Copper Oxide Thin Films Research Articles

Supercapacitor performance of pure and Ni-doped CuO electrodes prepared by USP

Abstract In this study, the ultrasonic spray pyrolysis (USP) technique was employed to fabricate pure and 3% Ni-doped copper oxide (CuO) thin films (TFs) on In2O3/SnO2 (ITO) coated glass substrates. X-ray diffraction (XRD) analysis revealed that both pure and 3% Ni-doped CuO TFs exhibit a polycrystalline structure with the tenorite phase oriented preferentially along the (111) plane. The morphological properties of these TFs were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging. Energy dispersive x-ray spectroscopy (EDX) confirmed that the deposited TFs achieved the desired stoichiometry. The electrochemical properties of both pure and 3% Ni-doped CuO TFs were evaluated using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). At a current density of 1 A g−1, the specific capacitance of pure CuO TFs was found to be 78 F g−1, decreasing to 2 F g−1 at 10 A g−1. In contrast, Ni-doped CuO TFs exhibited a specific capacitance of 722 F g−1 at 1 A g−1 and 20 F g−1 at 10 A g−1. These results indicate that Ni-doping significantly enhances the specific capacitance values. The superior performance of Ni-doped CuO electrodes is attributed to their uniformly high porosity and improved electrical conductivity, demonstrating Ni-doped CuO as an optimal electrode material for pseudocapacitors.

Hydrogen activation by rhodium under the cover of a copper oxide thin film

The activation of reactants by catalytically active metal sites at metal-oxide interfaces is important for understanding the effect of metal-support interactions on nanoparticle catalysts and for tuning activity and selectivity. Using a combined experimental and theoretical approach, we studied the activation of H2 and the effect of CO poisoning on isolated Rh atoms completely or partially covered by a copper oxide (Cu2O) thin film. Temperature-programmed desorption (TPD) experiments conducted in ultra-high vacuum (UHV) show that neither a partially nor a fully oxidized Cu2O layer grown on a Rh/Cu(111) single-atom alloy can activate hydrogen in UHV. However, in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) experiments performed at elevated H2 pressures reveal that Rh significantly accelerates the reduction of these Cu2O thin films by hydrogen. Remarkably, the fastest reduction rate is observed for the fully oxidized sample with all Rh sites covered by Cu2O. Both TPD and AP-XPS data demonstrate that these covered Rh sites are inaccessible to CO, indicating that Rh under Cu2O is active for H2 dissociation but cannot be poisoned by CO. In contrast, an incomplete oxide film leaves some of the Rh sites exposed and accessible to CO, and hence prone to CO poisoning. Density functional theory calculations demonstrate that unlike many reactions in which hydrogen activation is rate limiting, the rate-determining step in the dissociation of H2 on thin-film Cu2O with Rh underneath is the adsorption of H2 on the buried Rh site, and once adsorbed, the dissociation of H2 is barrierless. These calculations also explain why H2 can only be activated at higher pressures. Together, these results highlight how different the reactivity of atomically dispersed Rh in Cu can be depending on its accessibility through the oxide layer, providing a way to engineer Rh sites that are active for hydrogen activation but resilient to CO poisoning.

Surface engineering of CuO-Cu2O heterojunction thin films for improved photoelectrochemical water splitting

