Cluster model studies on oxygen sites at the (010) surfaces of V2O5 and MoO3

Cluster model studies have been performed to examine the electronic structure and adsorption properties near structurally different oxygen sites at the (010) surfaces of vanadium pentoxide, V₂O₅, and molybdenum trioxide, MoO₃. In addition, adsorption of hydrogen at the oxygen sites and desorption of OH groups has been studied in order to find site specific differences. The electronic properties and total energies of the clusters have been obtained from ab initio density functional theory (DFT) calculations. The surface oxygen sites are found to be ionic where bridging oxygens become more negative than terminal ones. Further, hydrogen adsorbs at all oxygen sites where binding is strongest at the bridge sites on the V₂O₅(010) surface whereas on MoO₃(010) the terminal sites are preferred. The latter difference can be understood by simple geometric arguments. Surface OH groups formed by H adsorption and involving terminal oxygens are strongly bound to the surface whereas those involving bridging oxygens are mobile and become available for subsequent reactions.     

Surface metallization of Cu/Ni/Au coatings on diamond/Cu composite materials for heat sink application

Electroless-plating and electro-plating have been used to deposit Cu-Ni-Au coating on diamond/Cu composites. Before electroless copper plating, pretreatment should be applied to the surface of composites by means of boiled HNO₃ etching, sensitization with SnCl₂ and activation with PdCl₂. The influence of pre-treatment on the electroless copper plating and electroplating Ni/Au is studied in this paper. Scanning electronic microscope, energy dispersive spectroscopy and optical microscope are used to examine microstructure and morphologies of coatings. Results indicated that the uniform and tight bonded Cu/Ni/Au coating have been successfully deposited on the diamond/Cu composites. Meanwhile, high temperature baking, solder wetting and the polarization curve tests are used to evaluate the adhesion strength, solderability and corrosion resistance of Cu/Ni/Au coatings in detail. Investigated results indicated that diamond/Cu covered with Cu-Ni-Au coatings exhibited excellent solderability and mechanical properties.     

铜基超疏水表面防覆冰/抗霜冻特性分析

超疏水表面具有良好的防覆冰性能,有望改善低温条件下设备和设施的可靠性。本文采用氨气腐蚀法,制备具有微纳结构的铜表面,通过低表面能氟硅烷修饰后,金属铜表面表现出超疏水特性,其水接触角可达152.1°。利用电镜扫描、接触角测量、结冰和结霜实验分别对超疏水铜表面的表面结构、湿润性能和防覆冰性能进行研究。结果表明,超疏水表面的防覆冰/抗霜冻性能不仅与表面的粗糙度有关,还受液滴在固体表面的湿润状态的影响。当液滴在具有微-纳米结构的超疏水表面处于Cassie状态时,液滴与金属表面的接触面积小,液滴结冰速率较慢,金属表面同时具有较好的防覆冰和抗结霜性;而当液滴在金属疏水表面处于Wenzel状态时,霜晶与固体表面的接触面积增加,加快霜层的生长,金属表面的抗结霜性明显降低。     

Density functional studies of the electronic structure and adsorption at molybdenum oxide surfaces

The electronic structure and bonding at different oxygen sites of MoO₃(0 1 0) and (1 0 0) surfaces is reviewed on the basis of ab initio density functional theory (DFT-LCGTO) cluster calculations. The clusters are chosen as finite sections of the ideal MoO₃ surface where cluster embedding is achieved by bond saturation with hydrogen terminator atoms yielding clusters up to Mo₇O₃₀H₁₈. Resulting charge density distributions and binding properties are analyzed by populations, bond orders, and electrostatic potential maps. Interatomic binding at the surface is determined by both ionic and covalent contributions with a clear distinction between terminal oxygens and different bridging surface oxygens. Electronic differences between the MoO₃ (0 1 0) and (1 0 0) surfaces are found to be mainly due to the different atom arrangement while local atom charging and binding properties seem surface independent. The electronic surface parameters influence the behavior and reactions of adsorbed molecules as will be shown for H, OH, and C₃H₅ adsorbates.     

