- Ruhr-Universität Bochum

Ion-induced secondary electron emission at a target surface is an essential mechanism for laboratory plasmas, i.e. magnetron sputtering discharges. Electron emission, however, is strongly affected by the target condition itself such as oxidation. Data of oxidized targets, however, are very sparse and prone to significant systematic errors, because they were often determined by modeling the complex behavior of the plasma. Thus, it is difficult to isolate the process of ion-induced electron emission from all other plasma-surface-interactions. By utilizing ion beams, the complex plasma environment is avoided and electron yields are determined with higher accuracy. In this study, ion-induced secondary electron emission coefficients (SEECs) of clean, untreated (air-exposed), and intentionally oxidized copper and nickel surfaces were investigated in such a particle beam experiment. Pristine and oxidized metal foils were exposed to beams of singly charged argon ions with energies of 0.2 keV-10 keV. After the ion beam treatment, the surface conditions were analyzed by ex-situ X-ray photoelectron spectroscopy measurements. Further, a model for the electron emission of a partly oxidized surface is presented, which is in agreement with the experimental data. It was found, that oxidized and untreated/air-exposed surfaces do not show the same SEEC: for intentionally oxidized targets, the electron yields were smaller by a factor of 2 than for untreated/air-exposed surfaces. SEECs of oxides were found to be between the values for clean and for untreated metal surfaces. Further, the SEEC was at maximum for untreated/air-exposed surfaces and at minimum for clean surfaces; the electron yields of untreated/air-exposed and clean surfaces were in agreement with values reported in the literature. © 2022 The Author(s). Published by IOP Publishing Ltd.

Grazing incidence X-ray diffraction (GIXRD) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) were employed to study the microstructure evolution and stress development in the nanocrystalline Cu100−X-ZrX (2.5 at% ≤ x ≤ 5.5 at%) alloy thin films. Small Zr additions to Cu led to significant lattice parameter anisotropy in the as-deposited Cu-Zr thin films both due to macroscopic lattice strain and stacking faults in the Cu matrix. Strain free lattice parameters obtained after the XRD stress analysis of Cu-Zr thin films confirmed formation of a supersaturated substitutional Cu-Zr solid solution. For the first time, the study of film microstructure by XRD line profile analysis (XLPA) confirmed progressive generation of dislocations and planar faults with increasing Zr composition in Cu-Zr alloy films. These microstructural changes led to the generation of tensile stresses in the thin films along with considerable stress gradients across the films thicknesses which are quantified by the traditional dψhkl−Sin2ψ and GIXRD stress measurement methods. The origin of tensile stresses and stress gradients in the Cu-Zr film are discussed on the basis of film growth and heterogeneous microstructure with changing Zr composition. © 2021

Premature failure of rail and bearing steels by White-Etching-Cracks leads to severe economic losses. This failure mechanism is associated with microstructure decomposition via local severe plastic deformation. The decomposition of cementite plays a key role. Due to the high hardness of this phase, it is the most difficult obstacle to overcome in the decaying microstructure. Understanding the mechanisms of carbide decomposition is essential for designing damage-resistant steels for industrial applications. We investigate cementite decomposition in the bearing steel 100Cr6 (AISI 52100) upon exposure to high-pressure torsion (maximum shear strain, Ƴmax = 50.2). Following-up on our earlier work on cementite decomposition in hardened 100Cr6 steel (Qin et al., Act. Mater. 2020 [1]), we now apply a modified heat treatment to generate a soft-annealed microstructure where spherical and lamellar cementite precipitates are embedded in a ferritic matrix. These two precipitate types differ in morphology (spherical vs. lamellar), size (spherical: 100–1000 nm diameter, lamellar: 40–100 nm thickness) and composition (Cr and Mn partitioning). We unravel the correlation between cementite type and its resistance to decomposition using multi-scale chemical and structural characterization techniques. Upon high-pressure torsion, the spherical cementite precipitates did not decompose, but the larger spherical precipitates (≥ 1 μm) deformed. In contrast, the lamellar cementite precipitates underwent thinning followed by decomposition and dissolution. Moreover, the decomposition behavior of cementite precipitates is affected by the type of matrix microstructure. We conclude that the cementite size and morphology, as well as the matrix mechanical properties are the predominating factors influencing the decomposition behavior of cementite. The compositional effects of Cr and Mn on cementite stability calculated by complementary density functional theory (DFT) calculations are minor in the current scenario. © 2021 Elsevier B.V.

The atomic cluster expansion (ACE) provides a general, local, and complete representation of atomic energies. Here we present an efficient framework for parametrization of ACE models for elements, alloys, and molecules. To this end, we first introduce general requirements for a physically meaningful description of the atomic interaction, in addition to the usual equivariance requirements. We then demonstrate that ACE can be converged systematically with respect to two fundamental characteristics—the number and complexity of basis functions and the choice of nonlinear representation. The construction of ACE parametrizations is illustrated for several representative examples with different bond chemistries, including metallic copper, covalent carbon, and several multicomponent molecular and alloy systems. We discuss the Pareto front of optimal force to energy matching contributions in the loss function, the influence of regularization, the importance of consistent and reliable reference data, and the necessity of unbiased validation. Our ACE parametrization strategy is implemented in the freely available software package pacemaker that enables largely automated and GPU accelerated training. The resulting ACE models are shown to be superior or comparable to the best currently available ML potentials and can be readily used in large-scale atomistic simulations. ©2022 American Physical Society

Selective laser melting (SLM), taking advantage of its inherent rapid cooling rates and near-net-shape forming ability, has been employed to fabricate bulk metallic glasses (BMGs). However, crystallization is frequently triggered during the SLM process, which results in the loss of advantageous properties of BMGs, such as extremely high hardness and near-theoretical yield strength. Although many studies have been conducted to investigate SLM of BMGs, there is still a lack of knowledge about the microstructural and compositional evolution during the laser beam processing, particularly the micromechanical property response upon crystallization. In the present work, a systematic investigation is performed to gain a much better understanding about the evolution of microstructure and composition as well as the corresponding micromechanical property change during multiple laser beam melting. The material used in this study is an industrial-grade Zr-based BMG Zr59.3Cu28.8Al10.4Nb1.5 (AMZ4) with two different oxygen levels. AMZ4 demonstrates its good thermal stability by the fact that observable crystalline structure appears around the melt pool only after more than once laser beam treatment. The compositional stability of AMZ4 is manifested by the homogeneous elemental distribution on the melt pool area after even twenty-five laser beam remelting. The laser-metal interaction, melting and subsequent solidification are not effectively influenced by the emerging and expanding of crystallization zone (or heat affected zone, HAZ). Higher oxygen content results in not only a larger HAZ but also more quenched-in nuclei at the melt pool bottom. The HAZ does not exhibit a fully crystallized structure, but rather has a mixture of amorphous and crystalline phases. Crystallization of AMZ4 leads to an increase in hardness and Young's modulus of the material. © 2022 Elsevier B.V.

Reduction of nitric oxide was investigated using Cu electrodes in acid and neutral pH conditions. Analysis of Cu discs in stagnant electrolyte by Electrochemical Mass Spectrometry (EC-MS), revealed the favorable formation of ammonia (and hydrogen) in acidic electrolyte, while N2O and N2 are formed in significant quantities at neutral conditions. Additional performance evaluation of Cu electrodes in hollow fiber geometry, was performed using 10 vol % NO in Ar supplied through the porous electrode structure and off-line determination of ammonia by 1H NMR spectroscopy. The pH dependent performance of the Cu hollow fiber is in agreement with EC-MS data at low gas flow rates, showing the highest ammonia selectivity in acidic conditions. However, at relatively high gas flow rates, almost 90 % faradaic efficiency and a NH3 production rate of 400 μmol h−2 cm−2 were obtained in neutral electrolyte at −0.6 V vs RHE, likely due to enhanced availability of NO at the electrode surface, suppressing the hydrogen evolution reaction. This approach shows conversion of waste NO gas to valuable green fertilizer components is possible. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH

We demonstrate by Raman Spectroscopy that simultaneous reduction of NO3- and CO2 on Cu surfaces leads to formation of Cu-C[tbnd]N–like species, showing Raman bands at 2080 and 2150 cm−1 when associated with reduced or oxidized Cu surfaces, respectively. Furthermore Cu-C[tbnd]N–like species are soluble, explaining vast restructuring of the Cu surface observed after co-electrolysis of CO2 and nitrate. Oxidation of deposited Cu-C[tbnd]N–like species results in the formation of NO. Cu-C[tbnd]N–like species do not form in electrolytes containing i) NH4+ and CO2, or ii) NO3- and HCOO-, suggesting these likely originate from Cu-CO, the commonly accepted intermediate in electrochemical reduction of CO2, and Cu-NHx species, previously identified in the literature as intermediate towards C-N bond formation. The implications of the previously unresolved formation of Cu-C[tbnd]N–like species for the development of electrodes and processes for electrochemical formation of carbon-nitrogen bonds, including urea, amines or amides, are briefly discussed. © 2022 The Authors

Electrocatalytic recycling of waste nitrate (NO3−) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3−-to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3− reduction to NO2−, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3−-to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3− concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm−2 h−1 in 0.1 M NO3− at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports. © 2022, The Author(s).

The adsorption orientation of molecules on surfaces influences their reactivity, but it is still challenging to tailor the interactions that govern their orientation. Here, we investigate how the substituent and the surface structure alter the adsorption orientation of halogenated benzene molecules from parallel to tilted relative to the surface plane. The deviation of the parallel orientation of bromo-, chloro-, and fluorobenzene molecules adsorbed on Cu(111) and Cu(110) surfaces is determined, utilising the surface selection rule in reflection-absorption infrared spectroscopy. On Cu(111), all three halogenated molecules are adsorbed with their molecular plane almost parallel to the surface at low coverages. However, they are tilted at higher coverages; yet, the threshold coverages differ. On Cu(110), merely bromo- and chlorobenzene follow this trend, albeit with a lower threshold for both. In contrast, fluorobenzene molecules are tilted already at low coverages. The substantial influence of the halogen atom and the surface structure on the adsorption orientation, resulting from an interplay of molecule-molecule and molecule-surface interactions, is highly relevant for reactivity confined to two dimensions. © 2022 the Owner Societies.

The electrochemical properties of high strength 7xxx aluminium alloys strongly depend on the substitutional occupancy of Zn by Cu and Al in the strengthening η-phase with the two-sublattice structure, and its microstructural and compositional prediction is the key to design of new generation corrosion resistant alloys. In this work, we have developed a chemical-potential-based phase-field model capable of describing multi-component and two-sublattice ordered phases, during commercial multi-stage artificial ageing treatments, by directly incorporating the compound energy CALPHAD formalism. The model developed has been employed to explore the complex compositional pathway for the formation of the η-phase in Al-Zn-Mg-Cu alloys during heat treatments. In particular, the influence of alloy composition, solute diffusivity, and heat treatment parameters on the microstructural and compositional evolution of η-phase precipitates, was systematically investigated from a thermodynamic and kinetic perspective and compared to electron probe microanalysis validation data. The simulated η-phase growth kinetics and the matrix residual solute evolution in the AA7050 alloy indicates that Zn depletion mainly controlled the η-phase growth process during the early stage of ageing, resulting in fast η-phase growth kinetics, enrichment of Zn in the η-phase, and an excess in residual Cu in the matrix. The gradual substitution of Zn by Cu atoms in the η-phase during the later ageing stage was in principle a kinetically controlled process, owing to the slower diffusivity of Cu relative to Zn in the matrix. It was also found that the higher nominal Zn content in alloys like the AA7085 alloy, compared to the AA7050 alloy, could significantly enhance the chemical potential of Zn, but this had a minor influence on Cu, which essentially led to the higher Zn content (and consequently lower Cu) seen in the η-phase. Finally, substantial depletion of Zn and supersaturation of Cu in the matrix of the AA7050 alloy was predicted after 24 h ageing at 120 ∘C, whereas the second higher-temperature ageing stage at 180 ∘C markedly enhanced the diffusion of Cu from the supersaturated matrix into the η-phase, while the matrix residual Zn content was only slightly affected. © 2021 The Author(s)

Nanocatalyst optimisation through electrochemical dealloying has been employed as a successful strategy to increase catalytic activity, while reducing the need for precious metals. We present here a new pathway to influence the electrochemical dealloying, through external homogeneous magnetic fields. A homogeneous magnetic field with a flux density of 450 mT in two orientations, parallel or perpendicular to the current direction, was used during electrochemical dealloying using cyclic voltammetry of AgAu nanoparticles. We found increased porosity for low dealloying cycle numbers and improved catalytic properties after longer cycling, compared to nanoparticles dealloyed in the absence of magnetic fields. These findings demonstrate that magnetic fields applied during electrochemical dealloying have currently untapped potential that can be used to influence material properties in a new way and give researchers another powerful tool for material design. © 2022

The current Coronavirus Disease 19 (COVID-19) pandemic has exemplified the need for simple and efficient prevention strategies that can be rapidly implemented to mitigate infection risks. Various surfaces have a long history of antimicrobial properties and are well described for the prevention of bacterial infections. However, their effect on many viruses has not been studied in depth. In the context of COVID-19, several surfaces, including copper (Cu) and silver (Ag) coatings have been described as efficient antiviral measures that can easily be implemented to slow viral transmission. In this study, we detected antiviral properties against Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) on surfaces, which were coated with Cu by magnetron sputtering as thin Cu films or as Cu/Ag ultrathin bimetallic nanopatches. However, no effect of Ag on viral titers was observed, in clear contrast to its well-known antibacterial properties. Further enhancement of Ag ion release kinetics based on an electrochemical sacrificial anode mechanism did not increase antiviral activity. These results clearly demonstrate that Cu and Ag thin film systems display significant differences in antiviral and antibacterial properties which need to be considered upon implementation. © 2022, The Author(s).

Gas diffusion electrodes (GDE) obtained by sputtering metal films on polytetrafluoroethylene (PTFE) membranes are among the most performant electrodes used to electrochemically reduce CO2. The present work reveals several essential aspects for fabricating performant PTFE-based gas diffusion electrodes (GDEs) for CO2 electroreduction (CO2R). We show that adding an additive layer (a mixture of carbon and Nafion™ or Nafion™ only) is required for stabilizing the metal catalyst film (Cu), deposited via sputtering on the PTFE membrane, during the CO2R experiments. We found that the PTFE membrane thickness used in the GDE fabrication plays an essential role in electrode performance. The quantification of the products formed during the CO2R conducted in a flow-cell electrolyzer revealed that on thinner membranes, CO2R is the dominant process while on thicker ones, the H2 formation is promoted. Thus, the PTFE membrane influences the CO2 transport to the catalyst layer and can be used to promote the CO2R while maintaining a minimum H2 production. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH

Bimetallic tandem catalysts have emerged as a promising strategy to locally increase the CO flux during electrochemical CO2 reduction, so as to maximize the rate of conversion to C−C-coupled products. Considering this, a novel Cu/C−Ag nanostructured catalyst has been prepared by a redox replacement process, in which the ratio of the two metals can be tuned by the replacement time. An optimum Cu/Ag composition with similarly sized particles showed the highest CO2 conversion to C2+ products compared to non-Ag-modified gas-diffusion electrodes. Gas chromatography and in-situ Raman measurements in a CO2 gas diffusion cell suggest the formation of top-bound linear adsorbed *CO followed by consumption of CO in the successive cascade steps, as evidenced by the increasingνC−H bands. These findings suggest that two mechanisms operate simultaneously towards the production of HCO2H and C−C-coupled products on the Cu/Ag bimetallic surface. © 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.

Grain boundaries (GBs) are planar lattice defects that govern the properties of many types of polycrystalline materials. Hence, their structures have been investigated in great detail. However, much less is known about their chemical features, owing to the experimental difficulties to probe these features at the atomic length scale inside bulk material specimens. Atom probe tomography (APT) is a tool capable of accomplishing this task, with an ability to quantify chemical characteristics at near-atomic scale. Using APT data sets, we present here a machine-learning-based approach for the automated quantification of chemical features of GBs. We trained a convolutional neural network (CNN) using twenty thousand synthesized images of grain interiors, GBs, or triple junctions. Such a trained CNN automatically detects the locations of GBs from APT data. Those GBs are then subjected to compositional mapping and analysis, including revealing their in-plane chemical decoration patterns. We applied this approach to experimentally obtained APT data sets pertaining to three case studies, namely, Ni-P, Pt-Au, and Al-Zn-Mg-Cu alloys. In the first case, we extracted GB specific segregation features as a function of misorientation and coincidence site lattice character. Secondly, we revealed interfacial excesses and in-plane chemical features that could not have been found by standard compositional analyses. Lastly, we tracked the temporal evolution of chemical decoration from early-stage solute GB segregation in the dilute limit to interfacial phase separation, characterized by the evolution of complex composition patterns. This machine-learning-based approach provides quantitative, unbiased, and automated access to GB chemical analyses, serving as an enabling tool for new discoveries related to interface thermodynamics, kinetics, and the associated chemistry-structure-property relations. © 2022 The Authors

Different loadings of Cu single atoms were anchored on a graphitic carbon nitride (g-C3N4) matrix using a two-step thermal synthesis method and applied in liquid-phase cyclohexene oxidation under mild conditions using molecular O2 as the oxidizing agent. The oxidation state of Cu was determined to be Cu+, which is in linear coordination with two neighboring nitrogen atoms at a distance of 1.9 Å. The catalyst with 0.9 wt % Cu pyrolyzed at 380 °C was found to exhibit the best catalytic performance with the highest conversion up to 82% with an allylic selectivity of 55%. It also showed high reusability over four catalytic runs without any detectable Cu leaching. Cyclohexene oxidation followed first-order kinetics with an apparent activation energy of 66.2 kJ mol-1. The addition of hydroquinone as a radical scavenger confirmed that cyclohexene oxidation proceeds via a radical mechanism. Time-resolved in situ attenuated total reflection infrared (ATR-IR) spectroscopy was carried out to qualitatively monitor the cyclohexene oxidation pathways. The comparison with the homogeneous analogue Cu(I) iodide indirectly verified the linearly N-coordinated single Cu(I) species to be the active sites for cyclohexene oxidation. © 2021 American Chemical Society.

Understanding the structure-property relations of non-precious metal heteroatom co-doped carbon electrocatalysts exhibiting high activity as well as long-term durability for both ORR and OER remains challenging but is indispensable for the development of bifunctional ORR/OER electrocatalysts. We propose B-N-co-doped graphitic 2D carbon nanostructures impregnated with controlled amount of transition metals (M-BCN; M=Co, Ni, Fe, Cu) as bifunctional ORR/OER electrocatalysts. Co-BCN outperformed the Ni-, Fe-, Cu-based BCN catalysts exhibiting potential values of 0.87 V and 1.62 V at −1 mA/cm2 and 10 mA/cm2 during ORR and OER, respectively. Importantly, Co-BCN shows bifunctional cyclic stability (Δη; EOER−EORR=0.75 V) of up to 300 cycles in 1 M KOH for a duration of 20 h with total activity loss of only 10.2 % (ORR) and 6.2 % (OER), respectively. A low loading of the metal precursors was used to preserve porosity and to facilitate the formation of metal nanoparticles or M−NxB/C type species embedded in the graphitic carbon layers. The B-N-co-doped graphitic layers also protect the embedded metal nanoparticles explaining the observed long-term stability. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH

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.

Motivated by the recent experiments suggesting the importance of nematicity in the phase diagrams of iron-based and cuprate high-Tc superconductors, we study the influence of nematicity on the collective modes inside the superconducting state in a nonequilibrium. In particular, we consider the signatures of collective modes in short-time dynamics of a system with competing nematic and s- and d-wave superconducting orders. In the rotationally symmetric state, we show that the Bardasis-Schrieffer mode, corresponding to the subdominant pairing, hybridizes with the nematic collective mode and merges into a single in-gap mode, with the mixing vanishing only close to the phase boundaries. For the d-wave ground state, we find that nematic interaction suppresses the damping of the collective oscillations in the short-time dynamics. Additionally, we find that even inside the nematic s+d-wave superconducting state, a Bardasis-Schrieffer-like mode leads to order parameter oscillations that strongly depend on the competition between the two pairing symmetries. We discuss the connection of our results to the recent pump-probe experiments on high-Tc superconductors. © 2021 American Physical Society.

The effectiveness of the mechanism of precipitation strengthening in metallic alloys de-pends on the shapes of the precipitates. Two different material systems are considered: tetragonal γ′′ precipitates in Ni-based alloys and tetragonal θ′ precipitates in Al-Cu-alloys. The shape formation and evolution of the tetragonally misfitting precipitates was investigated by means of experiments and phase-field simulations. We employed the method of invariant moments for the consistent shape quantification of precipitates obtained from the simulation as well as those obtained from the experiment. Two well-defined shape-quantities are proposed: (i) a generalized measure for the particles aspect ratio and (ii) the normalized λ2, as a measure for shape deviations from an ideal ellipse of the given aspect ratio. Considering the size dependence of the aspect ratio of γ′′ precipitates, we find good agreement between the simulation results and the experiment. Further, the precipitates’ in-plane shape is defined as the central 2D cut through the 3D particle in a plane normal to the tetragonal c-axes of the precipitate. The experimentally observed in-plane shapes of γ′′-precipitates can be quantitatively reproduced by the phase-field model. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Grain boundaries (GBs) in metals usually increase electrical resistivity due to their distinct atomic arrangement compared to the grain interior. While the GB structure has a crucial influence on the electrical properties, its relationship with resistivity is poorly understood. Here, we perform a systematic study on the resistivity-structure relationship in Cu tilt GBs, employing high-resolution in situ electrical measurements coupled with atomic structure analysis of the GBs. Excess volume and energies of selected GBs are calculated using molecular dynamics simulations. We find a consistent relation between the coincidence site lattice (CSL) type of the GB and its resistivity. The most resistive GBs are in the high range of low-angle GBs (14°-18°) with twice the resistivity of high angle tilt GBs, due to the high dislocation density and corresponding strain fields. Regarding the atomistic structure, GB resistivity approximately correlates with the GB excess volume. Moreover, we show that GB curvature increases resistivity by ∼80%, while phase variations and defects within the same CSL type do not considerably change it. © 2021 The Authors. Published by American Chemical Society.

The atomic cluster expansion is a general polynomial expansion of the atomic energy in multi-atom basis functions. Here we implement the atomic cluster expansion in the performant C++ code PACE that is suitable for use in large-scale atomistic simulations. We briefly review the atomic cluster expansion and give detailed expressions for energies and forces as well as efficient algorithms for their evaluation. We demonstrate that the atomic cluster expansion as implemented in PACE shifts a previously established Pareto front for machine learning interatomic potentials toward faster and more accurate calculations. Moreover, general purpose parameterizations are presented for copper and silicon and evaluated in detail. We show that the Cu and Si potentials significantly improve on the best available potentials for highly accurate large-scale atomistic simulations. © 2021, The Author(s).

By considering the valence-electron concentration of 3d transition-metal alloys and compounds, we develop 3d high-entropy alloy Mn12.1Fe34.2Co33.5Ni12.3Cu7.9 with 8.7 electrons per atom, which is identical to that of Fe65Ni35 Invar. We carry out X-ray diffraction, scanning electron microscopy, magnetization, thermal expansion, and elastic modulus measurements, by which we show that the HEA alloy indeed carries Invar properties. This is evidenced particularly by the observed spontaneous volume magnetostriction and the lattice softening covering a broad temperature-range around the ferromagnetic Curie temperature. © 2021 American Physical Society.

The phase-like behavior of grain boundaries (GBs), recently evidenced in several materials, is opening up new possibilities in the design of alloy microstructures. In this context, GB phase diagrams are contributing to a predictive description of GB segregation and (interfacial) phase changes. The influence of chemo-mechanical solute-GB interactions on the GB phase diagram remains elusive so far. This is particularly important for multi-component alloys where the elastic interactions among solute atoms, of various sizes and bonding energies, can prevail, governing a complex co-segregation phenomenon. Recently, we developed a density-based model for GB thermodynamics that intrinsically accounts for GB elasticity in pure elements. In this work, we incorporate the homogeneous and heterogeneous elastic energies associated with the solutes into the density-based framework. We derive the multi-component homogeneous elastic energy by generalizing the continuum misfitting sphere model and extend it for GBs. The density-based free energy functional directly uses bulk CALPHAD thermodynamic data. The model is applied to binary and ternary Al alloys. We reveal that the elastic energy can profoundly affect the GB solubility and segregation behavior, leading to Cu segregation in otherwise Cu-depleted Al GBs. Consequently, GB segregation transition, i.e., a jump in the GB segregation as a function of alloy composition, is revealed in Al-Cu and Al-Cu-Mg alloy systems with implications for subsequent GB precipitation in these alloys. CALPHAD-informed elasticity-incorporated GB phase diagrams enable addressing a broader range of GB phenomena in engineering multi-component alloys. © 2021 Elsevier B.V.

High-entropy alloys (HEAs) and compositionally complex alloys (CCAs) represent new classes of materials containing five or more alloying elements (concentration of each element ranging from 5 to 35 at. %). In the present study, HEAs are defined as single-phase solid solutions; CCAs contain at least two phases. The alloy concept of HEAs/CCAs is fundamentally different from most conventional alloys and promises interesting properties for industrial applications (e.g., to overcome the strength-ductility trade-off). To date, little attention has been paid to the weldability of HEAs/CCAs encompassing effects on the welding metallurgy. It remains open whether welding of HEAs/CCAs may lead to the formation of brittle intermetallics and promote elemental segregation at crystalline defects. The effect on the weld joint properties (strength, corrosion resistance) must be investigated. The weld metal and heat-affected zone in conventional alloys are characterized by non-equilibrium microstructural evolutions that most probably occur in HEAs/CCAs. The corresponding weldability has not yet been studied in detail in the literature, and the existing information is not documented in a comprehensive way. Therefore, this study summarizes the most important results on the welding of HEAs/CCAs and their weld joint properties, classified by HEA/CCA type (focused on CoCrFeMnNi and AlxCoCrCuyFeNi system) and welding process. © 2021, The Author(s).

The grain boundary (GB) microchemistry and precipitation behaviour in high-strength Al-Zn-Mg-Cu alloys has an important influence on their mechanical and electrochemical properties. Simulation of the GB segregation, precipitation, and solute distribution in these alloys requires an accurate description of the thermodynamics and kinetics of this multi-component system. CALPHAD databases have been successfully developed for equilibrium thermodynamic calculations in complex multi-component systems, and in recent years have been combined with diffusion simulations. In this work, we have directly incorporated a CALPHAD database into a phase-field framework, to simulate, with high fidelity, the complex kinetics of the non-equilibrium GB microstructures that develop in these important commercial alloys during heat treatment. In particular, the influence of GB solute segregation, GB diffusion, precipitate number density, and far-field matrix composition, on the growth of a population of GB η-precipitates, was systematically investigated in a model Al-Zn-Mg-Cu alloy of near AA7050 composition. It is shown that the GB solute distribution in the early stages of ageing was highly heterogeneous and strongly affected by the distribution of GB η-precipitates. Significant Mg and Cu GB segregation was predicted to remain during overageing, while Zn was rapidly depleted. This non-trivial GB segregation behaviour markedly influenced the resulting precipitate morphologies, but the overall precipitate transformation kinetics on a GB were relatively unaffected. Furthermore, solute depletion adjacent to the GB was largely determined by Zn and Mg diffusion, which will affect the development of precipitate free zones during the early stages of ageing. The simulation results were compared with scanning transmission electron microscopy and atom probe tomography characterisation of alloys of the similar composition, with good agreement. © 2021

In this work, we experimentally establish the isothermal nanofacet evolution at an asymmetric ∑5 tilt grain boundary in the Cu-Ag system using a diffusion couple approach. We investigate the nanofacet formation along the grain boundary in dependence of the Ag solute excess concentration. The initial grain boundary dissociates into asymmetric Ag-lean segments and Ag-rich symmetric (210) segments. Increasing Ag excess leads to an increase in Ag-rich facet segment length, while the length of the asymmetric facets remains constant. From this, we construct a grain boundary nanofaceting diagram deduced from our experiments relating local atomic structure, overall inclination and Ag solute excess. © 2021 The Author(s)

The aluminum alloy 2618A is applied for engine components such as radial compressor wheels which operate for long time at elevated temperatures. This results in coarsening of the hardening precipitates and degradation in mechanical properties during the long-term operation, which is not taken into account in the current lifetime prediction models due to the lack of quantitative microstructural and mechanical data. To address this issue, a quantitative investigation on the evolution of precipitates during long-term aging at 190 °C for up to 25,000 h was conducted. Detailed transmission electron microscopy (TEM) was combined with Brinell hardness measurements and thorough differential scanning calorimetry (DSC) experiments. The results show that GPB zones and S-phase Al2CuMg grow up to < 1,000 h during which the GPB zones dissolve and S-phase precipitates form. For longer aging times, only S-phase precipitates coarsen, which can be well described using the Lifshitz–Slyozov–Wagner theory of ripening. A thorough understanding of the underlying microstructural processes is a prerequisite to enable the integration of aging behavior into the established lifetime models for components manufactured from alloy 2618A. © 2021, The Author(s).

High-quality copper metal thin films are demanded for a number of advanced technologies. Herein, a facile ALD (atomic layer deposition) process for the fabrication of Cu metal films directly from two solid readily usable precursors, copper acetylacetonate as the source of copper and hydroquinone as the reductant is reported. This process yields highly crystalline, dense, specularly reflecting, and electrically conductive Cu films with an appreciably high growth rate of 1.8 Å/cycle at deposition temperatures as low as 160 to 240 °C. © 2021 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH

Cu-based catalysts have shown structural instability during the electrochemical CO2reduction reaction (CO2RR). However, studies on monometallic Cu catalysts do not allow a nuanced differentiation between the contribution of the applied potential and the local concentration of CO as the reaction intermediate since both are inevitably linked. We first use bimetallic Ag-core/porous Cu-shell nanoparticles, which utilise nanoconfinement to generate high local CO concentrations at the Ag core at potentials at which the Cu shell is still inactive for the CO2RR. Usingoperandoliquid cell TEM in combination withex situTEM, we can unequivocally confirm that the local CO concentration is the main source for the Cu instability. The local CO concentration is then modulated by replacing the Ag-core with a Pd-core which further confirms the role of high local CO concentrations. Product quantification during CO2RR reveals an inherent trade-off between stability, selectivity and activity in both systems. © The Royal Society of Chemistry 2021.

Developing highly efficient and selective electrocatalysts for the CO2 reduction reaction to produce value-added chemicals has been intensively pursued. We report a series of CuxOyCz nanostructured electrocatalysts derived from a Cu-based MOF as porous self-sacrificial template. Blending catalysts with polytetrafluoroethylene (PTFE) on gas diffusion electrodes (GDEs) suppressed the competitive hydrogen evolution reaction. 25 to 50 wt % teflonized GDEs exhibited a Faradaic efficiency of ≈54 % for C2+ products at −80 mA cm−2. The local OH− ions activity of PTFE-modified GDEs was assessed by means of closely positioning a Pt-nanoelectrode. A substantial increase in the OH−/H2O activity ratio due to the locally generated OH− ions at increasing current densities was determined irrespective of the PTFE amount. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

The effects of anisotropic interfacial properties and heterogeneous elasticity on the growth and ripening of plate-like θ’-phase (Al2Cu) in Al-1.69 at.% Cu alloy are studied. Multi-phase-field simulations are conducted and discussed in comparison with aging experiments. The precipi-tate/matrix interface is considered to be anisotropic in terms of its energy and mobility. We find that the additional incorporation of an anisotropic interfacial mobility in conjunction with the elastic anisotropy result in substantially larger aspect ratios of the precipitates closer to the experimental observations. The anisotropy of the interfacial energy shows comparably small effect on the precip-itate’s aspect ratio but changes the interface’s shape at the rim. The effect of the chemo-mechanical coupling, i.e., the composition dependence of the elastic constants, is studied as well. We show that the inverse ripening phenomenon, recently evidenced for δ’ precipitates in Al-Li alloys (Park et al. Sci. Rep. 2019, 9, 3981), does not establish for the θ’ precipitates. This is because of the anisotropic stress fields built around the θ’ precipitates, stemming from the precipitate’s shape and the interaction among different variants of the θ’ precipitate, that disturb the chemo-mechanical effects. These results show that the chemo-mechanical effects on the precipitation ripening strongly depend on the degree of sphericity and elastic isotropy of the precipitate and matrix phases. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Bimetallic silver-copper electrocatalysts are promising materials for electrochemical CO2 reduction reaction (CO2RR) to fuels and multi-carbon molecules. Here, we combine Ag core/porous Cu shell particles, which entrap reaction intermediates and thus facilitate the formation of C2+ products at low overpotentials, with gas diffusion electrodes (GDE). Mass transport plays a crucial role in the product selectivity in CO2RR. Conventional H-cell configurations suffer from limited CO2 diffusion to the reaction zone, thus decreasing the rate of the CO2RR. In contrast, in the case of GDE-based cells, the CO2RR takes place under enhanced mass transport conditions. Hence, investigation of the Ag core/porous Cu shell particles at the same potentials under different mass transport regimes reveals: (i) a variation of product distribution including C3 products, and (ii) a significant change in the local OH- activity under operation. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH

The restriction imposed by the lattice structure of different surfaces is used to investigate the influence of the distance between two monomers on their ability to bind to each other. We compare the interaction of ammonia monomers at two distinct distances imposed by the surface structure of a Cu(511) high-index surface to that of a Cu(110) low-index surface using low-temperature scanning tunneling microscopy, inelastic tunneling spectroscopy, and density functional theory. Frustrated translational and rotational modes, the Mulliken and Bader charge analyses, and electrostatic potential mapping indicate chemisorption of ammonia monomers on both surfaces, with their dipoles oriented perpendicular to the surface plane. At a larger intermolecular distance of around 0.51 nm on step edges of Cu(511), the monomers slightly repel each other due to electrostatic repulsion. At a shorter distance of around 0.36 nm perpendicular to the close-packed rows on Cu(110), a noticeable charge transfer between adjacent monomers indicates binding, that is, dimer formation in parallel orientation. This binding energy of the molecules compensates for the electrostatic repulsion. Our results outline how the choice of the surface structure may be utilized to alter the intermolecular interaction of solvent molecules and to enforce or suppress dimer formation. ©

Cu–Cr/55 vol% diamond composites with 1 wt % (Cu–1Cr/55Dia), 2 wt % (Cu–2Cr/55Dia), and 3 wt % (Cu–3Cr/55Dia) Cr additives, respectively, are fabricated by a hot forging method. The diamond particle surfaces are nearly completely covered by the formed carbides interface for the Cu–3Cr/55Dia composite, and the Cu–3Cr/55Dia has the highest measured thermal conductivity among the three fabricated composites (433 Wm−1K−1). High Resolution Transmission Electron Microscopy analyses suggest that a double-layered interface structure is formed between the copper matrix and the diamond particle in the Cu–3Cr/55Dia, which is composed of 160 nm-thick Cr3C2 and 2 nm-thick Cr23C6. This interface structure, together with high relative density of the composite, high interface coverage of diamond, thin interface layer, and formation of coherent atomic boundaries, significantly contributes to obtaining high thermal conductivity for the Cu–3Cr/55Dia composite. The Diffuse Mismatch Model and Differential Effective Medium model are modified for establishing the quantitative relationship among interface characteristics, interface thermal conductance, and the composite's thermal conductivity, based on considering the composite's interface structure and phonon transmission theory. The predicted thermal conductivity value is well matched with the measured value for the Cu–3Cr/diamond (487 Wm−1K−1 vs 433 Wm−1K−1). This helps understand heat transfer behavior in the Cu–Cr/diamond composites. © 2020 Elsevier Ltd

A combination of complementary high-energy X-ray diffraction, containerless solidification during electromagnetic levitation and transmission electron microscopy is used to map in situ the phase evolution in a prototype Cu-Zr-Al glass during flash-annealing imposed at a rate ranging from 102 to 103 K s−1 and during cooling from the liquid state. Such a combination of experimental techniques provides hitherto inaccessible insight into the phase-transformation mechanism and its kinetics with high temporal resolution over the entire temperature range of the existence of the supercooled liquid. On flash-annealing, most of the formed phases represent transient (metastable) states – they crystallographically conform to their equilibrium phases but the compositions, revealed by atom probe tomography, are different. It is only the B2 CuZr phase which is represented by its equilibrium composition, and its growth is facilitated by a kinetic mechanism of Al partitioning; Al-rich precipitates of less than 10 nm in a diameter are revealed. In this work, the kinetic and chemical conditions of the high propensity of the glass for the B2 phase formation are formulated, and the multi-technique approach can be applied to map phase transformations in other metallic-glass-forming systems. © 2021, The Author(s).