The efficient production of green hydrogen poses a significant challenge that requires the development of active, low-cost, and stable catalysts. Copper oxide has emerged as a highly effective photocatalyst for water splitting, offering the advantages of being nontoxic, abundant, and inexpensive. Nonetheless, the photoelectrochemical water splitting (PEC) process can be enhanced through surface modification. In this study, we utilized single-source precursors for aerosol-assisted chemical vapor deposition (AACVD) in order to deposit thin films of copper oxide (CuO-Cu2O) heterojunctions onto a substrate composed of fluorine-doped tin oxide (FTO). The chosen precursor for this purpose was copper (II) nitrate hemi(pentahydrate). To further optimize the CuO-Cu2O films, a novel acid treatment involving the addition of varying quantities of acetic acid (AA) to the precursor solution was employed. Remarkably, this acid treatment resulted in a significant improvement in the photocurrent density of the CuO-Cu2O heterojunction. Notably, a 3 mL acid-treated CuO-Cu2O thin film exhibited an impressive photocurrent measure of −6.8 mA/cm2 at 0.0 V vs RHE in 0.5 M Na2SO4 electrolyte, compared to the performance of the untreated CuO-Cu2O thin film (−2.8 mA/cm2 at 0.0 V vs RHE). This catalyst demonstrated stability and a threefold increase in hydrogen production performance. The increase in photocurrent densities is closely linked to the influence of AA on two key factors: particle growth and structural defects, such as oxygen vacancies. This relationship has been confirmed through the examination of SEM, AFM, and PL spectra results. The findings of this study not only offer a novel approach to catalyst design but also propose a practical method for photoelectrochemical water splitting. This method holds great promise for achieving sustainable and renewable energy sources, as well as efficient green hydrogen production.

Effect of gamma and ultraviolet irradiation on the optical properties of copper oxide nanostructured thin films by chemical spray pyrolysis

Nanostructured copper oxide thin films were grown by the chemical spray pyrolysis (CSP) technique. Utilizing a homemade spray pyrolysis method, thin films are created. This work investigates the role of gamma ray and ultraviolet ray irradiation on the optical properties of copper oxide thin films(CuO) prepared. In this framework, used different substrate temperatures 300 °C, 350 °C, and 400 °C for the layers were grown on glass for the prepared CuO thin films. UV–visible spectrometer, field emission scanning electron microscopy (FE-SEM) and X-ray diffraction patterns(XRD) measurements were all used to characterize the samples. The UV–visible spectroscopy showed a decrease in the absorbance and the optical band gap of CuO thin films with the increase in the higher substrate temperatures before irradiation. Additionally, surface plasmon resonance peaks (λSPR) were observed at 329 nm. FE-SEM images revealed spherical-like shapes with an average diameter range of 48 nm,56 nm and 62 nm for 300 °C, 350 °C, and 400 °C, respectively. An analysis of X-rays revealed that CuO thin films contained the crystallographic planes of a monoclinic and an orthorhombic crystal system. Also, when samples were exposed to gamma and UVC radiation, the absorbance intensity of CuO thin films increased, but the optical band gap decreased.

Selectivity of a Copper Oxide CO2 Reduction Electrocatalyst Shifted by a Bioinspired pH-Sensitive Polymer.

A bioinspired polymeric membrane capable of shifting the selectivity of a copper oxide electrocatalyst in the CO2 reduction reaction is described. The membrane is deposited on top of copper oxide thin films from wet deposition techniques under controlled conditions of humidity and self-assembles into an arranged network of micrometer-sized pores throughout the polymer cross-section. The membrane was composed of a block copolymer with a precisely controlled ratio of poly-4-vinylpyridine and poly(methyl methacrylate) blocks (PMMA-b-P4VP). The intrinsic hydrophobicity, together with the porous nature of the membrane's surface, induces a Cassie-Baxter wetting transition above neutral pH, resulting in water repulsion from the catalyst surface. As a consequence, the catalyst's surface is shielded from surrounding water molecules under CO2 electroreduction reaction conditions, and CO2 molecules are preferentially located in the vicinity of the catalytically active area. The CO2 reduction reaction is therefore kinetically favored over the hydrogen evolution reaction (HER).

Effect of doping level on the photoconduction and chemiresistive ethanol gas sensing of lanthanum-doped CuO films

