of magnitude faster than diffusion of Fe, Mg and most other divalent cations in olivine; such diffusion of Li in olivine will be much slower than the rates of diffusion in clinopyroxene and plagioclase crystals at the same conditions. Fractionation of isotopes of Li by diffusion is likely to be a transient phenomenon and is more likely to be observed in crystals showing zoning of Li concentrations. © 2009 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.gca.2009.10.016
  • 2010 • 16 Effect of Sm substitution on ferroelectric and magnetic properties of BiFeO3
    Khomchenko, V.A. and Paixão, J.A. and Shvartsman, V.V. and Borisov, P. and Kleemann, W. and Karpinsky, D.V. and Kholkin, A.L.
    Scripta Materialia 62 238-241 (2010)
    Investigation of crystal structure and multiferroic properties of polycrystalline Bi1-xSmxFeO3 (0.1 ≤ x ≤ 0.2) samples was performed by X-ray diffraction, piezoresponse force microscopy and SQUID-magnetometry techniques. It was shown that increasing samarium content induced a polar-to-nonpolar phase transition near x = 0.2. Within the polar region, a rhombohedral and two orthorhombic modifications of Bi1-xSmxFeO3 were found. It was shown that samarium substitution resulted in the appearance of spontaneous magnetization, which was significantly enhanced upon the composition-driven transition from a rhombohedral to an orthorhombic phase. © 2009 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.scriptamat.2009.11.005
  • 2010 • 15 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 • 14 Formation, stability and crystal structure of the r phase in Mo-Re-Si alloys
    Bei, H. and Yang, Y. and Viswanathan, G.B. and Rawn, C.J. and George, E.P. and Tiley, J. and Chang, Y.A.
    Acta Materialia 58 6027-6034 (2010)
    The formation, stability and crystal structure of the σ phase in Mo-Re-Si alloys were investigated. Guided by thermodynamic calculations, six critically selected alloys were arc melted and annealed at 1600 °C for 150 h. Their as-cast and annealed microstructures, including phase fractions and distributions, the compositions of the constituent phases and the crystal structure of the r phase were analyzed by thermodynamic modeling coupled with experimental characterization by scanning electron microscopy, electron probe microanalysis, X-ray diffraction and transmission electron microscopy. Two key findings resulted from this work. One is the large homogeneity range of the r phase region, extending from binary Mo-Re to ternary Mo-Re-Si. The other is the formation of a r phase in Mo-rich alloys either through the peritectic reaction of liquid + Moss → σ or primary solidification. These findings are important in understanding the effects of Re on the microstructure and providing guidance on the design of Mo-Re-Si alloys. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2010.07.020
  • 2010 • 13 Influence on diamonds during the spraying of diamond-bronze abrasive coatings
    Tillmann, W. and Vogli, E. and Nebel, J. and Buck, V. and Reuter, S.
    Journal of Thermal Spray Technology 19 350-357 (2010)
    Detonation spraying provides the opportunity to produce diamond grinding tools for the machining of stone, cement, and concrete. Especially the atmospheric conditions of the spraying process yield in a high production flexibility. However, during detonation spraying, the oxygenic atmosphere as well as the thermal and kinetic energy have an impact on the processed diamond. Despite its importance for the tools' performance, the influence of the spraying process on the superabrasive diamond is predominantly unknown. The potential decrease of the diamond durability and strength due to degradation effects during the production of sprayed diamond-CuSn 85/15 composites has not yet been determined. X-ray diffraction and Raman spectroscopy were used to verify thermally initiated surface reactions of the sprayed diamonds after exposure to the spraying process. Additionally, reference measurements on the degradation of diamonds in oxidizing and inert conditions were carried out to compare the spraying results. Differential thermal and thermogravimetric analyses were employed. To validate the mechanical properties of the diamond superabrasives, friability tests and fracture force tests were performed. It was found that under optimized detonation spraying conditions the thermal and mechanical impact remains low enough to ensure a good reliability of the processed diamonds. The diamond crystal structure endured the spraying process without detectable graphitization or oxidation. Deterioration indicators were not observed in SEM micrographs, x-ray diffraction patterns or Raman spectra. Furthermore, a high durability and strength of the sprayed diamonds were confirmed by mechanical testing. © 2009 ASM International.
    view abstractdoi: 10.1007/s11666-009-9418-y
  • 2010 • 12 Intramolecular electronic interactions between nonconjugated arene and quinone chromophores
    Jansen, G. and Kahlert, B. and Klärner, F.-G. and Boese, R. and Bläser, D.