We investigate the shape of monatomic high Cu islands on a Cu(111) surface by variable-temperature scanning tunneling microscopy between 110 K and 240 K. Low temperature dendrites evolve towards more compact shapes at increasing temperature; finally reaching the equilibrium shape of a hexagon with rounded corners. Time-lapsed imaging at increasing temperature reveals the onset of shape change to be at ≈170 K, corresponding to the onset of edge and corner diffusion of atoms along the island's borders. Despite a substantial variation for individual islands at each temperature, the mean fractal dimension increases monotonously between 170 K up to 240 K, from the smallest to the largest values feasible for islands grown on surfaces. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.

Aiming at revealing plastic deformation mechanisms of nanoindentation tests, we investigate the crystallographic orientation-influenced indentation size effect in the Berkovich nanoindentation tests of single crystalline copper, by using the nonlocal crystal plasticity finite element approach and specifically designed experiments. In our simulation model of nanoindentation, a new geometrically necessary dislocation density-based crystal plasticity model is proposed, and the utilized model parameters are calibrated by fitting the measured load-displacement curves of indentation tests. Then the size of plastic zone of indentation tests is defined by the surface pile-up profile, i.e. the diameter of a circle consisting of material points with half of maximum pile-up height. It is found that the modified plastic zone model incorporated with the newly developed scaling factor provides good predication of the indentation depth-dependent hardness of single crystalline copper. © 2020 Elsevier Ltd

Metal alloy catalysts can develop complex surface structures when exposed to reactive atmospheres. The structures of the resulting surfaces have intricate relationships with a myriad of factors, such as the affinity of the individual alloying elements to the components of the gas atmosphere and the bond strengths of the multitude of low-energy surface compounds that can be formed. Identifying the atomic structure of such surfaces is a prerequisite for establishing structure-property relationships, as well as for modeling such catalysts in ab initio calculations. Here, we show that an alloy, consisting of an oxophilic metal (Cu) diluted into a noble metal (Ag), forms a meta-stable two-dimensional oxide monolayer, when the alloy is subjected to oxidative reaction conditions. The presence of this oxide is correlated with selectivity in the corresponding test reaction of ethylene epoxidation. In the present study, using a combination of in situ, ex situ, and theoretical methods (NAP-XPS, XPEEM, LEED, and DFT), we determine the structure to be a two-dimensional analogue of Cu2O, resembling a single lattice plane of Cu2O. The overlayer holds a pseudo-epitaxial relationship with the underlying noble metal. Spectroscopic evidence shows that the oxide's electronic structure is qualitatively distinct from its three-dimensional counterpart, and because of weak electronic coupling with the underlying noble metal, it exhibits metallic properties. These findings provide precise details of this peculiar structure and valuable insights into how alloying can enhance catalytic properties. Copyright © 2020 American Chemical Society.

High temperature ferromagnetic shape memory alloys (HT-FSMAs) in form of a thin film materials library of Ni–Mn–Ga, alloyed with Fe, Co and Cu has been fabricated by co-sputtering and characterized by high-throughput screening techniques. The weak dependence of martensitic transformation temperature and tetragonal ratio of the martensitic lattice on the doping composition and their irregular variation are ascribed to the competitive influence of the alloying elements Fe, Co and Cu. © 2019 Acta Materialia Inc.

Determining the exact pairing symmetry of the superconducting order parameter in candidate unconventional superconductors remains an important challenge. Recently, a new method, based on phase sensitive quasiparticle interference measurements, was developed to identify gap sign changes in isotropic multiband systems. Here we extend this approach to the single-band and multiband nodal d-wave superconducting cases relevant, respectively, for the cuprates and likely for the infinite-layer nickelate superconductors. Combining analytical and numerical calculations, we show that the antisymmetrized correction to the tunneling density of states due to nonmagnetic impurities in the Born limit and at intermediate-scattering strength shows characteristic features for sign-changing and sign-preserving scattering wave vectors, as well as for the momentum-integrated quantity. Furthermore, using a realistic approach accounting for the Wannier orbitals, we model scanning tunneling microscopy data of Bi2Sr2CaCu2O8+δ, which should allow the comparison of our theory with experimental data. © 2020 American Physical Society.

Ni–Ti–based shape memory alloys (SMAs) have found widespread use in the last 70 years, but improving their functional stability remains a key quest for more robust and advanced applications. Named for their ability to retain their processed shape as a result of a reversible martensitic transformation, SMAs are highly sensitive to compositional variations. Alloying with ternary and quaternary elements to fine-tune the lattice parameters and the thermal hysteresis of an SMA, therefore, becomes a challenge in materials exploration. Combinatorial materials science allows streamlining of the synthesis process and data management from multiple characterization techniques. In this study, a composition spread of Ni–Ti–Cu–V thin-film library was synthesized by magnetron co-sputtering on a thermally oxidized Si wafer. Composition-dependent phase transformation temperature and microstructure were investigated and determined using high-throughput wavelength dispersive spectroscopy, synchrotron X-ray diffraction, and temperature-dependent resistance measurements. Of the 177 compositions in the materials library, 32 were observed to have shape memory effect, of which five had zero or near-zero thermal hysteresis. These compositions provide flexibility in the operating temperature regimes that they can be used in. A phase map for the quaternary system and correlations of functional properties are discussed with respect to the local microstructure and composition of the thin-film library. © 2020 THE AUTHORS

Recently 1:12 magnets of Sm-(Fe,V) have shown promising coercivities and the potential to be alternative rare-earth-lean permanent magnets. In this work, we investigated the effects of partial substitution of Cu, Mo and Ti for V in the magnets prepared by hot compaction and hot deformation of mechanically milled powders. The microstructure of the Sm-Fe-(V,Cu) and Sm-Fe-(V,Ti) hot-deformed magnets consisted in fine grains with sizes between 50 and 150 nm. The Sm-Fe-(V,Cu) magnet showed the best performance with μ0Hc=0.96 T, μ0Mr=0.49 T, (BH)max=42kJm−3 and TC=362∘C. Atom probe tomography of this magnet revealed the presence of a thin Sm17.5Fe71.5V8Cu3 intergranular phase of 3-6 nm surrounding the 1:12 nanograins. The addition of a small amount of Cu, not only improved the magnetic properties but also hindered the grain growth during hot deformation. Micromagnetic simulations of the magnetization reversal agreed with the experimental values of coercivity. The presence of the intergranular phase reduces the number of grains that switch simultaneously. © 2020 Acta Materialia Inc.

The electrocatalytic reduction of carbon dioxide (CO2) by means of renewable energies is widely recognized as a promising approach to establish a sustainable closed carbon cycle economy. However, widespread application is hampered by the inherent difficulty in suppressing the hydrogen evolution reaction and controlling the overall process selectivity. Further critical parameters are the limited solubility of CO2 in many electrolytes and its hindered mass transport to the electrodes. Herein we report on a series of nanoparticle Cu electrocatalysts on different carbon supports and their potential to perform the electrochemical CO2 reduction under supercritical conditions (scCO2). Herein, CO2 serves as the reaction medium and reactant alike. By a detailed comparison to ambient conditions we show that scCO2 conditions largely suppress the undesirable hydrogen evolution and favor the production of formic acid by the Cu electrodes. Furthermore, we show that scCO2 conditions significantly prevent Cu nanoparticle agglomeration during electrocatalysis. © 2020 American Chemical Society.

Conductive and yet strong copper alloys are essential materials in highly mechanically loaded electrical devices. We demonstrate a novel in-situ synthesis approach via laser metal deposition (LMD) in a lean copper alloy, Cu–3.4Cr–0.6Nb (at%). Strengthening in the lean alloy comes from chromium nano-scale precipitates formed in-situ (4 nm diameter; number density 8 × 1023 m−3) and from Laves phase particles (< 1 µm diameter; 2.2 vol%), dispersed across the microstructure. This dual dispersion, in a nearly pure copper matrix, is achieved through a suited combination of chromium alloying and cooling rate during LMD synthesis. The as-synthesized alloy has a conductivity of 68% IACS (International Annealed Copper Standard) and a Vickers hardness of 146, at room temperature. The latter is 11% above the value reported for the strongest lean reference ternary alloy Cu–8Cr–4Nb (at%). The in-situ synthesis approach averts any heat treatment step, which has been an essential step previously in conventional manufacturing, for realizing the property combination in lean Cu–Cr based system. © 2020

The introduction of high-entropy alloys (HEA) into the field of shape memory alloys offers enormous potential for improving their functional properties. It is shown how a successive increase in chemical complexity results in strictly monotonically enlarged and increasingly distorted lattices. With increasing the number of elements added to the alloy, the effect of solid solution strengthening appears to be curtailed and first insights into the contribution of additional mechanisms based on lattice distortions are possible. The alloys developed in this study, reaching from ternary NiTiHf to senary TiZrHfCoNiCu, show a great potential to exploit interatomic interactions regarding improvement of functional fatigue. Despite the absence of stress plateaus related to detwinning, recovery effects at loads above 1000 MPa and significant strain recoveries are shown. © 2020, ASM International.

Bimetallic Co-Cu catalysts are widely applied in higher alcohol synthesis (HAS), but the formation of the final active structure has not yet been fully clarified, especially for Co-rich catalysts. We investigated the structural evolution of a Co-Cu catalyst (Co:Cu = 2) from the hydrotalcite precursor containing additional Al3+ and Zn2+ to the final active state after 80 h under reaction conditions at 280 °C and 60 bar. The reconstruction of the bimetallic Co-Cu nanoparticles obtained by H2 reduction was induced by the feed gas consisting of an equimolar H2 and CO syngas mixture resulting in fast phase separation and sintering of metallic Cu0 and Co0 in the first 2 h time on stream (TOS) and a continuous carbidization of Co0 forming Co2C and its sintering until steady state was reached after 40 h TOS. An intergrowth of metallic Cu0 nanoparticles with Co2C nanoparticles was observed to occur under reaction conditions. The high selectivity to oxygenates amounting to 41% compared with 29% to hydrocarbons is ascribed to the multi-functional Co2C/Cu0 interface enabling dissociative CO adsorption, hydrogenation and CO insertion. The formation of hydrogenated carbon species (CxHy) originating from dissociative CO chemisorption is assumed to be favored by hydrogen spillover from Cu0 to Co2C. The adsorption sites for molecular CO provided by both Cu0 and Co2C facilitate its insertion into the CxHy intermediates thus leading to a higher selectivity to alcohols following the Anderson-Schulz-Flory distribution. © 2020 Elsevier Inc.

This paper demonstrates a carbene stabilized precursor [Cu(tBuNHC)(hmds)] with suitable volatility, reactivity and thermal stability, that enables the spatial plasma-enhanced atomic layer deposition (APP-ALD) of copper thin films at atmospheric pressure. The resulting conductive and pure copper layers were thoroughly analysed and a comparison of precursor and process with the previously reported silver analogue [Ag(tBuNHC)(hmds)] revealed interesting similarities and notable differences in precursor chemistry and growth characteristics. This first report of APP-ALD grown copper layers is an important starting point for high throughput, low-cost manufacturing of copper films for nano- and optoelectronic devices. © 2020 The Royal Society of Chemistry.

High entropy shape memory alloys (HESMAs) represent a relatively young class of functional materials. They show a reversible martensitic phase transformation which allows to exploit shape memory effects at relatively high temperatures. HESMAs represent ordered complex solid-solutions. Their high temperature phase is of B2 type, and various elements (e.g. Ni, Cu, Ti, Zr, Hf) occupy sites in specific sub-lattices. In the present work, we study the processing and the functional properties of HESMAs. We study effects of chemical complexity on solidification microstructures and martensitic transformations. Binary, ternary, quaternary, quinary and senary model alloys were investigated using advanced microstructural and thermal characterization methods. The results show that element partitioning during solidification results in a redistribution of individual alloy elements in dendritic/interdendritic regions. Surprisingly, the atomic ratios of the two groups of elements which occupy the Ni- (first group: Ni, Cu and Pd) and Ti-sub-lattice (second group: Ti, Zr, Hf) are maintained. This allows the material to form martensite throughout its heterogeneous microstructure. The effect of chemical complexity/composition on martensite start temperatures, MS, is discussed on the basis of valence electron concentrations, cV. Some of the alloys fall into MS(cV)-regimes which are uncommon for classical Ni-Ti-based shape memory alloys. In the present work, a new HESMA of type NiCuPdTiZrHf was identified which has the potential to provide maximum shape memory strains close to 15%. © 2020

The determination of the most stable structures of metal clusters supported at solid surfaces by computer simulations represents a formidable challenge due to the complexity of the potential-energy surface. Here, we combine a high-dimensional neural network potential, which allows us to predict the energies and forces of a large number of structures with first-principles accuracy, with a global optimization scheme employing genetic algorithms. This very efficient setup is used to identify the global minima and low-energy local minima for a series of copper clusters containing between four and ten atoms adsorbed at the ZnO(101¯0) surface. A series of structures with common structural features resembling the Cu(111) and Cu(110) surfaces at the metal-oxide interface has been identified, and the geometries of the emerging clusters are characterized in detail. We demonstrate that the frequently employed approximation of a frozen substrate surface in global optimization can result in missing the most relevant structures. © 2020 Author(s).

Thin-film material libraries in the ternary and quaternary metal oxide systems Fe-V-O, Cu-V-O, and Cu-Fe-V-O were synthesized using combinatorial reactive co-sputtering with subsequent annealing in air. Their compositional, structural, and functional properties were assessed using high-throughput characterization methods. Prior to the investigation of the quaternary system Cu-Fe-V-O, the compositions (Fe61V39)Ox and (Cu52V48)Ox with promising photoactivity were identified from their ternary subsystems Fe-V-O and Cu-V-O, respectively. Two Cu-Fe-V-O material libraries with (Cu29-72Fe4-27V22-57)Ox and (Cu11-55Fe27-73V12-34)Ox composition spread were investigated. Seven mixed ternary and quaternary phase regions were identified: I (α-Cu3FeV6O26/FeVO4), II (Cu5V2O10/FeVO4/α-Cu3Fe4V6O26), III (Cu5V2O10), IV (Cu5V2O10/FeVO4, V (FeVO4/γ-Cu2V2O7/α-Cu3Fe4V6O26), VI (β-Cu2V2O7/α-Cu3Fe4V6O26/FeVO4), and VII (β-Cu3Fe4V6O26/FeVO4). In the investigated composition range, two photoactive regions, (Cu53Fe7V40)Ox and (Cu45Fe21V34)Ox, were identified, exhibiting 103 μA/cm2 and 108 μA/cm2 photocurrent density for the oxygen evolution reaction at 1.63 V vs reversible hydrogen electrode, respectively. The highest photoactive region (Cu45Fe21V34)Ox comprises the dominant α-Cu3Fe4V6O24 phase and minor FeVO4 phase. This photoactive region corresponds to having an indirect bandgap of 1.87 eV and a direct bandgap of 2.58 eV with an incident photon-to-current efficiency of 30% at a wavelength of 310 nm. © 2020 Author(s).

The boundary between two crystal grains can decompose into arrays of facets with distinct crystallographic character. Faceting occurs to minimize the system's free energy, i.e., when the total interfacial energy of all facets is below that of the topologically shortest interface plane. In a model Al-Zn-Mg-Cu alloy, we show that faceting occurs at investigated grain boundaries and that the local chemistry is strongly correlated with the facet character. The self-consistent coevolution of facet structure and chemistry leads to the formation of periodic segregation patterns of 5-10 nm, or to preferential precipitation. This study shows that segregation-faceting interplay is not limited to bicrystals but exists in bulk engineering Al alloys and hence affects their performance. © 2020 authors. Published by the American Physical Society.

Elemental copper can be utilized to generate C-C bonds in order to synthesize nanographenes in a mechanochemical environment. Utilizing the solvent-free environment of a ball mill, we present a facile and highly sustainable concept for the internal C-C coupling in oligo-phenyls on the example of triphenylene and extend it to the transformation of hexaphenylbenzene into hexa-peri-hexabenzocoronene as a benchmark nanographene. © 2020 American Chemical Society.

Alloying nanocrystalline copper (Cu) with immiscible elements, such as tantalum (Ta) and zirconium (Zr), is a promising technique to manipulate grain boundary properties and by this suppress grain growth at elevated temperatures. However, insights on the atomistic origins on the influence of impurity elements on grain boundaries are lacking. In this study, the atomistic effects of Ta and Zr on [111] tilt grain boundaries in Cu are investigated by high resolution scanning transmission electron microscopy techniques. In case of Ta, the formation of spherical, nano-scale precipitates in close vicinity to the grain boundaries is observed, but no sign of segregation. The particles induce a repelling force to migrating boundaries and act as local pinning points. The segregation of Zr is observed to occur either at confined grain boundary steps or homogeneously along the boundaries without steps. In both cases a strong disordering of the defect or grain boundary structure is revealed. Furthermore, at low Zr concentrations it induces structural grain boundary transitions and partial atomic reordering of the grain boundary structural units. © 2020 Acta Materialia Inc.

The theory of grain boundary (the interface between crystallites, GB) structure has a long history1 and the concept of GBs undergoing phase transformations was proposed 50 years ago2,3. The underlying assumption was that multiple stable and metastable states exist for different GB orientations4–6. The terminology ‘complexion’ was recently proposed to distinguish between interfacial states that differ in any equilibrium thermodynamic property7. Different types of complexion and transitions between complexions have been characterized, mostly in binary or multicomponent systems8–19. Simulations have provided insight into the phase behaviour of interfaces and shown that GB transitions can occur in many material systems20–24. However, the direct experimental observation and transformation kinetics of GBs in an elemental metal have remained elusive. Here we demonstrate atomic-scale GB phase coexistence and transformations at symmetric and asymmetric [11 1 ¯] tilt GBs in elemental copper. Atomic-resolution imaging reveals the coexistence of two different structures at Σ19b GBs (where Σ19 is the density of coincident sites and b is a GB variant), in agreement with evolutionary GB structure search and clustering analysis21,25,26. We also use finite-temperature molecular dynamics simulations to explore the coexistence and transformation kinetics of these GB phases. Our results demonstrate how GB phases can be kinetically trapped, enabling atomic-scale room-temperature observations. Our work paves the way for atomic-scale in situ studies of metallic GB phase transformations, which were previously detected only indirectly9,15,27–29, through their influence on abnormal grain growth, non-Arrhenius-type diffusion or liquid metal embrittlement. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.

Microstructural deformation at the grain level has an inherent impact on the achievable ultimate machining accuracy of polycrystalline materials. In the present work, numerical simulations and experiments of diamond cutting of polycrystalline copper are carried out to investigate the formation of surface step at grain boundaries on machined surface. Single crystal diamond cutting tool with straight cutting edge is chosen for experiments to mimic the tool geometry utilized in 2D crystal plasticity finite element simulations. Moreover, the same crystallography configuration of bi-crystal Cu is employed between experiments and simulations. Formation mechanisms of surface steps at grain boundaries are revealed by finite element simulations and corresponding experimental validation, as well as cross-sectional transmission electron microscope characterization. Finally, finite element simulations of orthogonal cutting of bi-crystal Cu are carried out to examine effects of both extrinsic cutting edge radius of diamond cutting tool and intrinsic misorientation angle of grain boundary on the propensity of grain boundary surface step formation. The present work provides theoretical guidelines on the strategy of suppressing grain boundary surface step formation for achieving superior surface finish of polycrystalline materials by diamond cutting. © 2019 Elsevier B.V.

Metal–organic frameworks containing multiple metals distributed over crystallographically equivalent framework positions (mixed-metal MOFs) represent an interesting class of materials, since the close vicinity of isolated metal centers often gives rise to synergistic effects. However, appropriate characterization techniques for detailed investigations of these mixed-metal metal–organic framework materials, particularly addressing the distribution of metals within the lattice, are rarely available. The synthesis of mixed-metal FeCuBTC materials in direct syntheses proved to be difficult and only a thorough characterization using various techniques, like powder X-ray diffraction, X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy, unambiguously evidenced the formation of a mixed-metal FeCuBTC material with HKUST-1 structure, which contained bimetallic Fe−Cu paddlewheels as well as monometallic Cu−Cu and Fe−Fe units under optimized synthesis conditions. The in-depth characterization showed that other synthetic procedures led to impurities, which contained the majority of the applied iron and were impossible or difficult to identify using solely standard characterization techniques. Therefore, this study shows the necessity to characterize mixed-metal MOFs extensively to unambiguously prove the incorporation of both metals at the desired positions. The controlled positioning of metal centers in mixed-metal metal–organic framework materials and the thorough characterization thereof is particularly important to derive structure–property or structure–activity correlations. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

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.

Shear deformation that dominates elementary chip formation in metal cutting greatly relies on crystal anisotropy. In the present work we investigate the influence of crystallographic orientation on shear angle in ultra-precision orthogonal diamond cutting of single crystalline copper by joint crystal plasticity finite element simulations and in-situ experiments integrated in scanning electron microscope. In particular, the experimental cutting conditions including a straight cutting edge are the same with that used in the 2D finite element simulations. Both simulations and experiments demonstrate a well agreement in chip profile and shear angle, as well as their dependence on crystallography. A series of finite element simulations of orthogonal cutting along different cutting directions for a specific crystallographic orientation are further performed, and predicated values of shear angle are used to calibrate an extended analytical model of shear angle based on the Ernst–Merchant relationship. © 2020 Elsevier Inc.

High entropy alloys are generally considered to be single phase material. This state is, however, typically a non-equilibrium state after fabrication at high cooling rates. Phase constitution after fabrication or heat treatment is mostly known for isothermal annealing only and for casts as well as rapidly quenched alloys. Knowledge on early phase separation stages of high entropy alloys and their mechanisms are missing so far. Here, we present results on phase separation at intermediate cooling rates, by characterization of gas atomized powder of the AlCoCr0.75Cu0.5FeNi alloy. Although investigation by X-ray diffraction and Electron Backscatter Diffraction indicates a single-phase nature of the powder particles, aberration-corrected scanning transmission electron microscopy and atom probe tomography reveal a nanoscale phase separation into Ni–Al-rich B2 and Fe–Cr-rich A2 regions as well as a high number density of 3.1 × 1024 Cu-rich clusters per m3 in the B2 matrix. The observed phase separation and cluster formation are linked to spinodal decomposition and nucleation processes, respectively. The study highlights that adequate characterization techniques need to be chosen when making statements about phase stability and structural evolution in compositionally complex alloys. © 2019 The Authors

The suitability of a commercial and industrially applied Cu-based catalyst for the synthesis of methanol by CO2 hydrogenation was investigated. Unexpectedly, this system showed high stability and well-performance under conditions that may be relevant for chemical energy conversion using hydrogen and energy from renewable technologies. This Cu-based catalyst demonstrated excellent suitability for dynamical process operation that may be essential for effective compensation of the volatility of renewable energy sources. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Since its first emergence in 2004, the high-entropy alloy (HEA) concept has aimed at stabilizing single- or dual-phase multi-element solid solutions through high mixing entropy. Here, this strategy is changed and renders such massive solid solutions metastable, to trigger spinodal decomposition for improving the alloys’ magnetic properties. The motivation for starting from a HEA for this approach is to provide the chemical degrees of freedom required to tailor spinodal behavior using multiple components. The key idea is to form Fe-Co enriched regions which have an expanded volume (relative to unconstrained Fe-Co), due to coherency constraints imposed by the surrounding HEA matrix. As demonstrated by theory and experiments, this leads to improved magnetic properties of the decomposed alloy relative to the original solid solution matrix. In a prototype magnetic FeCoNiMnCu HEA, it is shown that the modulated structures, achieved by spinodal decomposition, lead to an increase of the Curie temperature by 48% and a simultaneous increase of magnetization by 70% at ambient temperature as compared to the homogenized single-phase reference alloy. The findings thus open a pathway for the development of advanced functional HEAs. © 2020 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH

We investigate superstructures formed by CO2 on Ag(100) and Cu(111) from small clusters forming at 21 K up to multilayers grown at 43 K by low temperature scanning tunneling microscopy. On both surfaces, CO2 nucleates only at defects, here at co-adsorbed CO. At the lower adsorption temperature, superstructures of different symmetry coexist on both surfaces at submonolayer coverage, while the superstructures formed at the higher adsorption temperature differ largely for the two surfaces. On Ag(100), the CO2 monolayer exhibits a long-range order interrupted by antiphase domain boundaries. On Cu(111), a random distribution of domain structures of different symmetry leads to a monolayer without long-range order. Surprisingly, the degree of ordering is inverted for the 2nd layer of CO2. On Ag(100), the coexistence of different superstructures in the 2nd layer leads to reduced long-range order. On Cu(111), a hexagonal 2nd layer exhibits long-range order. A layer of a similar superstructure, hexagonal with long-range order, exists as the 3rd layer of Ag(100). Despite the different substrates, a multitude of common structural features of CO2 exist. Hexagonal layers grow with a long-range order on less ordered layers on both surfaces. Our results suggest that the preferred structure of a CO2 layer is hexagonal. © 2020 the Owner Societies.

High-strength Al-Zn-Mg-Cu alloys are highly susceptible to stress corrosion cracking (SCC) which severely limits their lifetime. Reversion and re-aging (RRA) temper provides a higher SCC resistance at no loss in strength, yet the microstructural origins of these enhanced properties remain elusive. In an Al-Zn-Mg-Cu alloy, we show that the fine precipitate dispersion in the grain interiors is similar in the peak aged and RRA tempers. However, upon RRA, precipitates inside the grains are enriched in Cu, lowering the Cu matrix content, and reducing the relative difference in the Cu precipitate composition between bulk and grain boundaries. This study enriches the current understanding on the critical role of Cu related to SCC resistance in Al-Zn-Mg-Cu alloys. © 2020

The influence of (Al,Zn)3Zr dispersoids on the precipitation of the main strengthening (Mg,Zn)-rich phases was investigated during isothermal aging of a model Al-Zn-Mg-Cu-Zr alloy. Upon homogenization of the alloy, dispersoids of (Al,Zn)3Zr with a L12 structure are present. Isothermal aging at 120 °C for 0.5 h leads to the homogeneous formation of spherical GP zones in the α-Al matrix and heterogeneous nucleation on (Al,Zn)3Zr dispersoids. After 2 h of aging, GP zones remain present in the α-Al matrix while the accelerated transformation of GP zones to plate-shaped (Mg,Zn)-rich ηʹ precipitates is shown on the {111} planes at the interface of the L12 dispersoids. Even at grain boundaries, the similar composite structure comprising ηʹ precipitates on the coarser Zr-dispersoid is observed, along with 10-nm wide precipitate-free zones around them. The composition and structure of pre-existing dispersoids, their role in the formation of the composite structure are discussed. © 2020

The microstructure and the fracture behavior of TiZrHfCoNiCu high entropy shape memory alloys with two different compositions were investigated. An unusual microstructure featuring pattern-forming nanoprecipitates was observed in dendritic and the interdendritic regions of both alloys. The unique higher-level order of these precipitates does not follow concentration gradients but is influenced by homogeneity and mechanical stress. The results also demonstrate that high entropy alloys are not necessarily homogeneous single-phase solid solutions. Moreover, it appears that solid solution strengthening as the primary mechanism also has to be questioned. © 2020 Acta Materialia Inc.

The structural changes of copper hexacyanoferrate (CuHCF), a Prussian blue analogue, which occur when used as a cathode in an aqueous Zn-ion battery, are investigated using electron microscopy techniques. The evolution of ZnxCu1−xHCF phases possessing wire and cubic morphologies from initial CuHCF nanoparticles are monitored after hundreds of cycles. Irreversible introduction of Zn ions to CuHCF is revealed locally using scanning transmission electron microscopy. A substitution mechanism is proposed to explain the increasing Zn content within the cathode material while simultaneously the Cu content is lowered during Zn-ion battery cycling. The present study demonstrates that the irreversible introduction of Zn ions is responsible for the decreasing Zn ion capacity of the CuHCF cathode in high electrolyte concentration. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Deformation behavior at grain levels greatly affects the machining characteristics of crystalline materials. In the present work, we investigate the influence of material anisotropy on ultra-precision diamond cutting of single crystalline and polycrystalline copper by experiments and crystal plasticity finite element simulations. Specifically,diamond turning and in situ SEM orthogonal cutting experiments are carried out to provide direct experimental evidence of the material anisotropy-dependent cutting results in terms of machined surface morphology and chip profile. Corresponding numerical simulations with the analysis of built stress further validate experimental results and reveal the mechanisms governing the material anisotropy influence.The above findings provide insight into the fabrication of ultra-smooth surfaces of polycrystalline metals by ultra-precision diamond turning. © 2020, The Author(s).

In hard coating development there is a need for fast and efficient screening methods to assess the influence of changes in composition and structure evolution on the mechanical behavior. Nanoindentation constitutes a method that allows fast and efficient probing of mechanical properties. For another important mechanical characteristic of hard coatings, the fracture toughness, no quick benchmark test to compare coatings with various compositions and/or morphologies, exist. Therefore, the goal of this investigation was to determine if a tensile test setup allows for fast and efficient qualitative screening of fracture toughness trends in hard coatings compared to accurate but time consuming micro-bending beam experiments. TiAlN and VAlN, each deposited on ductile Cu-substrates, were chosen for this investigation. In situ scanning electron microscopy tensile tests were performed. Here, the strain at crack initiation of the coating was utilized as the experimental parameter, which is most representative for the fracture toughness. The experiments indicate that TiAlN exhibits a higher fracture toughness than VAlN. This was confirmed using time demanding in situ micro-bending beam fracture experiments. Hence, it is established that under the given conditions macroscopic in situ SEM tensile tests can be used as a fast and efficient screening method for fracture toughness trends of hard coatings. © 2020 Elsevier B.V.

We combined experimental investigations and theoretical calculations to unveil an abnormal magnetic behavior caused by addition of the nonmagnetic element Cu in face-centered-cubic FeNiCoMn-based high-entropy alloys (HEAs). Upon Cu addition, the probed HEAs show an increase of both Curie temperature and saturation magnetization in as-cast and homogenized states. Specifically, the saturation magnetization of the as-cast HEAs at room temperature increases by 77% and 177% at a Cu content of 11 and 20 at. %, respectively, compared to the as-cast equiatomic FeNiCoMn HEA without Cu. The increase in saturation magnetization of the as-cast HEAs is associated with the formation of an Fe-Co rich phase in the dendritic regions. For the homogenized HEAs, the magnetic state at room temperature transforms from paramagnetism to ferromagnetism after 20 at. % Cu addition. The increase of the saturation magnetization and Curie temperature cannot be adequately explained by the formation of Cu enriched zones according to atom probe tomography analysis. Ab initio calculations suggest Cu plays a pivotal role in the stabilization of a ferromagnetic ordering of Fe, and reveal an increase of the Curie temperature caused by Cu addition which agrees well with the experimental results. The underlying mechanism behind this phenomenon lies in a combined change in unit-cell volume and chemical composition and the related energetic stabilization of the magnetic ordering upon Cu alloying as revealed by theoretical calculations. Thus, the work unveils the mechanisms responsible for the Cu effect on the magnetic properties of FeNiCoMn HEAs, and suggests that nonmagnetic elements are also crucial to tune and improve magnetic properties of HEAs. © 2020 American Physical Society.

