Surface Properties Of Cu Research Articles

Thermodynamic, structural and surface properties of Cu–Zr liquid alloy at different temperatures: A theoretical approach

Thermodynamic, structural and surface properties of Cu–Zr liquid alloy at different temperatures: A theoretical approach

Toward Durable CO2 Electroreduction with Cu-Based Catalysts via Understanding Their Deactivation Modes.

The technology of CO2 electrochemical reduction (CO2ER) provides a means to convert CO2, a waste greenhouse gas, into value-added chemicals. Copper is the most studied element that is capable of catalyzing CO2ER to obtain multicarbon products, such as ethylene, ethanol, acetate, etc., at an appreciable rate. Under the operating condition of CO2ER, the catalytic performance of Cu decays because of several factors that alters the surface properties of Cu. In this review, these factors that cause the degradation of Cu-based CO2ER catalysts are categorized into generalized deactivation modes, that are applicable to all electrocatalytic systems. The fundamental principles of each deactivation mode and the associated effects of each on Cu-based catalysts are discussed in detail. Structure- and composition-activity relationship developed from recent in situ/operando characterization studies are presented as evidence of related deactivation modes in operation. With the aim to address these deactivation modes, catalyst design and reaction environment engineering rationales are suggested. Finally, perspectives and remarks built upon the recent advances in CO2ER are provided in attempts to improve the durability of CO2ER catalysts.

Effect of Ti/Si and Ti/TiN/Si interlayers on the structure, properties, and tribological behavior of an a-C film deposited onto a C17200 copper-beryllium alloy

Reduced hardness and wear resistance may limit SAE C17200 copper‐beryllium alloy use in manufacturing applications, such as plunger tips of die casting machines and as cores and inserts for steel dies in injection molding processes. In order to improve the surface properties of Cu—Be alloys, amorphous carbon (a-C) films have been selected since these coatings may show high hardness, low wear rate and low coefficient of friction. However, the adhesion of carbonaceous films on Cu—Be alloys remains a challenge. Two interlayer compositions (Ti/Si and Ti/TiN/Si) were deposited onto Cu—Be disks and silicon wafers to assess amorphous carbon adhesion on substrates made of Cu—Be alloy. The microstructure and topography of the coatings were examined by Field Emission Scanning Electron Microscopy (FESEM) coupled with X-ray dispersive energy spectroscopy (EDS). The chemical composition depth profile was measured by glow discharge optical emission spectroscopy (GDOES), which confirmed distinct coating layers of Ti, Si, a-C (C1 and C2 conditions-pDCMS). A TiN extra layer presence was obtained for the C3 and C4 conditions-pDCMS reactive, confirmed by small angle XRD analysis. Raman scattering spectroscopy showed a higher quantity of sp3 carbon bonds for C3 and C4 coating conditions compared to C1 and C2. Instrumented indentation tests indicated a higher hardness and reduced elastic modulus for C3 and C4 coating systems, corroborating Raman results, in terms of a higher concentration of sp3 bonds. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and coherence correlation interferometry (CCI) were used to characterize the coatings' surface features and scratch tracks after the tests. In addition, ramp load scratch tests were conducted to assess coating adhesion to the Cu—Be alloy substrate by measuring critical loads and the coefficient of friction. The highest critical loads to failure (Lc2) and (Lc3) were found for the Ti/TiN/Si interlayer sample (C4 condition), indicating that this interlayer improved the coating contribution to a gradual increase in the hardness and promotion of an enhanced adhesion strength of the a-C coating.

Increasing Antibacterial Efficiency of Cu Surfaces by targeted Surface Functionalization via Ultrashort Pulsed Direct Laser Interference Patterning

AbstractCopper (Cu) exhibits great potential for application in the design of antimicrobial contact surfaces aiming to reduce pathogenic contamination in public areas as well as clinically critical environments. However, current application perspectives rely purely on the toxic effect of emitted Cu ions, without considering influences on the interaction of pathogenic microorganisms with the surface to enhance antimicrobial efficiency. In this study, it is investigated on how antibacterial properties of Cu surfaces against Escherichia coli can be increased by tailored functionalization of the substrate surface by means of ultrashort pulsed direct laser interference patterning (USP‐DLIP). Surface patterns in the scale range of single bacteria cells are fabricated to purposefully increase bacteria/surface contact area, while parallel modification of the surface chemistry allows to involve the aspect of surface wettability into bacterial attachment and the resulting antibacterial effectivity. The results exhibit a delicate interplay between bacterial adhesion and the expression of antibacterial properties, where a reduction of bacterial cell viability of up to 15‐fold can be achieved for E. coli on USP‐DLIP surfaces in comparison to smooth Cu surfaces. Thereby, it can be shown how the antimicrobial properties of copper surfaces can be additionally enhanced by targeted surface functionalization.