Undoped and lanthanum (La)-doped copper oxide (CuO) thin films were prepared by the nebulizer spray pyrolysis technique. The X-ray diffraction analysis revealed that the effective doping of lanthanum does not alter the monoclinic crystalline structure of copper oxide thin films. Raman spectra confirmed the crystalline quality of undoped and La-incorporated CuO films. From, scanning electron micrograph images, the La-doped CuO films exhibit spherical particles. Energy dispersive X-ray analysis confirmed the existence of copper, lanthanum and oxygen elements. The doping of La-substituted CuO films showed a minimum bandgap when compared to undoped CuO film. The oxidation states of Cu 2p, La 3d and O 1s elements were observed. The electrical resistivity of the films was considerably decreased due to the doping of La ions in CuO matrix. The photoluminescence spectra show that the doping of La ions increases the defect states and shows increased intensity. The time resolved photoluminescence analysis revealed that an extended carrier lifetime was observed for the La-doped films. The La-doped CuO sensors achieved a superior gas sensing performance at room temperature and exhibited quick response and recovery times, suggesting that the sensor has the potential for the detection of harmful volatile gases in real-world applications. The photoconductive investigation revealed that the La-doped CuO films exhibited higher charge-transporting properties and increased light-harvesting ability. This study sheds light on designing gas sensors working under ambient conditions and photosensors for optoelectronic devices.

Synthesis of CuO Thin Film Incorporated with Nanostructured Nd2O3 Deposited by Pulsed Laser Deposition for Ammonia Sensing Applications

This study involved depositing thin films of copper oxide (CuO) and copper oxide films incorporated with neodymium oxide (Nd2O3) in various weight ratios using the pulsed laser deposition technique to fabricate an ammonia gas sensor. The characteristics of the developed films were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence spectroscopy (PL) techniques. The study investigated the impact of incorporating Nd2O3 into the CuO film on its sensing characteristics. The X-ray analysis revealed a polycrystalline structure of CuO with a crystal size of 19 nanometers. Furthermore, incorporating CuO and Nd2O3 formed a mixed phase comprised of both CuO and Nd2O3. The average crystallite size varied with the Nd2O3 incorporation rate from 19[Formula: see text]nm to 14.7[Formula: see text]nm. With increasing Nd2O3 incorporation ratios, the surface morphology changed from smooth to spherical-like nanostructures, and the average particle sizes varied from 28[Formula: see text]nm to 130[Formula: see text]nm. The PL spectrum analysis results confirmed that the incorporation of Nd2O3 resulted in a change in the peak intensity of the PL spectrum, with a significant increase in the peak associated with oxygen vacancies, contributing to the improvement of the sensor response. The incorporation of Nd2O3 greatly enhanced the sensitivity of the as-deposited CuO film. The sample with 5 wt.% Nd2O3 exhibited the maximum sensitivity, reaching 180% against 79 ppm NH3 at a working temperature of 50[Formula: see text]C.

Oxidation characteristics of copper oxide thin films deposited by direct current sputtering under substrate temperature and post-deposition copper-ion implantation

The oxidation and structural, optical and morphological properties of copper oxide thin films deposited by direct current magnetron sputtering under different substrate temperatures and oxygen (O2) partial pressures, and subsequent 200 keV Cu ion implantation are investigated. The colour of the films progressively changed from yellowish brown to dark brown and oxide phase from Cu2O to Cu4O3 to CuO through mixed phases with increase in oxygen partial pressure from 20 to 90 % of the working pressure and substrate temperature from room temperature (27 °C) to 350 °C. The rate of oxidation and crystallinity of the films substantially increased with increase in substrate temperature. The ion implantation in the room temperature deposited films produced significant crystallization and decrystallization with respect to the ion fluence, and that in 350 °C substrate temperature deposited films instigated Cu-rich phase. The substrate temperature and ion implantation engendered distinctive red shift of the absorption edge and prevalent changes in the interference patterns in the optical spectra of the films. The calculated direct band gap values of the films are in the range of 1.7 to 2.42 eV, which decreased to the range of 1.65 to 2.17 eV on ion implantation. The indirect band gap of the films with predominant Cu4O3 and CuO phases are in the range of 1.23 to 1.49 eV. The refractive index and extinction coefficient of the films at 1100 nm are in the range of 2.1 to 2.5 and 0.03 to 0.12, which increased to the range of 3 to 7 and 0.2 to 0.45, respectively, on ion implantation. The films displayed agglomeration of the particles and directional growth of the agglomerates with respect to O2 partial pressure and substrates temperature, and increase in the size of the particles / agglomerates, and rough surface morphology on ion implantation.