In this study, using a natural and green protein R-phycoerythrin (R-PE) extracted from marine Porphyra yezoensis as the stabilizer and reducer, silver nanoparticles (AgNPs) were synthesized. Based on this, a highly sensitive and selective method for the detection of Cu2+ ions was developed using R-PE-AgNPs as fluorescent probe. The interactions between R-PE-AgNPs and Cu2+ ions were systematically characterized by fluorescence spectroscopy, transmission electron microscopy (TEM), elemental mapping and Fourier transform infrared (FTIR). It was found that Cu2+ ions could cause aggregation of the R-PE-AgNPs, accompanied by the greatly increased particle size. Importantly, the method offered a wide linear detection range from 0 μM to 100.0 μM with a detection limit of 0.0190 μM. Moreover, the proposed method was successfully applied to analyze Cu2+ ions in tap water and lake water samples, acquiring satisfactory recovery between 91.6% and 102.2%. Such a green, fast and cost-effective fluorimetric method of the R-PE-AgNPs probe has great potential for tracing Cu2+ ions in diverse aqueous media. © 2018 Elsevier Inc.

The study of mechanical properties of materials at high temperatures at the microstructural length regime requires dedicated setups for testing. Despite the advances in the instrumentation in these setups over the last decade, further optimization is required in order to extend the temperature range well-beyond 600 °C. Particularly, an improvement of the contact temperature measurement is required. A design with a novel approach of temperature measurement with independent tip and sample heating is developed to characterize materials at high temperatures. This design is realized by modifying a displacement controlled room temperature microstraining rig with the addition of two miniature hot stages, one each carrying the sample and indenter tip. The sample reaches temperatures of >600 °C with a 50 W diode laser system. The stages have slots for the working sample as well as a reference sample on both ends for precise temperature measurements, relying on the symmetry of the stage toward the ends. The whole setup is placed inside a custom-made steel chamber, capable of attaining a vacuum of 10-4 Pa. Alternatively, the apparatus can be operated under environmental conditions by applying various gases. Here, the unique design and its high temperature capabilities will be presented together with the first results of microtension experiments on freestanding copper thin films at 400 °C. © 2019 Author(s).

The important role of grain boundaries for the mechanical properties of polycrystalline materials has been recognized for many decades. Up to now, the underlying deformation mechanisms at the nano- and micro scale are not understood quantitatively. An overview of the synthesis and subsequent mechanical testing of specific grain boundaries at the micro and sub-micro scale is discussed in the present contribution, including various methods for producing one or multiple specific, crystallographically well-defined grain boundaries. Furthermore, established micromachining methods for isolating and measuring local dislocation-grain boundary interactions are portrayed. Examples of the techniques described are shown with to the aid of copper grain boundaries. © Carl Hanser Verlag, München

Metal-exchanged zeolites with small pore sizes have attracted much attention in recent years due to their application in the selective catalytic reduction (SCR) of NOx in diesel engines. Typically, copper-chabazite (e.g. Cu-SSZ-13) has been gradually used as an SCR catalyst in heavy-duty diesel vehicles over the last decade due to its relatively excellent catalytic performance and stability. However, most SSZ-13 zeolites are still prepared via the traditional hydrothermal process in the presence of organic templates, requiring consecutive solid separation and thermal treatment steps to achieve the final zeolite products. In recent years, several strategies for the environmentally friendly preparation of zeolites have been reported, which are also applicable for the synthesis of zeolites for emission control applications. These concepts include copper-amine templating, organotemplate-free synthesis, and solvent-free synthesis. In this review, we briefly summarize the potential advantages of the environmentally friendly synthesis of zeolites for SCR. © The Royal Society of Chemistry 2019.

The kinetics of glycerol hydrodeoxygenation to 1,2-propanediol via the selective cleavage of the primary C-O bond was systematically studied in the aqueous phase over a co-precipitated Cu/ZrO2 catalyst. Unsupported pure metallic Cu was used as reference catalyst. Batch experiments were performed in an autoclave by varying the reaction temperature (175–225 °C), H2 partial pressure (25–35 bar) and initial glycerol concentration (2–8 wt%). The Cu/ZrO2 catalyst was found to be highly selective to 1,2propanediol (up to 95%), and ethylene glycol was obtained as major by-product from parallel C–]C bond hydrogenolysis. The apparent activation energies amounting to 106 and 105 kJ mol-1 for Cu/ZrO2 and pure metallic Cu, respectively, of the hydrodeoxygenation pathway provide further evidence for metallic Cu acting as the active site. Kinetic analysis of the rate of glycerol consumption yielded a zero-order dependence on the concentration of glycerol suggesting an essentially almost full coverage of adsorbed glycerol as most strongly bound organic adsorbate. In contrast, a first-order dependence on hydrogen concentration was observed. Hydrogen is assumed to be not only required for the fast hydrogenation of the intermediate acetol, but also for the removal of adsorbed atomic oxygen originating from water dissociation to create empty sites for dissociative glycerol adsorption. Thus, the active Cu sites are assumed to be fully adsorbate-covered under reaction conditions. © 2019 Elsevier B.V.

Increased demand for light-weighting in passenger vehicles has created a need for strong, light, ductile materials to be used in body-in-white applications. The AA6xxx-series of aluminum alloys are suitable candidates meeting most requirements but can fall short of the formability demands of designers, necessitating an understanding of what controls the formability in this alloy series. This work examines the effect of copper alloying in AA6xxx on the pre-ageing and natural ageing responses of the microstructure and mechanical properties. The changes in microstructure observed by differential scanning calorimetry and hardness testing are related to the work-hardening and strain-rate sensitivity parameters for these alloys measured by tensile testing. An observed asymmetry in the measured strain-rate sensitivity associated with increasing versus decreasing strain rate changes suggests that a different mechanism operates for the two conditions. It is postulated how this asymmetry in strain-rate sensitivity will impact the necking and ductility behaviour of these alloys. © 2019, The Minerals, Metals & Materials Society.

The kinetics of glycerol hydrodeoxygenation to 1,2-propanediol via the selective cleavage of the primary C-O bond was systematically studied in the aqueous phase over a co-precipitated Cu/ZrO 2 catalyst. Unsupported pure metallic Cu was used as reference catalyst. Batch experiments were performed in an autoclave by varying the reaction temperature (175–225 °C), H 2 partial pressure (25–35 bar) and initial glycerol concentration (2–8 wt%). The Cu/ZrO 2 catalyst was found to be highly selective to 1,2propanediol (up to 95%), and ethylene glycol was obtained as major by-product from parallel C–]C bond hydrogenolysis. The apparent activation energies amounting to 106 and 105 kJ mol -1 for Cu/ZrO 2 and pure metallic Cu, respectively, of the hydrodeoxygenation pathway provide further evidence for metallic Cu acting as the active site. Kinetic analysis of the rate of glycerol consumption yielded a zero-order dependence on the concentration of glycerol suggesting an essentially almost full coverage of adsorbed glycerol as most strongly bound organic adsorbate. In contrast, a first-order dependence on hydrogen concentration was observed. Hydrogen is assumed to be not only required for the fast hydrogenation of the intermediate acetol, but also for the removal of adsorbed atomic oxygen originating from water dissociation to create empty sites for dissociative glycerol adsorption. Thus, the active Cu sites are assumed to be fully adsorbate-covered under reaction conditions. © 2019 Elsevier B.V.

Light elements play a crucial role on the microstructure and properties of conventional alloys and steels. Oxygen is one of the light elements which is inevitably introduced into nanocrystalline alloys during manufacturing. Here, we report that severe plastic deformation can fragment the oxides formed in powder processing and eventually cause oxygen dissolution in the matrix. A comparative investigation on Cu-Fe nanocrystalline alloys generated from different initial materials, blended powders and arc-melted bulk materials which have different oxygen contents, reveals that fragmented oxides at grain boundaries effectively decrease the grain boundary mobility, markedly facilitating grain refinement. In contrast, those oxygen atoms dissolved as interstitials in the Cu-Fe matrix lead to lattice expansion and significant decrease of stacking fault energy locally as validated by density functional theory. Such oxygen-mediated microstructure gives rise to enhanced strength and superior structural stability. The remarkable tailoring effect of oxygen can be employed to engineer nanocrystalline materials with desired properties for different applications. © 2018 Acta Materialia Inc.

Alternative buffer layers in CIGSe are deposited mainly using chemical bath deposition because of its benefits like simplicity, good film quality and surface/step coverage. All the layers in CIGSe cell stack such as back contact, absorber and window layers are deposited by vacuum–deposition methods such as coevaporation, sputtering, and sometimes thermal evaporation, except for the buffer layer. Therefore, in the present work we demonstrate the feasibility to deposit In2S3 by RF magnetron sputtering reaching cell efficiencies of 13.6%, which is the highest value available for sputtered In2S3 in literature to date. Absorber surface damage and nonuniform buffer layer thickness are the primary limitations when using sputtering, and hence need to be eliminated for reaching reasonable cell efficiencies. We studied the extent of sputter induced damage on CIGSe absorber as well as the sputtering– and annealing–induced intermixing phenomenon at the In2S3/Cu(In,Ga)Se2 interface at the subnanometer level using atom probe tomography. We have also shown that a post deposition annealing not only significantly improves the crystallinity of In2S3, but also recovers the surface damage caused by sputter-induced intermixing resulting in an improved p-n Junction quality (as shown by the electron beam induced current investigations), and substantially improves cell efficiency. The present work opens a new way for designing efficient and industry–compatible CIGSe cells using sputter–deposited Cd-free buffer layers. Moreover, this work clearly demonstrates that this novel and fully vacuum–deposited CIGSe cell meets the standard requirements, in terms of chemistry, structure, and electrical performance of a working cell for the PV industry. © 2019 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd.

Anisotropy is one central influencing factor on achievable ultimate machined surface integrity of metallic materials. Specifically, grain boundary has a strong impact on the deformation behaviour of polycrystalline materials and correlated material removal at the microscale. In the present work, we perform molecular dynamics simulations and experiments to elucidate the underlying grain boundary-associated mechanisms and their correlations with machining results of a bi-crystal Cu under nanocutting using a Berkovich tool. Specifically, crystallographic orientations of simulated bi-crystal Cu with a misorientation angle of 44.1° are derived from electron backscatter diffraction characterization of utilized polycrystalline copper specimen. Simulation results reveal that blocking of dislocation motion at grain boundaries, absorption of dislocations by grain boundaries and dislocation nucleation from grain boundaries are operating deformation modes in nanocutting of the bi-crystal Cu. Furthermore, heterogeneous grain boundary-associated mechanisms in neighbouring grains lead to strong anisotropic machining behaviour in the vicinity of the grain boundary. Simulated machined surface morphology and machining force evolution in the vicinity of grain boundary qualitatively agree well with experimental results. It is also found that the geometry of Berkovich tool has a strong impact on grain boundary-associated mechanisms and resultant ploughing-induced surface pile-up phenomenon. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the IMMT

Enzymes can perform complex multistep cascade reactions by linking multiple distinct catalytic sites via substrate channeling. We mimic this feature in a generalized approach with an electrocatalytic nanoparticle for the carbon dioxide reduction reaction comprising a Ag core surrounded by a porous Cu shell, providing different active sites in nanoconfined volumes. The architecture of the nanozyme provides the basis for a cascade reaction, which promotes C-C coupling reactions. The first step occurs on the Ag core, and the subsequent steps on the porous copper shell, where a sufficiently high CO concentration due to the nanoconfinement facilitates C-C bond formation. The architecture yields the formation of n-propanol and propionaldehyde at potentials as low as-0.6 V vs RHE. Copyright © 2019 American Chemical Society.

The production of acetaldehyde through biomass-derived ethanol dehydrogenation is a sustainable alternative compared to the fossil-feedstock based process, for which Cu-based catalysts are considered to be the most efficient. Herein, we modified the surface of silicon carbide (SiC) to alter the properties of the interface from SiO2-rich to C-rich, and we prepared a series of Cu-supported catalysts (Cu/SiC, Cu/SiO2/SiC, and Cu/C/SiC) with the aim of insight into the effect of the interface structure and composition on catalytic dehydrogenation of ethanol. At 280 °C, the Cu/SiO2/SiC catalyst exhibits high ethanol conversion due to the excellent dispersion of Cu nanoparticles promoted by SiO2-rich interface. In contrast, Cu nanoparticles dispersed on C/SiC shows somewhat lower activity but excellent acetaldehyde selectivity with trace amounts of by-products under identical reaction conditions. This difference is attributed to the fast removal of acetaldehyde because of its low affinity for the relatively inert C-rich interface (C/SiC). This work provides an in-depth understanding of Cu−Si−C multi-interfacial structure and the ethanol dehydrogenation behavior, which may shed light on the design of novel catalysts with tailored interfacial structures. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

We report on atom probe tomography studies of variable chemical decorations at extended defects in Cu-poor and Zn-rich Cu2ZnSnSe4 thin films. For a precursor film, which was co-evaporated at 320C, grain boundaries and dislocations are found enriched with Cu. Furthermore, Na out-diffusion from the soda-lime glass substrate occurs even at such a low temperature, resulting in Na segregation at defects. In contrast, stacking faults in the precursor film show clear Zn enrichment as well as Cu and Sn depletion. After an annealing step at 500C, we detect changes in the chemical composition of grain boundaries as compared to the precursor. Moreover, we measure an increase in the grain boundary excess of Na by one order of magnitude. We show that grain boundaries and dislocations in the annealed Cu2ZnSnSe4 film exhibit no or only slight variations in composition of the matrix elements. Thus, the effect of annealing is a homogenization of the chemical composition. © 2019 American Physical Society.

Mechanical properties of crystalline materials strongly correlate with deformation behaviour at the grain level. In the present work, we establish a 3D crystal plasticity finite element model of nanoscratching of single crystalline copper using a Berkovich probe, which is capable of addressing the crystallography influence. In particular, nanoindentation experiments and high resolution electron back-scatter diffraction characterization are jointly carried out to precisely calibrate parameters used in the crystal plasticity finite element model. Subsequent finite element simulations of nanoscratching are performed to reveal fundamental deformation behaviour of single crystalline copper in terms of mechanical response and surface pile-up topography, as well as their dependence on crystallographic orientation. Furthermore, nanoscratching experiments with the same parameters used in the finite element simulations are carried out, the results of which are further compared with predication results by the finite element simulations. Simulation data and experimental results jointly demonstrate the strong anisotropic characteristics of single crystalline copper under nanoscratching, due to the crystallographic orientation dependent coupled effects of intrinsic dislocation slip and extrinsic discrete stress distribution by probe geometry. © 2019 Elsevier B.V.

Microstructural-related deformation behavior leads to anisotropic machining characteristics of polycrystalline materials. In the present work, we develop a crystal plasticity finite element model of ultra-precision diamond cutting of polycrystalline copper, aiming to evaluate the influence of grain boundaries on the correlation between microscopic deformation behavior of the material and macroscopic machining results. The crystal plasticity dealing with the anisotropy of polycrystalline copper is implemented in a user subroutine (UMAT), and an efficient element deletion technique based on the Johnson-Cook damage model is adopted to describe material removal and chip formation. The effectiveness of as-established crystal plasticity finite element model is verified by experiments of nanoindentation, nanoscratching and in-situ diamond microcutting. Subsequent crystal plasticity finite element simulation of diamond cutting across a high angle grain boundary demonstrates significant anisotropic machining characteristics in terms of machined surface quality, chip profile and cutting force, due to heterogeneous plastic deformation behavior in the grain level. © 2019

The relatively low hydrothermal stability of Al-rich Cu-SSZ-13 catalysts hinders their practical application in ammonia selective catalytic reduction (NH 3 -SCR) reaction. Rare-earth ions were introduced into the Al-rich SSZ-13 zeolite using an organotemplate-free synthesis prior to the exchange of Cu 2+ ions. Among the rare-earth ions tested (Ce, La, Sm, Y, Yb), Y shows significant enhancement of the hydrothermal stability and NH 3 -SCR activities after severe hydrothermal aging at 800 °C for 16 h when compared with Cu-SSZ-13 without Y. Cu-Y-SSZ-13 catalysts with various amounts of Y were prepared, and it is found that with increasing Y content, the low temperature NO conversions can be improved even after hydrothermal aging. SEM-EDX analysis together with two-dimensional multiple quantum magic-angle-spinning nuclear magnetic resonance ( 23 Na MQ MAS NMR) confirms that the Y ions are successfully incorporated into the ion-exchange sites of the SSZ-13 zeolite. Results from 27 Al MAS, 29 Si MAS NMR, temperature-programmed desorption of ammonia (NH 3 -TPD) and quantitative 1 H MAS NMR indicate that Y can stabilize the framework Al and also preserve the Brønsted acid sites in the Al-rich SSZ-13 zeolite. The hydrogen temperature programmed reduction (H 2 -TPR), ultraviolet-visible-near infrared spectroscopy (UV-vis-NIR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of nitric oxide (NO) or NH 3 adsorption demonstrate that introduction of Y ions causes Cu 2+ ions to preferentially occupy the 6-MR, which has high hydrothermal stability. However, too much of Y may lead to activity loss at both low and high temperatures. The optimized Al-rich Cu-Y-SSZ-13 with 2.8 wt% of copper (Cu) and 1.3 wt% of Y displays almost the same deNO x activities as the conventional organotemplated high silica Cu-SSZ-13 catalyst in a wide reaction temperature window of 150-650 °C after severe hydrothermal treatment. Rare-earth ions could be an effective additive for Cu-SSZ-13 catalysts to further improve their hydrothermal stability for practical applications. © 2019 The Royal Society of Chemistry.

We follow the decay of two-dimensional Ag nanoclusters, called islands, on Cu-Ag core-shell supports by variable low temperature scanning tunneling microscopy in the temperature range between 160 and 260 K. We reveal two qualitatively different types of decay mechanisms, either linear in time, indicative of an interface-limited decay, or non-linear in time, indicative of diffusion-limited decay. In contrast to conventional decay on monometallic supports, the decay exponent of the diffusion-limited decay depends on temperature; it varies by one order of magnitude. Moreover, the decay rate decreases with increasing temperature. This unusual behaviour is traced back to the temperature-dependent shell of the core-shell support. © 2019 The Royal Society of Chemistry.

Highly sensitive and selective gas sensors based on heterostructured p-CuO/n-SnO2 core-shell nanowires (NWs) with precisely controlled shell thickness were synthesized through a sequential process combining a solution processing and atomic layer deposition. The gas sensing devices were fabricated on micro-electromechanical systems, which has triggered great research interest for low power consumption and highly integrated design. The designed p-CuO/n-SnO2 core-shell NW structured gas sensors exhibited superior gas sensing performance, which is closely related to the thickness of the SnO2 shell. Specifically, p-CuO/n-SnO2 core-shell NWs with a 24 nm thick SnO2 shell displayed a high sensitivity (Ra/Rg) of 2.42, whose rate of resistance change (i.e. 1.42) is 3 times higher than the pristine CuO NW sensor when detecting 50 ppm formaldehyde (HCHO) at 250 °C. The enhanced gas sensing performance could be attributed to the formation of p-n heterojunction which was revealed by specific band alignment and the heterojunction-depletion model. Besides, the well-structured p-CuO/n-SnO2 core-shell NWs achieved excellent selectivity for HCHO from commonly occurred reducing gases. In a word, such heterostructured p-CuO/n-SnO2 core-shell NW gas sensors demonstrate a feasible approach for enhanced sensitive and selective HCHO detection. © 2019 Elsevier B.V.

Highly sensitive and selective gas sensors based on heterostructured p-CuO/n-SnO 2 core-shell nanowires (NWs) with precisely controlled shell thickness were synthesized through a sequential process combining a solution processing and atomic layer deposition. The gas sensing devices were fabricated on micro-electromechanical systems, which has triggered great research interest for low power consumption and highly integrated design. The designed p-CuO/n-SnO 2 core-shell NW structured gas sensors exhibited superior gas sensing performance, which is closely related to the thickness of the SnO 2 shell. Specifically, p-CuO/n-SnO 2 core-shell NWs with a 24 nm thick SnO 2 shell displayed a high sensitivity (R a /R g ) of 2.42, whose rate of resistance change (i.e. 1.42) is 3 times higher than the pristine CuO NW sensor when detecting 50 ppm formaldehyde (HCHO) at 250 °C. The enhanced gas sensing performance could be attributed to the formation of p-n heterojunction which was revealed by specific band alignment and the heterojunction-depletion model. Besides, the well-structured p-CuO/n-SnO 2 core-shell NWs achieved excellent selectivity for HCHO from commonly occurred reducing gases. In a word, such heterostructured p-CuO/n-SnO 2 core-shell NW gas sensors demonstrate a feasible approach for enhanced sensitive and selective HCHO detection. © 2019 Elsevier B.V.

Overcoming the trade-off between strength and ductility in metallic materials is a grand challenge. Recently, materials with a gradient nano-grained (GNG) surface layer adhering to a ductile coarse-grained (CG) substrate have been proposed to overcome this long-standing dilemma. Constitutive modeling and simulation are crucial to understand the deformation mechanisms controlling the strength and ductility in GNG/CG materials, and to enable theory to guide microstructure optimization for upscaling. Here, we develop a dislocation mechanism based size-dependent crystal plasticity model, where multiple dislocation evolution mechanisms are considered. Furthermore, damage evolution and mechanically driven grain growth during the deformation of GNG/CG materials are incorporated into the constitutive model to study the role of microstructure gradient in the overall plastic response. The developed size-dependent constitutive model was implemented within a finite-strain crystal plasticity finite element framework, and used to predict the tensile mechanical behavior of GNG/CG copper, including yield stress, strain-hardening and ductility with a highly simplified geometrical representation of the microstructure. The simulations reveal some of the underlying deformation mechanisms controlling ductility and strengthening in terms of the spatial distribution and temporal evolution of microstructure and damage. The model was also used to demonstrate optimization of strength and ductility of GNG/CG copper. By manipulating the thickness of the GNG layer and the grain size of the CG substrate, the strength increase is associated with a loss of ductility showing the same linear inverse relationship observed experimentally for GNG/CG copper, which indicates the improvement over the typical nonlinear trade-off between strength and ductility. © 2018 Elsevier Ltd.

Cu-Cr alloys with ∼32 at.% Cr were rapidly solidified by splat quenching or laser melting techniques with the intention to form a very fine grained, non-equilibrium nanostructure similar to those obtained by severe plastic deformation or thin film deposition. The rapidly solidified Cu-Cr alloys were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Both synthesis techniques lead to a similar two-phase microstructure with a nearly pure fcc Cu matrix with μm grain sizes and bcc Cr particles highly supersaturated with Cu. Splat quenching provides finer bcc particles with dimensions of less than 50 nm compared to laser melting with particle sizes of 100–2000 nm. In case of laser melting, (14 ± 2) at.% Cu are contained in the bcc phase, while splat quenching freezes (20 ± 2) at.% Cu in the bcc particles. The microstructures are discussed and compared to the non-equilibrium microstructures reported in literature using severe plastic deformation and thin films deposition. © 2019 Elsevier B.V.

The iron-based superconductor FeSe offers a unique possibility to study the interplay of superconductivity with purely nematic as well magnetic-nematic order by pressure (p) tuning. By measuring specific heat under p up to 2.36 GPa, we study the multiple phases in FeSe using a thermodynamic probe. We conclude that superconductivity is bulk across the entire p range and competes with magnetism. In addition, whenever magnetism is present, fluctuations exist over a wide temperature range above both the bulk superconducting and the magnetic transitions. Whereas the magnetic fluctuations are likely temporal, the superconducting fluctuations may be either temporal or spatial. These observations highlight similarities between FeSe and underdoped cuprate superconductors. © 2019 American Physical Society.

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).

Cu(In,Ga)S2-based solar cells are interesting tandem partners for Si or chalcopyrite solar cells, but suffer from a low open-circuit voltage. Recently, record efficiencies have been achieved by using higher growth temperatures for the absorber. To understand the effect of higher growth temperatures, we investigate the structural and electronic properties of CuInS2 absorbers. By investigating the absorber alone as opposed to complete solar cells, we can separate changes in the absorber from effects of the interface properties. We show that the quasi-Fermi-level splitting, which indicates the maximum open-circuit voltage an absorber is capable of, increases with higher growth temperature. The quasi-Fermi-level splitting is limited by a deep defect, the concentration of which decreases with higher growth temperature and is less prominent in Cu-rich films. Thus, we demonstrate that the open-circuit voltage of CuInS2-based solar cells is limited to below 850 mV by the absorber itself, independent of the interface. In contrast to the changes in the electronic properties, the structural properties are rather independent of temperature within the range investigated but are significantly influenced by the composition. © 2019 authors. Published by the American Physical Society.

Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Se2 films, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSe2 grown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Se2 and Cu(In,Ga)3Se5 phase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells. © 2018 The Author(s).

Oxygen contamination is a problem which inevitably occurs during severe plastic deformation of metallic powders by exposure to air. Although this contamination can change the morphology and properties of the consolidated materials, there is a lack of detailed information about the behavior of oxygen in nanocrystalline alloys. In this study, aberration-corrected high-resolution transmission electron microscopy and associated techniques are used to investigate the behavior of oxygen during in situ heating of highly strained Cu-Fe alloys. Contrary to expectations, oxide formation occurs prior to the decomposition of the metastable Cu-Fe solid solution. This oxide formation commences at relatively low temperatures, generating nanosized clusters of firstly CuO and later Fe2O3. The orientation relationship between these clusters and the matrix differs from that observed in conventional steels. These findings provide a direct observation of oxide formation in single-phase Cu-Fe composites and offer a pathway for the design of nanocrystalline materials strengthened by oxide dispersions. © 2018 The Author(s).

A composition-spread Cu-Zr thin film library with Zr contents from 2.5 up to 6.5 at.% was synthesized by magnetron sputtering on a thermally oxidized Si wafer. The compositional and microstructural variations of the Cu-Zr thin film across the composition gradient were examined using energy dispersive X-ray spectroscopy, X-ray diffraction, and high-resolution scanning and transmission electron microscopy of cross-sections fabricated by focused ion beam milling. Composition-dependent hardness and elastic modulus values were obtained by nanoindentation for measurement areas with discrete Zr contents along the composition gradient. Similarly, the electrical resistivity was investigated by 4-point resistivity measurements to study the influence of Zr composition and microstructural changes in the thin film. Both, the mechanical and electrical properties reveal a significant increase in hardness and resistivity with increasing Zr content. The trends of the mechanical and functional properties are discussed with respect to the local microstructure and composition of the thin film library. © 2017

Atom probe tomography enables precise quantification of the composition of second phase particles from their early stages, leading to improved understanding of the thermodynamic and kinetic mechanisms of phase formation and quantify structure-property relationships. Here we demonstrate how approaches developed for small-angle scattering can be adapted to atom probe tomography. By exploiting nearest-neighbor distributions and radial distribution function, we introduce a parameter free methodology to efficiently extract information such as particle size, composition, volume fraction, number density and inter-particle distance. We demonstrate the strength of this approach in the analysis of a precipitation-hardened model Al-Zn-Mg-Cu high-strength lightweight alloy. © 2018 Elsevier Ltd

A novel carbon material with an ultra-hydrophilic surface and an ordered arrangement of uniformly sized mesopores is synthesized via a solvent-free nanocasting approach conducted in a planetary ball mill. The synthesis involves a mechanochemical coordination reaction of bipyridine and copper chloride and its subsequent carbonization. Stemming from the synergistic effect of uniformly dispersed 34 wt% of heteroatoms and the highly ordered mesoporous structure (specific surface area >1000 m2 g-1, pore volume >1.2 cm3 g-1), the apparent water contact angle of the material is 0°-an unprecedented value for carbon materials. This novel type of carbon, with its tailorable pore structure, constitutes an ideal model material for fundamental investigations and can open new perspectives for advanced applications of porous carbons where polar wettability is crucial. Moreover, the solvent-free ball milling synthesis concept paves the way towards many novel materials, that syntheses are currently suffering from solubility issues in the nanocasting process. © 2018 The Royal Society of Chemistry.

We combined transmission Kikuchi diffraction and atom probe tomography techniques to investigate the relationship between the structure and chemistry of grain boundaries in Cu(In,Ga)Se2 thin films. Kikuchi patterns with the tetragonal structure of Cu(In,Ga)Se2 were simulated to emphasize the pseudosymmetry issue in this material system and, hence, the orientation determination ambiguity in case of indexing with a cubic zinc-blende structure. We compared these patterns with experimental data. We detect an elemental redistribution at random high-angle grain boundaries but no chemical fluctuations at Σ3 twin boundaries. The atom probe tomography analyses reveal Cu depletion as well as In and Se enrichment at random grain boundaries and, at some random grain boundaries, a slight Ga depletion. This In on Cu scenario is accompanied by cosegregation of Na and K originating from the soda-lime glass substrate. The amount of impurity segregation does vary not only from one grain boundary to another but also along an individual grain boundary. Hence, our results suggest that the degree of passivation of detrimental, nonradiative recombination centers does differ not only between Σ3 twin boundaries and random grain boundaries but also within the same random grain boundary. Copyright © 2017 John Wiley & Sons, Ltd.

In this paper, a direct chemical vapor deposition (CVD) approach is applied for the first time to synthesize high quality copper oxide (CuO), copper tungstate (CuWO4) and tungsten oxide (WO3) on F:SnO2 (FTO) substrates for photocatalytic water splitting. Variation of process parameters enables us to tune the stoichiometry of the deposits to obtain stoichiometric, W-rich, and Cu-rich deposits. It is found that the presence of Cu in WO3 thin films reduces the bandgap and enhances the absorption properties of the material in the visible range. The photoelectrocatalytic performance of stoichiometric CuWO4 was found to be superior to that of WO3 oxide under frontside illumination when thin films were used. However, detailed photoelectrochemical investigations of both thin and thicker CuWO4 films reveal that the incorporation of copper also decreases the mobility of both electrons and holes, the latter being the performance-limiting factor. These results are in line with our first-principles calculations of the electronic structure of CuWO4. A charge carrier mobility and diffusion length of ∼6× 10-3 cm2 V-1 s-1 and 30 nm were determined by time-resolved microwave conductivity measurements, values comparable to those of undoped bismuth vanadate (BiVO4). Our findings establish new insights into the advantages and limits of CuWO4-based photoanodes, and suggest a possibility of using very thin CuWO4 films on top of highly absorbing semiconductors with optimal electronic properties. © The Royal Society of Chemistry 2018.

Beyond dilute coverage, the collective diffusion of molecules might enhance material transport. We reveal an enhanced mobility of molecular dimers by separating two motions, diffusion and rotation, of CO dimers on elemental Ag(100) as well as on a dilute Cu alloy of Ag(100). From time-lapsed scanning tunneling microscopy movies recorded between 15 and 25 K, we determine the activation energy of dimer diffusion on elemental Ag(100) to be, at (40±2) meV, considerably smaller than the one for monomer diffusion, at (72±1) meV. The alloyed Cu atoms reduce the dimer mobility facilitating to determine their rotational barrier separately to be (39±3) meV. Disentangling different degrees of freedom suggests that a rotational motion is at the origin of enhanced dimer diffusivity. © 2018 American Physical Society.

The dehydrogenation of ethanol to acetaldehyde (DHEA) is an environmentally benign alternative for synthetic chemistry and for the fine chemical industry. The key is to design Cu-based catalysts with certain structures to obtain high acetaldehyde selectivity. Herein, hybrid C@SiO2 hollow submicron spheres were designed and synthesized using a confined pyrolysis method. This hybrid structure processes a layer of carbon-silica hybrid shell. After loading the Cu, the Cu/C@SiO2 catalyst exhibited 36.1% conversion of ethanol and ∼99% acetaldehyde selectivity at 260 °C. The hybrid support combined the two favorable properties of carbon and silica and thus improving both selectivity and stability. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Friction Stir Welding (FSW) imparts both heat and deformation to the metal being joined, producing profound microstructural changes that determine the weld properties. In the case of welding of aerospace aluminium alloys, the most important change is the modification of the size, nature, and fraction of strengthening precipitates. To understand these changes requires the ability to measure the microstructural evolution during the welding process. This paper describes a new tool, the FlexiStir system, a portable friction stir unit designed for use in a high-energy synchrotron beamline that enables in-situ studies of microstructural evolution during FSW. FlexiStir has been used to measure precipitate evolution during FSW of aluminium alloy 7449-TAF and provide time-resolved measurement of precipitate size and volume fraction via small angle X-ray scattering (SAXS). These measurements have been interpreted with the aid of a previously developed microstructural model. The model predictions and SAXS measurements are in good qualitative agreement and demonstrate the complex precipitate transformation, dissolution, and reprecipitation events that occur during welding. © 2018

A potential pulse-assisted approach was used to immobilize Myrothecium verrucaria bilirubin oxidase at planar and nanoporous gold electrodes (NPG) containing pores of ca. 20 nm and ca. 40 nm in diameter. An increase in the current due to the bioelectrocatalytic reduction of oxygen by MvBOD-modified gold electrodes obtained from a 20 μL drop by the proposed pulse-assisted approach was observed when compared to the response obtained with electrodes modified by drop-casting. This increase likely arises from a preferential orientation of MvBOD molecules at the planar gold surface obtained by fast switching of the potential pulses between opposite charges. The concomitant ion stirring effect induces the attraction of the enzymes to the charged gold surface and forces access to the internal pore volume of the NPG. Immobilization of MvBOD using the potential pulse-assisted approach significantly increases current densities by facilitating the electron transfer between the enzyme and the electrode surface. © 2017 Elsevier B.V.

Tensile tests were carried out in high-purity, polycrystalline copper alloys with three concentrations of sulfur impurities (14, 27 and 7920 at ppm) at temperatures between 20 °C and 400 °C. The ductility drops with increasing sulfur concentration and temperature while the ultimate tensile strength increases. The alloys exhibit a grain size of several millimeters and contain mostly random grain boundaries (GBs). The microstructure and composition is investigated by transmission electron microscopy (TEM) and atom probe tomography (APT). The microstructure of the samples with sulfur contents of 14 and 27 ppm consists of globular grains and neither of the microanalytical techniques employed reveals the formation of Cu-sulfides or sulfur segregation to GBs. Even after annealing at 500 °C, no sulfide formation or sulfur segregation to GBs was detected. In the alloy with a sulfur content of 7920 ppm, a dendritic structure is observed and in the interdendritic region monoclinic Cu2S precipitates with a size range from 5 nm to several μm are observed at GBs and also within the grains. The influence of S on the ductility is discussed considering the TEM and APT results. © 2018 Acta Materialia Inc.

