Electrochromism of the electroless deposited cuprous oxide films

Thin cuprous oxide films were prepared by a low cost, chemical deposition (electroless) method onto glass substrates pre-coated with fluorine doped tin oxide. The X-ray diffraction pattern confirmed the Cu₂O composition of the films. Visible transmittance spectra of the cuprous oxide films were studied for the as-prepared, colored and bleached films. The cyclic voltammetry study showed that those films exhibited cathode coloring electrochromism, i.e. the films showed change of color from yellowish to black upon application of an electric field. The transmittance across the films for laser light of 670 nm was found to change due to the voltage change for about 50%. The coloration memory of those films was also studied during 6 h, ex-situ. The coloration efficiency at 670 nm was calculated to be 37 cm²/C.     

Study on the effect of annealing on the electrical properties of n-type cuprous oxide

n-Type cuprous oxide was synthesized by controlling the bath pH of the electro-deposition. Thereafter, cuprous oxide films were annealed in nitrogen at different temperatures. The electrical properties of n-type cuprous oxide films before and after annealing were studied by the capacitance-voltage measurements. By analysis of the Mott-Schottky curves, it was found that the carrier concentration of cuprous oxide films varied with the deposition bath pH and the annealing temperature. Also, the flat-band potential shifted with the increasing annealing temperature.     

Characterization of copper oxide thin films deposited by the thermal evaporation of cuprous oxide (Cu2O)

Thin films of copper oxide were deposited by thermal evaporation of cuprous oxide (Cu₂O) powder. The substrates were either unheated or heated to a temperature of 300 °C. The films were also annealed in air at a temperature of 500 °C for 3 h. The films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and UV-visible spectrophotometry. The effects of the substrate temperature and post-deposition annealing on the chemical, structural and optical properties of the films were investigated. As-deposited films on unheated substrates consisted of mixed cupric oxide (CuO) and Cu₂O phases, with a higher concentration of the Cu₂O phase. However, the films deposited on heated substrates and the annealed films were predominantly of the CuO phase.     

Photoactive TiO2/CuxO composite films for photocatalytic degradation of methylene blue pollutant molecules

Applying photocatalysts for utilizing solar energy is attractive because of its clean and limitless characteristics, but they have giant obstacles such as wide bandgaps, photocorrosion, and rapid charge recombinations to overcome for applications. In this study, the TiO₂/Cu_xO composite films are investigated as photoactive materials for the photodegradation ofmethylene blue (MB) pollutant molecules under standard sun light illumination. The TiO₂ layer is firstly fabricated on the FTO substrate by a doctor blade method, and then the second copper component is introduced by a spin-coating. Then, the composite films are thermally sintered to form cuprous and cupric oxides. This additional copper oxide phases plays a crucial role in achieving high photodegradation performance of MB under light irradiation. The best MB photodegradability from the TiO₂/Cu_xO composite films was achieved with the 3.6 wt% Cu_xO content case, and it is probably due to the effective charge separations with reduced recombinations in the copper oxide phases by the Z-scheme band arrangements between Cu₂O and CuO components. The composite films were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy for the film surface and cross-sectional morphology, crystalline structure, atomic binding energy, and light absorbance, respectively.     

Synthesis and electrochromic study of sol-gel cuprous oxide nanoparticles accumulated on silica thin film

In this study, electrochromic properties of cuprous oxide nanoparticles, self-accumulated on the surface of a sol-gel silica thin film, have been investigated by using UV-visible spectrophotometry in a lithium-based electrolyte cell. The cuprous oxide nanoparticles showed a reversible electrochromic process with a thin film transmission reduction of about 50% in a narrow wavelength range of 400-500 nm, as compared to the bleached state of the film. Using optical transmission measurement, we have found that the band gap energy of the films reduced from 2.7 eV for Cu₂O to 1.3 eV for CuO by increasing the annealing temperature from 220 to 300 °C in an N₂ environment for 1 h. Study of the band gaps of the as-deposited, colored and bleached states of the nanoparticles showed that the electrochromic process corresponded to a reversible red-ox conversion of Cu₂O to CuO on the film surface, in addition to the reversible red-ox reaction of the Cu₂O film. X-ray photoelectron spectroscopy indicated that the copper oxide nanoparticles accumulated on the film surface, after annealing the samples at 200 °C. Surface morphology of the films and particle size of the surface copper oxides have also been studied by atomic force microscopy analysis. The copper oxide nanoparticles with average size of about 100 nm increased the surface area ratio and surface roughness of the silica films from 2.2% and 0.8 nm to 51% and 21 nm, respectively.     