    Journal of the American Chemical Society 132 8581-8592 (2010)
    The novel surprisingly colorful dark blue and orange-red molecular clips 1 and 2 containing a central p-benzoquinone spacer-unit and anthracene or napththalene sidewalls were synthesized by DDQ oxidation of the corresponding colorless hydroquinone clips 7 and 8. The colors of the quinone clips result from broad absorption bands in the visible range (1, λ<inf>max</inf> = 537 nm and 2, λ<inf>max</inf> = 423 and λ<inf>shoulder</inf> =515 nm) showing bathochromic shifts of 112 and 90 nm, respectively, compared to the similarly tetraalkyl-substituted duroquinone 31, even though the clips 1 and 2 only contain insulated π systems as chromophores, a central tetraalkyl-substituted p-benzoquinone spacer-unit and two anthracene or two naphthalene sidewalls. To elucidate the electronic properties of these clips, we prepared the compound 3, the anti-configured isomer of clip 2, and the benzene-, naphthalene-, and anthracene-substituted quinones 4, 5, and 6, the so-called "half-clips". The "half-clips" 6 and 5 show a similar color change and the same trend in the UV/vis absorption spectra as the anthracene and naphthalene clip 1 and 2. This finding already rules out that the color of these systems is a result of "through-space" π-π interactions between the aromatic sidewalls in the molecular clips 1 and 2. Quantum chemical ab initio calculations provide good evidence that the bathochromic shift of the absorption band at the longest wavelength observed in the UV/vis spectra of the clip quinones 2, 3, and 1 and the "half- clip" quinones 4, 5, and 6 with an increasing number of rings in the anellated aromatic unit (from benzene to anthracene) is the result of an increasing configuration interaction between a n → π* excitation of the quinoid component and a π → π* excitation with intramolecular charge transfer (CT) character. The initial π orbitals involved here and in higher lying transitions mainly stem from through-space interactions between π orbitals of the aromatic sidewalls and π orbitals of the quinone moiety with varying degree of mixing. The configuration interaction in the excited states can be considered to be a homoconjugation, that is, the relevant charge transfer states are formed across an allegedly insulating aliphatic bridge. The UV/vis spectra of the molecular clips 1-3, the "half-clips" 4-6, and the quinones 32 and 33 simulated by means of quantum chemical ab initio calculations agree well with the experimental spectra. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ja910362j
  • 2010 • 11 Investigation of the internal substructure of microbands in a deformed copper single crystal: Experiments and dislocation dynamics simulation
    Dmitrieva, O. and Svirina, J.V. and Demir, E. and Raabe, D.
    Modelling and Simulation in Materials Science and Engineering 18 (2010)
    We investigate the internal structure of microbands in a shear-deformed copper single crystal. The microstructure is characterized using high-resolution electron backscatter diffraction. The occurrence of microbands is due to the alternation of local orientation, which is characteristic of a deformation laminate. These microbands contain a substructure consisting of further local 1°-orientation alternations. A two-dimensional discrete dislocation dynamics model is used to describe the orientation substructure within the microbands. The boundary conditions for the simulation were estimated from the distribution of the geometrically necessary dislocation density obtained from the orientation map. The dislocation arrangement in the dynamic simulation explains the formation of the experimentally observed substructure. © 2010 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0965-0393/18/8/085011
  • 2010 • 10 Liquid injection MOCVD grown binary oxides and ternary rare-earth oxide as alternate gate-oxides for logic devices
    Thomas, R. and Ehrhart, P. and Waser, R. and Schubert, J. and Devi, A. and Katiyar, R.S.