We show that chemistry can be used to trigger a nanofaceting transition. In particular, the segregation of Ag to an asymmetric tilt grain boundary in Cu is investigated. Aberration-corrected electron microscopy reveals that annealing the bicrystal results in the formation of nanometer-sized facets composed of preferentially Ag-segregated symmetric Σ5{210} segments and Ag-depleted {230}/{100} asymmetric segments. Our observations oppose an anticipated trend to form coarse facets. Atomistic simulations confirm the nanofacet formation observed in the experiment and demonstrate a concurrent grain boundary phase transition induced by the anisotropic segregation of Ag. © 2018 authors. Published by the American Physical Society.

Surface segregation, restructuring, and sintering phenomena in size-selected copper-nickel nanoparticles (NPs) supported on silicon dioxide substrates were systematically investigated as a function of temperature, chemical state, and reactive gas environment. Using near-ambient pressure (NAP-XPS) and ultrahigh vacuum X-ray photoelectron spectroscopy (XPS), we showed that nickel tends to segregate to the surface of the NPs at elevated temperatures in oxygen- or hydrogen-containing atmospheres. It was found that the NP pretreatment, gaseous environment, and oxide formation free energy are the main driving forces of the restructuring and segregation trends observed, overshadowing the role of the surface free energy. The depth profile of the elemental composition of the particles was determined under operando CO2 hydrogenation conditions by varying the energy of the X-ray beam. The temperature dependence of the chemical state of the two metals was systematically studied, revealing the high stability of nickel oxides on the NPs and the important role of high valence oxidation states in the segregation behavior. Atomic force microscopy (AFM) studies revealed a remarkable stability of the NPs against sintering at temperatures as high as 700 °C. The results provide new insights into the complex interplay of the various factors which affect alloy formation and segregation phenomena in bimetallic NP systems, often in ways different from those previously known for their bulk counterparts. This leads to new routes for tuning the surface composition of nanocatalysts, for example, through plasma and annealing pretreatments. © 2017 American Chemical Society.

Understanding the composition evolution of grain boundaries and grain boundary precipitation at near-atomic scale in aluminum alloys is crucial to tailor mechanical properties and to increase resistance to corrosion and stress corrosion cracking. Here, we elucidate the sequence of precipitation on grain boundaries in comparison to the bulk in a model Al-Zn-Mg-Cu alloy. We investigate the material from the solution heat treated state (475 °C), through the very early stages of aging to the peak aged state at 120 °C and further into the overaged regime at 180 °C. The process starts with solute enrichment on grain boundaries due to equilibrium segregation accompanied by solute depletion in their vicinity, the formation of Guinier–Preston (GP) zones in the solute-enriched grain boundary regions, and GP zones growth and transformation. The equilibrium segregation of solutes to grain boundaries during aging accelerates this sequence compared to the bulk. Analysis of the ∼10 nm wide precipitate-free zones (PFZs) adjacent to the solute-enriched grain boundaries shows that the depletion zones are determined by (i) interface equilibrium segregation; (ii) formation and coarsening of the grain boundary precipitates and (iii) the diffusion range of solutes in the matrix. In addition, we quantify the difference in kinetics between grain boundary and bulk precipitation. The precipitation kinetics, as observed in terms of volume fraction, average radius, and number density, is almost identical next to the depletion zone in the bulk and far inside the bulk grain remote from any grain boundary influence. This observation shows that the region influenced by the grain boundaries does not extend beyond the PFZs. © 2018 Acta Materialia Inc.

The effect of linkers with extended π-system on the topological preference of (4,4)-connected copper paddle-wheel-based metal-organic frameworks (MOFs) was investigated using the reverse topological approach (RTA) in which a genetic algorithm (GA) and the DFT-derived force field MOF-FF were used for ranking and predicting the most stable phase. Three tetracarboxylate linkers bearing different functionality, namely, phenylene (L1), naphthalene (L2), and anthracene (L3) groups, were studied. All potential topologies including nbo-b, ssa, ssb, pts, and lvt-b were considered. The computational results reveal that nbo-b is the most stable topology for all three investigated linkers. However, L2 is also formed in ssb according to experimental findings. Our simulation results show that the CH-π interactions with a Y-shaped configuration between naphthalene moieties of L2 stabilize the ssb framework. Unlike L2, CH-π interactions are not favorable for L1 and L3 because of unsuitable size of the π-system. The results of the RTA predictions are in agreement with experimentally reported data, suggesting the capability of RTA for accurate structural predictions of MOFs. More importantly, this work shows the exemption of reticular chemistry in which linker functionalization can result in alteration of the resulting topology, as found in the case of linker L2. © 2018 American Chemical Society.

The gas-phase atomic/molecular layer deposition (ALD/MLD) technique is strongly emerging as a viable approach to fabricate new exciting inorganic-organic hybrid thin-film materials. However, much less effort has been made to develop new precursors specifically intended for ALD/MLD; this applies to both the organic and inorganic precursors, and in the latter case in particular to transition metal precursors. Here we introduce copper bisdimethylaminopropoxide (Cu(dmap)2) as a promising transition metal precursor for ALD/MLD to be combined with a variety of organic precursors with different backbones and functional groups, i.e. hydroquinone (HQ), terephthalic acid (TPA), 4,4′-oxydianiline (ODA), p-phenylenediamine (PPDA) and 1,4-benzenedithiol (BDT). Hybrid Cu-organic thin films were obtained from all five organic precursors with appreciably high growth rates ranging from 1.0 to 2.6 Å per cycle. However, the Cu(dmap)2 + HQ process was found to yield hybrid Cu-organic films only at temperatures below 120 °C, while at higher temperatures metallic Cu films were obtained. The films were characterized by XRR, GIXRD, FTIR, Raman, XPS and UV-Vis spectroscopy. © The Royal Society of Chemistry.

Copper-infiltrated tool steels potentially combine the good mechanical properties of tool-steels and the superior electrical and thermal conductivity of copper. However, their effective properties greatly depend on the constitution of the components as well as their topology. In this work, the copper-infiltrated cold-work tool steel of type X245VCrMo9-4-4 is analyzed. The thermal conductivity (TC) of the composite and its components is measured and their topology is analyzed by means of X-ray microtomography (μCT). Using the digitized topology and the attained properties, numerical FE simulations were laid out, which allowed the detailed investigation of heat transfer in the material. The results indicate, that 1) the simulated thermal conductivity is very sensitive to the assumed thermal boundary conductance (TBC) 2) the TBC can be approximated by iteratively converging the simulation results to the measured TC 3) both components contribute to the effective thermal conductivity (1/6 steel + 5/6 copper) and act as a bypass for each other, preventing hot spots 4) small increases in the copper content increase the TC by shortening the effective heat conduction path. © 2018 Elsevier Ltd

We present the first measurement of the strain rate sensitivity of the ideal dislocation slip transmission through a coherent Σ3{111} copper twin boundary. For this purpose we have deformed 129 geometrically identical samples at different strain rates. The micron-sized samples are either single crystalline (87 pillars) or contain one vertical Σ3{111} twin boundary (42 pillars). The strain rate sensitivity of the ideal slip transmission event is 0.015 ± 0.009. This value is considerably lower than the strain rate sensitivity observed for nano-twinned bulk materials, which is addressed to multiple simultaneously activated deformation processes present in the latter case. The activation volume of the ideal slip transmission points towards a cross-slip like transmission process of dislocations through the twin boundary. Furthermore, the high number of geometrically identical samples is used to discuss the ability to identify the strength distribution function of micropillars. © 2018 Acta Materialia Inc.

A copper(I) 3,5-diphenyltriazolate metal–organic framework (CuTz-1) was synthesized and extensively characterized by using a multi-technique approach. The combined results provided solid evidence that CuTz-1 features an unprecedented Cu5tz6 cluster as the secondary building unit (SBU) with channels approximately 8.3 Å in diameter. This metal–organic framework (MOF) material, which is both thermally and chemically (basic and acidic) stable, exhibited semiconductivity and high photocatalytic activity towards the degradation of dyes in the presence of H2O2. Its catalytic performance was superior to that of reported MOFs and comparable to some composites, which has been attributed to its high efficiency in generating .OH, the most active species for the degradation of dyes. It is suggested that the photogenerated holes are trapped by CuI, which yields CuII, the latter of which behaves as a catalyst for a Fenton-like reaction to produce an excess amount of .OH in addition to that formed through the scavenging of photogenerated electrons by H2O2. Furthermore, it was shown that a dye mixture (methyl orange, methyl blue, methylene blue, and rhodamine B) could be totally decolorized by using CuTz-1 as a photocatalyst in the presence of H2O2 under the irradiation of a Xe lamp or natural sunlight. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

A series of Cu/ZrO2 catalysts with nominal CuO loadings of 5, 10, 18 and 31 wt.% was synthesized by co-precipitation, characterized and applied in the hydrodeoxygenation of glycerol under mild reaction conditions (200 °C, 25 bar H2). These catalysts were highly selective for the cleavage of C−O bonds while preserving C−C bonds leading to 95 % selectivity to 1,2-propanediol. The conversion of glycerol was observed to be linearly correlated with the specific copper surface area derived from N2O frontal chromatography. The reaction was found to occur through the dehydration of glycerol to acetol followed by its hydrogenation to 1,2-propanediol. Metallic copper was identified as the active site for both reactions suggesting the acid ZrO2 sites to be blocked by water. Reusability studies showed that the catalyst was relatively stable and the conversion decreased by only 18 % after three cycles. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The microscopic details of the suppression of antiferromagnetic order in the Kondo-lattice series Ce1-xLaxCu2Ge2 due to nonmagnetic dilution by La are revealed through neutron diffraction results for x=0.20, 0.40, 0.75, and 0.85. Magnetic Bragg peaks are found for 0.20≤x≤0.75, and both the Néel temperature TN and the ordered magnetic moment per Ce μ linearly decrease with increasing x. The reduction in μ points to strong hybridization of the increasingly diluted Ce 4f electrons, and we find a remarkable quadratic dependence of μ on the Kondo-coherence temperature. We discuss our results in terms of local-moment- versus itinerant-type magnetism and mean-field theory and show that Ce1-xLaxCu2Ge2 provides an exceptional opportunity to quantitatively study the multiple magnetic interactions in a Kondo lattice. © 2018 American Physical Society.

We present a novel alloy design strategy for cost-efficient high modulus steels with an increased stiffness / mass density ratio. The concept is based on the liquid metallurgy synthesis of Fe – Cr – B based alloys, straightforward processability, and well tuneable mechanical properties via plain heat treatments. The base alloy Fe – 18 Cr – 1.6 B (wt%) contained 14–17 vol% of (Cr,Fe)2B particles of ellipsoidal morphology in a ferritic matrix. Hot rolled materials revealed a specific modulus of 32.8 GPa g−1 cm3, exceeding that of conventional Fe-Cr steels by almost 30%. Mechanical properties obtained are comparable to TiB2 based high modulus steels. Addition of 1 wt% Cu to the base alloy did not interact with the formation, fraction, size and morphology of (Cr,Fe)2B particles, and allowed to mildly increase the strength values by ageing treatments, however at the price of a reduction of the specific modulus. C additions of 0.2 wt% did not affect the (Cr,Fe)2B particle microstructure greatly, but free C dissolved in the matrix enables for the first time to utilize the wide range of microstructures and mechanical properties of established C-containing high strength steels also in high modulus steels. © 2018 Elsevier B.V.

One of the main obstacles to the industrial application of laser micro-spot welding of copper is the poor process repeatability at common laser wavelengths. The inhomogeneities in the oxide layer in combination with the high reflectivity of copper itself are often stated as the main reason for the poor repeatability of welding results. However, the typical local variations of the reflectivity alone are not sufficient to describe the instability of the welding process completely. Through numerical FEM simulations, the temperature dependence of the absorptivity could be identified as the main reason for the narrowing of the process window. The effect of the temperature-dependent absorptivity is enhanced by the temperature-dependence of the heat conductivity and slightly reduced by the enthalpy of fusion. The results of the simulation show a good agreement with experimental data. © 2018 IOP Publishing Ltd.

Surface pile-up topography is very significant for property extraction in nanoindentation tests. In the present work, we perform crystal plasticity finite element simulations of Berkovich nanoindentation of single crystalline copper with different crystallographic orientations, which derive quantitatively comparable mechanical properties and surface pile-up topographies with experimental data. Simulation results demonstrate that there is a coupled effect of crystallographic orientation of indented material and indenter geometry on surface pile-up behavior, due to the interaction between intrinsic dislocation slip events and extrinsic discrete stress distribution patterns. Based on the relative spatial orientation between crystallographic orientation of indented material and indenter geometry, a surface pile-up density factor mp is proposed to qualitatively characterize the propensity of surface pile-up behavior in nanoindentation tests of single crystalline copper. © 2018 Elsevier Ltd

In Cu-zeolite based selective catalytic reduction of NOx with NH3 (NH3-SCR), Cu species (in particular CuI) solvated by NH3 molecules are predicted theoretically to be highly mobile with their mobility being decisive for the NH3-SCR reactivity at low temperatures (<250 °C). Direct experimental observation of the Cu mobility after NH3 solvation, however, has not been achieved yet. Here we show that complex impedance-based modulus spectroscopy, performed by following the corresponding dielectric relaxation processes at high frequencies (104 to 106 Hz), can be applied to monitor directly the dynamic local movement of Cu ions in zeolite catalysts under NH3-SCR related reaction conditions. Simultaneous in situ impedance and infrared spectroscopy studies, assisted by periodic DFT calculations with reliable van der Waals dispersion corrections, allowed us to identify the key factors determining the local dynamics of Cu ions in two representative Cu-zeolites, i.e. Cu-ZSM-5 and Cu-SAPO-34. The co-adsorption and interaction of NO and NH3 on CuII sites led to the formation of highly mobile CuI species and NH4+ intermediates, and, consequently, significantly enhanced local dynamics of Cu ions in both zeolite catalysts. The re-oxidation of CuI, which is the rate-determining step of NH3-SCR reaction, was more favorable in Cu-SAPO-34 than in Cu-ZSM-5, which can be attributed to the close coupling of NH4+ intermediate and Cu site promoting the formation of CuII-NO2/NH4+. As a result, the overall local dynamics of Cu, largely determined by CuI species, is less dependent on the NH4+ intermediate in Cu-SAPO-34 than in Cu-ZSM-5. © 2018 Elsevier B.V.

Formation and dissolution of oxide on copper under transpassive conditions, i.e. during OER and transpassive dissolution, in alkaline electrolyte was investigated by a combination of electrochemical techniques and in situ and operando Raman and photoluminescence (PL) spectroscopy, as well as spectropscopic ellipsometry. Experiments were conducted under potentiodynamic and potentiostatic polarisation in 0.1M NaOH. In chronoamperometry experiments with steps between potentials, oxide thickness continued increasing beyond the onset of OER. The thickness dropped significantly from >10 nm to <5 nm ≈400 mV above the OER onset. The presence of CuO, Cu2O and Cu4O3 was observed by Raman spectroscopy after the onset of OER. Correlating with the thickness drop, strong PL was observed at 1.55 eV, indicating the formation of singly charged oxygen vacancies VO+, following the classical PL spectrum interpretation from the literature. PL observation speaks against vacancy pair coalescence as mechanism of dissolution. After electrochemical experiments, the films were n-type semiconductors, not p-type conductors as expected for copper oxides. Results indicate that transpassive dissolution may be triggered by the instability of the oxide with respect to defect formation. © 2017 Elsevier Ltd

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.

The grain boundary character distribution (GBCD) of nanotwinned copper, fabricated by electroplating inside small-scale through-wafer vias, was characterized using a stereological interpretation of electron backscatter diffraction maps. The GBCD of electroplated nanotwinned copper, specified by five macroscopic parameters (three for the lattice misorientation and two for the grain boundary plane inclination), is similar to the GBCD of coarse-grained polycrystalline copper used here as a reference material. The GBCD was compared to calculated grain boundary energies determined from atomistic simulations. We find that the grain boundary population in the electroplated nanotwinned and coarse-grained reference copper is both on average inversely correlated to the grain boundary energies. The slopes of the relationships between grain boundary population and energy for the most highly populated misorientations (Σ3, Σ9, and Σ11) are different. The relationships are strongly influenced by the geometric constraints at the triple junctions and multiple twinning, which enhanced the observed frequencies of Σ9 boundaries. The results suggest that the grain boundary network and the GBCD in the polycrystalline specimens are strongly influenced by the microstructure, grain boundary energy, and multiple twining. © 2016, Springer Science+Business Media New York.

We report the thermal stability of supersaturated CuCr nanocrystallines alloys at the atomic resolution using modern spherical aberration-corrected transmission electron microscopy (TEM) via performing in-situ structural and spectroscopy experiments. It is found that CuCr nanocrystallines are not only subjected to a structural change but also undergo a chemical evolution upon annealing. Chemical destabilization of supersaturated CuCr nanocrystallines occurs at a quite low temperature. Heating triggers a rapid separation of Cu and Cr grains at the forced intermixing zone, accompanied by an obvious decrease of average interface width whereas the grain growth is not significant. Elemental profiles and images recorded in real time reveal that the local compositions vary with heating, which in turn permits to derive the concentration of excess vacancy generated by deformation and observe its evolution with temperature, further to analyze the dynamic behavior in nanocrystalline materials. Electronic structure changes at the interface forced intermixing zone are revealed by the fine structure analysis. The study uncovers the interplay between the thermal stability and chemical decomposition process of bulk nanostructured materials in real-time. © 2017

The catalytic hydrogenation of ethyl acetate to ethanol was studied at ambient pressure in the temperature range from 463 K to 513 K using Cu/ZrO2 catalysts obtained by co-precipitation as a function of the Cu loading. The hydrogenation was established as a reproducible probe reaction by determining optimal reaction parameters without deactivation or thermodynamic limitations. Power-law kinetics were determined yielding an apparent activation energy of 74 kJ mol−1 and reaction orders of 0.1–0.3 for H2 and −0.4 to 0.1 for ethyl acetate in the temperature range from 473 K to 503 K. Metallic Cu was found to be essential for the hydrogenation, but the catalytic activity was not proportional to the Cu surface area derived from N2O decomposition and temperature-programmed H2 desorption experiments identifying Cu/ZrO2 as bifunctional catalyst. The acidic sites of the ZrO2 matrix were probed by temperature-programmed experiments with ethyl acetate and NH3. Cu0 is assumed to provide atomic hydrogen by dissociative adsorption and spillover, but the reaction rate is more affected by the tight contact between the embedded Cu nanoparticles and the X-ray amorphous ZrO2 matrix. © 2017 Elsevier Inc.

The Cr phase separation process and kinetics of a metastable Cu96Cr4 alloy film were investigated by isothermal annealing at different temperatures of up to 500 °C using transmission electron microscopy. It is shown that the Cr phase separation proceeds predominantly via enrichment of Cr at grain boundaries and grain boundary diffusion. Temperature dependent diffusion coefficients and the activation energy for grain boundary diffusion of Cr in face–centered cubic Cu are determined from analytical in–situ transmission electron microscopy experiments. In addition, the influence of electron beam irradiation on the diffusion kinetics is considered. © 2016 Elsevier B.V.

The difference in quantitative analysis performance between the voltage-mode and laser-mode of a local electrode atom probe (LEAP3000X HR) was investigated using a Fe-Cu binary model alloy. Solute copper atoms in ferritic iron preferentially field evaporate because of their significantly lower evaporation field than the matrix iron, and thus, the apparent concentration of solute copper tends to be lower than the actual concentration. However, in voltage-mode, the apparent concentration was higher than the actual concentration at 40 K or less due to a detection loss of matrix iron, and the concentration decreased with increasing specimen temperature due to the preferential evaporation of solute copper. On the other hand, in laser-mode, the apparent concentration never exceeded the actual concentration, even at lower temperatures (20 K), and this mode showed better quantitative performance over a wide range of specimen temperatures. These results indicate that the pulsed laser atom probe prevents both detection loss and preferential evaporation under a wide range of measurement conditions. © 2017 Elsevier B.V.

Carbon dioxide electroreduction to chemicals and fuels powered by renewable energy sources is considered a promising path to address climate change and energy storage needs. We have developed highly active and selective copper (Cu) nanocube catalysts with tunable Cu(100) facet and oxygen/chlorine ion content by low-pressure plasma pretreatments. These catalysts display lower overpotentials and higher ethylene, ethanol, and n-propanol selectivity, resulting in a maximum Faradaic efficiency (FE) of ∼73% for C2 and C3 products. Scanning electron microscopy and energy-dispersive X-ray spectroscopy in combination with quasi-in situ X-ray photoelectron spectroscopy revealed that the catalyst shape, ion content, and ion stability under electrochemical reaction conditions can be systematically tuned through plasma treatments. Our results demonstrate that the presence of oxygen species in surface and subsurface regions of the nanocube catalysts is key for achieving high activity and hydrocarbon/alcohol selectivity, even more important than the presence of Cu(100) facets. © 2017 American Chemical Society.

New catalysts are needed to achieve lower overpotentials and higher faradaic efficiency for desirable products during the electroreduction of CO2. In this study, we explore the size-dependence of monodisperse gold-copper alloy nanoparticles (NPs) synthesized by inverse micelle encapsulation as catalysts for CO2 electroreduction. X-ray spectroscopy revealed that gold-copper alloys were formed and were heavily oxidized in their initial as prepared state. Current density was found to increase significantly for smaller NPs due to the increasing population of strongly binding low coordinated sites on NPs below 5nm. Product analysis showed formation of H2, CO, and CH4, with faradaic selectivity showing a minor dependence on size. The selectivity trends observed are assigned to reaction-induced segregation of gold atoms to the particle surface and altered electronic or geometric properties due to alloying. © 2016.

Solid-liquid interfaces play an important role in many fields like electrochemistry, corrosion, and heterogeneous catalysis. For understanding the related processes, detailed insights into the elementary steps at the atomic level are mandatory. Here we unravel the properties of prototypical surface-defects like adatoms and vacancies at a number of copper-water interfaces including the low-index Cu(111), Cu(100), and Cu(110), as well as the stepped Cu(211) and Cu(311) surfaces. Using a first-principles quality neural network potential constructed from density functional theory reference data in combination with molecular dynamics and metadynamics simulations, we investigate the defect diffusion mechanisms and the associated free energy barriers. Further, the solvent structure and the mobility of the interfacial water molecules close to the defects are analyzed and compared to the defect-free surfaces. We find that, like at the copper-vacuum interface, hopping mechanisms are preferred compared to exchange mechanisms, while the associated barriers for hopping are reduced in the presence of liquid water. The water structure close to adatoms and vacancies exhibits pronounced local features and differs strongly from the structure at the ideal low-index surfaces. Moreover, in particular at Cu(111) the adatoms are very mobile and hopping events along the surface are more frequent than the exchange of coordinating water molecules in their local environment. Consequently, adatom self-diffusion processes at Cu(111) involve entities of adatoms and their associated solvation shells. © 2017 American Chemical Society.

Novel copper ketoiminate compounds were synthesized and for the first time applied for additive-free solution-based deposition of nanoscale copper oxide thin films. The two closely related compounds, namely the bis[4-(2-ethoxyethyl-imino)-3-pentanonato] copper, [Cu(EEKI)(2)], and bis[4-(3-methoxypropylimino)- 3-pentanonato] copper, [Cu(MPKI)(2)], were characterized by means of elemental and thermogravimetric analysis (TGA), as well as electron impact mass spectrometry (EI-MS). The advantages of these compounds are that they are liquid and possess excellent solubility in common organic solvents in addition to an optimum reactivity towards ambient moisture that enables a facile solution-based approach to nanoscale copper oxide thin films. Moreover, no additives or aging is needed to stabilize the solution processing of the copper oxide layers. [Cu(MPKI)(2)] was tested in detail for the deposition of copper oxide thin films by spin coating. Upon one-step annealing, high-quality, uniform, crystalline copper oxide thin films were deposited on Si, SiO2, as well as on quartz substrates. Structural, morphological and compositional characteristics of the copper oxide nanostructures were investigated in detail by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and a combined analysis using Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA). It was possible to control the copper oxide phases (CuO and Cu2O) by systematic tuning of the post-deposition annealing conditions. The functional properties in terms of optical band gap were investigated using UV/Vis spectroscopy, while the transport properties, such as resistivity, mobility and carrier concentration were analyzed employing Hall measurements, which confirmed the p-type conductivity of the copper oxide layers.

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.

Experimental and phase field studies of age hardening response of a high purity Al-4Cu-1Li-0.25Mn-alloy (mass %) during isothermal aging are conducted. In the experiments, two hardening phases are identified: the tetragonal θ' (Al2Cu) phase and the hexagonal T1 (Al2CuLi) phase. Both are plate shaped and of nm size. They are analyzed with respect to the development of their size, number density and volume fraction during aging by applying different analysis techniques in TEM in combination with quantitative microstructural analysis. 3D phase-field simulations of formation and growth of θ' phase are performed in which the full interfacial, chemical and elastic energy contributions are taken into account. 2D simulations of T1 phase are also investigated using multi-component diffusion without elasticity. This is a first step toward a complex phase-field study of T1 phase in the ternary alloy. The comparison between experimental and simulated data shows similar trends. The still unsaturated volume fraction indicates that the precipitates are in the growth stage and that the coarsening/ripening stage has not yet been reached. © 2017 by the authors.

Compression of micropillars is routinely used to measure the material response under uniaxial load. In bi-crystalline pillars an S-shaped grain-boundary together with an S-shaped pillar is often observed after deformation raising the question of its origin and consequences for stress-strain materials data. In addition to dislocation and grain-boundary based mechanisms, this observation can be caused by buckling and subsequent post-buckling deformation. Deviations from the classical pre- and post-buckling deformation behavior are assigned to imperfections, which are categorized in extrinsic and intrinsic imperfections in this work. In the present paper, the S-shaped actual deformation state is particularly promoted by an intrinsic imperfection, caused by a material heterogeneity (due to the bi-crystal arrangement). This kind of deformation behavior is investigated by micro-compression experiments on 7 × 7 × 21 μm3 sized bi-crystal copper pillars with nearly elastic (axial Young's modulus) homogeneity and identical Schmid factors for both grain orientations. Complementary finite element simulations are performed, in which also the role of friction and of an extrinsic imperfection in the form of initial misalignment of the loading on the S-shape are considered. There, a material model describing the flow stress distribution caused by a dislocation pile-up at the grain-boundary is applied. Finally, suggestions to prevent buckling and, thus, transversal post-buckling displacements during micropillar compression tests are given with the goal to extract engineering stress-strain curves. © 2016 Acta Materialia Inc.

A twin surface dielectric barrier discharge consisting of an aluminium oxide plate with grid-structured copper traces on both sides is presented. Due to the size of the electrode configuration spatially resolved optical emission spectroscopy for characterisation of the discharge is performed on two different length scales in order to show its homogeneous behaviour. A broadband echelle spectrometer is employed for a comparison of the plasma parameters at different sites along the copper traces with a spatial resolution on a scale of millimetres. In addition, an ICCD camera with bandpass filters yields homogeneity of the plasma parameters on a scale of micrometres at a given node of the grid-structured copper traces. The discharge is shown to be homogeneous all along the electrode. However, due to the changing composition of the gas stream, it cannot be concluded that the gas phase chemistry follows the same trend. Therefore, FTIR spectroscopy of cysteine is used to monitor the spatial dependence of the gas phase chemistry, showing a transition from purely oxygen-related modifications at the front of the electrode to a mixture of oxygen-related and nitrogen-related modifications at the rear. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In situ Raman and in situ EPR spectroscopy in combination with electrochemistry have been used to investigate the behavior of mixed cobalt nickel and cobalt copper oxides in the oxygen evolution reaction (OER). All experiments were carried out in homemade electrochemical cells using 0.1 M KOH as the electrolyte. The OER activities vary depending on the annealing conditions of the catalyst precursors, also reflected by different behaviours during the in situ spectroscopic experiments. The different activity of the Co/Ni oxides is most likely related to the formation of either γ- or β-NiO(OH), characterized by distinct features in the Raman spectra. Thus, a higher percentage of β-NiO(OH) is present in the more active catalyst. A different behaviour of Co/Cu catalysts has been shown by in situ Raman spectroscopy too, but the active phase could not be identified because of missing spectral features. However, in situ EPR spectroscopy revealed the partial dissolution of Cu(II), suggesting the formation of a Co-enriched oxide/hydroxide surface. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Glycerol is a major by-product of the biodiesel production and is therefore produced in high quantities. While currently there are limited possible applications for this highly functionalized molecule, glycerol can be a cheap and abundant feedstock for value-added products that are accessible by selective oxidation. Usually, the selective oxidation of glycerol utilizes expensive noble metal catalysts, such as Au, Pt, and Pd. Here we report the selective oxidation of glycerol in basic media, using ordered mesoporous Cu-Al2O3 catalysts with various Cu loadings prepared by a facile soft-templating method. The materials were characterized in detail by nitrogen physisorption, vis-NIR spectroscopy, EDX, low- and wide-angle XRD, XPS, and TEM. Subsequently the reaction conditions for glycerol oxidation were optimized. The catalytic oxidation of glycerol yields C3 products, such as glyceric acid and tartronic acid, and also C2 and C1 products, such as glycolic acid, oxalic acid, and formic acid. Moreover, the role of the solvent on the catalytic reaction was investigated, and the addition of various co-solvents to the aqueous reaction mixture was found to increase the initial reaction rate up to a factor of three. The trends of the initial reaction rates correlate well with the polarity of the water/co-solvent mixtures. The prepared Cu-Al2O3 catalysts are a more cost-efficient and environmentally viable alternative to the reported noble metal catalysts. © 2017 The Royal Society of Chemistry.

The thermal stability of evaporated copper–chromium alloy films was studied by correlating hardness trends from nanoindentation to nanostructural–compositional changes from transmission electron microscopy. In particular, the hardness evolution with ageing time at ambient and elevated temperatures of two compositions, dilute (Cu96Cr4) and chromium-rich (Cu67Cr33) solutions, was studied. Due to the negligible mutual miscibility of copper and chromium, the chosen solid solutions are trapped in metastable states as supersaturated solid solutions with face-centred cubic and body-centred cubic phases. Nano-mechanical probing of the nanostructural evolution as a function of temperature provided interesting insights into the phase separation of these systems. © 2016, Springer Science+Business Media New York.

Cu-In-Sn alloys are among the suggested materials to replace Pb-Sn alloys traditionally used in joining processes by the electronic industry. Thorough thermodynamic understanding is required for the selection/design of adequate and efficient alloys for specific applications. Understanding the effects that high cost elements such as In have on microstructure and phase stability is imperative for industrial use. In this work ternary alloys were prepared by melting high purity elements (5N) for selected compositions of the 17 at.% Cu isopleth, and cooling down to reproduce process conditions. Chemical composition was determined using scanning electron microscopy equipped with electron probe microanalysis. Measurements of transition temperatures were done by heat-flux differential scanning calorimetry. We present a comprehensive comparison between our experimental results and phase diagram calculations using Liu et al. (J Electron Mater 30:1093, 2001) thermodynamic description based in the CALPHAD method, available in the literature. © 2017 ASM International

By employing various synthetic conditions, such as Cu(NO3)2·3H2O and Cu(BF4)2·6H2O as copper ion sources and different solvents, defect-engineered analogues of metal–organic framework (MOF) [Cu3(BTC)2] (HKUST-1; BTC = 1,3,5-benzenetricarboxylate) with isophthalate (IP) incorporation (DEMOFs) were synthesised and characterised by powder XRD, SEM, IR spectroscopy, thermogravimetric analysis, NMR spectroscopy and N2 sorption. The results show that the choice of counter ions impacts the properties of the samples especially at high concentrations of IP. The combination of DMF and Cu(BF4)2·6H2O turns out to be superior for DEMOFs with IP incorporation up to 25 %. Ultrahigh-vacuum IR spectra recorded upon CO adsorption together with the results of X-ray photoelectron spectroscopic studies show the generation of coordinatively unsaturated Cu+ sites. The results suggest the presence of two different defect types, that is, missing-linker defects and missing paddlewheels for high concentrations of IP. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We systematically studied the microstructure, mechanical and physical properties of hyper-eutectic Fe – TiB2 high modulus steels (20 vol% TiB2) with (Si, Mn, Ni) and Cu additions for the formation of G-phase and Cu precipitates during ageing treatments. Alloying with Si, Mn and Ni led predominantly to pronounced solid solution strengthening, reaching tensile strength (UTS) values up to 1100 MPa after quenching. While G-phase formation could be observed in aged materials, its preferential formation on grain boundaries significantly deteriorated ductility. Its effects on strength were partially balanced by a decrease of grain boundary density. Additions of 1 and 2 wt% Cu, respectively, led to lower strength in the as quenched state, but also to significant strengthening via ageing. The peak ageing conditions as well as the Cu particle structure and size are comparable to values reported for Cu strengthened interstitial free steels and Fe-Cu alloys. Both alloying additions slightly lowered the specific elastic modulus of the HMS, most pronounced for Cu addition with a drop of about 3 GPa cm3 g− 1 per wt% and also promoted embrittlement. Microstructure-property relationships and consequences for future alloy design, especially towards more ductile hypo-eutectic HMS, are outlined and discussed. © 2017

Micro pillar compression is used to analyze the strain rate dependence of copper pillars containing a penetrable high-angle grain boundary via in situ compression tests at strain rates ranging from  10− 1 to 10− 4 s− 1. While the grain-boundary containing pillars exhibit a clear strain-rate dependence of m = 0.04 ± 0.02, their single crystal counterparts seem to have a weak strain rate dependence of m = 0.01 ± 0.01. The results strongly suggest that the movement of the dislocation line in the grain boundary, required to change its orientation from the incoming to the outgoing slip plane, is the critical process in deforming this kind of grain-boundary containing pillars. © 2017 Acta Materialia Inc.