Photoelectrochemical solar cell studies on electroplated cuprous oxide thin films

Cuprous oxide (Cu₂O) is an interesting p-type semiconductor with a band gap of 2 eV suitable for solar cell applications. Deposition of Cu₂O thin films by electrodeposition from aqueous solutions is a low temperature and inexpensive technique. in the present work, Cu₂O thin films were cathodically deposited on Cu and tin oxide coated glass substrates by the cathodic reduction of copper (II) lactate solution. The optimized deposition conditions to synthesize cuprous oxide thin films were experimentally identified as; Deposition potential: −0.555 V versus SCE, pH: 9.0 ± 0.1, Bath temperature: 70^∘C. X-ray diffraction studies revealed the formation of single phase cubic Cu₂O films. The effect of annealing on the structure and morphology of Cu₂O thin films are studied. The dielectric susceptibility, optical conductivity and packing density are evaluated. Photoelectrochemical solar cells based on p-Cu₂O films are constructed. Spectral response studies indicate a peak in photo current density around 600 nm corresponding to the band gap of Cu₂O thin films. The effects of annealing, chemical etching and photo etching on the solar cell parameters are studied.     

Dependence of solar selectivity of copper-black films on their structure,chemical composition and morphology

The composition and morphology of anodically grown solar-selective copper-black films have been investigated using X-ray photoelectron spectroscopy with depth profiling, scanning electron microscopy and X-ray diffraction. It has been found that the films showing the best selectivity have their top layer consisting predominantly of crystalline cupric oxide (CuO). In the underlying region the dominating phase is cuprous oxide (Cu₂O) with Cu/O ratio increasing systematically towards the copper substrate. It is shown that the enhanced absorption in the solar region of the spectrum is due to the stacking of layers with graded composition and also due to the surface morphology of the film.     

On the growth of cuprous oxide films

{lcub;001}rcub; cuprous oxide (Cu₂O) films were epitaxially grown. From the two methods which were used (the oxidation of copper films and the direct evaporation of bulk Cu₂O) only the oxidation of copper yielded good single-crystal films. It was found that the optimum conditions were an oxidation temperature of 450°C with a partial pressure of oxygen of 2×10^-5 Torr and, after oxidation, a further annealing at a pressure of 10^-8 Torr.     

One-step chemical bath deposition and photocatalytic activity of Cu2O thin films with orientation and size controlled by a chelating agent

Nanocrystalline cuprous oxide (Cu₂O) thin films were prepared via a one-step chemical bath deposition (CBD) method. The effects of a chelating agent on the orientation, morphology, crystallite size, and photocatalytic activity of the thin films were carefully examined using X-ray diffractometry, scanning electron microscopy, and UV–vis spectrophotometry. The results confirmed that the crystallite size as well as the orientation of the films was dependent on the volume of trisodium citrate (TSC), demonstrating that the band gap ranged from 2.71 eV to 2.49 eV. The morphology and number density of the thin films also depended on the volume of TSC. In addition, the obtained Cu₂O thin films could degrade methyl orange (MO) efficiently in the presence of H₂O₂ under visible-light irradiation, and the mechanism for the enhanced photocatalytic activity of the Cu₂O thin films with the assistance of H₂O₂ was also explored in detail.     

Influence of thermal annealing on microstructural,morphological, optical properties and surface electronic structure of copper oxide thin films

In this study, effect of the post-deposition thermal annealing on copper oxide thin films has been systemically investigated. The copper oxide thin films were chemically deposited on glass substrates by spin-coating. Samples were annealed in air at atmospheric pressure and at different temperatures ranging from 200 to 600°C. The microstructural, morphological, optical properties and surface electronic structure of the thin films have been studied by diagnostic techniques such as X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV–VIS) absorption spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The thickness of the films was about 520 nm. Crystallinity and grain size was found to improve with annealing temperature. The optical bandgap of the samples was found to be in between 1.93 and 2.08 eV. Cupric oxide (CuO), cuprous oxide (Cu₂O) and copper hydroxide (Cu(OH)₂) phases were observed on the surface of as-deposited and 600 °C annealed thin films and relative concentrations of these three phases were found to depend on annealing temperature. A complete characterization reported herein allowed us to better understand the surface properties of copper oxide thin films which could then be used as active layers in optoelectronic devices such as solar cells and photodetectors.     