Growth of Copper on Single Crystalline ZnO: Surface Study of a Model Catalyst

Copper, vapor-deposited on the polar, Zn-terminated ZnO(0001) surface is investigated in view of its suitability as model system for the technologically important Cu/ZnO catalyst. The structure and electronic properties of Cu clusters on ZnO(0001)–Zn have been studied with scanning tunneling microscopy (STM), low energy electron diffraction (LEED), ultraviolet photoelectron spectroscopy (UPS), and low-energy He⁺ ion scattering (LEIS). At room temperature copper grows as two-dimensional (2D) clusters only at very low coverages of 0.001–0.05 equivalent monolayers (ML). At coverages greater than 0.01 ML, 3D clusters start to develop. This is contrasted to Cu growth on the oxygen-terminated ZnO(0001bar) surface, where a strong adhesion between Cu and the ZnO substrate results in an initial wetting of the surface by Cu. On ZnO(0001)–Zn, surface roughness and sputter damage change the growth mode to more 2D-like. Annealing in UHV results in well-separated, hexagonal clusters rotationally aligned with the substrate. Annealing of 2–5 ML Cu deposits on the ZnO(0001)–Zn surface in 10⁻⁶ mbar O₂ results in the formation of a (√3 × √3)R30° superstructure with respect to the ZnO lattice. This superstructure likely contains Cu⁺ sites. The suitability of the different surface morphologies to probe specific sites that are thought to be active for catalytic processes is discussed.     

Strained thin copper films as model catalysts in the materials gap

Thin copper films on silicon constitute model systems to investigate the influence of lattice strain on activity in heterogeneous catalysis. Thin copper films on silicon were investigated by ultraviolet photoelectron spectroscopy (UPS) to reveal the effect of strain in the copper films on the electronic structure of the surface. For cleaned and adsorbate-free surfaces, no effect of strain on the electronic structure was detected by UPS. Conversely, an oxygen-containing film exhibited a distinct effect of strain induced by cyclic heating and cooling on the electronic structure. Comparison with studies on a Cu single crystal under methanol oxidation reaction conditions revealed a characteristic hysteresis behavior in both the adsorbate structure and the catalytic properties of the metal surface. Hence, copper model systems that are suitable to unravel the correlation between strain and catalytic activity need to take the disordered microstructure of ‘‘real’’ copper catalysts into account. The present experiments reveal the correlation between surface restructuring and catalysis on the one side and the influence of lattice strain on either restructuring or the electronic structure of the surface on the other side.     

Copper–zinc particles with zinc-enriched surfaces generated via spray pyrolysis

Copper is an inexpensive replacement for silver in electronic applications such as solar cell metallization, electromagnetic interference packaging, and printable electronics. However, copper has a characteristically low reduction potential under ambient conditions, favoring formation of non-conducting copper oxides. Here, a spray pyrolysis method of producing oxidation resistant copper particles with surfaces rich in zinc, without need for post-fabrication modifications is described. The effects of precursor and reactor parameters on the particle surface composition with respect to the bulk composition are explored. At reactor temperature conditions of 1000?°C with a precursor containing 90 at% copper–10 at% zinc, the formation of desired morphologies was achieved, smooth dense particles with surfaces enriched in zinc. Increasing the concentration of zinc in the precursor did not improve enrichment, and instead led to the formation of a zinc diamine chloride [Zn(NH₃)₂Cl₂] byproduct.

© 2018 American Association for Aerosol Research     

纤维增强PA6/HDPE复合材料的性能

制备不同配比的碳纤维(CF)、玻璃纤维(GF)增强PA6/HDPE复合材料.对其摩擦磨损性能和力学性能进行测试,用显微镜对复合材料拉伸断面进行观察.结果表明:碳纤和玻纤对PA6/HDPE复合材料的摩擦磨损性能和力学性能均有一定的改善作用,其中碳纤质量含量为3％时对PA6/HDPE复合材料力学性能和摩擦磨损性能的改善效果较好,其拉伸强度、弯曲强度及冲击强度比未加纤维的PA6/HDPE分别提高了21.6％、38.8％和40.5％;其100 N和200 N载荷下的磨损量分别为未加纤维的PA6/HDPE的71.5％和75.6％.     