Elucidating the Structure of the Cu-Alkaline Electrochemical Interface with the Laser-Induced Temperature Jump Method

A detailed description of the Cu–electrolyte interface is vital to understand the electrocatalytic properties of Cu surfaces. Herein, we combine cyclic voltammetry and the laser-induced temperature...

Interactions of C5F10O Molecule With Cu (1 1 0) and (1 0 0) Surfaces Based on Density Functional Theory

This paper based on density functional theory (DFT) investigate the interaction of C5-PFK molecule with Cu (110) and (100) surfaces, in order to analyze the chemical compatibility of Cu metal in the environment of C 5 F 10 O (C5-PFK) insulation gas. The frontier molecular orbital theory implies that the C = O group in the C5-PFK molecule can interact strongly with the Cu surfaces. The results show that both Cu (110) and (100) surfaces have strong interactions with the C5-PFK molecule, showing chemisorption of the molecule, with E ad of -1.17 and -1.03 eV, respectively. Meanwhile, the C5-PFK molecule performs strong electron-accepting behavior in the interactions, which captures 0.262 and 0.204 e from the Cu (110) and (100) surface, respectively. Even though, the geometric and electronic properties of Cu surface are not largely impacted, as supported by the basically unchanged morphologies and DOS curves of Cu surfaces before and after gas adsorption. These findings manifest the favorable stability and compatibility of Cu metal in the C5-PFK environment. Our work uncovers the safe operation of C5-PFK immersed insulation devices with Cu-based generatrix and shell in a long running, which is of great significance to guarantee the safe operation of the power system.

(Invited) Chalcopyrites for Solar Water Splitting: Soft X-Ray and Electron Spectroscopy of the Chemical and Electronic Surface Structure

In this presentation, it will be demonstrated that the combination of soft x-ray and electron spectroscopies (using lab-based surface characterization and high-brilliance synchrotron radiation) can be used to gain insights into the electronic and chemical surface properties of Cu(In,Ga)(S,Se)2-based chalcopyrite devices for solar water splitting. It will be shown that x-ray and UV photoelectron spectroscopy (XPS and UPS), x-ray-excited Auger electron spectroscopy (XAES), inverse photoemission (IPES), x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS) can be suitably combined to derive band edge positions, band gaps, work functions, and electronic level alignments. Furthermore, insights into chemical stability can be gained, both with experiments in ultra-high vacuum, as well as under in situ and operando conditions.

Selective Leaching and Surface Properties of Cu–Al–Ni Shape Memory Alloys

Selective Leaching and Surface Properties of Cu–Al–Ni Shape Memory Alloys

(Invited) Chalcopyrites and III-V Semiconductors for Solar Water Splitting--a Detailed Look at the Electronic and Chemical Surface Structure

This presentation will discuss the chemical and electronic surface properties of Cu(In,Ga)(S,Se)2- and GaInP2-based materials in view of their use in solar water-splitting devices. Many of the primary requirements for photoelectrochemistry (such as efficiency and stability) are directly related to such properties, but it is generally quite difficult to paint a comprehensive surface picture, in particular in operando environments. The talk will focus on results obtained with a tool chest of soft x-ray and electron spectroscopies, with primary emphasis on high-brilliance synchrotron radiation experiments. It will be shown how photoelectron spectroscopy (PES), also under “ambient pressure” conditions, inverse photoemission (IPES), x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS) can be suitably combined to derive surface electronic band gaps, study local chemical bonding and electronic level alignment, and gain insights into chemical stability.

Improve the Overall Performances of Lithium Ion Batteries by a Facile Method of Modifying the Surface of Cu Current Collector with Carbon

ABSTRACT We have developed a facile and mass-producible strategy named electric discharge method to successfully improve the surface properties of Cu foils with rough carbon layer. Electrochemical tests in half-cells demonstrate that the coated carbon layer can significantly reduce the polarization resistance and enhance the reversible capacity of graphite anode when utilizing the Cu foils as current collector for lithium ion batteries. More importantly, the developed carbon coated Cu anode current collector can also improve the overall performances of LiFePO 4 full cells in terms of enhanced rate capability (from 887.9 to 946.3 mAh at 4C rate), reduced polarization voltage (11.7 mV lower at 4C rate), longer cycle life (about 650 increased cycles if taking 80 % capacity retention as the end of cycle life when used at 1 C rate) as well as improved low-temperature performance (capacity retention: 42.87% vs. 38.85% at -20 °C).