Employing ab initio calculations we demonstrate that the complex structural modulations experimentally observed in ultrathin Fe films on Cu(001) originate from Fe bulk phases that arise under extreme deformations. Specifically, we show that the structural modulations correspond to the motifs observed when transforming fcc Fe to bcc Fe in the Pitsch orientation relationship [(001)fcc||(110)bcc]. The observed structural equivalence between surface and unstable bulk structures naturally explains the experimentally reported magnetic and structural transitions when going from low (two to four MLs) to intermediate (four to ten MLs) film coverages. © 2017 American Physical Society.

The physical mechanisms of the laser-induced periodic surface structures (LIPSS) formation are studied in this paper for single-pulse irradiation regimes. The change in the LIPSS period with wavelength of incident laser radiation is investigated experimentally, using a picosecond laser system, which provides 7-ps pulses in near-IR, visible, and UV spectral ranges. The experimental results are compared with predictions made under the assumption that the surface-scattered waves are involved in the LIPSS formation. Considerable disagreement suggests that hydrodynamic mechanisms can be responsible for the observed pattern periodicity. © 2017 Elsevier B.V.

The scaling behavior of Ti-Ni-Cu shape memory thin-film micro- and nanowires of different geometry is investigated with respect to its influence on the martensitic transformation properties. Two processes for the highthroughput fabrication of Ti-Ni-Cu micro- to nanoscale thin film wire libraries and the subsequent investigation of the transformation properties are reported. The libraries are fabricated with compositional and geometrical (wire width) variations to investigate the influence of these parameters on the transformation properties. Interesting behaviors were observed: Phase transformation temperatures change in the range from 1 to 72 °C (austenite finish, (Af), 13 to 66 °C (martensite start, Ms) and the thermal hysteresis from -3.5 to 20 K. It is shown that a vanishing hysteresis can be achieved for special combinations of sample geometry and composition. © 2017 American Chemical Society.

In situ ball milling of solid catalysts is a promising yet almost unexplored concept for boosting catalytic performance. The continuous preferential oxidation of CO (CO-PROX) under in situ ball milling of Cu-based catalysts such as Cu/Cr2O3 is presented. At temperatures as low as −40 °C, considerable activity and more than 95 % selectivity were achieved. A negative apparent activation energy was observed, which is attributed to the mechanically induced generation and subsequent thermal healing of short-lived surface defects. In situ ball milling at sub-zero temperatures resulted in an increase of the CO oxidation rate by roughly 4 orders of magnitude. This drastic and highly selective enhancement of CO oxidation showcases the potential of in situ ball milling in heterogeneous catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Atom probe tomography and transmission electron microscopy are used to study the formation of nano-sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin-films. For a Cu-rich precursor, which was deposited at 320 °C under Cu- and Zn-rich growth conditions, Cu2-xSe grains at the surface are detected. During annealing the precursor at 500 °C in a SnSe + Se atmosphere most of the Cu2-xSe is transformed to Cu2ZnSnSe4 via the consumption of excessive ZnSe and incorporation of Sn. However, atom probe tomography studies also reveal the formation of various nanometer-sized Cu-Sn-Se particles close to the CdS/Cu2ZnSnSe4 interface. One of those particles has a composition close to the Cu2SnSe3 compound. This phase has a smaller band gap than Cu2ZnSnSe4 and is proposed to lead to a significant drop in the open-circuit voltage and could be the main cause for a detrimental p-n junction and the zero efficiency of the final device. Possible effects of the other phases on solar cell performance and formation mechanisms are discussed as well. © 2017 Acta Materialia Inc.

The effect of a pre-strain on the plasticity of copper single crystals subjected to in situ microshear deformation in a scanning electron microscope (SEM) is investigated. Pre-strains of 6.5 and 20% are imposed using [1 0 0] tensile testing. During tensile pre-deformation, several slip systems are activated and irregularly spaced slip bands form. A trace analysis revealed the presence of several slip bands on the tensile specimen near the grips while one family of slip bands parallel to the (1 1 1) crystallographic plane were detected in the middle of the tensile specimen. From the middle of the pre-deformed tensile specimens double microshear samples were prepared using focused ion beam (FIB) machining such that the [0 -1 -1] (1 -1 1) slip system could be directly activated. The results show how microshear behavior reacts to different levels of tensile pre-deformation. Sudden deformation events (SDEs) are observed during microshear testing. The critical stress associated with the first SDE is shown to increase with increasing pre-deformation as a result of an increasing number of slip bands introduced during pre-deformation per shear zone. The results allow also to obtain information on the interaction between dislocations activated during microshearing ([0 -1 -1] (1 -1 1)) and those which were introduced during tensile pre-deformation ([1 0 -1] (1 1 1) and [1 -1 0] (1 1 1)). When these slip systems interact glissile junctions and Lomer-Cottrell locks are likely to form. In the light of this analysis, we rationalize the occurrence of sudden deformation events based on piled up dislocation assemblies which overcome Lomer-Cottrell lock barriers. © 2016 Acta Materialia Inc.

A series of Co-modified Cu/ZnO/Al2O3 methanol synthesis catalysts with different Na loadings was prepared and applied in higher alcohol synthesis (HAS) at 280 °C, 60 bar and a ratio of H2/CO = 1. The bulk and surface properties of the catalysts were characterized after reduction and after 40 h time on stream (TOS) without exposing the catalysts to air during the transfer and the measurements. Increased presence of metallic Co0 after reduction at 350 °C was confirmed by X-ray photoelectron spectroscopy indicating metallic Cu0 to act as a reduction promoter. Catalysts with low Na loadings (≤0.6 wt%) showed strong initial deactivation presumably due to coking of isolated Co0 surface sites favoring hydrocarbon formation. The selectivity to higher alcohols gradually increased during the first 10 h TOS indicating enhanced Cu-Co surface alloy formation considered as active sites for HAS. In contrast, with high Na loadings (≥0.8 wt%) deactivation did not occur and stable performance with constant CO conversion and product distribution was observed indicating significantly altered structural properties. High Na loadings caused the stabilizing amorphous oxide matrix to collapse resulting in strong sintering of the metallic Cu particles, and an increased carbidization of metallic Co0 forming bulk Co2C was observed by X-ray diffraction. Close contact between metallic Co0 and Co2C, which is known to facilitate molecular CO adsorption, is assumed to generate additional active sites for HAS. © 2016 Elsevier Inc. All rights reserved.

Cu-containing photocathodes are generally limited by fast photocorrosion under working conditions. Hence stabilization of these materials is a key factor in their potential application for the light-induced hydrogen evolution reaction (HER). In order to identify new materials, oxidized Cu-Si-Ti metallic thin film precursor materials libraries were evaluated using a combinatorial approach. High-throughput photoelectrochemical characterization using an automated optical scanning droplet cell was performed on a material library to analyze doping and alloying effects on the light-induced HER. The results revealed that compositions near Ti-doped CuSiO3 (dioptase and copper-polysilicate) and Si-doped Cu3TiOx act as comparatively stable and highly active materials for HER. © 2016 The Royal Society of Chemistry.

Nucleation of soft magnetic Fe3Si nanocrystals in Cu-free Fe74.5Si15.5Nb3B7 alloy, upon rapid (10 s) and conventional (30 min) annealing, was investigated using x-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and atom probe tomography. By employing rapid annealing, preferential nucleation of Fe3Si nanocrystals was achieved, whereas otherwise there is simultaneous nucleation of both Fe3Si and undesired Fe-B compound phases. Analysis revealed that the enhanced Nb diffusivity, achieved during rapid annealing, facilitates homogeneous nucleation of Fe3Si nanocrystals while shifting the secondary Fe-B crystallization to higher temperatures resulting in pure soft magnetic nanocrystallization with very low coercivities of ∼10 A/m. © 2016 AIP Publishing LLC.

Copper and iron bimetal modified Al-rich Beta zeolites from template-free synthesis were prepared for selective catalytic reduction (SCR) of NOx with NH3 in exhaust gas streams. Comparing to the Cu-based and Fe-based mono-component Beta catalysts, Cu(3.0)-Fe(1.3)-Beta bi-component catalyst shows better low-temperature activity and wider reaction-temperature window. Over 80% of NO conversion can be achieved at the temperature region of 125–500 °C. Due to the synergistic effect of copper and iron evidenced by XRD, UV–Vis–NIR, EPR and XPS measurements, the dispersion state of active components as well as the ratio of Cu2+/Cu+ and Fe3+/Fe2+ were improved over Cu(3.0)-Fe(1.3)-Beta. Isolated Cu2+ and Fe3+ ions which located at the exchange sites could be the active species at the low-temperature region, while FeOx cluster species may be more important to the high-temperature activity. During the test of sulfur resistance, Fe-containing samples including Cu(3.0)-Fe(1.3)-Beta and Fe(2.7)-Beta-4 present better performance compared to Cu(4.1)-Beta-4. Deactivation of Cu-based catalyst is attributed to the easier deposition of sulfates over the surface according to the results of TGA coupled with TPD experiments. © 2016 Elsevier Inc.

Solid-liquid interfaces have received considerable attention in recent years due to their central role in many technologically relevant fields like electrochemistry, heterogeneous catalysis and corrosion. As the chemical processes in these examples take place primarily at the interface, understanding the structural and dynamical properties of the interfacial water molecules is of vital importance. Here, we use a first-principles quality high-dimensional neural network potential built from dispersion-corrected density functional theory data in molecular dynamics simulations to investigate water-copper interfaces as a prototypical case. After performing convergence tests concerning the required supercell size and water film diameter, we investigate numerous properties of the interfacial water molecules at the low-index copper (111), (100) and (110) surfaces. These include density profiles, hydrogen bond properties, lateral mean squared displacements and residence times of the water molecules at the surface. We find that in general the copper-water interaction is rather weak with the strongest interactions observed at the Cu(110) surface, followed by the Cu(100) and Cu(111) surfaces. The distribution of the water molecules in the first hydration layer exhibits a double peak structure. In all cases, the molecules closest to the surface are predominantly allocated on top of the metal sites and are aligned nearly parallel with the oxygen pointing slightly to the surface. The more distant molecules in the first hydration layer at the Cu(111) and Cu(100) surfaces are mainly found in between the top sites, whereas at the Cu(110) surface most of these water molecules are found above the trenches of the close packed atom rows at the surface. © 2016 the Owner Societies.

The desorption kinetics of hydrogen from a polycrystalline Cu/ZrO2 catalyst was investigated under atmospheric pressure using temperature-programmed desorption (TPD) experiments in a microreactor set-up. Different heating rates were applied under equal conditions with a carefully reduced catalyst. The hydrogen TPD peaks were symmetric and centered slightly above 300 K indicating associative desorption of H2 from metallic Cu. Using heating rate variation, the kinetic parameters Ades and Edes were determined to be 1.24 × 109 s-1 and 68 kJ mol-1, respectively. As the modeling with constant values of Ades and Edes yielded signals which were too narrow, dependence of Edes on coverage was introduced applying Edes - K (ΘH)n. By application of the "full-analysis" method an optimal fit to the experimental data was found. Setting n = 1 resulted in the best fit and a value of 61 kJ mol-1 - (6.25 kJ mol-1 × ΘH) for Edes was determined. © Springer Science+Business Media New York 2016.

The selectivity of heterogeneously catalyzed chemical reactions is well-known to be dependent on nanoscale determinants, such as surface atomic geometry and composition. However, principles to control the selectivity of nanoparticle (NP) catalysts by means of mesoscopic descriptors, such as the interparticle distance, have remained largely unexplored. We used well-defined copper catalysts to deconvolute the effect of NP size and distance on product selectivity during CO2 electroreduction. Corroborated by reaction-diffusion modeling, our results reveal that mesoscale phenomena such as interparticle reactant diffusion and readsorption of intermediates play a defining role in product selectivity. More importantly, this study uncovers general principles of tailoring NP activity and selectivity by carefully engineering size and distance. These principles provide guidance for the rational design of mesoscopic catalyst architectures in order to enhance the production of desired reaction products. © 2015 American Chemical Society.

Although the hydrogen evolution reaction (HER) is one of the fastest electrocatalytic reactions, modern polymer electrolyte membrane (PEM) electrolysers require larger platinum loadings (∼0.5-1.0 mg cm-2) than those in PEM fuel cell anodes and cathodes altogether (∼0.5 mg cm-2). Thus, catalyst optimization would help in substantially reducing the costs for hydrogen production using this technology. Here we show that the activity of platinum(111) electrodes towards HER is significantly enhanced with just monolayer amounts of copper. Positioning copper atoms into the subsurface layer of platinum weakens the surface binding of adsorbed H-intermediates and provides a twofold activity increase, surpassing the highest specific HER activities reported for acidic media under similar conditions, to the best of our knowledge. These improvements are rationalized using a simple model based on structure-sensitive hydrogen adsorption at platinum and copper-modified platinum surfaces. This model also solves a long-lasting puzzle in electrocatalysis, namely why polycrystalline platinum electrodes are more active than platinum(111) for the HER.

We present size-dependent crystal plasticity finite element simulations of the deformation microstructure, plastic flow and texture evolution in multilayered Cu-Nb composites during cold rolling. The model is based on a constitutive framework incorporating thermally activated dislocation slip, mechanical twinning and non-crystallographic shear banding. It also accounts for the dislocation density evolution and its dependence on initial grain size. By performing a series of quadricrystal simulations considering characteristic heterophase microstructures, the underlying micromechanics and texture of the composites are explored. Significant shear banding occurs in both phases, primarily determined by their initial orientations. For each phase, the activation of shear banding is also affected by the mechanical properties and orientations of the adjacent phase. For composites with an initial single layer thickness of 35 μm or 4 μm, the layer thickness reduction after rolling is non-uniform and the typical rolling textures for bulk pure metals develop in the respective phases. For the 75 nm initial single layer thickness composite, both phases are reduced uniformly in thickness and the initial orientations prevail. The predictions agree well with experimental observations in cold-rolled Cu-Nb thin films. The simulations reveal that for the composites with initial single layer thickness of micrometer scale, dislocation slip is the dominant deformation mechanism although shear banding increasingly carries the deformation at larger strains. For the samples with initial single layer thickness of a few tens of nanometers, shear banding and dislocation slip are the dominant mechanisms. This transition in deformation characteristics leads to different textures in micrometer- and nanometer-scaled multilayers. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The efficiency of the direct electrochemical CO2 reduction can be improved by the development of new alloy catalysts, but to do so a highly resolved composition screening remains to be connected to complex sample preparation and time consuming analysis. We have developed a technique that allows a fast and easy initial catalyst composition screening by analyzing thin film composition spread samples, utilizing a scanning flow cell coupled to an online electrochemical mass spectrometer (SFC-OLEMS). As a first case example, the investigation of a Cu–Co thin film material library demonstrates the benefits and high potential of this approach. In particular, a shift in selectivity toward C2 species for low Co content (5–15 at.%) has been found and is discussed as being related to changed adsorption energies of intermediate products and the consequent modification of reaction pathways. © 2016 Elsevier Inc.

There is an urgent need to develop technologies that use renewable energy to convert waste products such as carbon dioxide into hydrocarbon fuels. Carbon dioxide can be electrochemically reduced to hydrocarbons over copper catalysts, although higher efficiency is required. We have developed oxidized copper catalysts displaying lower overpotentials for carbon dioxide electroreduction and record selectivity towards ethylene (60%) through facile and tunable plasma treatments. Herein we provide insight into the improved performance of these catalysts by combining electrochemical measurements with microscopic and spectroscopic characterization techniques. Operando X-ray absorption spectroscopy and cross-sectional scanning transmission electron microscopy show that copper oxides are surprisingly resistant to reduction and copper+ species remain on the surface during the reaction. Our results demonstrate that the roughness of oxide-derived copper catalysts plays only a partial role in determining the catalytic performance, while the presence of copper+ is key for lowering the onset potential and enhancing ethylene selectivity.

Even though lead-free Sn-Ag-Cu based solder alloys are emerging as promising candidates to replace well-established but hazardous lead-containing solders, they suffer from limited knowledge about their mechanical performance. To ensure the high reliability demands in microelectronics, fracture properties need to be quantified with respect to crucial microstructural elements like Cu6Sn5 intermetallic compounds formed at common Cu metallization interfaces. While indentation fracture testing methods have shown varying fracture toughness values, micro-cantilever fracture testing is applied in this work on FIB-prepared single-crystalline Cu6Sn5 cantilevers to clarify on the microstructure-fracture relationship. © 2016 Elsevier B.V.

The quaternary Q phase is an important precipitate phase in the Al-Cu-Mg-Si alloy system and its accurate thermodynamic description is crucial for further tailoring this material class for light-weight structural applications. In order to achieve an improved thermochemical parameter set of this phase, we used a combination of experimental measurements and first-principles calculations, which was focussed on the heat capacity. Its accurate experimental determination required the preparation of pure samples of Q phase and sophisticated calorimetric measurements. On the theoretical side, a simultaneous treatment of lattice vibrations within the quasiharmonic approximation, electronic excitations, and configuration entropy within the compound energy formalism were required to achieve a complete description of the heat capacity. The evaluation demonstrates the high predictive power of the first-principles as well as the Calphad modeling. © 2015, ASM International.

Understanding the redox properties of metal oxide based catalysts is a major task in catalysis research. In situ electron paramagnetic resonance (EPR) spectroscopy is capable of monitoring the change of metal ion valences and formation of active sites during redox reactions, allowing for the identification of ongoing redox pathways. Here in situ EPR spectroscopy combined with online gas analysis, supported by ex situ X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), temporal analysis of product (TAP), and mass spectrometry (MS) studies, was utilized to study the redox behavior of CuO-CeO2 catalysts under PROX conditions (preferential oxidation of carbon monoxide in hydrogen). Two redox mechanisms are revealed: (i) a synergetic mechanism that involves the redox pair Ce4+/Ce3+ during oxidation of Cu0/Cu+ species to Cu2+ and (ii) a direct mechanism that bypasses the redox pair Ce4+/Ce3+. In addition, EPR experiments with isotopically enriched 17O2 established the synergetic mechanism as the major redox reaction pathway. The results emphasize the importance of the interactions between Cu and Ce atoms for catalyst performance. With the guidance of these results, an optimized CuO-CeO2 catalyst could be designed. A rather wide temperature operation window of 11 K (from 377 to 388 K), with 99% conversion efficiency and 99% selectivity, was achieved for the preferential oxidation of CO in a H2 feed. © 2016 American Chemical Society.

Fe-Si-B-Nb-Cu alloys are attractive for high frequency applications due to their low coercivity and high saturation magnetization. Here, we study the effect of stress annealing on magnetic microstructure in Fe73.5Si15.5B7Nb3Cu1 using off-axis electron holography and the Fresnel mode of Lorentz transmission electron microscopy. A stress of 50 MPa was applied to selected samples during rapid annealing for 4 s, resulting in uniaxial anisotropy perpendicular to the stress direction. The examination of focused ion beam milled lamellae prepared from each sample revealed a random magnetic domain pattern in the sample that had been rapidly annealed in the absence of stress, whereas a highly regular domain pattern was observed in the stress-annealed sample. We also measured a decrease in domain wall width from ∼ 94 nm in the sample annealed without stress to ∼ 80 nm in the stress-annealed sample. © 2016 Author(s).

The mechanical behavior of Cu-Cr nanolayered films and an alloy film of nominal composition Cu20Cr80 at.% was studied by microcompression testing at temperatures from 25 °C to 300 °C. Comparing nanolayered films, plastic deformation and failure occurred at consistently higher stress levels in the film with the smaller layer thicknesses. Plasticity in the nanolayered films always initiated in the softer Cu layers followed by a finite strain-hardening response in the stress-strain curves. Failure indicated by a strain-softening response following the higher peak strength due to shearing and tearing at columnar boundaries of Cr was observed in the nanolayered films at 25 °C and 100 °C. A transition from shearing and crack formation across the Cu-Cr interfaces leading to anomalous grain growth or beading of the nanocrystalline Cu layers was observed at elevated temperatures of 200 °C and 300 °C. On the other hand, the Cu20Cr80 at.% alloy film exhibited failure by columnar buckling consistently at elevated temperatures, but shearing promoted by buckling at the highest strengths among the films at ambient temperature. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

This study aims to better understand the influence of crystallographic structure and impurity decoration on the recombination activity at grain boundaries in multicrystalline silicon. A sample of the upper part of a multicrystalline silicon ingot with intentional addition of iron and copper has been investigated. Correlative electron-beam-induced current, electron backscatter diffraction, and atom probe tomography data for different types of grain boundaries are presented. For a symmetric coherent Σ3 twin boundary, with very low recombination activity, no impurities are detected. In case of a non-coherent (random) high-angle grain boundary and higher order twins with pronounced recombination activity, carbon and oxygen impurities are observed to decorate the interface. Copper contamination is detected for the boundary with the highest recombination activity in this study, a random high-angle grain boundary located in the vicinity of a triple junction. The 3D atom probe tomography study presented here is the first direct atomic scale identification and quantification of impurities decorating grain boundaries in multicrystalline silicon. The observed deviations in chemical decoration and induced current could be directly linked with different crystallographic structures of silicon grain boundaries. Hence, the current work establishes a direct correlation between grain boundary structure, atomic scale segregation information, and electrical activity. It can help to identify interface-property relationships for silicon interfaces that enable grain boundary engineering in multicrystalline silicon. Copyright © 2015 John Wiley & Sons, Ltd.

In thin film deposition processes, the deposition temperature is one of the crucial process parameters for obtaining films with desired properties. Usually the optimum deposition temperature is found by conducting several depositions sequentially in a time consuming process. This paper demonstrates a facile and rapid route of the simultaneous thin film deposition at six different deposition temperatures ranging from 100 to 1000 °C. Cuprite (Cu2O) was chosen for the study as this material is of interest for energy applications. The thin films are assessed for their crystallographic, microstructural, Raman scattering, and photoelectrochemical properties. The results show that the utilization of a step heater leads to the rapid optimization of thin film microstructures of an absorber material used in photoelectrochemistry. This results in a structure zone diagram for Cu2O. For a substrate temperature of 600 °C, an optimum between crystallinity and morphology occurs. © 2015 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim.

Thermal spray processes are widely used for the manufacture of advanced coating systems, e.g. metallic coatings for wear and corrosion protection. The desired coating properties are closely related to the microstructure, which is highly influenced by the processing parameters, such as temperature, size and velocity of the sprayed particles. In this paper, large scale Molecular Dynamics simulations are conducted to investigate the microstructure formation mechanisms during the spraying process of hot nano-particles onto a substrate at room temperature using pure copper as a benchmark material representing for a wider class of face-centered-cubic metals. To evaluate the influence of processing parameters on the coating morphology, a number of simulations are performed in which the initial temperature, size and velocity of copper particles are systematically varied in order to investigate the thermal and microstructural evolution during impaction. Two distinct types of microstructural formation mechanisms, resulting in different coating morphologies, are observed in the present investigation, which are either governed by plastic deformation or by the process of melting and subsequent solidification. Furthermore, a thermodynamically motivated model as a function of the particle temperature and velocity is developed, which predicts the microstructural mechanisms observed in the simulations. The results provide an elementary insight into the microstructure formation mechanisms on an atomistic scale, which can serve as basic input for continuum modeling of thermal spray process. © 2015 Published by Elsevier B.V.

Cd and impurity redistribution in the vicinity of CdS/CIGS interface is studied by means of atom probe tomography (APT). We find an increase of the Cd content in the CIGS layer and redistribution of O at the CdS/CIGS interface after annealing the samples at 200 °C, 250 °C, or 300 °C. Very small amounts (∼0.1 at. %) of Na impurity where observed at the p-n junction independent on the heat treatment. Simultaneously, the I-V measurements of the treated samples show a drop in the open circuit voltage and thus of the efficiency compared to the untreated sample. The effect of Cd diffusion in CIGS and of O and Na segregation at the CdS/CIGS interface on the cell performance is discussed. © 2015 IEEE.

An Au-Cu-Al thin film materials library prepared by combinatorial sputter-deposition was characterized by high-throughput experimentation in order to identify and assess new shape memory alloys (SMAs) in this alloy system. Automated resistance measurements during thermal cycling between -20 and 250 °C revealed a wide composition range that undergoes reversible phase transformations with martensite transformation start temperatures, reverse transformation finish temperatures and transformation hysteresis ranging from -15 to 149 °C, 5 to 185 °C and 8 to 60 K, respectively. High-throughput X-ray diffraction analysis of the materials library confirmed that the phase-transforming compositions can be attributed to the existence of the β-AuCuAl parent phase and its martensite product. The formation of large amount of phases based on face-centered cubic (Au-Cu), Al-Cu and Al-Au is responsible for limiting the range of phase-transforming compositions. Selected alloys in this system show excellent thermal cyclic stability of the phase transformation. The functional properties of these alloys, combined with the inherent properties of Au-based alloys, i.e. aesthetic value, oxidation and corrosion resistance, makes them attractive as smart materials for a wide range of applications, including applications as SMAs for elevated temperatures in harsh environment. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The depth-dependent chemical constitution of Ti51Ni38Cu11 thin films of different total film thickness from 400 to 50-nm was characterized using X-ray photoelectron spectroscopy (XPS). It was analyzed how reaction layers, which form on the surface of the film significantly change the chemical composition of the transforming phase, which leads in turn to altered phase transformation properties. For thinner films, the deviation from the nominal chemical composition increases. For a film thickness of 50-nm, a Ti loss of ≈9-at% is observed. The Ni content is increased by ≈5-at%, whereas the Cu content stays relatively constant for films of different thickness. The results are summarized in a layer model, which supports designing nanoscale shape memory thin films. Ti51Ni38Cu11 thin films of different film thickness are investigated regarding the influence of the reaction layers on the chemical composition of the transforming phase and the corresponding functional properties. A model is proposed describing the different reaction layers on the surface of the thin film and at the substrate/thin film interface. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly sensitive and efficient biosensors play a crucial role in clinical, environmental, industrial, and agricultural applications, and tremendous efforts have been dedicated to advanced electrode materials with superior electrochemical activities and low cost. Here, we report a three-dimensional binder-free Cu foam-supported Cu2O nanothorn array electrode developed via facile electrochemistry. The nanothorns growing in situ along the specific direction of <011> have single crystalline features and a mesoporous surface. When being used as a potential biosensor for nonenzyme glucose detection, the hybrid electrode exhibits multistage linear detection ranges with ultrahigh sensitivities (maximum of 97.9 mA mM-1 cm-2) and an ultralow detection limit of 5 nM. Furthermore, the electrode presents outstanding selectivity and stability toward glucose detection. The distinguished performances endow this novel electrode with powerful reliability for analyzing human serum samples. These unprecedented sensing characteristics could be ascribed to the synergistic action of superior electrochemical catalytic activity of nanothorn arrays with dramatically enhanced surface area and intimate contact between the active material (Cu2O) and current collector (Cu foam), concurrently supplying good conductivity for electron/ion transport during glucose biosensing. Significantly, our findings could guide the fabrication of new metal oxide nanostructures with well-organized morphologies and unique properties as well as low materials cost. © 2015 American Chemical Society.

Infiltration of tool steels with copper is a suitable and cheap method to create dense parts using powder metallurgy. In this work, it is shown that the copper network that forms inside the steel skeleton during infiltration enhances the thermal conductivity of the resulting composite. The level of enhancement is dependent on the thermal conductivity of the copper phase and the volume fraction of copper. Multiple heat treatments of this composite revealed a strong dependency between the thermal conductivity of the composite and the solution state of Fe in the copper network. The latter is highly dependent on the heat-treated condition of the multi-phase material. Using infiltration, the thermal and electrical conductivity was increased from (Formula presented.) respectively, for aged steel-copper composite in comparison with original X245VCrMo9-4-4 steel. In addition, a model alloy that represents the copper-phase network in the composite was manufactured. By measuring both, the thermal conductivity of this model alloy and the bulk steel, and comparing it to the data for the composite, different models for calculating the overall conductivity of the composite are discussed. © 2015, The Author(s).

Uniaxial compression experiments on single- and twinned bicrystalline Cu samples using conventional and scanning in situ transmission electron microscopy reveal no increase in flow stress for the bicrystals. Dislocation curvature and dislocation source size analysis combined with indenter force measurements show agreement between local internal stresses acting on the dislocations and external stresses imposed by the indenter, indicating no stress concentrations due to the twin boundary. Furthermore, the dislocation density evolution shows stochastic variations but never a complete dislocation starvation. © 2015 Acta Materialia Inc.

We generalize the theory of Cooper-pairing by spin excitations in the metallic antiferromagnetic state to include situations with electron and/or hole pockets. We show that Cooper-pairing arises from transverse spin waves and from gapped longitudinal spin fluctuations of comparable strength. However, each of these interactions, projected on a particular symmetry of the superconducting gap, acts primarily within one type of pocket. We find a nodeless -wave state is supported primarily by the longitudinal fluctuations on the electron pockets, and both transverse and longitudinal fluctuations support nodal -wave symmetry on the hole pockets. Our results may be relevant to the asymmetry of the AF/SC coexistence state in the cuprate phase diagram. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Copper microcantilevers were produced by focused ion beam milling and tested in situ using a scanning electron microscope. To provide different interfaces for piling up dislocations, cantilevers were fabricated to be single crystalline, bicrystalline, or single crystalline with a slit in the region of the neutral axis. The aim of the experiment was to study the influence of dislocation pile-ups on (i) strength and (ii) Bauschinger effects in micrometer-sized, focused ion beam milled bending cantilevers. The samples were loaded monotonically for several times under displacement control. Even though the cantilevers exhibited the same nominal strain gradient the strength varied by 34% within the three cantilever geometries. The Bauschinger effect can be promoted and prohibited by the insertion of different interfaces. © 2015 Materials Research Society.

Abstract The yield strengths and deformation mechanisms of Cu-Cr nanolayered and alloyed thin films were studied by microcompression testing at elevated temperatures. The mechanical response of the films with alternating layers of Cu and Cr with sub-100 nm interlayer thicknesses and alloyed films of the same average composition was compared to determine the role of the interfaces on deformation. Higher resistance to plastic flow at elevated temperatures was exhibited by the nanolayered films with smaller interlayer thickness among the layered films, while the alloyed film revealed an anomalous increase in strength with temperature exhibiting a deformation mechanism similar to the pure Cr film. © 2015 Acta Materialia Inc.

A fundamental knowledge and understanding of the adhesion behaviour of metal-polymer systems is important as interface failure leads to a complete breakdown of flexible devices. A combination of in situ atomic force microscopy for studying topological changes and in situ synchrotron based stress measurements both during film tensile testing were used to estimate the adhesion energy of a thin bilayer film. The film systems consisted of 50-200 nm Cu with a 10 nm Cr adhesion layer on 50 μm thick polyimide. If the Cu film thickness is decreased to 50 nm the Cr interlayer starts dominating the system behaviour. An apparent transition from plastic to predominantly brittle deformation behaviour of the Cu can be observed. Then, compressive stresses in the transverse direction are high enough to cause delamination and buckling of the Cr interlayer from the substrate. This opens a new route to induce buckling of a brittle interlayer between a ductile film and a compliant substrate which is used to determine the interfacial adhesion energy. © 2015 Taylor & Francis.

In the present work, we investigate the wear mechanisms of a Cu bi-crystal containing a random high angle grain boundary by means of molecular dynamics simulations. The underlying deformation behavior of the material is analyzed and further related to the observed characteristics of mechanical response and resulting morphology of the worn surface. In particular, the grain boundary-associated mechanisms are characterized by advanced analysis techniques for lattice defects. Our simulation results indicate that in addition to dislocation slip and dislocation-grain boundary interactions, grain boundary migration plays an important role in the plastic deformation of Cu bi-crystal. It is found that the wear behavior of Cu depends on the crystallographic orientation of the worn surface and can be altered quite significantly by the presence of a grain boundary. © 2015 Elsevier B.V.

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.

Thin metal films deposited on polymer substrates are used in flexible electronic devices such as flexible displays or printed memories. They are often fabricated as complicated multilayer structures. Understanding the mechanical behavior of the interface between the metal film and the substrate as well as the process of crack formation under global tension is important for producing reliable devices. In the present work, the deformation behavior of copper films (50-200 nm thick), bonded to polyimide directly or via a 10 nm chromium interlayer, is investigated by experimental analysis and computational simulations. The influence of the various copper film thicknesses and the usage of a brittle interlayer on the crack density as well as on the stress magnitude in the copper after saturation of the cracking process are studied with in situ tensile tests in a synchrotron and under an atomic force microscope. From the computational point of view, the evolution of the crack pattern is modeled as a stochastic process via finite element based cohesive zone simulations. Both, experiments and simulations show that the chromium interlayer dominates the deformation behavior. The interlayer forms cracks that induce a stress concentration in the overlying copper film. This behavior is more pronounced in the 50 nm than in the 200 nm copper films. © Acta Materialia Inc. Published by Elsevier Ltd.

A local electrode atom probe has been employed to trace the onset of Cu clustering followed by their coarsening and subsequent growth upon rapid (10s) annealing of an amorphous Fe73.5Si15.5Cu1Nb3B7 alloy. It has been found that the clustering of Cu atoms introduces heterogeneities in the amorphous matrix, leading to the formation of Fe rich regions which crystallizes pseudo-homogeneously into Fe-Si nanocrystals upon annealing. In this paper, we present the data treatment method that allows for the visualization of these different phases and to understand their morphology while still quantifying them in terms of their size, number density and volume fraction. The crystallite size of Fe-Si nanocrystals as estimated from the atom probe data are found to be in good agreement with other complementary techniques like XRD and TEM, emphasizing the importance of this approach towards accurate structural analysis. In addition, a composition driven data segmentation approach has been attempted to determine and distinguish nanocrystalline regions from the remaining amorphous matrix. Such an analysis introduces the possibility of retrieving crystallographic information from extremely fine (2-4nm sized) nanocrystalline regions of very low volume fraction (< 5Vol%) thereby providing crucial in-sights into the chemical heterogeneity induced crystallization process of amorphous materials. © 2015 Elsevier B.V.