Ionic conductivity of PEO9: Cu(CF3SO3)2: Al2O3 nano-composite solid polymer electrolyte

Cu⁺⁺ ion containing solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO₉:Cu(CF₃SO₃)₂ made by complexing copper triflate (CuTf₂) with PEO appears to show scientifically intriguing transport properties. Although some copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the species involved are yet to be established. In order to obtain enhanced ionic conductivities and also to contribute towards understanding the ionic transport process in Cu⁺⁺ ion containing, PEO based composite polymer electrolytes, we have studied the system PEO₉: CuTf₂: Al₂O₃ incorporating 10 wt.% of alumina filler particles of grain size 10 μm, 37 nm, 10–20 nm and also particles of pore size 5.8 nm. Thermal and electrical measurements show that the system remains amorphous down to room temperature. The composite electrolyte is predominantly an ionic conductor with electronic conductivity less than 2%. The triflate (CF₃SO₃⁻) anions appear to be the dominant carriers. The presence of alumina grains has enhanced the conductivity significantly from room temperature up to 100 °C. The nano-porous grains with 5.8 nm pore size and 150 m²/g specific surface area exhibited the maximum conductivity enhancement. This enhancement has been attributed to Lewis acid–base type surface interactions of ionic species with O²⁻ and OH⁻ groups on the filler grain surface.     

Metal/polymer interfaces with designed morphologies

The morphology of a metal/polymer interface is important for many properties, e.g. its adhesional strength. Starting from the basic processes occurring in the initial stages of metal/polymer interface formation, it is possible to obtain different morphologies by variation of the preparation conditions. In this report we present selected examples from our own work of how metal/polymer interfaces with different morphologies can be prepared by evaporating noble metals (Au, Ag, Cu) onto chemically different polymers, i.e. bisphenol-trimethyl cyclohexane polycarbonate (TMC-PC), pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide (PI), and on Teflon AF 1601. The interfaces were characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The combination of these techniques allows one to determine morphological parameters such as the concentration and distribution of metal clusters at the surface and in the near-surface region. Using low deposition rates and elevated temperatures, spread-out metal/polymer interfaces can be formed, whereas the use of high deposition rates and moderate temperatures results in relatively sharp interfaces. Another approach to obtain a defined morphology is to form large metal clusters of 10-30 nm diameter on the polymer surface and embed them into the polymer in a controlled manner by a subsequent annealing process. First experiments on the macroscopic adhesion of Au and Cu on TMC-PC showed that the initially low peel strength could be increased substantially by subsequent annealing above the glass transition temperature.     

XPS and UPS in situ study of oxygen thermal desorption from nanocrystalline diamond surface oxidized by different process

The chemistry of oxygen bonding on the diamond surface is a rich area of surface science research. It is well known that different surface terminations lead to strong variation of the material work function. This effect in diamond assumes peculiar consequences. In fact the oxidized diamond surface is hydrophilic, due to the high work function it shows a positive electron affinity and it is non conductive. On the contrary hydrogenation completely changes the orientation of the surface dipoles, the surface becomes hydrophobic, the work function lowers leading to a negative electron affinity. In addition hydrogen induces subsurface carriers which render the diamond surface semiconducting. These distinctive electronic properties make the diamond surface very interesting for the fabrication of surface field effect transistors just playing with the oxygen/hydrogen chemistry. Hydrogenation is generally obtained during the diamond synthesis in plasma reactors. Differently, the diamond surface oxidation may be accomplished with different processes (wet chemistry, plasma, UV irradiation).The realization of electronic devices calls for a complete understanding of the carbon-oxygen interactions, their stability and their influence on the electronic properties of diamond. Aim of this work is to explore the properties of diamond surfaces oxidized with piranha mixture, with O₂ plasma and with UV irradiation in a pure O₂ atmosphere. Each of these oxidized surfaces were annealed in situ at different temperatures and analyzed with photoelectron spectroscopies. Decreases of the oxygen concentration obtained via thermal desorption are then correlated with variations of the electronic properties obtained from UPS analyses.     

Synthesis of DME from syngas on the bifunctional Cu–ZnO–Al2O3/Zr-modified ferrierite: Effect of Zr content

The catalytic activity on the coprecipitated Cu–ZnO–Al₂O₃/Zr-ferrierite (CZA–ZrFER) with different Zr content from 0 to 5 wt.% was investigated for the direct synthesis of dimethylether (DME) from H₂-deficient and biomass-derived model syngas (H₂/CO molar ratio = 0.93). The catalytic functionalities, such as CO conversion and DME selectivity, showed their maxima on the bifunctional catalyst with 3 wt.% Zr-modified ferrierite. Detailed characterization studies were conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH₃-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), copper surface area measurements by N₂O titration method, electronic states of copper by IR analysis and particle size measurement by XRD and TEM analysis. The number of acid sites measured by NH₃-TPD on the bifunctional catalysts decreased monotonously with the increase of Zr content, meanwhile, the acidic strength is found to be minimal on the catalyst showing best performance. The reducibility of copper oxide and the surface area of metallic copper also exhibited their maximum values at the same Zr composition indicating that these are responsible for the optimum functionality of the bifunctional CZA–ZrFER catalyst. The role of easily reducible copper species with small particle size and the suppressed strong acidic sites is also emphasized in the consecutive reaction from syngas to DME on the bifunctional catalyst. The different behavior of intrinsic rate of the bifunctional catalysts is also well correlated with the metallic surface area of copper and the amount of acidic sites with their acidic strength.     