Influence of Oxygen Flow Rate on the Phase Structures and Properties for Copper Oxide Thin Films Deposited by RF Magnetron Sputtering

Influence of Oxygen Flow Rate on the Phase Structures and Properties for Copper Oxide Thin Films Deposited by RF Magnetron Sputtering

Effects of Rapid Heat Treatments on the Properties of Cu2O Thin Films Deposited at Room Temperature Using an Ammonia-Free SILAR Technique

We report herein the analysis of the properties of copper(I) oxide thin films deposited by an optimized ammonium-free successive ion layer adsorption and reaction (SILAR) technique. The Cu2O thin film deposition process was carried out at room temperature using copper acetate monohydrate, sodium citrate as complexing agent, and hydrogen peroxide as precursors of copper and oxygen ions, respectively. The harmless and easy-to-handle sodium citrate replaces the volatile NH4OH commonly employed as complexing agent in the SILAR technique for the deposition of metal oxide thin films. The optical, structural, morphological, and electrical properties of the as-deposited Cu2O thin films were studied as a function of the number of cycles during deposition, as well as their modifications produced by the effect of rapid thermal annealing (RTA) in vacuum in a temperature range of 200–250°C for 1 min, 3 min, and 5 min. The as-deposited thin films had cubic crystalline structure corresponding to the Cu2O phase as determined by x-ray diffraction (XRD), with a direct energy bandgap of 2.43–2.51 eV depending on the number of cycles, and electrical resistivity of the order of 103 Ω cm. The XRD and x-ray photoelectron spectroscopy (XPS) analysis of the Cu2O thin films treated by RTA demonstrated an increase of the crystal size with time and temperature of the RTA and reduction effects from Cu2+ to Cu1+ oxidation states. On the other hand, the RTA treatments also decreased their energy bandgap to 2.38 eV and electrical resistivity to 102 Ω cm. The high energy bandgap values of the Cu2O thin films were attributed to quantum confinement effects produced by their small crystal size in the range of 3.6–8.6 nm.Graphical

Effect of vacuum-ultraviolet irradiation on structure and resistivity of epitaxial copper oxide thin films

Effect of vacuum-ultraviolet irradiation on structure and resistivity of epitaxial copper oxide thin films

Influence of solution pH dependency on structure, optical with photoelectrochemical characteristics of SILAR deposited copper oxide thin films

Photoelectrochemical (PEC) technology is a promising approach for converting solar energy into chemical energy, offering significant potential for renewable energy applications. In this work, the CuO thin film was fabricated with different pH value in between 8.5 ± 0.1 and 10.5 ± 0.1 via Successive Ionic Layer Adsorption and Reaction (SILAR) method. The Effect of pH on thickness, structural, morphological, elemental composition and optical properties were investigated by using stylus profilometry, XRD, SEM, TEM, EDX, UV–vis and PL. The XRD results showed that as the pH increased, the crystallite size increased from 19.24 nm to 25.62 nm, with a monoclinic phase along the (111) direction. The CuO film deposited at pH value 10.5 ± 0.1 exhibit well defined identical particle with its size in the range between 200 and 300 nm was confirmed by SEM and TEM analysis. As the pH increased from 8.5 ± 0.1 to 10.5 ± 0.1, the CuO film bandgap (Eg) value reduced from 1.52 eV to 1.42 eV with indirect transition. The CuO photocathode deposited at pH 10.5 ± 0.1 shows maximum photocurrent density of 1.45 mA/cm2 at −0.1 V vs. RHE in 0.5 M Na2SO4 solution. Furthermore, the Electrochemical Impedance Spectroscopy (EIS) analysis shows, the CuO (pH 10.5 ± 0.1) electrode have higher conductivity value of 0.6862 S/cm compared CuO at pH 8.5 ± 0.1 (0.2779 S/cm) and CuO at pH 9.5 ± 0.1 (0.4646 S/cm) electrodes.