Impact of environmental conditions on the chemical surface properties of Cu(In,Ga)(S,Se)2 thin-film solar cell absorbers

Environmentally driven aging effects play a crucial role in thin-film solar cells based on Cu(In,Ga)(S,Se)2, both for long-term stability and short air exposure during production. For a better understanding of such effects, Cu(In,Ga)(S,Se)2 absorber surfaces were investigated by x-ray photoelectron and Auger electron spectroscopy after exposure to different environmental conditions. Identical absorbers were stored in a nitrogen atmosphere, in damp heat, and under ambient conditions for up to 14 days. We find varying degrees of diffusion of sulfur, copper, and sodium towards the surface, with potential impact on the electronic surface structure (band gap) and the properties of the interface to a buffer layer in a solar cell device. Furthermore, we observe an oxidation (in decreasing order) of indium, copper, and selenium (but no oxidation of sulfur). And finally, varying amounts of carbon- and oxygen-containing adsorbates are found. In particular, the findings suggest that, for ambient air exposure, sodium carbonate is formed at the surface.

First-principles analysis of properties of Cu surfaces

Using first-principles pseudopotential plane wave method, the energy, atomic geometry and electronic density of states of FCC Cu crystal and its (111), (110) and (100) surface models were calculated and analyzed. According to the calculated results of the surface energy, the structural stability of the Cu surfaces increases for Cu (110), Cu (100), Cu (111) surfaces successively. The relaxation extent of the surface atoms decreases successively with the increasing the number of the layers. For the inwards relaxation of the surface layer atoms, Cu (110) surface moves maximum, Cu (100) takes second place, Cu (111) surface moves least. It was found that the relaxation of the surface atom layers not only causes the change of geometrical structures of the surface models but also leads to the change of peak contour of density of states (DOS) of surface layer atoms comparing with crystal inside. The increment of the total energy caused by these change is the main reason of the surface energy. And that the Cu (110) surface having higher activity than that of Cu(111) and Cu(100) surfaces may be attributed to its apparent rising of the surface layer atoms DOS in the high energy level.

Catalytic systems based on multicomponent oxides of 3d-metals and Si-containing carriers for CO oxidation reaction

The catalytic activity and surface properties of Cu–Co–Fe oxide catalysts formed on silica gel, powdery β-SiC, and β-SiC nanofibers for CO oxidation reaction are studied. A method, involving including initial acidic treatment of silicon carbide nanofibers with a mixture of hydrofluoric and nitric acids, has been developed for obtaining a highly defective surface layer for the formation of Cu2(OH)3NO3 active mass.

Influence of surface topography on frictional properties of Cu surfaces under different lubrication conditions: Comparison of dry, base oil, and ZnS nanowire-based lubrication system

This work deals with the frictional properties of ductile Cu surfaces of varying morphologies under three different lubrication conditions including dry, base oil only, and nanowire+base oil. It was found that the frictional properties of base oil and nanowire-based lubrication system strongly depended on the surface topography while the friction for the dry surfaces was independent of the surface topography.

Synthesis, Control, and Characterization of Surface Properties of Cu2O Nanostructures

The ability to control nanostructure shape can strongly affect the overall properties of that system. Here we report the ability to deterministically control nanostructure shape, surface facet orientation, and surface potentials of the oxide semiconductor Cu(2)O. Epitaxial Cu(2)O nanostructures with different shapes and geometries-from boxes to pyramids to huts-have been grown via pulsed laser deposition. By varying the adatom energy and flux per laser pulse we can tune the nature of the nanostructure geometry, the total density of features, the relative surface area to volume ratio, and can create polar, nonequilibrium surfaces. In addition to detailed structural analysis of the nanostructures, high-resolution Kelvin probe force microscopy has been used to systematically analyze the surface potential and electronic structure of the (100), (110), and (111) surfaces of Cu(2)O. These studies suggest that each surface, possessing a unique atomic structure, gives rise to different surface energy levels of conduction and valence bands and the formation of electronic surface junctions. The implication of these findings in terms of a range of applications is discussed.

