Comparative investigation on copper oxides by depth profiling using XPS,RBS and GDOES

Depth profiling has been performed by using X-ray photoelectron spectrometry (XPS) in combination with Ar-ion sputtering, Rutherford backscattering spectrometry (RBS) and glow discharge optical emission spectrometry (GDOES). The data obtained by XPS have been subjected to factor analysis in order to determine the compositional layering of the copper oxides. This leads to two or three relevant components within the oxide layers consisting of Cu(2)O or CuO dependent on the sample preparation. GDOES measurements show sputtering profiles which are seriously influenced by a varying sputter rate. To ensure the results obtained so far, RBS measurements of the oxide layers have been carried out in order to discover artefacts of the other methods used and to demonstrate the excellent suitability of RBS for quantitative analysis of these layers. Chemical analysis consisting of (1) carrier-gas fusion analysis (CGFA) and (2) selective dissolution of Cu(2)O/CuO allows the determination of the total amount of oxygen and copper, respectively, and can serve as a cornerstone of quantitative analysis.     

Curing and properties of chloroprene and butadiene rubber (CR/BR) blends cross-linked with copper(I) oxide or copper(II) oxide

This paper discusses the curing and properties of chloroprene and butadiene rubber (CR/BR) blends cross-linked with copper(I) oxide (Cu₂O) or copper(II) oxide (CuO). The results revealed that the cross-linking degree of CR/BR blends decreased with the increasing amount of butadiene rubber (BR) in the blends. The mechanical properties of cured CR/BR blends depended on the proportion of elastomers in blends, as well as on the type and amount of the cross-linking agent (Cu₂O, CuO). The cross-linking of CR/BR/Cu₂O or CR/BR/CuO blends followed according to cationic mechanism, using Lewis acid, copper(I) chloride (CuCl) or copper(II) chloride (CuCl₂) generated in situ. Additionally, the prepared compositions, both unfilled and filled, were characterized by very high resistance to flame.     

Surface chemical and geometrical properties of pure copper powder intended for binder jetting and sintering

One novel important application of sinter-based additive manufacturing involving binder jetting is copper-based products. Three different variants of nominally pure copper powder having particle size distributions with D90 < 16, 22, or 31 μm were investigated in this study. The packing behavior and the flow properties using dynamic test and shear cell, as well as specific surface area were evaluated. The analyses employed illustrate the multidimensional complexity. Because different measurements capture different aspect of the powder, it is imperative to apply a characterization approach involving different methods. Surface chemical analysis by means of X-ray photoelectron spectroscopy (XPS) showed that all powder variants were covered by Cu₂O, CuO, and Cu (OH)₂, with Cu₂O being dominant in all cases. The finest powder with D90 < 16 μm tended to have higher relative amount of copper in divalent state. The average apparent oxide thickness estimated by XPS depth profiling showed that the two coarser variants had similar overall average oxide thickness, whereas the finest one possessed smaller oxide thickness. The surface chemistry of the powder grades is found to be related to their rheological behavior in dynamic condition. Considering the specific surface areas in combination with the average oxide thicknesses, the amount of surface bound oxygen was estimated to be about ~220 ppm for all three variants. Specific concerns need to be taken during the sintering of powder to keep oxygen level below that of electrolytic pitch copper (400 ppm).     

Influence of surface morphology on the oxidation of metal electrodes studied by in-situ grazing incidence x-ray diffractometry