Characterization of Pt?CAu and Ni?CAu Clusters on TiO2(110)

The surface composition and properties of Pt?CAu and Ni?CAu clusters on TiO₂(110) have been studied by scanning tunneling microscopy (STM), low energy ion scattering (LEIS) and soft X-ray photoelectron spectroscopy (sXPS). STM studies show that bimetallic clusters are formed during sequential deposition of the two metals, regardless of the order of deposition. At the 2?ML of Au/2?ML of Pt or Ni coverages studied here, the second metal contributes to the growth of existing clusters rather than forming new pure metal clusters. LEIS experiments demonstrate that the surfaces of the bimetallic clusters are almost 100% Au when 2?ML of Au is deposited on top of 2?ML of Pt or Ni. However, a much larger fraction of Pt or Ni (50 and 20%, respectively) remains at the surface when 2?ML of Pt or Ni is deposited on 2?ML of Au, most likely due to limited diffusion of atoms within the clusters at room temperature. According to sXPS investigations, the binding energies of the metals in the bimetallic clusters are shifted from those observed for pure metal clusters; the Pt(4f_7/2) and Ni(3p_3/2) peaks are shifted to lower binding energies while the position of the Au(4f_7/2) peak is dominated by surface core level shifts. Pure Pt clusters as well as 0.4?ML of Au on 2 ML of Pt clusters reduce the titania support upon encapsulation after annealing to 800?K, whereas 2?ML of Au on 2?ML of Pt clusters do not reduce titania, presumably because there is no Pt at the surface of the clusters. Pure Ni clusters are also known to become encapsulated upon heating, but the reduction of titania is much less extensive compared to that of pure Pt clusters.     

Effects of Surface Modifications on the Peel Strength of Copper Based Polymer/Metal Interfaces with Characteristic Morphologies

This paper summarizes a study on the effect of changes in surface chemistry on the peel strength of copper/polymer interfaces. Two different surface topographics were created and evaluated, one produced by cleaning and etching in sodium persulfate, the other by etching then mechanically roughening using 180 grit sandpaper. Both surfaces were then oxidized in an alkaline/oxidizing treatment to form cupric oxide. Ion implantation and benzotriazole priming modified the surface chemistry of the cupric oxide samples. After lamination to form an epoxy/copper interface, peel strength measurements were taken. The results showed that ion implantation degraded the peel strength while priming with benzotriazole improved the peel strength compared with the unmodified cupric oxide. In a separate comparison study, peel strength measurements were taken on interfaces formed from copper oxides with the same oxide structure but with widely different gross morphologies, “As laminated” adhesive strength was virtually the same. The bonded interfaces were aged at elevated temperature and the peel strength obeyed first order degradation kinetics. Two terms can be determined from the degradation studies, the first is the long term peel strength, A(∞), and the other is Ω, the degradation rate with units of time^-1. A value of A(∞) was 3.0 lbs/in for etched copper interfaces while A(∞) was 0.5 lbs/in for the sanded interfaces.     

Synthesis and morphological transformation of BaWO4 crystals: Experimental and theoretical insights

BaWO₄ crystals have been obtained by a co-precipitation method, and their structures were characterized by X-ray diffraction and Rietveld refinement techniques, while field emission scanning electron microscopy was utilized to investigate the morphology of the as-synthesized aggregates. Geometries, bulk electronic properties, surface energies, and surface tension of the obtained BaWO₄ crystals were evaluated using first-principles quantum mechanical calculations. A theoretical model based on the Wulff construction was introduced to explain possible crystal morphologies by tuning their surface chemistry, which is related to the relative stability of the faceted crystals. Both the experimental and theoretical data revealed the presence of (112), (001), and (100) facets with low values of surface energy in the BaWO₄ crystals. The experimental morphologies of the as-synthesized samples are similar to the theoretically obtained shapes when surface energy values for the (001) and (100) surfaces are increased simultaneously.     