Nanoscale investigations of the electronic surface properties of Cu(In,Ga)Se 2 thin films by scanning tunneling spectroscopy

In this work we investigate the electronic surface properties of polycrystalline Cu(In,Ga)Se 2 thin films by locally resolved scanning tunneling spectroscopy (STS). From current imaging tunneling spectroscopy (CITS) maps of an area of ( 2 × 2 ) μ m 2 we observe distinct granular inhomogeneities, where current–voltage ( I( U)) spectra differ from grain to grain and vary between metallic and semiconducting characteristics. Due to the high density of defect states at the Cu(In,Ga)Se 2 surface, the metallic I( U) characteristics is not surprising. In the case of the semiconducting I( U) characteristics, we suggest a preferential oxidation of particular grains, which passivates defect levels at the surface. This is supported by the presence of gallium and indium oxides detected by global X-ray photoelectron spectroscopy. Furthermore, we recorded I( U) spectra from different grains under supra band gap laser illumination, which always show semiconducting characteristics. This behavior can be explained by a saturated occupation of defect states by photoexcited charge carriers. By evaluating differential conductance ( dI/ dU) spectra under illumination from various grains, we estimate the average surface band gap to ( 1.4 ± 0.2 ) eV and compare the valence band onset with results from macroscopic ultraviolet photoelectron spectroscopy. The high lateral resolution of our CITS data allows also to study electronic properties at grain boundaries, which are discussed with regard to a recent STS study on a non-oxidized sample.

Ab initio investigation of the surface properties of Cu(111) and Li diffusion in Cu thin film

Ab initio density-functional calculations have been performed to investigate the surface properties of Cu(111) and lithium diffusion in copper thin film. The calculation results including lattice constant, cohesive energy, work function and surface energy are in fair agreement with that derived from corresponding experiments. The various diffusion pathways such as diffusion of lithium as a substitution atom and various mechanisms are investigated with ab initio molecular dynamics. The energy barrier has been calculated corresponding to each possible pathway. Theoretically, we have identified that lithium can diffuse through copper thin film by successive nearest neighbor vacancy-atom exchanges, therefore, the nearest neighbor vacancy assisted jumping is deduced to be the most probable by comparing the different mechanisms. It is found that more free diffusion may be observed by increasing the number of copper vacancies in the thin film. It is also confirmed that the diffusion is more obvious as temperature is increased.

Structure, thermodynamic, electrical and surface properties of Cu–Mg binary alloy: complex formation model

In the present paper, we have studied the alloying behaviour of Cu–Mg alloy on the basis of the formation of chemical complexes near the melting point along with the pseudopotential technique. The former has been used to compute the partial and total structure factors, heat of formation, heat of mixing, entropy of mixing, concentration fluctuation at long wavelength limit S cc(0) and chemical short-range order parameter (CSRO) of the alloy. The results are in reasonably good agreement with experiment. The pseudopotential technique has been used to compute the local screened form factor on the basis of the Shaw model needed for the computation of electrical resistivity of the alloy. The surface tension has also been studied. Useful inferences have been drawn from the computed result.

Effect of temperature on the surface properties of Cu–Sn liquid alloys

The concentration and temperature dependence of the surface tension and surface composition of Cu–Sn liquid alloys have been theoretically investigated with the application of statistical mechanical model based on layered structures. Our study suggests an increase in the surface tension ( σ) with the increase of Cu concentration. Maximum increase in σ has been found around the compound forming concentration, i.e. Cu 0.75Sn 0.25. With regard to the effect of temperature on activity coefficient (γ), our study shows positive temperature coefficient at compound forming concentration, i.e. C Cu=0.75. The temperature buffering (d σ/d T=0) was found to occur around the equi-atomic composition. It may be inferred that positive temperature coefficient might be due to progressive dissociation at the surface of atomic clusters/associates/complexes associated with the γ-phase of the system. So far as surface segregation is concerned, the surface is quite enriched with Sn-atoms at all bulk concentrations. However, the extent of segregation decreases with the increase of the temperature.

Influence of Na and H2O on the surface properties of Cu(In,Ga)Se2 thin films

The influence of humidity on the electronic structure of Na-containing polycrystalline Cu(In,Ga)Se2 thin films on soda-lime glass substrates has been investigated by x-ray and UV photoemission as well as by Auger electron spectroscopy. Different interactions between coadsorbed Na, H2O, and the Cu(In,Ga)Se2 surface are revealed at low temperatures and upon annealing at room temperature. Both, reversible and irreversible interactions such as a H2O-induced reduction of the Na surface content and the formation of a Na–O–Cu(In,Ga)Se2 complex are observed. Our findings can be correlated with the influence of ambient conditions on Cu(In,Ga)Se2 solar cell adsorbers and demonstrate the importance of adequate encapsulation of Na-containing Cu(In,Ga)Se2-based thin-film solar cells.