The successful application of in-situ grazing incidence x-ray diffractometry (GIXD) for the investigation of oxidation processes at copper electrodes in pH 12 electrolytes is demonstrated. A penetration/escape depth of about 1 μm could be detected for a smooth polycrystalline copper foil and an x-ray incidence angle of 1.7°. Oxide layers generated at overpotentials less than about 0.5 V in respect to the equilibrium formation potentials of Cu₂O or CuO, respectively, showed a dependence of the crystalline oxide formation on the defect density of the copper substrate. Highly disordered ground or polished specimens exhibited an order of magnitude higher GIXD reflexes from crystalline Cu₂O than electrodeposited copper. Beyond overpotentials of 0.5 V, this epitaxial information for the Cu₂O crystal growth became irrelevant. Further, GIXD turned out to be an appropriate tool to monitor atmospheric corrosion processes under thin humidity films with oxygen access. When oxygen diffusion through the polymer window membrane is allowed, oxygen reduction led to the concurrent formation of a crystalline CuO phase coexisting with amorphous Cu(OH)₂ and Cu₂O, though the potential was kept in the region of Cu₂O. Received: 30 July 1997 / Revised: 28 May 1998 / Accepted: 13 July 1998     

Emf Measurements on Nanocrystalline Copper-Doped Ceria

Mixed oxide samples of nanostructured Cu_xCe_1−xO_2−yof various composition were generated by (i) chemical precipitation and ball milling and (ii) inert gas condensation. X-ray diffraction measurements suggested that copper oxide was dissolved in nanostructured cerium oxide up to concentrations ofx=0.15. Solid electrolyte cells of the typeA, Cu₂O/CuBr/Cu_xCe_1−xO_2−y(A=Cu or CuO) showed reversible cell voltages. The ratio of the formal chemical activities of CuO and Cu₂O dissolved in nanostructured cerium oxide were calculated from the cell voltages. The results are discussed in terms of an apparent macroscopic solubility, due to interfacial segregation of copper oxide on nanostructured cerium oxide.     

Influence of bath temperatures on the wettability of copper films surface prepared by electroless plating method on beech wood

Copper films were coated on beech wood substrates by electroless plating method. The influence of bath temperature on the copper films properties was studied by varying the bath temperatures 25, 35, 45 and 55 °C. Scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD) pattern, X‐ray photoelectron spectroscopy (XPS), micro Raman spectroscopy and contact angle measurements were used to both characterize the physical and chemical copper films properties and understand the influence of bath temperature on the wettability of copper surface. In our studies, we have found that the gained copper mass significantly increased at 55 °C. The crystalline nature of the coated copper was confirmed by XRD. The presence of Cu₂O and CuO was observed by XPS and micro Raman techniques, which confirms the oxidization of the coated copper surface. Also these characterization techniques have shown the big influence of bath temperature on the morphology, grain size, chemical composition and the film thickness of the coated copper. The wettability was highly influenced by increasing CuO on the coated copper, which is increased by the bath temperature. The contact angle measurements have demonstrated the influence of C―O, O―C?O and CuO components of the surface on the wettability of the samples. Copyright © 2016 John Wiley & Sons, Ltd.     

Plasma-assisted oxidation of Cu(100) and Cu(111)

Oxidized copper surfaces have attracted significant attention in recent years due to their unique catalytic properties, including their enhanced hydrocarbon selectivity during the electrochemical reduction of CO₂. Although oxygen plasma has been used to create highly active copper oxide electrodes for CO₂RR, how such treatment alters the copper surface is still poorly understood. Here, we study the oxidation of Cu(100) and Cu(111) surfaces by sequential exposure to a low-pressure oxygen plasma at room temperature. We used scanning tunnelling microscopy (STM), low energy electron microscopy (LEEM), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and low energy electron diffraction (LEED) for the comprehensive characterization of the resulting oxide films. O₂-plasma exposure initially induces the growth of 3-dimensional oxide islands surrounded by an O-covered Cu surface. With ongoing plasma exposure, the islands coalesce and form a closed oxide film. Utilizing spectroscopy, we traced the evolution of metallic Cu, Cu₂O and CuO species upon oxygen plasma exposure and found a dependence of the surface structure and chemical state on the substrate''s orientation. On Cu(100) the oxide islands grow with a lower rate than on the (111) surface. Furthermore, while on Cu(100) only Cu₂O is formed during the initial growth phase, both Cu₂O and CuO species are simultaneously generated on Cu(111). Finally, prolonged oxygen plasma exposure results in a sandwiched film structure with CuO at the surface and Cu₂O at the interface to the metallic support. A stable CuO(111) surface orientation is identified in both cases, aligned to the Cu(111) support, but with two coexisting rotational domains on Cu(100). These findings illustrate the possibility of tailoring the oxidation state, structure and morphology of metallic surfaces for a wide range of applications through oxygen plasma treatments.