During a switch event in a power semiconductor device temperature changes of up to 300 K can occur in the Cu layer. Repeated switching operations causes cyclic thermal cycling which may finally lead to thermomechanical fatigue with severe microstructural changes. In this study, the influence of the starting microstructure and film thickness (600 nm and 5000 nm) on thermomechanical fatigue was investigated for epitaxial and polycrystalline Cu films for up to 1000 thermal cycles. Severe surface roughening and a texture change (crystal rotation) are detected during thermal cycling for the polycrystalline Cu films, while the epitaxial films maintain their microstructure. Controlling the initial microstructure of a Cu layer in a device exposed to cyclic thermomechanical straining is a route to delay surface damage. © 2014 Elsevier B.V. All rights reserved.

A catalyst consisting of copper nanoparticles (15-20 nm in size) supported on ordered mesoporous cobalt monoxide was synthesized by the one-step reduction of ethanol from nanocast copper cobalt spinel oxides. The small-angle X-ray scattering patterns showed that the ordered mesostructure was maintained after post-treatment, and the cross-section scanning electron microscopy images showed that the Cu nanoparticles were distributed homogeneously throughout the mesoporous CoO framework. The materials were tested as noble-metal-free catalysts for the oxidation of glycerol under alkaline conditions. The catalytic data showed that the presence of Cu nanoparticles greatly enhanced the catalytic performance. Nothing noble: A catalyst consisting of copper nanoparticles (NPs, 15-20 nm in size) supported on ordered mesoporous cobalt monoxide is synthesized by the one-step reduction with ethanol from nanocast copper cobalt spinel oxides. As a noble-metal-free catalyst for the oxidation of glycerol, the presence of Cu NPs greatly enhances the catalytic performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In situ micromechanical compression tests on Cu pillars were performed to evaluate the influence of twin boundaries on the mechanical behavior. The 1. μm sized Cu samples on a Si substrate prepared by focused ion beam milling were either single crystalline or contained 2-5 twin boundaries that were inclined to the compression direction. The strengths of the pillars vary, depending on the crystal orientation, associated twin boundary inclination and orientation of slip systems. Results show, that multiple slip systems are activated in each pillar. However, slip parallel to the twin boundaries prevails due to the long mean free path for dislocation movement. © 2015 Elsevier B.V.

We report on atom probe tomography studies of the composition at internal interfaces in Cu2ZnSnSe4 thin-films. For Cu2ZnSnSe4 precursors, which are deposited at 320 °C under Zn-rich conditions, grain boundaries are found to be enriched with Cu irrespective of whether Cu-poor or Cu-rich growth conditions are chosen. Cu2ZnSnSe4 grains are found to be Cu-poor and excess Cu atoms are found to be accumulated at grain boundaries. In addition, nanometer-sized ZnSe grains are detected at or near grain boundaries. The compositions at grain boundaries show different trends after annealing at 500 °C. Grain boundaries in the annealed absorber films, which are free of impurities, are Cu-, Sn-, and Se-depleted and Zn-enriched. This is attributed to dissolution of ZnSe at the Cu-enriched grain boundaries during annealing. Furthermore, some of the grain boundaries of the absorbers are enriched with Na and K atoms, stemming from the soda-lime glass substrate. Such grain boundaries show no or only small changes in composition of the matrix elements. Na and K impurities are also partly segregated at some of the Cu2ZnSnSe4/ZnSe interfaces in the absorber, whereas for the precursors, only Na was detected at such phase boundaries possibly due to a higher diffusivity of Na compared to K. Possible effects of the detected compositional fluctuations on cell performance are discussed. © 2015 AIP Publishing LLC.

We review aspects of pattern formation in plastically deformed single crystals, in particular as described in the investigation of a copper single crystal shear experiment in [DDMR09]. In this experiment, the specimen showed a band-like microstructure consisting of alternating crystal orientations. Such a formation of microstructure is often linked to a lack of convexity in the free energy describing the system. The specific parameters of the observed bands, namely the relative crystal orientation as well as the normal direction of the band layering, are thus compared to the predictions of the theory of kinematically compatible microstructure oscillating between low-energy states of the non-convex energy. We conclude that this theory is suitable to describe the experimentally observed band-like structure. Furthermore, we link these findings to the models used in studies of relaxation and evolution of microstructure. ©Springer International Publishing Switzerland 2015.

Molecular dynamics simulations were performed to investigate dislocation network formations in a coherent twin boundary in Cu. Depending on the activated glide system, the initial flawless twin boundary can be heavily or sparsely decorated by a dislocation network. The dislocation mechanism leading to a heavy dislocation network at the twin boundary and its consequence on mechanical properties will be discussed. © 2015 Acta Materialia Inc.

Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N2O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N2O, temperature programmed desorption of H2, and kinetic experiments. The presence of ZnO dramatically influences the N2O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu-ZnO interface and can be used to easily quantify the intensity of Cu-Zn interaction. N2O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H2. A combination of N2O reactive frontal chromatography and H2 temperature-programmed desorption is used to analyze the interplay of copper and zinc oxide in methanol synthesis catalysts. This method provides an easy in situ approach to quantify the direct copper-zinc interaction (SMSI effect) and offers an important possibility to rational catalyst design also for other supported metal catalysts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2-15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity-selectivity-size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces. Our smallest nanoparticles (∼2 nm) enter the ab initio computationally accessible size regime, and therefore, the results obtained lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification. © 2014 American Chemical Society.

We optimize the magnetic and structural properties of Ni(Co,Cu)MnSn Heusler alloys for the magnetocaloric effect (MCE) by means of density functional theory combined with Monte Carlo simulations of a classical Heisenberg model. NiMnSn alloys show a drop of magnetization at the martensitic phase transition, which leads to the inverse MCE. We find either disordered or frustrated magnetic configurations directly below the martensitic transition temperature. However, the jump of magnetization at the magnetostructural transition is small as the austenite is in a ferrimagnetic state and not fully magnetized. For Co and Cu substitution, the structural phase transition temperature shifts to lower temperatures. In particular, Co substitution is promising, as the magnetization of the austenite increases by additional ferromagnetic interactions, which enhances the jump of magnetization. © 2014 IEEE.

In this study, the low-cycle fatigue properties (1-15,000 cycles) of electrodeposited Cu, which is frequently used as metallization in the semiconductor industry, is analyzed with respect to its microstructure. Freestanding Cu tensile samples 20 μm × 20 μm × 130 μm were fabricated by a lithographic process. The grain size of the samples was modified by using three different process conditions for electrochemical Cu deposition. All samples were subjected to cyclic tension-tension testing performed with a miniaturized stress-controlled stage in situ in a scanning electron microscope until failure occurred. The number of cycles sustained prior to failure depends on the accumulated creep strain and can be related to the failure strain in a tensile test. It will be shown that the microstructure influences the number of cycles to failure and the failure mode. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Melanin within melanosomes exists as eumelanin or pheomelanin. Distributions of these melanins have been studied extensively within tissues, but less often within individual melanosomes. Here, we apply X-ray fluorescence analysis with synchrotron radiation to survey the nanoscale distribution of metals within purified melanosomes of mice. The study allows a discovery-based characterization of melanosomal metals, and, because Cu is specifically associated with eumelanin, a hypothesis-based test of the 'casing model' predicting that melanosomes contain a pheomelanin core surrounded by a eumelanin shell. Analysis of Cu, Ca, and Zn shows variable concentrations and distributions, with Ca/Zn highly correlated, and at least three discrete patterns for the distribution of Cu vs. Ca/Zn in different melanosomes - including one with a Cu-rich shell surrounding a Ca/Zn-rich core. Thus, the results support predictions of the casing model, but also suggest that in at least some tissues and genetic contexts, other arrangements of melanin may co-exist. © 2014 John Wiley & Sons A/S.

We demonstrate that Ag adatoms are capable of stabilizing negatively charged copper-phthalocyanine (CuPc) molecules in a Ag-CuPc network at room temperature. For this aim, the structure of the Ag-CuPc coordination network at different molecule-adatom densities is investigated experimentally by scanning tunneling microscopy and theoretically by firstprinciples calculations. The islands formed at saturation adatom density, close to the source of adatoms, consist of a closed-packed layer without voids. The islands formed at lower adatom density consist of an irregular arrangement of larger entities, named subunits, mainly (CuPc)4Ag and (CuPc)6Ag2, which are interconnected in the same fashion as the CuPc molecules in the closed-packed layer. Silver adatoms in the subunits and between them differ by the number of molecules they link. The Ag-CuPc networks are stabilized, because the adsorption energy of CuPc molecules increases due to the presence of adatoms. © 2014 American Chemical Society.

Micrometer-sized compression pillars containing a grain boundary are investigated to better understand under which conditions grain boundaries have a strengthening effect. The compression experiments were performed on focused ion beam fabricated micrometer-sized bicrystalline Cu pillars including either a large-angle grain boundary (LAGB) or a coherent twin boundary (CTB) parallel to the compression axis and additionally on single-crystalline reference samples. Pillars containing a LAGB show increased strength, stronger hardening and smaller load drops compared to single crystals and exhibit a bent boundary and pillar shape. Samples with a CTB show no major difference in stress-strain data compared to the corresponding single-crystalline samples. This is due to the special orientation and symmetry of the twin boundary and is reflected in a characteristic pillar shape after deformation. The experimental findings can be related to the dislocation-boundary interactions at the different grain boundaries and are compared with three-dimensional discrete dislocation dynamics simulations. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A multi-functional flow set-up was developed for the rate- and temperature-controlled reduction of copper catalysts, their application in high-pressure methanol synthesis and the determination of the copper surface area by N2O frontal chromatography. The influence of constant-rate reduction on the catalytic properties of a ternary Cu/ZnO/Al2O3 catalyst was investigated. The temperature during the constant-rate reduction was found to decrease, indicating autocatalytic kinetics, but no significant catalytic effect of the milder reduction conditions was observed compared with a slow linear heating ramp. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.

In many practical applications, creep damage is the limiting factor of a component's lifetime. A micromechanical model of creep induced grain boundary damage is proposed, which allows for the simulation of creep damage in a polycrystal within the framework of finite element analysis. The model considers grain boundary cavitation and sliding according to a micromechanically motivated cohesive zone model while creep deformation of the grains is described following the slip system theory. The model can be applied to idealised polycrystalline structures, such as a Voronoi tessellation or, like demonstrated here, to real grain structures of miniature creep specimens. Creep tests with pure Cu single crystals and with a coarse-grained polycrystalline Cu-1 wt.% Sb alloy at 823 K have been performed and used to calibrate the polycrystal model. The grain structure of the polycrystalline Cu-Sb specimens has been revealed by the EBSD method. Extensive grain boundary sliding and cavitation has been observed in the crept specimens. Grain boundary sliding has been found to promote wedge-type damage at grain boundary triple junctions and to contribute significantly to the total creep strain. Furthermore, the assumed stress sensitivity of the models grain boundary cavity nucleation rate strongly influences the development of wedge-type damage. © 2013 Elsevier Ltd. All rights reserved.

Selective positioning of monolayer amounts of foreign atoms at the surface and subsurface regions of metal electrodes is a promising way to fine-tune the properties of the electrode/ electrolyte interface. The latter is critical as it largely governs the adsorption of electrolyte components and reaction intermediates and, therefore, controls many key electrocatalytic processes. Using model Pt(111) single-crystal electrodes, we demonstrate how the relative position of Cu atoms at the surface drastically changes the adsorption energies for (bi)sulfate anions. Our measurements involve pseudomorphic overlayers of Cu on Pt(111) as well as Cu-Pt(111) surface and sub-surface alloys, where Cu atoms were located either in the first or in the second atomic layers of Pt, respectively. In the case of Cu- Pt(111) surface alloys, specific adsorption of the anions starts earlier compared to the unmodified Pt(111) surface. In contrast, placing Cu atoms into the second atomic layer weakens the binding between the surface and the anions. Surprisingly, Cu pseudomorphic overlayers do not reveal any specific adsorption of (bi)sulfates (within the region of the overlayer stability). Taking into account that electrified interfaces between Pt(111) electrodes and sulfate-containing electrolytes often play the role of benchmark systems in fundamental physico-chemical and, particularly, electrocatalytic studies, our findings demonstrate a promising and relatively easy route of tuning the properties of these interfaces. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

We studied the texture and microstructure evolution in a plane strain compressed Cu-Ag metal matrix composite (MMC) with a heterophase microstructure using crystal plasticity finite element simulations. Lattice reorientations induced by both crystallographic (dislocation slip and twinning) and non-crystallographic (shear banding) mechanisms are addressed. First, simulations on a polycrystalline composite are made. Quite similar texture trends are observed for the composites and for the individual single-phase materials, namely, copper-type texture components in the Cu phase and brass-type texture components in the Ag phase. This result differs from experimental data that show less copper-type and more brass-type textures in both phases for the composite materials. To explore co-deformation mechanisms that lead to the specific crystallographic textures in the MMC, bicrystal simulations for the composite with specific initial orientation combinations are performed. The bicrystal simulations reproduce the experimentally observed trends of texture evolution in the respective phases of the composite, indicating that the localized stress and strain fields as well as the co-deformation mechanisms within the actual heterophase microstructure are well captured. The modeling shows that to accommodate plastic deformation between adjacent phases in the bicrystals, pronounced shear bands are triggered by stress concentration at the hetero-interfaces. With further deformation the bands penetrate through the phase boundaries and lead to larger lattice rotations. The simulations confirm that the shear banding behavior in heterophase composites is different from that in single-phase metals and the texture evolution in composite materials is strongly influenced by the starting texture, the local constraints exerted from the phase boundaries and the constitutive properties of the abutting phases. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A mixed-linker solid-solution approach was employed to modify the metal sites and introduce structural defects into the mixed-valence Ru II/III structural analogue of the well-known MOF family [M 3 II,II(btc)2] (M=Cu, Mo, Cr, Ni, Zn; btc=benzene-1,3,5-tricarboxylate), with partly missing carboxylate ligators at the Ru2 paddle-wheels. Incorporation of pyridine-3,5-dicarboxylate (pydc), which is the same size as btc but carries lower charge, as a second, defective linker has led to the mixed-linker isoreticular derivatives of Ru-MOF, which display characteristics unlike those of the defect-free framework. Along with the creation of additional coordinatively unsaturated sites, the incorporation of pydc induces the partial reduction of ruthenium. Accordingly, the modified Ru sites are responsible for the activity of the "defective" variants in the dissociative chemisorption of CO 2, the enhanced performance in CO sorption, the formation of hydride species, and the catalytic hydrogenation of olefins. The defect engineering in Ru-based metal-organic frameworks (MOFs) at coordinatively unsaturated metal centers (CUS) induces partial reduction of the metal nodes and leads to properties that are absent for the parent MOF, such as dissociative chemisorption of CO2 and enhanced sorption capacity of CO. The modified MOFs offer new perspectives as multifunctional materials whose performance is controlled by design of the defects. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multi-component nanoporous platinum-ruthenium-copper-osmium-iridium (np-PtRuCuOsIr) electrocatalyst has been facilely fabricated by chemical dealloying of mechanically alloyed AlCuPtRuOsIr precursor. The np-PtRuCuOsIr catalyst exhibits a typical three-dimensional bi-continuous interpenetrating ligament/channel structure with a length scale of ∼2.5 nm. The np-PtRuCuOsIr catalyst reaches a higher level in the mass activity (857.5 mA mgPt-1) and specific activity (3.0 mA cm-2) towards methanol oxidation compared to the commercial PtC catalyst (229.5 mA mgPt-1 and 0.5 mA cm-2 respectively). Moreover, the CO stripping peak of np-PtRuCuOsIr is 0.54 V (vs. SCE), 130 mV negative shift in comparison with the commercial PtC (0.67 V vs. SCE). The half-wave potential of np-PtRuCuOsIr is 0.900 V vs. RHE, 36 mV positive compared with that of the commercial PtC (0.864 V vs. RHE). The np-PtRuCuOsIr catalyst also shows 1.8 and 3.8 times enhancement in the mass and specific activity towards oxygen reduction than the commercial PtC. Moreover, the np-PtRuCuOsIr alloy exhibits superior oxygen reduction activities even after 15 K cycles, indicating its excellent long-term stability. The present np-PtRuCuOsIr can act as a promising candidate for the electrocatalyst in direct methanol fuel cells (DMFCs). © 2014 Elsevier B.V. All rights reserved.

A thin film composition gradient library of the Ni-Cu alloy system is generated through an electrodeposition technique using a complexing citrate electrolyte bath in a modified Hull cell. Energy dispersive X-ray spectroscopy, scanning electron microscopy and automated X-ray diffraction are performed to assess composition, surface morphology, and crystallographic structure of the deposited film as a function of the lateral position on the materials library. The results confirmed deposition of single phase polycrystalline f.c.c. Ni-Cu alloy system with varied lateral composition and lattice parameter, afcc as well. © 2014 The Electrochemical Society. All rights reserved.

The microstructural evolution of Al2Cu precipitates in an ultrafine-grained Al-3wt.% Cu model alloy produced by high-pressure torsion (HPT) was studied by in situ transmission electron microscopy (TEM). The precipitation growth was systematically investigated by isothermal heating experiments in the temperature range of 120 C to 170 C. The experimental data is analysed with respect of the diffusion kinetics and activation energy to determine the most prominent diffusion path: lattice or grain boundary diffusion. The results imply that grain boundary diffusion is the relevant mechanism for Al2Cu growth in the HPT deformed material. © 2014 Elsevier B.V. All rights reserved.

Catalyst considerations: Pt-Cu alloys are prepared as a thin-film material library with a composition gradient. By using a scanning flow cell coupled to on-line mass spectrometry, this library can be screened over to measure the activity towards the oxygen reduction reaction as well as the time-resolved dissolution of both alloy components in parallel. This results in comprehensive insights into the composition-dependent performance of the Pt-Cu system. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Split second: The photocatalytic activity of gallium oxide (β-Ga 2O3) depends strongly on the co-catalysts CuOx and chromia, which can be efficiently deposited in a stepwise manner by photoreduction of Cu2+ and CrO42-. The water-splitting activity can be tuned by varying the Cu loading in the range 0.025-1.5 wt %, whereas the Cr loading is not affecting the rate as long as small amounts (such as 0.05 wt %) are present. Chromia is identified as highly efficient co-catalyst in the presence of CuOx: it is essential for the oxidation of water. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly ordered mesoporous Cu-Ce-O catalysts with different Cu contents have been synthesized by using ordered mesoporous silica KIT-6 as a hard template. The mesostructural order of the negative replica is influenced by the ratio of Cu to Ce. Using XRD, HR-SEM, TEM and EDX analysis, it was found that the ordered mesostructures of the nanocomposites degenerate with increasing Cu concentration, due to CuO leaching during the template removal process and a phase separation at high Cu concentration. Cu ions can replace Ce-ion in the structure of CeO2 at Cu concentrations below 40mol%. However, the Cu concentration in the final materials is lower than expected from the ratio used in the synthesis. The activity in preferential oxidation of CO in H2-rich gases (PROX) was tested at a space velocity of 60,000mLh-1gcat -1. The activity of the mesoporous catalysts increases with the concentration of Cu and becomes stable for Cu concentrations higher than 20mol%. A CO conversion around 100 % can be attained with Cu0.20Ce0.80O2 as catalyst at 160°C. The exit CO concentration can be as low as 70ppm under these conditions. The CO2 selectivity can reach 100 % at low temperature (60- 80°C). Direct loading of CuO on the surface of mesoporous CeO2 leads to large CuO crystals and correspondingly low activity. The influence of the pretreatment atmosphere on activity was also studied. Oxidation-reduction-reoxidation cycling can improve the catalytic activity of the catalysts. © 2014 Elsevier B.V.

The high-Tc cuprate superconductors are close to antiferromagnetic order. Recent measurements of magnetic excitations have reported an intriguing similarity to the spin waves - magnons - of the antiferromagnetic insulating parent compounds, suggesting that magnons may survive in damped, broadened form throughout the phase diagram. Here we show by resonant inelastic X-ray scattering on Bi2Sr2CaCu2O8+δ (Bi-2212) that the analogy with spin waves is only partial. The magnon-like features collapse along the nodal direction in momentum space and exhibit a photon energy dependence markedly different from the Mott-insulating case. These observations can be naturally described by the continuum of charge and spin excitations of correlated electrons. The persistence of damped magnons could favour scenarios for superconductivity built from quasiparticles coupled to spin fluctuations. However, excitation spectra composed of particle-hole excitations suggest that superconductivity emerges from a coherent treatment of electronic spin and charge in the form of quasiparticles with very strong magnetic correlations. © 2014 Macmillan Publishers Limited. All rights reserved.

Influential support: Metal substrates affect the chemical properties of ZnO layers, which are important catalyst materials for the industrial production of methanol through the oxidation of CO. Interactions with the substrate lead to the formation of a new, planar ZnO thin-film phase, in which less highly oxidized Zn atoms bind CO more strongly than the Zn atoms in the normal wurtzite modification. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Density-functional theory calculations have been carried out to study the adsorption of methanethiolate and atomic sulfur as a nonmolecular reference at the Cu(111) surface. A large number of surface models have been investigated considering a variety of binding sites and coverages at the ideal and reconstructed surface. For methanethiolate, we find that the proposed [5013] supercell commonly used to approximate the experimentally observed noncommensurate pseudo(100) reconstruction yields the lowest surface energy, but several similar local minima exist differing in the positions of the copper atoms. None of these structures show the regular nearly square coordination of the thiolate species observed in scanning tunneling microscopy (STM). Modifying the chemical composition of the relaxed layer, e.g., by adding another copper atom, yields structures of comparable stability. It is thus very likely that the proposed supercell is not a good approximation to the true pseudo(100) phase and that larger unit cells are needed to allow for a realistic relaxation of the reconstructed layer. For atomic sulfur, it is well established that the most stable phase at Cu(111) is a (√7 × √7)R19.1 reconstruction. Its structure, however, has been discussed controversially in the literature for many years. While there is a consensus that the unit cell contains three sulfur atoms, there are still several competing models differing in the number of copper adatoms in the reconstructed layer. We find that three models have a very similar stability, and a three-copper adatom model is only marginally preferred. These results will be of importance for many fields from heterogeneous catalysis to covalent mechanochemistry and molecular nanomechanics. © 2012 American Chemical Society.

Detection of chemicals and biological species is an important issue to human health and safety. In this paper, we report the hydrothermal synthesis at 95 °C of Cu-doped ZnO low-dimensional rods for room-temperature (RT) sensing applications and enhanced sensor performances. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman and photoluminescence are used to characterize the material properties. To demonstrate the suitability of the Cu-doped ZnO rods for gas sensor applications and for comparison with pure ZnO, we fabricated a double rod device using Focused Ion Beam. The responses of pure-ZnO and Cu-doped ZnO rods studied in exactly the same condition are reported. We found that Cu-ZnO sensors have enhanced RT sensitivity, faster response time, and good selectivity. Miniaturized Cu-ZnO rod-based sensors can serve as a good candidate for effective H2 detectors with low power consumption. © 2012 Elsevier B.V.

The development of reliable interatomic potentials for large-scale molecular dynamics (MD) simulations of chemical processes at surfaces and interfaces is a formidable challenge because a wide range of atomic environments and very different types of bonding can be present. In recent years interatomic potentials based on artificial neural networks (NNs) have emerged offering an unbiased approach to the construction of potential energy surfaces (PESs) for systems that are difficult to describe by conventional potentials. Here, we review the basic properties of NN potentials and describe their construction for materials like metals and oxides. The accuracy and efficiency are demonstrated using copper and zinc oxide as benchmark systems. First results for a potential of the combined ternary CuZnO system aiming at the description of oxide-supported copper clusters are reported. Model of a copper cluster at the ZnO($10\overline {1} 0$) surface. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

To experimentally reveal the correlation between electrodeposited structure and electrolyte convection induced inside the concentration boundary layer, a highly inhomogeneous magnetic field, generated by a magnetized Fe-wire, has been applied to an electrochemical system. The influence of Lorentz and magnetic field gradient force to the local transport phenomena of copper ions has been studied using a novel two-component laser Doppler velocity profile sensor. With this sensor, the electrolyte convection within 500 μm of a horizontally aligned cathode is presented. The electrode-normal two-component velocity profiles below the electrodeposited structure show that electrolyte convection is induced and directed toward the rim of the Fe-wire. The measured deposited structure directly correlates to the observed boundary layer flow. As the local concentration of Cu2+ ions is enhanced due to the induced convection, maximum deposit thicknesses can be found at the rim of the Fe-wire. Furthermore, a complex boundary layer flow structure was determined, indicating that electrolyte convection of second order is induced. Moreover, the Lorentz force-driven convection rapidly vanishes, while the electrolyte convection induced by the magnetic field gradient force is preserved much longer. The progress for research is the first direct experimental proof of the electrolyte convection inside the concentration boundary layer that correlates to the deposited structure and reveals that the magnetic field gradient force is responsible for the observed structuring effect. © 2013 American Chemical Society.

Cu2MnAl films of different thicknesses (50, 70, and 100 nm) were grown by UHV RF-sputtering on a-plane sapphire or on MgO (100) substrates. Their structural and static magnetic properties have been studied by X-rays diffraction (XRD) and by vibrating sample magnetometry (VSM), respectively. The Cu2MnAl films exhibit a (100) and (110)-texture when grown on MgO and sapphire substrates, respectively. The best growth quality and the higher magnetization at saturation were obtained for the films grown on MgO. Dynamic magnetic properties were investigated using micro-strip line ferromagnetic resonance (MS-FMR). From the resonance measurements varying the direction and the amplitude of the in-plane and out-of-plane applied magnetic fields we derive the effective magnetization, the Landé g-factor (g = 2.11), the exchange constant (Aex = 0.34 μerg cm-1) and the magnetic anisotropy terms. The in-plane anisotropy can be described as a superposition of two terms showing a small twofold and a dominant fourfold symmetry. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrochemically driven "intercalation" of Cu into Te was used to prepare Cu2-xTe (0.2 < x ≤ 2) thin films and accurately control the composition of the resulting samples. A thorough theoretical analysis of the system using density functional theory (DFT) calculations showed that in the absence of external electric fields the driving forces for Cu atoms to move into the subsurface layers of the Te electrodes depend on the surface coverage of copper atoms. The Cu atoms tend to preferentially occupy the subsurface layers in the telluride films. The effective electric charge on Cu atoms inside the Te-electrodes is positive. These effective charge differences with respect to pure Cu and pure Te are only 0.2 e-. Scanning Kelvin probe (SKP), atomic force microscopy (AFM) and electrochemical techniques were used to characterise the surface status of the obtained samples. Both, DFT-calculated work function differences and the SKP-measured contact potential differences (CPD) change non-linearly with the variation of the film composition. Interfacial (solid/liquid) properties evaluated using electrochemical impedance spectroscopy depend on the nominal composition of the samples and display an abrupt change that correlates with a large change in the work function and CPD. While the proposed electrochemical synthetic route can efficiently and accurately control the composition of the Cu2-xTe thin films, SKP-measurements performed under close to ambient conditions in combination with DFT calculations can provide a promising tool to link fundamental surface properties and parameters which define the interface between solids and liquids. © The Royal Society of Chemistry 2013.

This study reveals the extraordinary effect of an individual twin boundary (TB) on the mechanical behaviors of Cu bicrystals with a TB parallel to the loading axis whose primary slip vectors are always parallel to the TB plane. With direct experimental evidence, it is shown that there is no strengthening effect of the TB on the bicrystal under microcompression, and the TB is intrinsically strong enough to resist fatigue cracking with the slip bands becoming the preferential cracking sites finally. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Critical factors for the commercial application of fuel cells are the high costs and the limited stability of Pt catalysts. In order to improve the activity and material efficiency, Pt-alloys with nonnoble metals play an essential role. However, stability remains a critical factor for this type of catalysts. In order to understand the dissolution of Pt-alloys and eventually improve their performance, we therefore analyze a Pt-Cu thin-film alloy with varying composition using a combinatorial screening approach coupled to online analytics. © The Electrochemical Society.

A method for the preparation of Pt(1 1 1) like thin films and thin film Cu-Pt(1 1 1) near-surface alloys (where Cu is preferentially located in the subsurface region) is reported in detail. Cyclic voltammograms of the resultant Pt(1 1 1)-like thin films in 0.1 M HClO4 demonstrate characteristic "butterfly" peaks attributed to the disorder/order phase transition in the adsorbed*OH layer, typical for a large Pt(1 1 1) crystals. Modification of the film surface with a monolayer of Cu and subsequent annealing in a reducing Ar/H2(5%) atmosphere, the voltammograms resemble those obtained for Cu-Pt(1 1 1) near-surface alloys prepared on commercial bulk single crystals. This method shows promise for the fabrication of extended (1 1 1)-type alloy surfaces of Pt and its alloys and can additionally be used to up-scale model objects for wider industrial and laboratory applications. © 2012 Elsevier Ltd.

The binding of antitumor flavonoids, namely 3-hydroxyflavone (3HF) and hesperidin (Hesp) with dsDNA was investigated in the absence and presence of Cu(II) using cyclic voltammetry and square wave voltammetry at the hanging mercury drop electrode. The reduction currents of 3HF, 3HF-Cu complex, and the 3HF-β-cyclodextrin inclusion complex decreased after intercalation into dsDNA. The intercalation of Hesp into dsDNA is weak. dsDNA is reduced at a potential of -1.48 V overlaying the reduction of Hesp. In contrast, in the presence of Cu(II), the interaction of Hesp with dsDNA leads to a much stronger intercalation. The binding constants of the flavonoid-Cu complex with dsDNA were evaluated and calibration graphs for the determination of dsDNA were obtained from the decrease in the peak current in the cyclic voltammograms of 3HF in the presence of dsDNA. The proposed method exhibited good recovery and reproducibility for indirect determination of dsDNA. © 2013 Springer-Verlag Berlin Heidelberg.

Compared with the existent techniques, atom probe tomography is a unique technique able to chemically characterize the internal interfaces at the nanoscale and in three dimensions. Indeed, APT possesses high sensitivity (in the order of ppm) and high spatial resolution (sub nm). Considerable efforts were done here to prepare an APT tip which contains the desired grain boundary with a known structure. Indeed, sitespecific sample preparation using combined focused-ion-beam, electron backscatter diffraction, and transmission electron microscopy is presented in this work. This method allows selected grain boundaries with a known structure and location in Cu(In, Ga)Se-2 thin-films to be studied by atom probe tomography. Finally, we discuss the advantages and drawbacks of using the atom probe tomography technique to study the grain boundaries in Cu(In,Ga)Se-2 thin-film solar cells.

We use atom probe tomography (APT) for resolving nanometer scale compositional fluctuations in Cu2ZnSnSe4 (CZTSe) thin-films prepared by co-evaporation and post-deposition annealing. We detect a complex, nanometer-sized network of CZTSe and ZnSe domains in these films. Some of the ZnSe domains contain precipitates having a Cu- and Sn-rich composition, where the composition cannot be assigned to any of the known equilibrium phases. Furthermore, Na impurities are found to be segregated at the CZTSe/ZnSe interface. The insights given by APT are essential for understanding the growth of CZTSe absorber layers for thin-film solar cells and for optimizing their optoelectronic properties. © 2013 American Institute of Physics.

The high prospects of exploiting the oxygen reduction reaction (ORR) for lucrative technologies, for example, in the fuel cells industry, chlor-alkali electrolysis, and metal-air batteries, to name but a few, have prompted enormous research interest in the search for cost-effective and abundant catalysts for the electrocatalytic reduction of oxygen. This chapter describes and discusses the electrocatalysis of oxygen reduction by metallomacrocyclic complexes and the prospect of their potential to be used in fuel cells. Since the main interest of most researchers in this field is to design catalysts which can achieve facile reduction of O2 at a high thermodynamic efficiency, this chapter aims to bring to light the research frontiers uncovering important milestones towards the synthesis and design of promising metallomacrocyclic catalysts which can accomplish the four-electron reduction of O2 at low overpotential and to draw attention to the fundamental requirements for synthesis of improved catalysts. Particular attention has been paid to discussion of the common properties which cut across these complexes and how they may be aptly manipulated for tailored catalyst synthesis. Therefore, besides discussion of the progress attained with regard to synthesis and design of catalysts with high selectivity towards the four-electron reduction of O2, a major part of this chapter highlights quantitative structure-activity relationships (QSAR) which govern the activity and stability of these complexes, which when well understood, refined, and carefully implemented should lead to rational design of better catalysts. A brief discussion about nonmacrocyclic copper (I) complexes, particularly Cu(I) phenanthrolines, and those with a laccase-like structure which exhibit promising activity for ORR has been included in a separate section at the end. © Springer-Verlag London 2013.

An accurate determination of the potential energy is the crucial step in computer simulations of chemical processes, but using electronic structure methods on-the-fly in molecular dynamics (MD) is computationally too demanding for many systems. Constructing more efficient interatomic potentials becomes intricate with increasing dimensionality of the potential-energy surface (PES), and for numerous systems the accuracy that can be achieved is still not satisfying and far from the reliability of first-principles calculations. Feed-forward neural networks (NNs) have a very flexible functional form, and in recent years they have been shown to be an accurate tool to construct efficient PESs. High-dimensional NN potentials based on environment-dependent atomic energy contributions have been presented for a number of materials. Still, these potentials may be improved by a more detailed structural description, e.g., in form of atom pairs, which directly reflect the atomic interactions and take the chemical environment into account. We present an implementation of an NN method based on atom pairs, and its accuracy and performance are compared to the atom-based NN approach using two very different systems, the methanol molecule and metallic copper. We find that both types of NN potentials provide an excellent description of both PESs, with the pair-based method yielding a slightly higher accuracy making it a competitive alternative for addressing complex systems in MD simulations. © 2012 American Institute of Physics.

In this work we study the CdS/Cu(In,Ga)Se 2 p-n junction region in Cu(In,Ga)Se 2 thin-film solar cells using atom probe tomography. A Cu-, Ga-depleted, and Cd-doped region of about 1 nm thickness is detected at the Cu(In,Ga)Se 2 side of the CdS/Cu(In,Ga)Se 2 interface. Furthermore, Cd is also found to be enriched at Cu(In,Ga)Se 2 grain boundaries connected to the CdS layer. Na and O impurities decorate the CdS/CIGS interface, where Na-rich clusters are preferentially located in CdS regions abutting to Cu(In,Ga)Se 2 grain boundaries. The experimental findings of this work demonstrate the capability of atom probe tomography in studying buried interfaces and yield vital information for understanding and modeling the p-n junction band structure in Cu(In,Ga)Se 2 solar cells. © 2012 American Institute of Physics.