Study of deposition temperature effect on spray-deposited copper oxide thin films and its schottky diodes

Due to its ideal optical and electrical properties for upcoming electronic devices, Cu2O is commonly regarded as one of the most promising p-type oxides. Copper (Cu) rapidly deposits mixed phases of its oxides. This article describes the spray deposition method for developing copper oxide thin films at temperatures between 200 and 400 °C on glass substrates coated with ITO. Through optimization of the deposition temperature, Cu2O-rich phases were attained in the copper oxide films, typically around 300 °C. A Cu-rich phase was seen at 200 °C deposition temperature, and this phase progressively diminished at higher temperatures. At 400 °C, the CuO phase began to enrich the films in the meantime. Analysis using an x-ray diffraction (XRD) verified the existence of Cu2O phases (111), (200), and (220). The crystallites were discovered to be between 17.49 and 20.32 nm in size for the films deposited between 300 and 400 °C. The x-ray Photoelectron Spectroscopy (XPS) identifies Cu and oxygen as the main components. Furthermore, it is demonstrated that the deposition temperature significantly affects the copper’s oxidation state. The Atomic Force Microscopy (AFM) investigation showed that as the temperature increased, surface roughness decreased. As the deposition temperature increased, the energy band gap of the deposited films widened from 1.67 to 2.85 eV, as observed by the UV–vis-NIR spectrophotometer. Moreover, the fabrication of Schottky diodes with Cu metal contacts is also reported. These fabricated diodes showed a proportionate rise in barrier height with increasing deposition temperature.

Study of The Optical Properties of Copper Oxide Thin Films Prepared by Chemical Spray Pyrolysis Technique

Study of The Optical Properties of Copper Oxide Thin Films Prepared by Chemical Spray Pyrolysis Technique

Physiochemical and electrical activities of nano copper oxides synthesised via hydrothermal method utilising natural reduction agents for solar cell application

Abstract The aim of this study is to explore the potential compatibility of copper oxide nano-powders synthesised via hydrothermal method for solar cell applications by triggering a reaction between copper acetate and various reducing agents derived from natural resources, including Arabic gum, molasses, starch, and vinegar. X-ray diffraction analysis revealed the crystalline phases of the synthesised materials, indicating the successful synthesis of copper oxide material, which was confirmed by identifying patterns that matched specific copper oxide phases. Fourier transform infrared spectroscopy was employed to analyse the molecular vibrations and chemical compounds present in the reducing agents. The reducing properties of the selected materials and their capacity to convert copper acetate into copper oxide were validated. Field-emission microscopy and transmission electron microscopy analyses of the synthesised copper oxide nanoparticles (NPs) revealed variations in particle size and morphology. These variations were dependent on the particular reducing agent utilised during synthesis. Moreover, the carrier concentration, mobility, and resistivity were evaluated as the electrical properties of the spin-coated copper oxide thin films. Hall effect analysis determined that the choice of reducing agent significantly influenced the carrier concentration (n) and mobility (µ) of the films. Remarkably, nano copper oxide films synthesised using starch exhibited irregular spherical grains with porous surfaces. Starch-synthesised samples showed the highest conductivity of n = 1.2 × 1019 cm−3 when compared with those synthesised with other reducing agents. This suggests that the porous surfaces in the starch-synthesised films may have contributed to their enhanced conductivity compared to films synthesised with alternative reducing agents. In summary, the findings emphasised the influence of the reducing agent on the size, morphology, and electrical conductivity of the copper oxide NPs.

Enhanced visible light-activated gas sensing properties of nanoporous copper oxide thin films

Metal oxide gas sensors are popular chemoresistive sensors. They are used for numerous tasks, including environmental and safety monitoring. Some gas-sensing materials exhibit photo-induced properties that can be utilized for enhanced gas detection by modifying the sensor selectivity and sensitivity when illuminated by light. Here, we present the gas sensing characteristics of highly nanoporous Cu2O thin films towards both electrophilic (NO2) and nucleophilic (C2H5OH, NH3) gas molecules under ambient temperature and modulated by visible light illumination of different colors (red: 632 nm, green: 530 nm, blue: 468 nm). Cu2O films were fabricated by reactive advanced gas deposition (AGD) technology. The surface and structural analysis of the samples confirm the deposition of nanoporous thin films of mixed copper oxide phases. The gas sensing property of Cu2O exhibited expected p-type semiconductor behavior upon electrophilic and nucleophilic gas exposures. Our results show that visible light illumination provides enhanced sensor response.