Combined reduction and sintering of preformed cuprous oxide strip

Abstract

A new method of making thin copper strip direct from cuprous oxide powder by an integrated powder technology route has been outlined. The proposed route consists of making, by a slurry method, a green cuprous oxide strip which is subsequently reduced with hydrogen to produce a porous copper strip. The strip is densified by hot rolling to produce a fully dense structure. The combined reduction and sintering behaviour of the green cuprous oxide strip is reported. The mechanism of reduction of the cuprous oxide with hydrogen at various temperatures is discussed, and the geometry of the reaction zone in the green oxide strip is described.

MST/183     

Mechanisms of carrier generation and transport in Ni-doped Cu2O

The density and mobility of hole carriers in Ni-doped and undoped cuprous oxide (Cu₂O) films prepared by pulsed laser deposition (PLD) from Ni-doped and undoped CuO targets, respectively, were measured in order to examine the mechanisms of carrier generation and transport in doped films. The temperature dependence of the carrier density of the films revealed that regardless of the Ni content, the activation energies of the acceptor level of the films are 0.22-0.25 eV. The temperature dependence of the mobility of the films changed from −0.58 to ∼0 by doping with Ni. These results evidenced that hole carriers in Ni-doped Cu₂O as well as in undoped Cu₂O were generated by Cu vacancies and were primarily scattered by neutral impurity scattering centers. X-ray diffraction (XRD) measurements of the films showed that the mass fraction of Cu₂O in the films decreased with increasing Ni content, while that of CuO increased. It was also found that the reduction process of CuO to Cu₂O was suppressed by the Ni doping.     

Electrodeposition and characterization of cuprous oxide

Films of cuprous oxide were electrodeposited potentiostatically and galvanostatically on a variety of substrates. The usable range of deposition parameters was determined and discussed. Uniform and adherent films of thickness up to 6 μm could be deposited galvanostatically and to higher values potentiostatically. The films were polycrystalline with grains of a few micrometers in size when deposited at 60 °C and one order of magnitude smaller when deposited at 49 °C. Regardless of the mode of deposition, the temperature of deposition and also the type of substrate, deposited films were highly oriented along the (100) plane parallel to the substrate surface. The composition of the films was found to be Cu₂O with an optical band gap of 1.95 eV.     

Octahedral cuprous oxide synthesized by hydrothermal method in ethanolamine/distilled water mixed solution

Octahedral cuprous oxide has been synthesized by a simple hydrothermal method using copper sulphate and sodium hydroxide as raw materials in ethanol amine/distilled water mixed solution. The synthesized cuprous oxide powders were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy. XRD pattern exhibited that the nanocrystalline nature with cubic structure for the synthesized nanostructures. Analysis results reveal that pH value of solution plays an important role in the formation of octahedron shape for cuprous oxide. A probable formation mechanism of octahedral cuprous oxide is also proposed.     

Fabrication of BaTiO3/Cu composite by reducing Cu2O under nitrogen atmosphere

BaTiO₃–Cu ferroelectric/metal composite was successfully fabricated by sintering Cu₂O-added BaTiO₃ pellet under nitrogen gas flow. In the results of XRD analysis of the sintered body, it was found that cuprous oxide was reduced to copper in the atmosphere of 100 ml/min nitrogen gas flow, but was not reduced and remained as itself in air. Lattice parameter changes of the specimens sintered at 1280 °C in 100 ml/min nitrogen gas flow indicated that solubility limit of cuprous oxide (Cu₂O) into BaTiO₃ is thought to be less than 1 wt%. The melt from cuprous oxide is thought as a good sintering aid to densify BaTiO₃. In this experiment, we determined the optimum sintering condition to get BaTiO₃–Cu ferroelectric/metal composite with more than 95% of relative density. From the results of DTA and TG analysis, cuprous oxide is considered to dissociate into copper and oxygen gas and form the eutectic melt of BaTiO₃–Cu at around 900 °C in more than 50 ml/min nitrogen flow rate atmosphere. Received: 29 October 2001 / Reviewed/Accepted: 3 November 2001     

In Situ Synthesis of Cuprous Oxide/Cellulose Nanofibers Gel and Antibacterial Properties