    ECS Transactions 33 211-219 (2010)
    ZrO2, HfO2 and DyScO3 thin films having thickness in the range 2-20 nm were grown on SiOx/Si(100) substrates in a multi-wafer planetary MOCVD reactor combined with a liquid delivery system using engineered precursors. Growth rate, surface morphology, crystal structure, crystal density of the as-deposited films were analysed as a function of deposition temperature. The influence of post deposition annealing on the densification and crystallization was studied. Electrical properties of MIS capacitor structures are also discussed. Results on the optimised gate stack of Pt/ZrO2/SiOx/Si, Pt/HfO2/SiOx/Si, Pt/DyScO3/SiOx/Si are finally compared; and DyScO 3 seems to be promising high-k material candidate compared to Group-IVB oxides for the coming technology nodes. ©The Electrochemical Society.
    view abstractdoi: 10.1149/1.3481608
  • 2010 • 9 Modification of GaAs surface by low-current Townsend discharge
    Gurevich, E.L. and Kittel, S. and Hergenröder, R. and Astrov, Y.A. and Portsel, L.M. and Lodygin, A.N. and Tolmachev, V.A. and Ankudinov, A.V.
    Journal of Physics D: Applied Physics 43 (2010)
    The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 μA cm-2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (< 1 eV) changes the crystal structure of the semiconductor for a depth of up to 10-20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (< 10 eV) forms an oxide layer, which is 5-10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase. © 2010 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/43/27/275302
  • 2010 • 8 Pd-Ga intermetallic compounds as highly selective semihydrogenation catalysts
    Armbrüster, M. and Kovnir, K. and Behrens, M. and Teschner, D. and Grin, Y. and Schlögl, R.
    Journal of the American Chemical Society 132 14745-14747 (2010)
    The intermetallic compounds Pd3Ga7, PdGa, and Pd 2Ga are found to be highly selective semihydrogenation catalysts for acetylene outperforming established systems. The stability of the crystal and electronic structure under reaction conditions allows the direct relation of structural and catalytic properties and a knowledge-based development of new intermetallic catalyst systems. In the crystal structure of PdGa palladium is exclusively surrounded by gallium atoms. The alteration of the Pd coordination in PdGa leads to a strong modification of the electronic structure around the Fermi level in comparison to elemental Pd. Electronic modification and isolation of active sites causes the excellent catalytic semihydrogenation properties. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ja106568t
  • 2010 • 7 Photoluminescence studies on structural defects and room temperature ferromagnetism in Ni and Ni-H doped ZnO nanoparticles
    Tong, L.-N. and Cheng, T. and Han, H.-B. and Hu, J.-L. and He, X.-M. and Tong, Y. and Schneider, C.M.
    Journal of Applied Physics 108 (2010)
    We explore the effects of hydrogenated annealing on the crystal structure, room temperature ferromagnetism (RT-FM) and photoluminescence (PL) properties of Ni-doped ZnO (Zn1-xNixO, x=0.0 to 0.2) nanoparticles prepared by a sol-gel method. The x-ray photoelectron spectra and x-ray diffraction data provide evidence that Ni has been incorporated into the wurtzite ZnO lattice as Ni2+ ions substituting for Zn2+ ions at x0.05. A secondary phase of NiO type begins to form inside ZnO when x≤0.05 and segregates from ZnO host lattice at x=0.2, leading to a large variation in the lattice constants of ZnO. The magnetization measurements show that the saturation magnetization (Ms) increases with increasing Ni concentration in the single-phase Zn1-xNixO (x≤0.05) nanoparticles. The secondary phase formation reduces the magnetization of Zn1-xNixO (x=0.1 and 0.15), while the segregation of NiO from the ZnO lattice at x=0.2 is accompanied by a large increase in M s again. The PL measurements show that the UV emission intensity of single-phase Zn1-xNixO (x≤0.05) nanoparticles increases with a blueshift in the UV emission line when the Ni concentration increases, while the dominant green emission intensity decreases with increasing Ni dopant. The PL data strongly suggest that the FM in single-phase Zn 1-xNixO (x≤0.05) nanoparticles is intrinsically correlated with a doping induced increase in the electron concentration in the conduction band of Ni-doped ZnO. After H2 -annealing, the single-phase Zn1-x NixO:H (x≤0.05) nanoparticles show increases in both coercivity and saturation magnetization. The PL and diffuse reflectance spectra suggest that hydrogen-related shallow donors and an improved sample quality may be responsible for the H2-annealing induced enhancement of the RT-FM. The obvious correlation between FM and carrier concentration in Ni and Ni-H doped ZnO points towards a mechanism of carrier-mediated FM for Ni-doped ZnO diluted magnetic semiconductors. © 2010 American Institute of Physics.