Mesoporous copper-alumina (Cu-Al 2O 3) with different copper contents was synthesized in a one-pot reaction via the evaporation-induced self-assembly of Pluronic P123 and the corresponding metal precursors in ethanolic solution in the presence of nitric acid. Mesoporous Cu-Al 2O 3 calcined at 400°C exhibits a large BET surface area of 265 m 2/g and a pore volume of 0.48 cm 3/g. XRD results indicate that the wall of mesoporous Cu-Al 2O 3 calcined at 400°C is amorphous, and that it is transformed to crystalline material by further thermal treatment at 800°C. Copper was formed as very small particles in the composite under 5% H 2 flow at high temperature. Moreover, the mesoporous structure did not collapse after the sample was reduced at 650°C for 4 h, and the copper particles with sizes of around 6 nm were well distributed through the entire mesoporous γ-Al 2O 3 network. Using the mesoporous Cu/γ-Al 2O 3 as a bifunctional catalyst for one-step dimethyl ether synthesis from synthesis gas, a CO conversion of 72% and a DME selectivity of 69% were obtained at 50 bar and 310°C. © 2012 Elsevier Inc. All rights reserved.

The compound BaMn 2As 2 with the tetragonal ThCr 2Si 2 structure is a local-moment antiferromagnetic insulator with a Néel temperature T N=625K and a large ordered moment μ=3.9μ B/Mn. We demonstrate that this compound can be driven metallic by partial substitution of Ba by K while retaining the same crystal and antiferromagnetic structures together with nearly the same high T N and large μ. Ba 1-xK xMn 2As 2 is thus the first metallic ThCr 2Si 2-type MAs-based system containing local 3d transition metal M magnetic moments, with consequences for the ongoing debate about the local-moment versus itinerant pictures of the FeAs-based superconductors and parent compounds. The Ba 1-xK xMn 2As 2 class of compounds also forms a bridge between the layered iron pnictides and cuprates and may be useful to test theories of high T c superconductivity. © 2012 American Physical Society.

Starting from the generalized t-J-G model Hamiltonian, we analyze the spin response in the superconducting cuprates taking into account both local and itinerant spin components which are coupled to each other self-consistently. We demonstrate that derived expression reproduces the basic observations of neutron scattering data in YBa 2Cu 3O 6+y compounds near the optimal doping level. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012.

The temperature dependent mechanical properties of the metallization of electronic power devices are studied in tensile tests on micron-sized freestanding copper beams at temperatures up to 400 °C. The experiments are performed in situ in a scanning electron microscope. This allows studying the micromechanical processes during the deformation and failure of the sample at different temperatures. © 2012 American Institute of Physics.

Polycrystalline copper wires with diameters of 25, 30 and 50m were annealed at temperatures between 200°C and 900°C, resulting in different microstructures with ratios of wire diameter to grain size between 1.1 and 15.6. The microstructure evolution and tensile behavior were studied systematically. In comparison with experimental data available in the literature, the results revealed that the tensile yield stresses of these micro-sized wires are influenced not only by the grain size but also by the ratio of wire diameter to grain size. This is clearly seen when comparing identical grain sizes but different wire diameters where thinner wires reveal smaller flow stress values. A model is proposed to explain the smaller is softer phenomenon, taking into account the higher strengthening effect of grain boundaries compared to the free surface. © 2012 Taylor & Francis.

The deformation mechanisms of nanotwinned Cu subjected to nanoscratching are investigated by means of molecular dynamics simulations. Scratching simulations on nanotwinned single-crystalline Cu with the twin planes parallel and perpendicular to the scratching direction are performed. Since the detwinning mechanism is completely suppressed in the former case, no apparent correlation between frictional coefficient and the twin spacing is observed. In samples where the twin planes are perpendicular to the scratching direction, the friction increases as the twin spacing decreases, and then decreases as the twin spacings become even smaller. It results from the competitive plastic deformation between the inclined dislocations and the detwinning mechanism. Subsequent simulations for nanotwinned polycrystalline Cu unveil that in addition to the grain-boundary-associated deformation mechanism, dislocation-mediated detwinning plays a significant role in the plastic deformation of nanotwinned Cu. The twin boundary spacing in turn affects nanotwinned materials to resist scratching via plastic deformation. We demonstrate via the nanoscratching tests that there exists a critical twin boundary spacing for which the friction coefficient is maximized and that this transition results from the competing deformation mechanisms in those nanotwinned materials. © 2012 American Physical Society.

The shape memory properties of the complete Ti-Ni-Cu thin film system were investigated using combinatorial methods, i.e. fabrication and high-throughput characterization of thin film materials libraries. Thin film composition spreads were deposited using a wedge-type multilayer technique and annealed at 500°C, 600°C and 700°C for 1 h for alloy formation. The complete composition regions showing reversible phase transformations were identified for each annealing temperature. These regions are well extended in comparison to prior knowledge. Furthermore, the composition-structure-property relations governing the phase transformation characteristics in the thin film samples were determined. For films annealed at 500°C and 600°C the transformation temperatures are highest for compositions close to Ti 50Ni 50-xCu x and decrease as the thin film compositions deviate. Similarly, the thermal transformation hysteresis is found to be smallest for "stoichiometric" (Ti 50Ni 50-xCu x) compositions. Precipitation of Ti-rich and (Ni,Cu)-rich phases is found to be responsible. With increasing annealing temperature the transformation temperatures increase and the thermal hysteresis values decrease for compositions showing B2→B19 phase transformation paths, due to coarsening of the precipitate phases. The alloying process of the multilayer thin films leads to the formation of the equilibrium phases. The formation of Guinier-Preston zones is suppressed. For thin films annealed at 700°C the transforming composition region is comparatively smaller and the phase transformation properties are influenced by Ti 2Ni precipitates. © 2012 Elsevier Ltd. All rights reserved.

A simple method is presented for the formation of thin films of Cu-Pt(111) near-surface alloys (NSA). In these thin films, the solute metal (Cu) is preferentially located in the second platinum layer and protected by a Pt surface layer. The NSA-films act as active and fairly stable electrocatalysts for the reduction of oxygen with the activity and stability which approach those for bulk single crystalline Pt-alloy surfaces and ∼5 times more active than state-of-the-art Pt thin films. © 2012 American Chemical Society.

Metallic copper nanoparticles have been efficiently dispersed and stabilized on nitrogen-doped carbon nanotubes. They are about 8-10 nm in diameter and highly resistant against bulk oxidation. Their catalytic activity and recyclability have been investigated in A 3-type coupling reactions for the synthesis of propargylamines. It was easily possible to prepare diastereomerically pure derivatives of proline and to efficiently recover and reuse the supported catalyst several times. © 2012 Elsevier B.V. All rights reserved.

CuO/ZnO nanocomposites were synthesized on Al 2O 3 substrates by a hybrid plasma-assisted approach, combining the initial growth of ZnO columnar arrays by plasma-enhanced chemical vapor deposition (PE-CVD) and subsequent radio frequency (RF) sputtering of copper, followed by final annealing in air. Chemical, morphological, and structural analyses revealed the formation of high-purity nanosystems, characterized by a controllable dispersion of CuO particles into ZnO matrices. The high surface-to-volume ratio of the obtained materials, along with intimate CuO/ZnO intermixing, resulted in the efficient detection of various oxidizing and reducing gases (such as O 3, CH 3CH 2OH, and H 2). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The influence of film thickness on the B2-B19 martensitic transformation properties of nanoscale Ti51Ni38Cu11 thin films with thicknesses ranging from 750 to 50 nm is reported. For these films an unexpected behavior of the phase transformation temperatures was observed: Af and Os initially decrease with decreasing film thickness but increase sharply again for thicknesses < 100 nm. The phase transformation temperatures and thermal hysteresis width range from 58 to 35 °C (Af) and 14 to ∼0 K, respectively. For the first time we can show that substrate-attached Ti-Ni-Cu thin films as thin as 50 nm show reversible B2-B19 phase transformations. Furthermore, it is shown that with decreasing film thickness a change in the tetragonality of the B19 martensite phase occurs. This leads to fulfilling the so-called λ2 criterion, causing a vanishing hysteresis for a film thickness of 75 nm. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Highly porous thin films based on a [Cu(bdc) 2] n (bdc = benzene-1,4-dicarboxylic acid) metal-organic framework, MOF, grown using liquid-phase epitaxy (LPE) show remarkable stability in pure water as well as in artificial seawater. This opens the possibility to use these highly porous coatings for environmental and life science applications. Here we characterize in detail the stability of these SURMOF 2 thin films under aqueous and cell culture conditions. We find that the material degrades only very slowly in water and artificial seawater (ASW) whereas in typical cell culture media (PBS and DMEM) a rapid dissolution is observed. The release of Cu 2+ ions resulting from the dissolution of the SURMOF 2 in the liquids exhibits no adverse effect on the adhesion of fibroblasts, prototype eukaryotic cells, to the substrate and their subsequent proliferation, thus demonstrating the biocompatibility of SURMOF 2 surface coatings. Thus, the results are an important step toward application of these porous materials as a slow release matrix, for example, for pharmaceuticals and growth factors. © 2012 American Chemical Society.

A non-syngas direct steam reforming route is investigated for the conversion of methanol to hydrogen and carbon dioxide over a CuZnGaOx catalyst at 150-200 °C. This route is in marked contrast with the conventional complex route involving steam reformation to syngas (CO/H 2) at high temperature, followed by water gas shift and CO cleanup stages for hydrogen production. Here we report that high quality hydrogen and carbon dioxide can be produced in a single-step reaction over the catalyst, with no detectable CO (below detection limit of 1 ppm). This can be used to supply proton exchange membrane fuel cells for mobile applications without invoking any CO shift and cleanup stages. The working catalyst contains, on average, 3-4 nm copper particles, alongside extremely small size of copper clusters stabilized on a defective ZnGa2O4 spinel oxide surface, providing hydrogen productivity of 393.6 ml g-1-cat h-1 at 150 °C. © 2012 Macmillan Publishers Limited. All rights reserved.

Structuring of Cu deposits was reported to occur during electrodeposition in magnetic gradient fields, recently. This work aims on increasing the knowledge about the convection-induced structuring mechanism. Therefore, in-situ velocity measurements by Astigmatism Particle Tracking Velocimetry were performed. The information gained by this study is used to choose pulse-reverse-plating parameters suitable for deposition of separated Cu structures. Additionally, it is demonstrated that the structure shape can be changed by varying the superimposed magnetic field gradients. The structure height can be adjusted by the number of pulse-reverse-plating cycles. The structuring mechanism is discussed for potentiostatic as well as for pulse-reverse-plating conditions with respect to the acting magnetic forces. ©The Electrochemical Society.

The observed mechanical behaviour of micron-sized samples raises fundamental questions about the influence of size on the underlying dislocation plasticity. In situ μLaue diffraction on a single crystalline copper bending beam was performed to study the feasibility of bending tests and their contribution to our understanding of size-dependent dislocation plasticity. Theoretical considerations lead to a minimum sample size where in situ Laue experiments are useable. A critical size is evidenced below which, depending on Young's modulus and maximum stress, the elastic and plastic contributions to the lattice curvature cannot be separated. The experiment shows the increase in geometrically necessary dislocations during plastic deformation followed by a decrease during unloading. This can be explained by the formation and dissolution of a dislocation pile-up at the neutral axis of the bending cantilever. The dissolution of the dislocation pile-up is caused by the back stress of the pile-up and a direct observation of the Bauschinger effect, which is consistent with the non-purely elastic mechanical behaviour when unloading the sample. © 2012 Taylor & Francis.

Fragmentation testing is frequently used to probe film fracture strain and the interfacial properties of thin brittle films on compliant substrates. A model based upon complete yield of the film/substrate interface is frequently used to analyse data after cracking has saturated. Additionally, the film is either assumed to have a single-valued failure stress or a distribution of strengths described by Weibull statistics. Recent work by the authors showed that consideration of film thickness variations and the application of neighbour ratio analysis brought 96% of the data for an Al x O y /Cu film/substrate system into compliance with the predictions for a film with a single-valued failure stress. In the present work Cr/PI (polyimide) and Cr/PET (polyethylene teraphthalate) systems are analysed according to the same methodology. The Cr films on polymer substrates crack such that the neighbour ratios considerably exceed the predicted limit of 2. The influence of the relative thickness of the film and substrate and the strain rate of the test is investigated. A deviation from the idealised mechanical model due to the large difference in elastic moduli of film and substrate is put forward as a possible cause of the observed behaviour. The importance of these results to the application of the interfacial yield model is discussed. © 2012 Taylor & Francis.

Three differently detailed kinetic models for methanol synthesis are derived for experimental data measured over a ternary copper catalyst. Two global reactor models for reaction design, including a power law and a Langmuir-Hinshelwood-Hougen-Watson approach, are presented. In addition a microkinetic model is adapted to describe the whole experimental data and is used to discuss dynamical changes occurring during methanol synthesis. The first global model based on power law kinetics is very precisely in predicting the integral rates of methanol production. The power law requires the inclusion of a water inhibition term to be applicable over the whole range of experiments. A semi-empirical Langmuir-Hinshelwood-Hougen-Watson model, taken from the literature, gives essentially the same results, even upon extrapolation. The third model, a microkinetic model, was successfully fitted with only two variables and is in reasonable agreement with the experimental data. For all models a sensitivity analysis shows the influencing parameters on the methanol production rate. The valid microkinetic model, however, can give qualitative estimations of the structure sensitivity and dynamic behavior of methanol synthesis. The dynamic change of active sites and of site distribution of different copper low-index planes along the reactor length is given and the inhibiting role of water, indicated by the power law and microkinetic model, is analyzed. © 2012 Elsevier B.V.

Alternating current scanning electrochemical microscopy (ACSECM) is used to investigate the inhibition of copper corrosion by four potential inhibitors, namely benzotriazole (BTAH), 5-methyl-benzotriazole (MBTAH), 2-mercaptobenzimidazole (MBI), and ethyl xanthate (EX). It is shown that the formation of inhibitor films on the metal can be followed from the decrease of the substrate's local electrochemical activity associated with the formation of inhibitor-containing surface layers. Sensitive imaging can be performed that accounts for changes in electrochemical activity of the modified surfaces, as well as for their corrosive attack from the environment. AC-SECM is shown to be a powerful technique for the investigation of corrosion processes. © 2012 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.

We present crystal plasticity finite element simulations of the texture evolution in α-brass polycrystals under plane strain compression. The novelty is a non-crystallographic shear band mechanism [Anand L, Su C. J Mech Phys Solids 2005;53:1362] that is incorporated into the constitutive model in addition to dislocation and twinning. Non-crystallographic deformation associated with shear banding leads to weaker copper and S texture components and to a stronger brass texture compared to simulations enabling slip and twinning only. The lattice rotation rates are reduced when shear banding occurs. This effect leads to a weaker copper component. Also, the initiation of shear banding promotes brass-type components. In summary the occurrence of non-crystallographic deformation through shear bands shifts face-centered-cubic deformation textures from the copper type to the brass type. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We present crystal plasticity finite element simulations of plane strain compression of α-Brass single crystals with different initial orientations. The aim is to study the fundamentals of mesoscale structure and texture development in face-centered-cubic (fcc) metals with low stacking fault energy (SFE). Shear banding depends on the initial orientation of the crystals. In Copper and Brass-R-oriented crystals which show the largest tendency to form shear bands, an inhomogeneous texture distribution induced by shear banding is observed. To also understand the influence of the micromechanical boundary conditions on shear band formation, simulations on Copper-oriented single crystals with varying sample geometry and loading conditions are performed. We find that shear banding can be understood in terms of a mesoscopic softening mechanism. The predicted local textures and the shear banding patterns agree well with experimental observations in low SFE fcc crystals. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Cu2MnAl Heusler alloy films were grown on MgO (001) substrates by using the ion beam sputtering technique. The films were post-annealed at varying temperatures in order to investigate the influence of annealing on crystal structure and magnetic properties. The structural properties of Cu 2MnAl films have been investigated by using x-ray diffraction (XRD) and magnetic properties have been investigated by both vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques. The experimental data indicates that the crystal structure of the films strongly depends on the annealing temperature. When the films were annealed at 200 °C, the saturation magnetization (Ms = 250 emu/cm3) achieved its maximum and the coercive field (Hc 7 Oe) reached its minimum with B2 ordered structure. In addition, FMR results have revealed that the Cu2MnAl film annealed 200 °C has the highest effective magnetization. The combination of structural and magnetic characterization indicates that the optimum growth temperature is 200 °C for the Cu2MnAl Heusler alloy films on MgO substrates. © Springer Science+Business Media, LLC 2011.

The atomic environments at metal surfaces differ strongly from the bulk, and, in particular, in case of reconstructions or imperfections at "real surfaces," very complicated atomic configurations can be present. This structural complexity poses a significant challenge for the development of accurate interatomic potentials suitable for large-scale molecular dynamics simulations. In recent years, artificial neural networks (NN) have become a promising new method for the construction of potential-energy surfaces for difficult systems. In the present work, we explore the applicability of such high-dimensional NN potentials to metal surfaces using copper as a benchmark system. A detailed analysis of the properties of bulk copper and of a wide range of surface structures shows that NN potentials can provide results of almost density functional theory (DFT) quality at a small fraction of the computational costs. © 2012 American Physical Society.

The present work investigates the effect of grain boundary chemistry and crystallography on creep and on creep damage accumulation in Cu-0.008 wt.% Bi and Cu-0.92 wt.% Sb at stresses ranging from 10 to 20 MPa and temperatures between 773 and 873 K. Small additions of Bi and Sb significantly reduce the rupture strain and rupture time during creep of Cu. High stress exponents (Cu-Bi) and high apparent activation energies for creep (Cu-Bi and Cu-Sb) are obtained. Sb promotes creep cavitation on random high-angle grain boundaries. Bi, on the other hand, causes brittle failure when small crack-like cavities cause decohesion. Both elements suppress dynamic recrystallization, which occurs during creep of Cu at high stresses and temperatures. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We have used density functional theory calculations to study non-periodic model systems for the ubiquitous layer-pillar metal organic frameworks built from paddle-wheel building blocks. Experimentally, these porous materials show nearly identical structures for both copper and zinc forming the paddle-wheel, but differ depending on the type of the metal center in their properties. Our theoretical results clearly reveal orbital directing effects for the d 9 Cu(ii) center, enforcing a square planar conformation, to be the main reason for the difference in contrast to the flexible d 10 Zn(ii) system. Surprisingly, this difference is directly visible in the structure of the bare vertex model without axial ligands, whereas in the case of pyridine coordination both copper and zinc complexes are structurally nearly indistinguishable. However, in the vibrational normal modes the higher degree of flexibility for the zinc-based systems is still noticeable, explaining the higher flexibility of the corresponding periodic MOFs. © 2012 The Royal Society of Chemistry.

The coincidence site lattice (CSL) concept is often used in microstructural characterization by researchers studying grain boundary engineering as a method for improving the performance of polycrystalline materials. It is assumed that a high degree of shared lattice sites in the boundary between two grains will result in improved mechanical properties. For practical application of the CSL concept to experimental results, a maximum deviation from ideal CSL orientation relationships must be defined to distinguish potential CSL boundaries from random boundaries that are not likely to exhibit "special" properties. Several different maximum deviation criteria have been proposed in the literature. In this study, four of these criteria are investigated for their effectiveness in predicting the creep cavitation resistance of boundaries of different CSL character in three model alloys: pure Cu, Cu-Bi, and Cu-Sb. Bi and Sb strongly segregate to Cu grain boundaries and are detrimental to creep life. The experimental observations are compared to simulation results for a non-textured polycrystal. It is observed that only boundaries related to cubic annealing twins (∑3 and ∑9) exhibit special resistance to creep cavitation, that boundaries with ∑ > 3 are affected by the presence of segregants, and that the fraction of non-∑(3,9) boundaries tracks closely with what would be expected from a random polycrystal. It is shown that more restrictive criteria result in more reliable characterization of the fraction of cavitation-resistant boundaries only because they exclude more non-∑(3,9) boundaries from the analysis. © 2011 Springer Science+Business Media, LLC.

The high temperature properties of metal/ceramic interfaces play an important role in the operation of microprocessors and coated products. Determination of the interface properties over a range of testing conditions is critical in understanding and improving the performance of such systems. Periodic cracking of ceramic films on metal substrates provides a direct measure of the interface strength. A model AlxOy/Cu system is investigated over temperatures of 25-650°C and at strain rates of 3.5{dot operator}10-2s-1 and 1.7{dot operator}10-5s-1. For this system it is found that temperature does not significantly affect the spacing of film cracks in the steady state, at a given strain rate. However, the high strain rate tests broaden the measured crack spacing distributions compared to the low strain rate tests. This broadening causes an increase in the average crack spacing at high strain rate. The minimum crack spacing was increased 15-20% by both increasing strain rate and increasing temperature. © 2011 Elsevier B.V.

A novel three-dimensional particle tracking velocimetry technique was used to examine the flow during electrodeposition of Cu. For the first time electrode-normal, circumferential, and radial velocities were spatially resolved during deposition in superimposed low and high magnetic gradient fields. In this way the complex interaction of magnetic field gradient force and Lorentz force induced convective effects could be measured and analyzed. Magnetic field gradient force induced electrolyte flow was detected only in high gradient magnetic fields, and it was found to be directed toward regions of gradient maxima. Since this electrode-normal flow causes enhanced transport of Cu 2+ ions from the bulk electrolyte to those regions of the working electrode where maxima of magnetic gradients are present, a structured deposit is formed during diffusion-limited electrodeposition. Lorentz force driven convection was observed during deposition in the low and the high magnetic gradient experiments. The overall fluid motion and the convection near the working electrode were determined experimentally and discussed with regard to the acting magnetic forces and numerical simulations. © 2011 American Chemical Society.

We have applied an accurate molecular mechanics force field, parametrized with respect to first-principles calculated reference data, for copper paddle wheel (Cu2(O2C)4) based metal organic frameworks to investigate possible systems with a 3,4-connected network topology. The results explain why the well-known HKUST-1 forms a tbo net, whereas for an extended linker, as in MOF-14, the pto topology is preferred. In particular, the complex structure of the latter system, consisting of two deformed and "interwoven" nets, is accurately predicted, and the necessary deformation energy can be quantified. In this context also all possible forms of interpenetration were considered. Finally, by designing a bromine-substituted extended linker the system can be forced back into the more open tbo topology. This first molecular mechanics investigation of the relative strain energies of MOF network topologies demonstrates that the structure is to a large extent defined by the intrinsic conformational preferences of the building blocks. Our approach allows to analyze and understand the reasons for this preference and can be used as a computational tool for the design of specific topologies. © 2011 American Chemical Society.

Periodic cracking experiments are frequently used in the assessment of interface quality in brittle film/compliant substrate systems. Through these techniques it is possible to extract a quantitative measure of interface shear strength and therefore assess the mechanical suitability of the films for application. The influence of film thickness inhomogeneities on the crack spacing is assessed in this study. While film thickness inhomogeneities are always present in thin film systems, only nominal thickness values have been considered up to this point. By defining two separate regimes of film thickness variation, roughness and unevenness, in relation to the crack spacing, the influence of such variation on the data is analysed. The results of this analysis are then considered in reference to a model system of an amorphous alumina film on a copper substrate (AlxOy/Cu), the limits of this analysis are then discussed. © 2011 Elsevier B.V.

The ability to measure the adhesion energy of metal thin films on polymer substrates is important for the design of reliable flexible electronic devices. One technique is to create well-defined areas of delamination (buckles) as a consequence of lateral compressive stresses induced by tensile straining of the film-substrate system. The adhesion energy is calculated from the buckle dimensions. In order to improve the adhesion between the metal film and polymer substrate, thin adhesion layers can be incorporated. However, interdiffusion and reactions can occur between the adhesion layer and the metal film when subjected to elevated temperatures. This is detrimental for the interfacial adhesion, as will be discussed for Cu films on polyimide with a Ti interlayer subjected to annealing at 350°C. © Carl Hanser Verlag GmbH & Co. KG.

In this paper a new micro-shear experiment is introduced using a double shear specimen machined by a focused ion beam technique. The micro-shear specimen is structured from pure copper promoting (111) [101] slip. Comparing scanning electron microscopy images before and after deformation provides evidence for localized shear. Load-displacement data identify a load plateau and characterize the localized shear process (critical shear-stress for activation of (111) [101] slip: 170 MPa). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA.

Hardness and Young's moduli values for TixNi90-xCu10 (37at.%< x< 67at.%) thin films from a continuous composition spread type materials library, annealed at 500°C for 1h, were determined at room temperature (martensitic state) and 80°C (austenitic state) using high-throughput nanoindentation experiments. These values are found to increase as the compositions deviate from Ti contents close to 50at.%. The increases in hardness is correlated to the presence of Ti-rich and (Ni,Cu)-rich precipitates resulting in precipitate hardening and grain size refinement (Hall-Petch effect). The increase of the Young's moduli is rationalized by considering the significantly higher Young's moduli of the different precipitate phases and applying the rule of mixtures. The contributions of the precipitate phases and the matrix to the combined Young's modulus were estimated by evaluating the load-displacement curves in detail. The obtained results are in good agreement with the Young's moduli determined from thin film curvature measurements [R. Zarnetta et al., Smart Mater. Struct. 19 (2010) 65032]. Thus, the experimental restrictions for nanoindentation experiments at elevated temperatures are concluded to not adversely affect the validity of the results. © 2011 Elsevier B.V.

Co-precipitation of Cu,Zn,(Al) precursor materials is the traditional way of synthesizing Cu/ZnO/(Al2O3) catalysts for industrial methanol synthesis. This process has been investigated by titration experiments of nitrate and formate solutions. It was found that the solidification of the single components proceeds sequentially in case of nitrates: Cu2+ is precipitated at pH 3 and Zn2+ (as well as Al3+) near pH 5. This behavior prevents a homogeneous distribution of all metal species in the initial precipitate upon gradual increase of pH and requires application of the constant pH micro-droplet method. This effect is less pronounced if formate instead of nitrate is used as counter ion. This can be explained by the strong modification of the hydrolysis chemistry of the metal ions due to the presence of formate anions, which act as ligands and buffer. A formate-derived Cu/ZnO/Al2O3 catalyst was more active in methanol synthesis compared to a nitrate-derived sample although the same crystallographic phases were present in the precursor after co-precipitation and ageing. The effect of precipitation temperature was studied for the binary CuZn nitrate model system. Increasing the temperature of co-precipitation above 50 °C leads to down-shift of the precipitation pH of Zn2+ by a full unit. Thus, in warm solutions more acidic conditions can be used for complete co-precipitation, while in cold solutions, some Zn2+ may remain dissolved in the mother liquor at the same precipitation pH. The higher limit of temperature is given by the tendency of the initial Cu precipitate towards formation of CuO by oxolation. On the basis of these considerations, the empirically determined optimal pH and temperature conditions of the industrially applied synthesis can be rationalized. © 2010 Elsevier B.V. All rights reserved.

We present a successful attempt of decoupling a dye molecule from a metallic surface via physisorption for enabling direct photoisomerization. Effective switching between the isomers is possible by exposure to UV light via the rotation pathway. © 2011 The Royal Society of Chemistry.

The disorder-order transition of a highly defective A2-ordered Cu 2MnAl film on MgO(0 0 1) upon annealing at 600 K was monitored by means of x-ray absorption spectroscopy (XAS) at the Cu and Mn L2,3 edges. Additionally, x-ray magnetic circular dichroism (XMCD) was employed to determine element-specific orbital and spin resolved magnetic moments of the Cu and Mn atoms. A small induced total magnetic moment of ≈0.04 0.01μB per atom was detected at the Cu sites, whereas a total magnetic moment of 3.57 0.52μB is carried by the Mn atoms. The experimental XAS and XMCD spectra of Cu agree reasonably with the results from ab initio calculations, magnetic moments derived by the sum rules are in accordance with the calculations. © 2011 IOP Publishing Ltd.

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.

Using the astigmatism particle tracking method in connection with a long-range microscope enables highly temporal and spatial resolved measurements of the three dimensional velocity field in a fluid volume by a single camera. Thus, the complex interplay of magnetic field gradient force and the Lorentz force induced convective effects was ana- lyzed experimentally for the first time. © Oldenbourg Wissenschaftsverlag.

The suitability of frequency-dependent alternating-current scanning electrochemical microscopy (4D AC-SECM) for investigation of thin passivating layers covering the surface of corrosion-inhibited metals has been demonstrated. Inhibition of copper corrosion by benzotriazole (BTAH) and methylbenzotriazole (MBTAH), which are effective inhibitors for this metal under many environmental conditions, was investigated. Strong dependencies were found for the AC z-approach curves with both the duration of the inhibitor treatment and the frequency of the AC excitation signal applied in AC-SECM. Both negative and positive feedback behaviours were observed in the AC approach curves for untreated copper and for Cu/BTAH and Cu/MBTAH samples. Negative feedback behaviour occurred in the low-frequency range, whereas a positive feedback effect was observed at higher frequencies. A threshold frequency related to the passage from negative to positive regimes could be determined in each case. The threshold frequency for inhibitor-modified samples was found always to be significantly higher than for the untreated metal, because the inhibitor film provides electrical insulation for the surface. Moreover, the threshold frequency increased with increasing surface coverage by the inhibitor. 4D AC-SECM was successfully applied to visualizing spatially resolved differences in local electrochemical activity between inhibitor-free and inhibitor-covered areas of the sample. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA.

Pure Cu was subjected to severe plastic predeformation by p=1, 2, 4, 8, 16 and 24 passes of equal channel angular pressing (ECAP) on route BC at ambient temperature and subsequently tested in uniaxial compression parallel to the extrusion direction at constant rate or constant stress and temperatures from ambient temperature up to 418K. The maximum compressive strength of the ECAPed Cu varies in a systematic fashion with p, until a steady state is finally reached between p=8 and 16 where the rate sensitivity of flow stress is maximal. The results are quantitatively interpreted in terms of the boundary structure, considering the superposition of hardening due to refinement of low-angle boundaries and softening due to enhanced thermal recovery at high-angle boundaries. Beyond the maximum the compressive strength declines with strain for relatively low rate and/or elevated temperature of compression. This is explained by dynamic grain coarsening towards the new steady state developing in compression. © 2011 Elsevier B.V.

CO adsorption at 1 MPa on Cu-Zn stearate colloids and supported Cu catalysts was studied in situ by attenuated total reflection infrared (ATR-IR) spectroscopy. Subsequent to thorough reduction by H2, the IR band at 2110-2070 cm-1 due to linearly adsorbed CO on clean metallic Cu was always observed initially on all Cu catalysts. During the exposure of Zn-containing samples to CO at high pressure, a new IR band at ca. 1975 cm -1 appeared in addition and increased in intensity even at room temperature. The detailed analysis of the IR spectra showed that the new IR band at ca. 1975 cm-1 was not related to coadsorbed carbonate/formate- like species, but to the content of Zn in the samples. This IR band was found to be more stable than that at 2110-2070 cm-1 during purging with inert gas. It disappeared quickly in synthetic air, pointing to a strongly reduced state of the Zn-containing Cu catalysts achieved during high-pressure CO exposure. It is suggested that CO can reduce ZnO to Zn in the presence of Cu, resulting in the formation of a CuZnx surface alloy. As the CO species with the characteristic IR band at ca. 1975 cm-1 binds more strongly to this CuZnx alloy than the linearly adsorbed CO to pure Cu, it is suggested to be adsorbed on a bridge site. © 2011 American Chemical Society.

Atom Probe Tomography was employed to investigate the distribution of impurities, in particular sodium and oxygen, in a cuinse2-based thin-film solar cell. It could be shown that sodium, oxygen, and silicon diffuse from the soda lime glass substrate into the cuinse2 film and accumulate at the grain boundaries. Highly dilute concentrations of sodium and oxygen were measured in the bulk. Selenium was found to be depleted at the grain boundaries. These observations could be confirmed by complementary energy dispersive X-ray spectroscopy studies. Our results support the model proposed by Kronik et al. (1998) [1], which explains the enhanced photovoltaic efficiency of sodium containing cuinse2 solar cells by the passivation of selenium vacancies at grain boundaries. © 2011 Elsevier B.V.

Elemental mixing at the CdS/ CuInSe2 interface of a thin-film solar cell was studied by means of atom probe tomography. A Cu-depleted and Cd-doped region (∼2 nm in width) was detected at the CuInSe2 surface, proving the existence of a buried p-n homojunction within the CuInSe2 absorber layer. Furthermore, CdS was found to infiltrate open pores existing in CuInSe2 during the chemical bath deposition. This could explain why chemical bath deposition of CdS leads to higher solar cell efficiencies compared to physical vapor deposition of CdS. © 2011 American Institute of Physics.

We report on a comparative study of Cu(In,Ga)Se 2 solar cells deposited on soda-lime glass and mild steel substrates, using atom probe tomography in conjunction with secondary ion mass spectrometry, x-ray fluorescence, current density-voltage, and external quantum efficiency measurements. Cu(In,Ga)Se 2 films deposited on soda-lime glass substrates and on steel substrates with a NaF precursor layer on top of the Mo back contact contain a significant amount of Na impurities and yield an enhanced open circuit voltage and fill factor. Using atom probe tomography, Na atoms are found to be segregated at grain boundaries and clustered in both bulk and grain boundaries. The atom probe data indicate that Na Cu point defects are most likely formed at grain boundaries, reducing the number of compensating In Cu point defects and thus contributing to an enhanced cell efficiency. However, for steel substrates the positive effect of Na on the cell performance is counterbalanced by the incorporation of Fe impurities into the Cu(In,Ga)Se 2 film. Fe atoms are homogeneously distributed inside the grains suggesting that Fe introduces point defects in the bulk © 2011 American Institute of Physics.