A low-pressure oxygen plasma oxidized Cu(100) and Cu(111) surfaces at room temperature. The time-dependent evolution of surface structure and chemical composition is reported in detail for a range of exposure times up to 30 min.     

The composite catalysts of Cu/CuxO nanoparticles supported on the carbon fibers were prepared for styrene oxidation reaction

In this paper a novel simple method for preparing two different catalysts with various‐valences copper was reported. Carbon nanofibers supported copper‐cuprous oxide nanoparticles (Cu‐Cu₂O NPs/CNFs) and copper oxide nanoparticles (CuO NPs/CNFs) through electrospinning, adsorption and reduction in the high‐pressure hydrogenation and the high‐temperature calcination methods. These catalysts were investigated by a series of characterizations and were applied in reaction in nitrogen atmosphere, which had a good catalytic activity and selectivity of benzaldehyde for the reaction. Above all, the new study has been certified clearly, in which Cu‐Cu₂O NPs/CNFs and CuO NPs/CNFs composite catalysts enhanced the generation of benzaldehydeand the excellent catalytic properties were exhibited.     

Characterization and Activity of Cu‐MnOx/γ‐Al2O3 Catalyst for Hydrogenation of Carbon Dioxide

The effect of manganese on the dispersion, reduction behavior and active states of surface of supported copper oxide catalysts have been investigated by XRD, temperature‐programmed reduction and XPS. The activity of methanol synthesis from CO₂/H₂ was also investigated. The catalytic activity over CuO‐MnO_x/γ‐Al₂O₃ catalyst for CO₂ hydrogenation is higher than that of CuO/γ‐Al₂O₃. The adding of manganese is beneficial in enhancing the dispersion of the supported copper oxide and make the TPR peak of the CuO‐MnK_x/γ‐Al₂O₃ catalyst different from the individual supported copper and manganese oxide catalysts, which indicates that there exists strong interaction between the copper and manganese oxide. For the CuO/γ‐Al₂O₃ catalyst there are two reducible copper oxide species; α and β peaks are attributed to the reduction of highly dispersed copper oxide species and bulk CuO species, respectively. For the CuO‐MnO_x/γ‐Al₂O₃ catalyst, four reduction peaks are observed, α peak is attributed to the dispersed copper oxide species; β peak is ascribed to the bulk CuO; γ peak is attributed to the reduction of high dispersed CuO interacting with manganese; δ peak may be the reduction of the manganese oxide interacting with copper oxide. XPS results show that Cu⁺ mostly existed on the working surface of the Cu‐Mn/γ‐Al₂O₃ catalysts. The activity was promoted by Cu with positive charge which was formed by means of long path exchange function between Cu? O? Mn. These results indicate that there is synergistic interaction between the copper and manganese oxide, which is responsible for the high activity of CO₂ hydrogenation.     

One-step green synthesis of cuprous oxide crystals with truncated octahedra shapes via a high pressure flux approach

Cuprous oxide (Cu₂O) was synthesized via reactions between cupric oxide (CuO) and copper metal (Cu) at a low temperature of 300 °C. This progress is green, environmentally friendly and energy efficient. Cu₂O crystals with truncated octahedra morphology were grown under high pressure using sodium hydroxide (NaOH) and potassium hydroxide (KOH) with a molar ratio of 1:1 as a flux. The growth mechanism of Cu₂O polyhedral microcrystals are proposed and discussed.     