    view abstractdoi: 10.1063/1.3460644
  • 2010 • 6 Proteus in the world of proteins: Conformational changes in protein kinases
    Rabiller, M. and Getlik, M. and Klüter, S. and Richters, A. and Tückmantel, S. and Simard, J.R. and Rauh, D.
    Archiv der Pharmazie 343 193-206 (2010)
    The 512 protein kinases encoded by the human genome are a prime example of nature's ability to create diversity by introducing variations to a highly conserved theme. The activity of each kinase domain is controlled by layers of regulatory mechanisms involving different combinations of post-translational modifications, intramolecular contacts, and intermolecular interactions. Ultimately, they all achieve their effect by favoring particular conformations that promote or prevent the kinase domain from catalyzing protein phosphorylation. The central role of kinases in various diseases has encouraged extensive investigations of their biological function and three-dimensional structures, yielding a more detailed understanding of the mechanisms that regulate protein kinase activity by conformational changes. In the present review, we discuss these regulatory mechanisms and show how conformational changes can be exploited for the design of specific inhibitors that lock protein kinases in inactive conformations. In addition, we highlight recent developments to monitor ligand-induced structural changes in protein kinases and for screening and identifying inhibitors that stabilize enzymatically incompetent kinase conformations. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/ardp.201000028
  • 2010 • 5 Studies regarding the homogeneity range of the zirconium phosphide telluride Zr2+δPTe2
    Tschulik, K. and Hoffmann, S. and Fokwa, B.P.T. and Gilleßen, M. and Schmidt, P.
    Solid State Sciences 12 2030-2035 (2010)
    The phosphide tellurides Zr2+δPTe2 (0 ≤ δ ≤ 1) can be synthesized from the elements in a solid state reaction or by thermal decomposition of Z. Zr2PTe2 decomposes under release of Te2(g) + P4(g) forming the homogeneity range Zr2+δPTe2. The growth of single crystals of Zr 2+δPTe2 succeeded by chemical vapour transport using iodine as transport agent from 830 °C in direction of higher temperatures up to 900 °C. Zr2+δPTe2 crystallizes in the rhombohedral space group R3m (no. 166) with lattice parameters a = 383(1)...386(1) pm and c = 2935(4)...2970(4) pm for δ = 0...1, respectively. Single crystal data have been determined for Zr 2.40(2)PTe2 with lattice parameters a = 385.24(4) pm and c = 2967.8(4) pm. The electronic structure and chemical bonding in Zr 2+δPTe2 was investigated by the linear muffin-tin orbital (LMTO) method. Both Zr2PTe2 and Zr 3PTe2 show non-vanishing DOS values at the Fermi level (EF) indicating metallic character. According to COHP bonding analyses, mainly the heteroatomic Zr-P and Zr-Te bonds are responsible for the structural stability of Zr3PTe2. The new Zr2-Te bond, which is not present in Zr2PTe2, is stronger than Zr1-Te and is thought to be responsible for the stability of phases having Zr in excess.
    view abstractdoi: 10.1016/j.solidstatesciences.2010.08.022
  • 2010 • 4 Synthesis and characterization of ag- or sb-doped zno nanorods by a facile hydrothermal route
    Lupan, O. and Chow, L. and Ono, L.K. and Cuenya, B.R. and Chai, G. and Khallaf, H. and Park, S. and Schulte, A.