Morphologies Adopted by Al2O3 Single-Crystal Surfaces in Contact with Cu Droplets

The morphologies of α-Al₂O₃ single-crystal substrates, annealed in contact with Cu droplets ranging in size from 1 to 10 μm, are observed by high-resolution scanning electron microscopy. After 45 min at 1373 K in a He-5% H₂ atmosphere, the alumina substrates display different shapes depending on their orientation and on the addition of small amounts of titanium to the copper. The alumina surface may remain flat, display a hollow of faceted spherical shape at the solid/liquid interface, or develop anisotropic ridges at the triple line. The shape changes result from the diffusion of the components of alumina that takes place to achieve a minimum interfacial energy of the drop–substrate system. Explanations of these features are proposed with a discussion of the conditions under which the Young equation can be used for characterizing wetting at high temperature.     

The chemical and electronic properties of oxygen-modified C/Mo(110): a model system for molybdenum oxycarbides

We have utilized oxygen-modified C/Mo(110) surfaces as model systems to determine the modification effect of oxygen in “oxycarbides.” Using cyclohexene, ethylene, and methanol as probe molecules, we observed that the reactivity of the O/C/Mo(110) surfaces depended strongly on the temperature at which oxygen was introduced onto the C/Mo(110) surface. The reaction pathways were determined using both temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). For example, the O/C/Mo(110) surface obtained by exposing the carbide surface to oxygen at 600 K became chemically inert toward all three molecules. On the other hand, the 900 K O/C/Mo(110) surface was active toward all three molecules, and for the most part retained the Pt-like reaction pathways observed on unmodified C/Mo(110). Furthermore, we have also compared the electronic properties of the O/C/Mo(110) surfaces using two synchrotron spectroscopies, soft X-ray photoelectron spectroscopy (SXPS) and near-edge X-ray absorption fine structure (NEXAFS); the results revealed similar electronic properties between the 900 K O/C/Mo(110) and unmodified C/Mo(110) surfaces.     

Liquid metal/ceramic interactions in the (Cu,Ag, Au)/ZrB2 systems

Wetting and spreading experiments on ZrB₂ in contact with liquid Cu, Ag and Au have been performed by the sessile drop technique under a vacuum. The wetting and spreading characteristics and the interfacial reactions are discussed as a function of time and of the metal involved. The interfacial morphologies, analysed by optical microscopy, SEM and EDS show the presence of regular interfaces without macroscopic reaction layers. Gold, to a very large extent and copper are shown to give rise to extensive penetration along grain-boundaries, whereas silver neither wets nor penetrates. Interfacial diffusion/dissolution is taken into account and the consequent changes in liquid metal surface tension and wetting behaviours have been evaluated by means of thermodynamic calculations.Moreover, interfacial energetics at the atomistic level has been investigated by means of pseudopotential-based Density Functional Theory (DFT) technique. It is shown how the calculation of the ideal work of separation on the specific transition metal borides-molten metal systems can be used to interpret the wetting behaviour. Moreover, the dependence of the adhesion behaviour on the electronic structure at the interface and on the interface epitaxy and composition is also briefly discussed.     

The Antimicrobial Properties of Titanium Nitride/Silver Nanocomposite Coatings

Titanium nitride surfaces with silver concentrations of TiN/4.6at%Ag, TiN/10.8at%Ag and TiN/16.7at%Ag were produced using magnetron deposition. Antimicrobial and topographic properties affecting the interactions of the surfaces with microorganisms were assessed using Pseudomonas aeruginosa (1 μm × 3 μm rod-shaped Gram-negative bacteria) and Staphylococcus aureus (1 μm coccus-shaped Gram-positive bacteria) with retention assays, live/dead staining, and strength of attachment measurements. Retention of P. aeruginosa on the surfaces increased with an increase in surface silver content, grain size and topography, but the cells were easily removed from the surface under water when a force was applied. S. aureus cells were retained in lower numbers, but once attached, cells were difficult to remove. S. aureus cells attached in increased numbers on surfaces with lower silver content and smaller dimension surface features. The modification of hard wearing surfaces by addition of silver increased the antimicrobial activity of the surface, but the spectrum of antimicrobial activity varied with the target cell and surface properties. This work demonstrates that a range of methods and cell types need to be tested against surfaces which either discourage cell colonization and/or are potentially antimicrobial since the novel surface properties produced may inadvertently select and give advantage to a particular cell species. This may, in turn, affect the predicted surface efficacy.