This paper discusses the advantages of pulsed laser atom-probe tomography (APT) to analyze Cu(In,Ga)Se 2-based solar cells. Electron backscatter diffraction (EBSD) was exploited for site-specific preparation of APT samples at selected Cu(In,Ga)Se 2 grain boundaries. This approach is very helpful not only to determine the location of grain boundaries but also to classify them as well. We demonstrate that correlative transmission electron microscopy (TEM) analyses on atom-probe specimens enable the atom-probe datasets to be reconstructed with high accuracy. Moreover, EBSD and TEM can be very useful to obtain complementary information about the crystal structure in addition to the compositional analyses. The local chemical compositions at grain boundaries of a solar grade Cu(In,Ga)Se 2 film are presented here. Na, K, and O impurities are found to be segregated at grain boundaries. These impurities most likely diffuse from the soda lime glass substrate into the absorber layer during cell fabrication and processing. Based on the experimental results, we propose that Na, K, and O play an important role in the electrical properties of grain boundaries in Cu(In,Ga)Se 2 thin films for solar cells. © 2011 IEEE.

Using vibrational imaging techniques including Fourier-transform infrared (FTIR) synchrotron microscopy, Raman microscopy, and scattering scanning near-field infrared microcscopy (s-SNIM), we mapped a sample of phosphor and copper ions implanted in a high-purity silicon wafer. While Raman microscopy monitors the structural disorder within the implantation fields, the aforementionedinfrared techniques provide a detailed picture of the distribution of the free carriers. On a large scale (tens of micrometers), we visualized the channeling effects of phosphor dopants in silicon using FTIR microscopy. In comparison, using s-SNIM we were able to image, on a nanometer scale, local variations of the dielectric properties of the silicon substrate due to the activation of copper dopants. © 2011 American Institute of Physics.

We report the synthesis of layered [Zn 2(bdc) 2(H 2O) 2] and [Cu 2(bdc) 2(H 2O) 2] (bdc = benzdicarboxylate) metal-organic frameworks (MOF) carried out using the liquid-phase epitaxy approach employing self-assembled monolayer (SAM) modified Au-substrates. We obtain Cu and Zn MOF-2 structures, which have not yet been obtained using conventional, solvothermal synthesis methods. The 2D Cu 2+ dimer paddle wheel planes characteristic for the MOF are found to be strictly planar, with the planes oriented perpendicular to the substrate. Intercalation of an organic dye, DXP, leads to a reversible tilting of the planes, demonstrating the huge potential of these surface-anchored MOFs for the intercalation of large, planar molecules. © 2011 American Chemical Society.

Electrochemical reduction of the dacarbazine-Cu2+complex was investigated using cyclic voltammetry and square wave voltammetry at a hanging mercury drop electrode. The reduction of the dacarbazine-Cu2+complex is irreversible. A reduction mechanism is proposed comprising a one-electron reduction of the Cu2+directly within the complex. The sharp peak of the adsorbed dacarbazine-Cu2+complex associated with an effective interfacial accumulation facilitates the determination of the anticancer drug dacarbazine in pharmaceutical formulations and biological fluids. Detection limits for dacarbazine of 6.12×10-10M, 1.57×10-10M and 1.97×10-9M were achieved for the determination of the drug in vial, human urine and serum, respectively. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In the present work, the influence of small amounts of Bi and Sb on the microstructural evolution of Cu during an ingot metallurgy processing route is investigated. Both elements are known to segregate to grain boundaries in Cu. Cu ingots with an outer diameter of 40 mm containing 0.008 wt.% Bi and 0.92 wt.% Sb, respectively, were vacuum induction melted, cast, and gradually swaged down to a final diameter of 11.7 mm with several intermediate annealing steps. Subsequent annealing treatments were conducted to investigate the microstructural evolution of the swaged bars. Optical microscopy, hardness testing and orientation imaging microscopy were used to characterize the deformation and recrystallization behavior, as well as the evolution of texture in the alloys. The results are then compared to those obtained for pure Cu. It is shown that even small amounts of alloying elements significantly alter the hardening behavior and suppress recrystallization at low temperatures. At higher temperatures, recrystallization in Cu, Cu-Bi and Cu-Sb leads to different textures. © 2011 Elsevier B.V. All rights reserved.

μLaue diffraction sheds light onto the deformation behavior of miniaturized samples. Here we present a new instrumental setup for the in situ deformation of micron sized specimens at BM32 of the ESRF synchrotron source. Furthermore, a compression test of a 7 μm sized single slip oriented copper pillar is presented, showing the activation of an unpredicted slip system due to misalignment and the formation of several sub-grains. The results of the compressed pillar as well as possibilities and crucial points for measuring and data evaluation are discussed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fatigue experiments on copper have shown that vacancy production leads to the evolution of extrusions, which are the preferred sites for fatigue crack initiation. However, experimental, analytical and numerical results for the critical edge-dislocation dipole annihilation distance vastly differ. This study performs molecular statics and molecular dynamics simulations at elevated temperature to investigate the discrepancies in annihilation distance. Vacancy forming edge dislocation dipoles are stable if their spacing exceeds 2 lattice spacings. If the dislocation dipole is perpendicular to the free surface in a thin sheet of material, jogs on edge dislocations lead to dipole annihilation. Our main conclusion is that dislocation generation, glide and stable edge dislocation dipoles are sufficient to lead to that extrusion growth, which results in fatigue crack initiation.

In the present work, the processing parameters which govern the evolution of microstructure during rotary swaging and intermediate/subsequent heat treatments in copper rods were studied. Copper ingots with an initial diameter of 40 mm were reduced to a final diameter of 11.7 mm by rotary swaging. Processing sequences were applied with different intermediate anneals and various final heat treatments. The resulting microstructures were characterized using orientation imaging microscopy, optical microscopy and hardness measurements. Special emphasis was placed on the evolution of microstructure with respect to the radial and longitudinal position in the rod. Most importantly, microstructural evidence for torsional loading during swaging was found, and a spiral grain morphology was observed. Moreover, localized deformation events were identified and evidence for abnormal grain growth was found. Finally, a combination of swaging and heat treatment parameters was identified which allowed a homogeneous grain structure to be produced. © Carl Hanser Verlag GmbH & Co. KG.

Thin films of [Cu3(btc)2]n (btc = 1,3,5-benzenetricarboxylate) metal organic framework were deposited in a stepwise manner on surfaces of flexible organic polymers. The thickness of films can be precisely controlled. The deposition of the first cycles was monitored by UV-vis spectroscopy. The porosity was proven by the adsorption of pyrazine, which was monitored by FT-IR and thermogravimetric analysis. The deposition of MOF thin films on flexible polymer surfaces might be a new path for the fabrication of functional materials for different applications, such as protection layers for working clothes and gas separation materials in the textile industry. © 2011 The Royal Society of Chemistry.

This paper presents the results of nanoindentation experiments on Cu single crystals and Cu grains in through silicon via (TSV) structures used for 3D integrated circuit (IC) stacking, at sub-10nm and several-10nm penetration depths. The reduced moduli for Cu single crystals change from an average value to the uni-directional values, as the penetration depths decrease from several-10nm to sub-10nm. At sub-10nm deformation, about one third of the indentations on Cu(111) and Cu(110) show fully elastic behavior, while all indentations on Cu(100) shows elastic-plastic behavior. The reduced modulus values extracted from indents on Cu(111) and Cu(110) with fully elastic behavior are about 195GPa and 145GPa, respectively. For penetration depths of several-10nm up to 50nm, the reduced modulus for Cu(100) varies between 50GPa to 100GPa. The averaged reduced moduli determined at relatively large penetration depths are explained with lattice rotation beneath the indentations. Since the activation of multiple slip systems is required for lattice rotation, the transition of the unidirectional reduced modulus to the averaged value with increasing penetration depths occurs differently for Cu(111) and Cu(100). Similar to the results from Cu single crystals, unidirectional reduced moduli are obtained for the Cu grains in TSV structures at sub-10nm penetration depths. © 2011 American Institute of Physics.

In order to shed more light on the role of magnetic gradient forces and Lorentz forces on the deposition pattern found recently at copper electrodes, experiments and numerical simulations have been performed in a simple geometry that consists of a single small cylindrical permanent magnet which is placed behind the cathode. The cylinder axis coincides with the magnetization direction and points normal to the electrode surface. The electrode is oriented vertically which allows a separate discussion of the influence of both forces. Experiments and numerical simulations are found to give very good qualitative agreement with respect to the deposition pattern. Our analysis clearly shows that the major influence is due to the action of the magnetic gradient force. Numerical simulations prove that the separate action of the Lorentz force does not reproduce the deposition structure. A detailed analytical discussion of the motion forced by the different magnetic forces in superposition with natural convection is given. © 2010 Elsevier Ltd All rights reserved.

Improving the functional stability of shape memory alloys (SMAs), which undergo a reversible martensitic transformation, is critical for their applications and remains a central research theme driving advances in shape memory technology. By using a thin-film composition-spread technique and high-throughput characterization methods, the lattice parameters of quaternary Ti-Ni-Cu-Pd SMAs and the thermal hysteresis are tailored. Novel alloys with near-zero thermal hysteresis, as predicted by the geometric nonlinear theory of martensite, are identified. The thin-film results are successfully transferred to bulk materials and near-zero thermal hysteresis is observed for the phase transformation in bulk alloys using the temperaturedependent alternating current potential drop method. A universal behavior of hysteresis versus the middle eigenvalue of the transformation stretch matrix is observed for different alloy systems. Furthermore, significantly improved functional stability, investigated by thermal cycling using differential scanning calorimetry, is found for the quaternary bulk alloy Ti50.2Ni34.4Cu12.3Pd3.1 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ti-Ni-Cu shape memory thin films within a broad composition range were investigated by the cantilever deflection method using combinatorial methods. Optimal compositions with improved functional properties, i.e.large recovery stress, high transformation temperatures, low thermal hysteresis width and small temperature interval of transformation, were identified using a newly defined figure of merit. Of the investigated alloys, Ti50Ni 41Cu9 and Ti45Ni46Cu9 exhibit the best shape memory properties for compositions showing a B2 → B19 and a B2 → R-phase transformation, respectively. © 2010 IOP Publishing Ltd.

The superconducting feedback resonance in inelastic neutron scattering (INS) has now been found in numerous unconventional superconductors of the cuprate, ferropnictide, and heavy fermion classes. The collective spin excitation appears below T c at an energy less than the quasiparticle threshold with momentum Q provided the gap changes sign under translation by Q. The resonance has been found in the heavy fermion (HF) superconductors CeCu 2Si 2, CeCoIn 5, and UPd 2Al 3, and recently in Fe-pnictide Ba 1-xK xFe 2As 2, BaFe 2-xCo xAs 2, BaFe 2-xNi xAs 2, and FeSe 1-xTe x compounds and may be a more general phenomenon. Of particular interest is the interaction of the 3d spin exciton with the 4f crystalline electric field (CEF) excitations in rare earth based unconventional superconductors like CeFeAsO 1-xF x pnictide and Nd 2-xCe xCuO 4 cuprate where a coupling between 3d spin resonance and 4f CEF excitations leads to intriguing interaction effects observed experimentally by INS. © The Author(s) 2010.

Micro-sized polycrystalline copper wires of diameters ranging from 5 μm to 36 μm were cyclically loaded under stress-control in many steps with increasing the applied stress amplitude after a saturation state in plastic strain is reached. It is observed that the thicker wires show smaller plastic strain at saturation as well as smaller creep strain compared to the thinner wires. The results were discussed combined with the monotonic tensile results of these micro-sized wires. © 2010 Published by Elsevier Ltd.

Single crystalline copper beams with thicknesses between 0.7 and 5 μm are manufactured with a focused ion beam technique and bent in a nanoindenter. The yield strengths of the beams show a mechanical size effect (smaller-is-stronger). The geometrically necessary dislocation (GND) densities estimated from misorientation maps do not explain the observed size effect. Also, accumulation of GNDs principally requires pre-straining. We hence introduce a mean-field breakdown theory and generalize it to small-scale mechanical tests other than bending. The mean-field breakdown limit is defined in terms of a microstructural correlation measure (characteristic dislocation bow-out length) below which the local availability of dislocation sources and not the density of GNDs dominates the mechanical size effect. This explains why a size dependence can occur for samples that are not pre-strained (by using a very small critical strain to define the yield strength). After pre-straining, when GNDs build up, they can contribute to the flow stress. The mean-field breakdown theory can also explain the large scatter typically observed in small-scale mechanical tests as the availability of sufficiently soft sources at scales around or below the correlation length does not follow statistical laws but highly depends on the position where the probe is taken. © 2009 Acta Materialia Inc.

Synthesis of ω-Al-Cu-Fe single phase material is reported. Microhardness tests performed over the temperature range 293-898K indicate a brittle-to-ductile transition between 673K and 823K. Fracture toughness was determined from indentation cracks at 293K. Both the hardness and fracture toughness are comparable to that of the icosahedral Al0.635Cu0.240Fe0.125 material. © 2010 Elsevier B.V.

X-ray amorphous thin films of the Heusler alloys Cu2MnAl and Co2MnSi have been prepared by magnetron sputter deposition at room temperature. In the amorphous state the Cu2MnAl phase is non-ferromagnetic; Co2MnSi is weakly ferromagnetic with a ferromagnetic Curie temperature of 170 K. By solid-state crystallization at high temperatures strong ferromagnetic order and high Curie temperatures are established in both alloys. The saturation magnetization of the Co 2MnSi alloy reaches 5.1μB/f.u. at 4 K, corresponding to 100% of the theoretical value; for Cu2MnAl we obtain 2.8μB/f.u. at 4 K, which corresponds to 87.5% of the theoretical value. In samples of the Co2MnSi phase with optimum saturation magnetization Bragg reflections as indicators of a long-range chemical order are missing, whereas for the Cu2MnAl phase Bragg reflections confirm epitaxial quality and long-range L21 order. © 2010 IOP Publishing Ltd.

We investigate the distance distribution of two anorganic molecules (CO, H2O), one organic radical (parabenzyne), and one strongly dipolar molecule (ortho-dinitrobenzene) on the (111) faces of copper and silver. Above the onset of diffusion, their distribution is influenced by the surface state and oscillates. While CO, H2O, and para-benzyne show the expected oscillation period of ≈λF / 2, ortho-dinitrobenzene oscillates with λF / 4. The position of the first maximum in these oscillations is consistent with a perfect scatterer for the anorganic molecules, but inconsistent for the radical and the dipolar molecule. This observation is utilized to explain the double periodicity observed in the distance distribution of ortho-dinitrobenzene. © 2010 Elsevier B.V. All rights reserved. All rights reserved.

Ab initio calculations are becoming increasingly important for designing new alloys as these calculations can accurately predict basic structural, mechanical, and functional properties using only the atomic composition as a basis. In this paper, fundamental physical properties (like formation energies and elastic constants) of a set of bcc Mg-Li and Mg-Li-based compounds are calculated using density functional theory (DFT). These DFT-determined properties are in turn used to calculate engineering parameters such as (i) specific Young's modulus (Y/p) or (ii) shear over bulk modulus ratio (G/B) differentiating between brittle and ductile behavior. These parameters are then used to identify those alloys that have optimal mechanical properties for lightweight structural applications. First, in case of the binary Mg-Li system, an Ashby map containing Y/r versus G/B shows that it is not possible to increase Y/r without simultaneously increasing G/B (i.e., brittleness) by changing only the composition of a binary alloy. In an attempt to bypass such a fundamental materials-design limitation, a set of Mg-Li-X ternaries (X=Ca, Al, Si, Cu, Zn) based on stoichiometric Mg-Li with CsCl structure was studied. It is shown that none of the studied ternary solutes is able to simultaneously improve both specific Young's modulus and ductility. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

We present a fully flexible and ab initio-derived molecular mechanics force field for the ubiquitous copper paddle-wheel building block Cu2 (O2C)4 in metal-organic frameworks. The force field expression is based on the established MM3 force field, extended by additional cross terms and specific bond-stretching and anglebending terms for the square-planar CuO4 coordination environment. Using reference data computed at the DFT level for nonperiodic reference systems, the parametrization is performed using an automated genetic algorithm optimization strategy in order to reproduce structure and low normal modes of the model systems. It is validated on the much investigated Cu-btc (HKUST-1) metal-organic framework. Beyond the structure, lattice-dynamic-dependent properties such as the bulk modulus and the observed negative thermal expansion effect of Cu-btc are quantitatively predicted by the force field without recourse with respect to experimental data. In connection with available parametrizations of various organic linkers, it can be useful for aiding the structure determination of known MOFs, but it also paves the way for the computational prescreening of yet unknown copper paddle-wheel-based frameworks. © 2010 American Chemical Society.

Highly loaded copper catalysts supported on alumina are synthesized applying the cyclic two-step CVD of the precursor copper(II)diethylamino-2- propoxide in a fluidized-bed reactor. Copper/zinc oxide/alumina composites are synthesized by either the CVD of the precursor bis[bis (trimethylsilyl) amido]zinc on Cu/Al2O3, or the CVD of the Cu precursor on Zn-pretreated alumina, impregnating with diethyl zinc in addition. The composites are extensively characterized by atomic absorption spectroscopy (AAS), elemental analysis (EA), mass spectrometry (MS), N2 physisorption, N2O reactive frontal chromatography (RFC), and X-ray diffraction (XRD). The Cu and ZnO nanoparticles originating from the efficient two-step procedure, consisting of adsorption and subsequent decomposition of the adsorbed species in two separated steps, are highly dispersed, X-ray amorphous, and, in the case of the Cu-containing catalysts, have high specific Cu surface areas. The catalytic activities are determined both in methanol synthesis, to judge the contact between the deposited Cu and ZnO nanoparticles, and in the steam reforming of methanol (SRM) to probe the stability of the Cu particles. The turn-over frequencies (TOF) in methanol synthesis of these Cu/ZnO/Al 2O3 catalysts are higher than that of a commercial ternary catalyst. The varied sequence of the CVD of Cu and ZnO on alumina leads to catalysts with similar activities in the case of similar specific Cu areas. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanoscale copper was selectively photodeposited onto the surface of hexadecylamine (HDA) stabilized (monodispersed not agglomerated) ZnO nanoparticles (NPs) of a diameter of 2-5 nm, which leads to HDA-stabilized Cu/ZnO NPs of varied Cu loading. The particles are soluble in non-polar organic solvents. The line broadening and the red shift of the surface plasmon band of Cu/ZnO NPs relative to HDA-stabilized Cu NPs, the profound decrease of the Cu/ZnO NPs visible photoluminescence at 525 nm, the increase of the UV emission intensity at 365 nm and the enhancement of the Raman scattering (RS) intensity in comparison to the parent ZnO NPs confirmed the interfacial contact between the Cu and ZnO phase. © 2010 the Owner Societies.

Electroplated copper films are known to change their microstructure due to the self-annealing effect. The self-annealing effect of electroplated copper films was investigated by measuring the time dependence of the film stress and sheet resistance for different layer thicknesses between 1.5 and 20 μm. While the sheet resistance was found to decrease as time elapsed, a size-dependent change in film stress was observed. Films with the thickness of 5 μm; and below decrease in stress, while thicker films initially reveal an increase in film stress followed by a stress relaxation at a later stage. This behavior is explained by the superposition of grain growth and grain-size-dependent yielding. © 2010 IEEE.

Structured copper layers were prepared by superimposition of inhomogeneous magnetic fields during the electrodeposition process. Self-made magnetic field templates were utilized for this purpose in order to demonstrate that even moderate magnetic flux densities applied at the working electrode are sufficient for this new structuring technique. The structuring effect was demonstrated for use of magnetic stray fields of magnetized Fe-wires as well as of permanent NdFeB-magnets. It was found that maxima of deposit thickness result in regions of maximum magnetic flux density. On the contrary, thickness minima are observed where the magnetic flux density at the working electrode is low. The results are discussed with respect to the acting magnetic forces and their influence on the deposition process. ©The Electrochemical Society.

We study the Bauschinger effect on a bent and straightened micro-sized single-crystal copper beam (width: 8.64 lm; thickness: 7.05 lm) over three consecutive cycles. The reverse yield strengths (straightening step) are much smaller than those in forward loading (bending step). An upper bound estimate shows a load drop of 73% (1st cycle), 76% (2nd cycle) and 83% (3rd cycle) relative to the forward yield stress. Electron backscatter diffraction reveals a dramatic reduction in the bending-induced misorientation gradients upon load reversal (straightening), documenting an unexpected form of microstructure reversibility. The observed Bauschinger softening is interpreted in terms of two effects. The first consists of internal backstresses that support load reversal. They are created by polarized dislocation arrays that are accumulated during forward bending. The second effect is the reduced requirement to activate dislocation sources during reverse loading as the dislocations that were stored during bending did not participate much in cross-hardening and, hence, serve as mobile dislocations upon reverse loading. After straightening the misorientation gradients are largely removed but the non-polarized dislocations remain. We therefore introduce a revised terminology, namely the "mechanical Bauschinger effect" and the "microstructural Bauschinger effect". The former term describes a yield stress drop and the latter one the degree of microstructure reversibility upon load path changes. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The self-annealing effect of electroplated copper films was investigated by measuring the time dependence of the film stress for different film thicknesses between 1.5μm and 20μm. This recrystallization process results in significant microstructure change and a film-thickness-dependent stress evolution at room temperature. This behavior can be explained by the superposition of grain growth and grain size dependent yielding. Existing models have been used and improved to describe the mechanisms related to stress evolution. © 2010 IEEE.

New emerging technologies in the field of flexible electronic devices require that metal films adhere well and flex with polymer substrates. Common thin film materials used for these applications include copper (Cu) with an adhesion interlayer of chromium (Cr). Copper can be quite ductile and easily move with the polymer substrate. However, Cr is more brittle and fractures at lower strains than Cu. This study aims to examine the fracture and subsequent buckling and delamination of strained Cr films on polyimide (PI). In-situ scanning electron microscope (SEM) straining is used to systematically study the influence of film thickness on fracture and buckling strains. Film fracture and delamination depend on film thickness, and increases in crack and buckle density with decreasing thickness are explored by a shear lag model. © 2009 The Minerals, Metals & Materials Society and ASM International.

Body centered cubic (bcc) Mg-Li-based alloys are a promising light-weight structural material. In order to tailor the Mg-Li composition with respect to specific industrial requirements, systematic materials-design concepts need to be developed and applied. Quantum-mechanical calculations are increasingly employed when designing new alloys as they accurately predict basic thermodynamic, structural, and functional properties using only the atomic composition as input. We have therefore performed a quantum-mechanical study using density functional theory (DFT) to systematically explore fundamental physical properties of a broad set of bcc MgLi-based compounds. These DFT-determined properties are used to calculate engineering parameters such as (i) the specific Young's modulus (Y/ρ) or (ii) the bulk over shear modulus ratio (B/G) which allow differentiating between brittle and ductile behavior. As we have recently shown, it is not possible to increase both specific Young's modulus, as a measure of strength, and B/G ratio, as a proxy for ductility, by changing only the composition in the binary bcc Mg-Li system. In an attempt to bypass such fundamental materials-design limitations, a large set of MgLi-X substitutional ternaries derived from stoichiometric MgLi with CsCl structure are studied. Motivated by the fact that for Mg-Li alloys (i) 3rd row Si and Al and (ii) 4th row Zn are industrially used as alloying elements, we probe the alloying performance of the 3rd (Na, Al, Si, P, S, Cl) and 4th row transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) elements. The studied solutes offer a variety of properties but none is able to simultaneously improve both specific Young's modulus and ductility. Therefore, in order to explore the alloying performance of yet a broader set of solutes, we predict the bulk modulus of MgX and LiX B2-compounds running over 40 different elements. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Electrochemical Cu deposition was performed from electrolytes containing 0.1-1 M CuSO4 in a well-defined magnetic gradient field. Patterned deposits resulted in all cases showing a strong correlation to this gradient field. It was observed that with increasing Cu2+ concentration the structuring effect decreases in terms of differences in topography and morphology. An explanation of this effect is presented based on local convection induced by the magnetic field gradient force which is dependent on the concentration gradient established during the deposition. Superimposed effects of Lorentz force driven convection were observed for high Cu2+ concentrations, and their influence on the deposition process was discussed. © 2010 Elsevier Ltd.

Molecular dynamics (MD) simulations were performed of the structural changes occurring through the liquid-glass transition in Cu-Zr alloys. The total scattering functions (TSF), and their associated primary diffuse scattering peak positions (Kp), heights (Kh) and full-widths at half maximum (KFWHM) were used as metrics to compare the simulations to high-energy X-ray scattering data. The residuals of difference between the model and experimental TSFs are ∼0.03 for the liquids and about 0.07 for the glasses. Over the compositional range studied, Zr1-xCux (0.1 ≤ x ≤ 0.9), Kp, Kh and KFWHM show a strong dependence on composition and temperature. The simulation and experimental data correlate well between each other. MD simulation revealed that the Cu-Zr bonds undergo the largest changes during cooling of the liquid, whereas the Cu-Cu bonds change the least. Changes in the partial-pair correlations are more readily seen in the second and third shells. The Voronoi polyhedra (VP) in glasses are dominated by only a few select types that are compositionally dependent. The relative concentrations of the dominant VPs rapidly change in their relative proportion in the deeply undercooled liquid. The experimentally determined region of best glass formability, xCu 65%, shows the largest temperature dependent changes for the deeply undercooled liquid in the MD simulation. This region also exhibits very strong temperature dependence for the diffusivity and the total energy of the system. These data point to a strong topological change in the best glass-forming alloys and a concurrent change in the VP chemistry in the deeply undercooled liquid. © 2010 Taylor & Francis.

The aim of this work is to investigate the microstructure evolution, stressstrain response and strain hardening behavior of microscale beams. For that purpose, two single crystal cantilever beams in the size dependent regime were manufactured by ion beam milling and beams were bent with an indenter device. A crystal plasticity material model for large deformations was implemented in a finite element framework to further investigate the effect of boundary constraints. Simulations were performed using bulk material properties of single crystal copper without any special treatment for the strain gradients. The difference between the slopes of the experimental and the simulated force displacement curves suggested negligible amount of strain gradient hardening compared to the statistical hardening mechanisms. © 2010 Elsevier Ltd. All rights reserved.

A new ferromagnetic shape memory thin film system, Fe-Pd-Cu, was developed using ab initio calculations, combinatorial fabrication and high-throughput experimentation methods. Reversible martensitic transformations are found in extended compositional regions, which have increased fcc-fct transformation temperatures in comparison to previously published results. High resolution transmission electron microscopy verified the existence of a homogeneous ternary phase without precipitates. Curie temperature, saturation polarization and orbital magnetism are only moderately decreased by alloying with nonmagnetic Cu. Compared to the binary system; enhanced Invar-type thermal expansion anomalies in terms of an increased volume magnetostriction are predicted. Complementary experiments on splat-fabricated bulk Fe-Pd-Cu samples showed an enhanced stability of the disordered transforming Fe70Pd30 phase against decomposition. From the comparison of bulk and thin film results, it can be inferred that, for ternary systems, the Fe content, rather than the valence electron concentration, should be regarded as the decisive factor determining the fcc-fct transformation temperature. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

An in situ tensile rig is proposed, which allows performing electrochemical (repassivation) experiments during dynamic mechanical testing of wires. Utilizing the basic components of a conventional tensile tester, a custom-made minitensile rig was designed and fabricated. The maximal force that can be measured by the force sensor is 80 N, with a sensitivity of 0.5 mV/V. The maximum travel range of the crosshead induced by the motor is 10 mm with a minimum step size of 0.5 nm. The functionality of the tensile test rig was validated by investigating Cu and shape memory NiTi wires. Wires of lengths between 40 and 50 mm with varying gauge lengths can be tested. An interface between wire and electrochemical setup (noncontact) with a smart arrangement of electrodes facilitated the electrochemical measurements during tensile loading. Preliminary results on the repassivation behavior of Al wire are reported. © 2010 American Institute of Physics.

Metal stearate-stabilized Cu nanoparticles, synthesized by an efficient one-step process, were applied in the continuous liquid-phase synthesis of methanol. After optimizing the reduction procedure, twofold higher rates of methanol formation were found for Cu-Zn colloids, compared to the conventional ternary Cu/ZnO/Al2O3 catalyst applied as fine powder in the liquid phase. Structural changes were investigated as a function of time on stream; after reduction in H2, spherical, well-separated 5-10 nm Cu particles stabilized by a Zn stearate shell were found. Under catalytic high-pressure conditions Zn stearate was hydrolyzed forming ZnO. High-resolution transmission electron microscopy revealed the presence of triangular ZnO prisms with truncated edges. Applying optimized synthesis conditions these triangularly shaped ZnO particles were found to be mostly attached to the spherical Cu particles. The catalytic results and the structural and spectroscopic characterization suggest that these ZnO particles act as a reservoir, releasing ZnOx species, which diffuse onto the Cu particles and promote the catalytic activity. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We investigate the formation of microscopic patterns in a copper single crystal deformed in a shear experiment. Using high-resolution electron backscatter diffraction imaging, we find a band-like microstructure consisting of confined areas in the sample with rotated lattice. Digital image correlation allows us to exactly determine the macroscopic state of deformation of the sample. This data can be used as a side condition to calculate the lamination parameters from the theory of kinematically compatible lamination of separate material regions, each deforming in single slip. The parameters given by the theory agree with the measured properties, i.e. a lattice rotation of 3° and a lamination normal rotated 7° counterclockwise from a 〈111〉 direction. © 2009 Acta Materialia Inc.

Paramagnetic Cu2+-ions have been electrodeposited under application of magnetic field gradients. Obtained deposits show a direct correlation of the distribution of magnetic flux density B at the electrode and the deposit thickness and morphology. In contrast to that no influence on the deposit structure has been observed for deposition of Bi from electrolytes containing diamagnetic Bi3+-ions. This indicates that the structuring effect is mainly based on the action of the magnetic gradient force. A structuring-mechanism has been proposed that also discusses influences of the Lorentz force. © 2009 Elsevier B.V. All rights reserved.

This work is focused on a joint experimental and theoretical characterization of M(hfa)2·TMEDA complexes [M=Cu, Co; hfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA=N,N,N′,N′- tetramethylethylenediamine], innovative CVD precursors for Cu-Co oxides. The structural, vibrational and thermal properties of the above compounds, as well as their fragmentation pathways, have been thoroughly analyzed by Fourier Transform Infrared Spectroscopy (FT-IR), Electrospray Ionization Mass Spectrometry (ES1-MS) and tandem Mass Spectrometry (MS/MS), ThermoGravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC). Results obtained by the above techniques have been integrated by ab-initio Density Functional Theory (DFT) calculations. The most relevant results, with particular regard to CVD applications of the target compounds, are presented and discussed. © The Electrochemical Society.

Micro-sized polycrystalline copper wires with diameters of 30 μm and 50 μm and mean grain sizes of 12 μm and 20.5 μm respectively were cyclically loaded under stress control over a life range of 1 × 102-4.7 × 105 cycles using a recently developed fibre tensile loading frame at frequencies of 2-9.9 Hz. This frame fits into a scanning electron microscope for in situ deformation and fatigue studies. The fatigue life of the thicker wires, compared to that of the thinner ones, was found to be longer at higher applied stress amplitude range, but shorter at lower applied stress amplitude range. The measurements of the elongation versus the number of cycles revealed three distinct regimes with different slopes, corresponding to different microstructural changes. The total elongation of the wire during the cyclic loading with a low applied stress amplitude was analysed with respect to microstructural changes observed in situ in a scanning electron microscope. © 2009 Elsevier B.V. All rights reserved.

The superconducting penetration depth λ(T) has been measured in RFeAsO0.9F0.1 (R=La, Nd) single crystals (R-1111). In Nd-1111, we find an upturn in λ(T) upon cooling and attribute it to the paramagnetism of the Nd ions, similar to the case of the electron-doped cuprate Nd-Ce-Cu-O. After the correction for paramagnetism, the London penetration depth variation is found to follow a power-law behavior, ΔλL(T) T2 at low temperatures. The same T2 variation of λ(T) was found in nonmagnetic La-1111 crystals. Analysis of the superfluid density and of penetration depth anisotropy over the full temperature range is consistent with two-gap superconductivity. Based on this and on our previous work, we conclude that both the RFeAsO (1111) and BaFe2As2 (122) families of pnictide superconductors exhibit unconventional two-gap superconductivity. © 2009 The American Physical Society.

The use of copper phthalocyanine as the copper precursor extremely diluted in a silica matrix (below 0.1%) was found to result in a very active catalyst in the selective oxidation of propene by oxygen to produce acrolein with selectivities above 50% and yields of ∼ 10%. © The Author(s) 2009.

A highly efficient one-step process to generate Cu-Zn colloids was developed, in which the colloidal particles were synthesized from Cu and Zn stearates by reduction with H2 in a continuously operated stirred tank reactor. The resulting spherical, well separated particles have a size of 5-10 nm, consisting of a crystalline Cu0 core (fcc) stabilized by a Zn stearate shell without long-range order. In situ attenuated total reflection FTIR spectroscopy was used to monitor the shift of the C-O stretching vibration of adsorbed CO as a function of temperature and pressure. The absence of the CO rotation-vibration bands of dissolved CO allowed us to obtain FTIR spectra at a CO pressure of 1.0 MPa at 473 K resulting in three shifted CO bands at 2030-2025, 1979-1978, and 1920 cm-1. These bands indicate the presence of reduced coadsorbed Zn species on the metallic Cu surface. Cyclic CO adsorption experiments demonstrated the dynamics of the interaction between the Cu core and the Zn stearate shell. © 2009 the Owner Societies.

Electropolishing of NiTiCu shape memory alloy was performed in methanolic sulfuric acid as a surface processing method. The current investigation, using a rotating disk electrode, aims at identifying appropriate electropolishing conditions for this alloy based on understanding the underlying mechanism. The influence of temperature, rotation rate, and sulfuric acid concentration (3 or 5 M H2 S O4) was quantified. Electropolishing in methanolic 5 M H2 S O4 is solely mass-transport-controlled, while a mixed control is found for the methanolic 3 M H2 S O4. This behavior is different from that of the binary NiTi alloy. From the electrochemical perspective, a methanolic 5 M H2 S O4 solution is more suitable for electropolishing NiTiCu. The activation energy for electrodissolution is 21.5 kJ mol-1. © 2008 The Electrochemical Society.