    Journal of Physical Chemistry C 114 12401-12408 (2010)
    ZnO nanorods doped with Ag and Sb have been synthesized by a facile hydrothermal technique. Crystal quality, morphology, chemical/electronic composition, local structure, and vibrational mode properties are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and micro-Raman spectroscopy. Evidence of dopant incorporation is demonstrated in the XPS measurements of both Sb-doped and Ag-doped ZnO nanorods. From XRD data, it was found that the doped ZnO nanorods have a lower degree of crystallinity. The lattice constants of doped ZnO nanorods were slightly larger than that of the pure samples. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/jp910263n
  • 2010 • 3 Synthesis and characterization of ZnO nanowires for nanosensor applications
    Lupan, O. and Emelchenko, G.A. and Ursaki, V.V. and Chai, G. and Redkin, A.N. and Gruzintsev, A.N. and Tiginyanu, I.M. and Chow, L. and Ono, L.K. and Roldan Cuenya, B. and Heinrich, H. and Yakimov, E.E.
    Materials Research Bulletin 45 1026-1032 (2010)
    In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650 °C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200 nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman spectroscopy (RS) have been used to characterize the ZnO nanowires. To investigate the suitability of the CVD synthesized ZnO nanowires for gas sensing applications, a single ZnO nanowire device (50 nm in diameter) was fabricated using a focused ion beam (FIB). The response to H2 of a gas nanosensor based on an individual ZnO nanowire is also reported. © 2010 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.materresbull.2010.03.027
  • 2010 • 2 Synthesis and structure analysis of RUB-50, an LEV-type aluminosilicate zeolite
    Yamamoto, K. and Ikeda, T. and Onodera, M. and Muramatsu, A. and Mizukami, F. and Wang, Y. and Gies, H.
    Microporous and Mesoporous Materials 128 150-157 (2010)
    An LEV-type aluminosilicate zeolite RUB-50 was synthesized in the presence of diethyldimethylammonium (DEDMA) cation as a structure-directing agent (SDA), and its crystal structure was analyzed in detail by the Rietveld refinement and the maximum entropy method (MEM). RUB-50 was crystallized from an Al-containing mother gel with relatively low water content. As-made RUB-50 contained a large amount of organic SDAs in the cavity, and therefore calcined RUB-50 exhibited a large micropore volume. Through the MEM analysis of the as-made RUB-50, the actual conformation of the SDA molecule occluded in the cavity emerged. In accordance with the structural analysis, quaternary ammonium cations possibly having molecular conformations similar to that of DEDMA successfully direct the crystallization of LEV-type zeolites. © 2009 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.micromeso.2009.08.016
  • 2010 • 1 Synthesis, characterization and structure analysis of UZM-22, a MEI-type zeolite framework structure
    Wang, G. and Marler, B. and Gies, H. and Fyfe, C.A. and Sidhu, P. and Yilmaz, B. and Müller, U.
    Microporous and Mesoporous Materials 132 43-53 (2010)
    ZSM-18 related zeolite UZM-22, framework type MEI, was synthesized with choline as structure directing agent (SDA). Sr2+ and Li+ are additional essential components in the synthesis. Rietveld structure analysis of the as synthesized sample confirmed the proposed crystal structure in space group P63/m with a = 13.1544(7) and c = 15.7409(3) and composition (Sr1.17Li0.05)[Si27.92Al6.08 O68]*3.69SDA*23.85H2O. Calcination showed that the material is stable up to at least 600 °C. Solid state NMR experiments revealed that the framework de-aluminated upon calcination and that Li is part of the as-made material as cation. N2 adsorption experiments confirmed the low framework density with a high surface area of 592 m2/g. The 12R pore has a diameter of 6.9 Å. Ammonium TPD revealed a high number of acid sites. © 2009 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.micromeso.2009.08.021