Production of hydrogen by oxidative steam reforming of methanol over Cu/SiO2 catalysts

Selective production of hydrogen by oxidative steam reforming of methanol (OSRM) was studied over Cu/SiO₂ catalyst using fixed bed flow reactor. Textural and structural properties of the catalyst were analyzed by various instrumental methods. TPR analysis illustrates that the reduction temperature peak was observed between 510?K and 532?K at various copper loadings and calcination temperatures and the peaks shifted to higher temperature with increasing copper loading and calcination temperature. The XRD and XPS analysis demonstrates that the copper existed in different oxidation states at different conditions: Cu₂O, Cu⁰, CuO and Cu(OH)₂ in uncalcined sample; CuO in calcined sample: Cu₂O and metallic Cu after reduction at 600?K and Cu⁰ and CuO after catalytic test. TEM analysis reveals that at various copper loadings, the copper particle size is in the range between 3.0?nm and 3.8?nm. The Cu particle size after catalytic test increased from 3.6 to 4.8?nm, which is due to the formation of oxides of copper as evidenced from XRD and XPS analysis. The catalytic performance at various Cu loadings shows that with increasing Cu loading from 4.7 to 17.3?wt%, the activity increases and thereafter it decreases. Effect of calcination shows that the sample calcined at 673?K exhibited high activity. The O₂/CH₃OH and H₂O/CH₃OH molar ratios play important role in reaction rate and product distribution. The optimum molar ratios of O₂/CH₃OH and H₂O/CH₃OH are 0.25 and 0.1, respectively. When the reaction temperature varied from 473 to 548?K, the methanol conversion and H₂ production rate are in the range of 21.9–97.5% and 1.2–300.9?mmol?kg^?1?s^?1, respectively. The CO selectivity is negligible at these temperatures. Under the optimum conditions (17.3?wt%, Cu/SiO₂; calcination temperature 673?K; 0.25 O₂/CH₃OH molar ratio, 0.5 H₂O/CH₃OH molar ratio and reaction temperature 548?K), the maximum hydrogen yield obtained was 2.45?mol of hydrogen per mole of methanol. The time on stream stability test showed that the Cu/SiO₂ catalyst is quite stable for 48?h.     

Catalysts for low-temperature methanol synthesis. I. A study of the reduction process

A study of the reduction of CuO in a ternary oxide system (Cu:Zn:Al, atomic ratio 62:14:24) demonstrated that at lower temperatures it occurred in two stages, whereas at higher temperatures it was no longer possible to display the formation of Cu₂O. The rate of reduction of CuO was strongly reduced on decreasing the partial pressure of hydrogen, while the presence of CO₂ stabilized the Cu₂O, delaying the reduction to copper. On the basis of simpler systems it was possible to demonstrate the activating effect of Al₂O₃ and the delaying effect of ZnO on the reduction of CuO.     

XPS,UPS, and STM studies of nanostructured CuO films

A Cu₁O_1.7 oxide film containing a large amout of superstoichiometric oxygen was obtained by low-temperature oxidation of metallic copper in the oxygen plasma. An STM study of the film structure showed that ～10 nm planar copper oxide nanocrystallites with particles packed parallel to the starting metal surface. In an XPS study, the spectral characteristics of the Cu2p and O1s lines indicated that particles with a CuO lattice formed (E _bnd(Cu2p _3/2) = 933.3 eV and a shake-up satellite, E _bnd(O1s) = 529.3 eV). The additional superstoichiometric oxygen is localized at the sites of contact of nanoparticles in the interunit space and is characterized by a state with the binding energy E _bnd(O1s) = 531.2 eV. Due to the formation of a nanostructure in the films during low-temperature plasma oxidation, the resulting copper oxide has a much lower thermal stability than crystalline oxide CuO.     