Cellulose nanofibers were synthesized by acetobacter xylinum (xylinum 1.1812). The cellulose nanofibers with 30-90 nm width constructed three-dimension network gel, which could be used as a wound dressing since it can provide moist environment to a wound. However, cellulose nanofibers have no antimicrobial activity to prevent wound infection. To achieve antimicrobial activity, the cellulose nanofibers can load cuprous oxide (Cu₂O) particles on the surface. The cuprous oxide is a kind of safe antibacterial material. The copper ions can be reduced into cuprous oxides by reducing agents such as glucose, N₂H₄ and sodium hypophosphite. The cellulose nanofibers network gel was soaked in CuSO₄ solution and filled with copper ions. The cuprous oxide nanoparticles were in situ synthesized by glucose and embedded in cellulose nanofibers network. The morphologies and structure of the composite gel were analyzed by FESEM, FTIR, WAXRD and inductively coupled plasma (ICP). The sizes of Cu₂O embedded in cellulose nanofibers network are 200-500 nm wide. The peak at 605 cm⁻¹ attributed to Cu(I)-O vibration of Cu₂O shits to 611 cm⁻¹ in the Cu₂O/ cellulose composite. The Cu₂O/ cellulose nanofibers composite reveals the obvious characteristic XRD pattern of Cu₂O and the results of ICP show that the content of Cu₂O in the composite is 13.1%. The antibacterial tests prove that the Cu₂O/ cellulose nanofibers composite has the high antibacterial activities which is higher against S. aureus than against E. coli.     

Experimental and first-principles theoretical studies on Ag-doped cuprous oxide as photocathode in photoelectrochemical splitting of water

Nanostructured thin films of undoped and Ag-doped cuprous oxide were deposited on indium tin oxide-coated glass substrate using simple spray pyrolysis method for their use as photocathode in photoelectrochemical (PEC) cell for solar energy based water splitting. Combination of experiments and first-principles density functional theory based calculations was used to determine and understand the effect of Ag substitution on electronic structure and PEC performance. Thin films were characterized using XRD, FE-SEM, UV–Vis spectroscopy and PEC measurements. The results of DFT calculations show that the top of valence band and bottom of conduction band of undoped Cu₂O lie at Г point of brillouin zone, respectively, suggesting that pure Cu₂O is a direct band gap material. Minimal changes appear in the band gap and band gap energies in the Ag-doped Cu₂O system, keeping it still a direct band gap material. A defect band appearance can be seen between ?4 and ?5 eV in the valence band consisting mainly of Ag 4d states and can be explained by a stronger interaction between the Ag 4d and O 2p, due to the larger Ag size. Ag-doped samples exhibit improved conductivity and fourfold increase in photocurrent density with respect to undoped samples.     

Characterization of Cl-doped n-type Cu2O prepared by electrodeposition

N-type doping of cuprous oxide (Cu₂O) films by chlorine (Cl) during electrodeposition was reported by the authors recently. A more detailed study on the effects of doping conditions on electrical properties of Cl-doped Cu₂O is presented in this paper. The resistivity of Cl-doped Cu₂O is affected by doping conditions, including Cu and Cl concentrations, different Cu and Cl precursors, complexing agent concentration, solution pH, and deposition temperature. It is believed that these conditions control the amount of Cl incorporated into the Cu₂O films, thus the doping level. The lowest resistivity obtained so far is 7 Ω-cm, suitable for solar cell applications. Photocurrent-potential measurements verify the n-type conductivity of Cl-doped Cu₂O. Scanning electron microscopy indicates a small grain size of around 100 nm in Cl-doped Cu₂O. X-ray diffraction confirms Cu₂O as the only detectable phase in the film.     

Thin films preparation by rf-sputtering of copper/iron ceramic targets with Cu/Fe = 1: From nanocomposites to delafossite compounds

In the Cu-Fe-O phase diagram, delafossite CuFeO₂ is obtained for the Cu^I oxidation state and for the Cu/Fe = 1 ratio. By decreasing the oxygen content, copper/spinel oxide composite can be obtained because of the reduction and the disproponation of cuprous ions. Many physical properties as for instance, electrical, optical, catalytic properties can then be affected by the control of the oxygen stoichiometry.In rf-sputtering technique, the bombardment energies on the substrate can be controlled by the deposition conditions leading to different oxygen stoichiometry in the growing layers.By this technique, thin films have been prepared from two ceramic targets: CuFeO₂ and CuO + CuFe₂O₄. We thus synthesized either Cu⁰/Cu_xFe_1−xO₄ nanocomposites thin films with various Cu⁰ quantities or CuFeO₂-based thin films.Two-probes conductivity measurements were permitted to comparatively evaluate the Cu⁰ content, while optical microscopy evidenced a self-assembly phenomenon during thermal annealing.     

基于嵌段聚醚酯多元醇的聚氨酯控释机理研究

针对海洋工程设备中弹性基材的防污特殊需求,合成聚乙二醇(PEG)/聚己内酯(PCL)嵌段共聚物PEG/CLX,并与HDI三聚体固化形成可降解聚氨酯,研究其亲水性能及降解性能,再将PEG/CLX与氧化亚铜等结合,制备成一系列的海洋防污涂层,研究其控释机理.