Thermal annealing effect on phase evolution, physical properties of DC sputtered copper oxide thin films and transport behavior of ITO/CuO/Al Schottky diodes

Herein, we report on the post-annealing temperature effect on the transport behavior of p-CuO/Al Schottky barrier diodes. In addition, the transformation of phase from Cu4O3 to CuO phase was studied. Copper oxide thin films were grown on soda lime glass substrates, and post-annealing temperature's influence on the films’ structural, chemical, morphological, and electrical characteristics was comprehensively examined. X-ray diffraction study revealed the development of polycrystalline tenorite phase (CuO) on annealing. Raman analysis also confirmed the formation of the tenorite phase (CuO) at higher annealing temperatures (400 °C and 500 °C). XPS study revealed the occurrence of the Cu4O3 phase for room temperature deposited sample and CuO phase at the higher annealing temperature. Using current–voltage analysis, the Chueng model, and the thermoelectric emission model, the Schottky behavior between the metal and semiconductor were investigated. The fabricated diode showed a rectification ratio of 103 at ± 2 V, with the barrier height ranging from 0.84 to 1.12 eV due to different annealing treatments. The attributes of the power law were employed to elucidate space charge-limited conduction and the process of tunneling across the density of interface traps in p-CuO/Al Schottky diodes. This study provides valuable insights into the behavior of the p-CuO/Al Schottky junction, enhancing our understanding of its characteristics.

Time-Resolved Sensitivity of a Cadmium-Doped Copper Oxide Thin Film as a Chlorine Gas Detector

Time-Resolved Sensitivity of a Cadmium-Doped Copper Oxide Thin Film as a Chlorine Gas Detector

Study on the Optical and Gas-Sensing Performance of Zn-doped CuO Films

The pure copper oxide thin film was deposited on glass substrates by SILAR method with 30 cycles. To examine the doping effect, Zn-doped films at different doping ratios were prepared under the same conditions as the undoped film. The XRD, SEM and Raman measurements were performed to investigate the morphological and structural properties of the samples. Analysis showed increasing aggregation and amorphous structure with doping. The optical parameters were characterized by spectrophotometer measurement and relevant formulas. The band gap energies were determined to increase from 2.50 to 2.79 eV with the increasing Zn rate. The Hervé and Vandamme, Moss and Ravindra relations were used to determine the refractive index. The room temperature gas-sensing performance for the undoped and doped samples were reported and the responses for 5 ppm gas were calculated as 249 %, 800 %, 189 % and 15 % for the CuO, 1Zn:CuO, 3Zn:CuO and 5Zn:CuO, respectively. The response of CuO thin films changed with doping, and 1% Zn doping rate was determined as the optimal rate in this study.

Crystal phase control of copper oxide thin films by process pressure during high power impulse magnetron sputtering

High-performance P-type cuprous oxide (Cu2O) film was prepared at room temperature by high power impulse magnetron sputtering. Optical emission spectra revealed that the ratio of Cu radicals/ions in the plasma significantly decreased with increasing process pressure due to the reduction of sputtering yield as the Cu target surface was oxidized by the increased oxygen radicals/ions. In addition, the increase of self-sputtering yield for Cu cations with increasing process pressure reduced the arrival ratio of Cu species at the substrate surface. As a result, the film crystal phase transformed from Cu2O to Cu4O3 and CuO with increasing process pressure. X-ray photoelectron spectra and Hall effect test results revealed that the oxygen vacancy defects in the films were passivated by the increased oxygen species at higher process pressure, leading to the inhibition of electron background and the emergence of net hole concentration. A mobility of 37.3 cm2/V·s was achieved, which is very high for room-temperature-deposited Cu2O film and comparable to high-temperature (300–600 °C) deposited/post-annealed Cu2O film. Finally, Cu2O thin film transistors (TFTs) exhibited reasonable switching characteristics with a low off-current of 0.3 nA without post-annealing treatment, showing an advantage in low-temperature preparation.