Formation and characterization of Cu<Subscript>x</Subscript>S layers on polyethylene film using the solutions of sulfur in carbon disulfide

Results of the formation of copper sulfide layers using the solutions of elemental sulfur in carbon disulfide as precursor for sulfurization are presented. Low density polyethylene film can be effectively sulfurized in the solutions of rhombic (α) sulfur in carbon disulfide. The concentration of sulfur in polyethylene increases with the increase of the temperature and concentration of sulfur solution in carbon disulfide and it little depends on the duration of sulfurization. Electrically conductive copper sulfide layers on polyethylene film were formed when sulfurized polyethylene was treated with the solution of copper (II/I) salts. Cu_xS layer with the lowest sheet resistance (11.2 Ω cm⁻²) was formed when sulfurized polyethylene was treated with copper salts solution at 80°C. All samples with formed Cu_xS layers were characterized by X-ray photoelectron spectroscopy. XPS analysis of obtained layers showed that on the layer’s surface and in the etched surface various compounds of copper, sulfur and oxygen are present: Cu₂S, CuS, CuO, S₈, CuSO₄, Cu(OH)₂ and water. The biggest amounts of CuSO₄ and Cu(OH)₂ are present on the layer’s surface. Significantly more copper sulfides are found in the etched layers.     

Preparation of cuprite (Cu2O), paramelaconite (Cu32+Cu21+O4) and tenorite (CuO) with magnetron sputtering ion plating: characterization by EPMA, XRD, HEED and SEM

Cu-O layers were deposited on Si-<100> wafers at 90°?C by means of reactive magnetron sputtering ion plating (R-MSIP). A Cu-target was sputtered in rf-mode by an oxygen/argon plasma, and the influence of the oxygen partial pressure on composition, structure, texture and morphology of the Cu-O layers was investigated. The analysis with EPMA, XRD, HEED and SEM yielded the following results: with an appropriate setting of the oxygen partial pressure, the oxygen content of the films could be controlled between 0 and 50 at-%. XRD bulk structure analysis shows changes in the crystal structure of the films with increasing oxygen content from the fcc structure of Cu, followed by the sc structure of Cu₂O (cuprite), the tetragonal structure of Cu₃ ²⁺Cu₂ ¹⁺O₄ (paramelaconite) to the monoclinic structure of CuO (tenorite). As revealed by HEED, the structure of the near-surface region of the latter two is the same as that of the bulk, whereas in the case of the films with fcc bulk structure, due to oxidation by air, the surface has the sc structure of Cu₂O, and in the case of the film with the sc structure, a monoclinic surface structure of CuO is observed. SEM analyses detected a disordered columnar growth of all Cu-O films.     

XPS depth profiling investigations on La2Zr2O7 layers prepared by chemical solution deposition

La₂Zr₂O₇ (LZO) layers have been recently investigated as potential buffer layers for superconducting YBa₂Cu₃O_7–x coated conductors deposited on Ni tapes. Chemical solution deposition was used for LZO layer preparation. X-ray photoelectron spectroscopy (XPS) depth profiling is demonstrated to be an important method for layer characterization in addition to X-ray diffraction techniques. XPS measurements revealed layers that are homogeneous in depth, very smooth, and have no significant impurities. A slight difference to the nominal La:Zr stoichimetry is discussed in combination with structural defects that are suspected from spectral changes during ion sputtering.     

A Polarographic Method Determing Cu(II), Cu(I) and Metallic Copper Contents in Copper Oxide Samples

Abstract

A polarographic procedure was developed which permits the analysis of powdered cupric and cuprous oxides in the presence of metallic copper. To determine CuO, Cu₂O and metallic copper content in the sample two weight aliquots were used. The first aliquot was dissolved in medium of 50 % ethanol + 3 M hydrochloric acid + saturated ascorbic acid solution. Insoluable metallic copper was determined polarographically after its' separation and additional dissolving in concentrated nitric acid.

The second sample aliquot was dissolved in 6 M hydrochloric acid and the ratio of Cu(I) / Cu(II) in the solution was determined from the polarographic curves. To calculate CuO, Cu₂O and Cu content in a sample the proposed procedure was applied. The developed method provides the accurate results of the determination of CuO, Cu₂O and Cu content in a powdered mixture. The reproducibility expressed as the relative standard deviation is from 1 % to 5 %.     

Untersuchung der ferromagnetischen Produkte der explosiven reaktionen zwischen Ammoniumeisencyanid und Kupfernitrat

The wet mixtures of ammonium hexacyanoferrate, (NH₄)₄[Fe(CN)₆], and cupric nitrate, Cu(NO₃)₂, react explosively when heated at 220 ?C. Among the solid products studied by chemical analysis, magnetic measurements and X-ray diffraction there are magnetite (Fe₃O₄), iron nitride (Fe₄N), gamma iron oxide (γ-Fe₂O₃), cuprous oxide (Cu₂O), alpha iron oxide (α-Fe₂O₃), cupric oxide (CuO), cuprous ferrite and metallic copper. Furthermore cupric hexacyanoferrate (Cu₂[Fe(CN)₆]) and ferric ferrocyanide (Fe₄[Fe(CN)₆]₃) have been found in weakly ferromagnetic products. The presence of these phases and their quantitative contribution depend upon the proportion of the initial salts and air supply.     

Fragmentation of diffusion zone in high-temperature oxidation of copper

Using thermogravimetry, microscopy and X-ray diffraction, high-temperature (600-900 °C) oxidation of copper wires and plates has been studied. An abrupt decrease in reaction rate after complete consumption of metal phase but long before reaching equilibrium has been observed. This phenomenon is connected to an irregular character of the development of the reaction diffusion zone. In contrast to the usually applied layer model, initially formed oxide layers separate into numerous aggregates of Cu₂O crystals chaotically scattered throughout the zone between thinner layers of CuO grains. Such fragmentation of the diffusion zone is induced by macro- and microcracks formed in copper scale under influence of mechanical stresses at metal-oxide phase boundary due to the difference in molar volume between copper and its oxides. The pattern of cracks provides channels of fast diffusion and maintains the reaction rate at high level but only until the source of crack formation remains in action.     

XPS for non-destructive depth profiling and 3D imaging of surface nanostructures

Depth profiling of nanostructures is of high importance both technologically and fundamentally. Therefore, many different methods have been developed for determination of the depth distribution of atoms, for example ion beam (e.g. O₂⁺, Ar⁺) sputtering, low-damage C₆₀ cluster ion sputtering for depth profiling of organic materials, water droplet cluster ion beam depth profiling, ion-probing techniques (Rutherford backscattering spectroscopy (RBS), secondary-ion mass spectroscopy (SIMS) and glow-discharge optical emission spectroscopy (GDOES)), X-ray microanalysis using the electron probe variation technique combined with Monte Carlo calculations, angle-resolved XPS (ARXPS), and X-ray photoelectron spectroscopy (XPS) peak-shape analysis. Each of the depth profiling techniques has its own advantages and disadvantages. However, in many cases, non-destructive techniques are preferred; these include ARXPS and XPS peak-shape analysis. The former together with parallel factor analysis is suitable for giving an overall understanding of chemistry and morphology with depth. It works very well for flat surfaces but it fails for rough or nanostructured surfaces because of the shadowing effect. In the latter method shadowing effects can be avoided because only a single spectrum is used in the analysis and this may be taken at near normal emission angle. It is a rather robust means of determining atom depth distributions on the nanoscale both for large-area XPS analysis and for imaging. We critically discuss some of the techniques mentioned above and show that both ARXPS imaging and, particularly, XPS peak-shape analysis for 3D imaging of nanostructures are very promising techniques and open a gateway for visualizing nanostructures.