Semiconducting Copper Oxide Research Articles

Influence of Treatment Time on the Synthesis of Copper Oxide Semiconductor Films by Cathode Cage Plasma Deposition

Influence of Treatment Time on the Synthesis of Copper Oxide Semiconductor Films by Cathode Cage Plasma Deposition

Coupling Cuprous Oxide with Upconversion Materials: A Holistic Approach to Efficient Solar Water Splitting

Photoelectrochemical (PEC) water splitting is a promising solution for harnessing solar radiation for hydrogen production. This technology combines sunlight capture and water electrolysis processes, resulting in the production of hydrogen and oxygen that can efficiently recombine in fuel cells. However, challenges in materials science still need resolution to establish PEC water splitting as a practical and competitive approach. Copper oxide semiconductors, particularly materials based on cuprous oxide (Cu2O), have attracted attention due to their abundant elemental availability, scalable synthesis methods, and inherent p-type characteristics. To improve the generated photocurrent of the photoelectrode system, photon upconversion (UC) materials can be implemented into water-splitting devices. TTA-based UC is particularly suitable for solar water splitting due to its efficient conversion at low photon intensity. This work highlights the potential application of TTA-based UC in solar-assisted water splitting and highlights the significance of photonic designs and nanointerface engineering to improve the light-harnessing properties of photoactive materials. To the best of our knowledge, our research group was the first to successfully implement the integration of photoactive materials for solar water splitting with an upconversion device based on the TTA mechanism. This strategy allows us to dramatically improve the light-harnessing properties of our photoelectrode by irradiating the photocatalyst from dual perspectives (front and back-side illumination). It has been demonstrated that Cu2O coupled with an upconverter (UC) outperforms bare Cu2O by 56% in terms of produced photocurrent density, namely bare Cu2O produces -0.32 mA·cm-2 at 0V (vs. RHE), whereas Cu2O/UC exhibits a photocurrent of -0.5 mA·cm-2. Figure 1

Copper oxide coupled with photon upconversion for solar water splitting

Photoelectrochemical water splitting is a promising solution for harnessing solar radiation for hydrogen production. Copper oxide semiconductors, particularly materials based on cuprous oxide, have attracted attention due to their abundant elemental availability and scalable synthesis methods. To improve the generated photocurrent of the photoelectrode system, photon upconversion materials can be implemented into water-splitting devices. Here, we demonstrate the potential application of triplet-triplet annihilation-based upconversion in solar-assisted water splitting and highlight the significance of photonic designs to improve the light-harnessing properties of photoactive materials. The triplet-triplet annihilation mechanism is particularly suitable due to its efficient conversion at low photon intensity, namely under 1-sun illumination. Our results show that Cu2O coupled with an upconverter outperforms bare Cu2O by 56% in terms of produced photocurrent density. We construct a hybrid water-splitting device with an extended absorption range by utilizing a semi-transparent 600 nm Cu2O film with a 5 nm Au underlayer.

Synthesis and characterization of semiconducting copper oxide nanoparticles and their impact on the physical properties of a nematic liquid crystalline material 4-pentyl-4′-cyanobiphenyl

Green synthesis of nanoparticles is a biological, eco-friendly and less expensive method which is free from chemical contaminants. In this work, copper oxide nanoparticles (CuO NPs) have been synthesized via green synthesis method. This method proved to be efficient for preparing CuO NPs at room temperature without using any inert atmosphere. The CuO NPs have been characterized using X-Ray Diffraction, Ultraviolet–Visible Spectroscopy and Fourier Transform Infrared Spectroscopy techniques which confirmed the proper synthesis of CuO NPs of the size 2–3 nm. Two different weight percents (0.2 and 0.5) of the synthesized CuO NPs have been dispersed in the nematogenic liquid crystalline material 4-pentyl-4′-cyanobiphenyl (5CB). The physical properties of pure 5CB and its nanocomposites were studied by differential scanning calorimetry, ultraviolet–visible spectroscopy and impedance spectroscopy. Thermodynamic and dielectric results show enhancement in the nematic to isotropic transition temperature of nanocomposites along with enhancement in conductivity as compared to its value for the pure 5CB. Through optical studies, the band gap has been estimated by the Tauc plots which suggest decrease in the optical band gaps of dispersed samples.

Photocatalytic Decomposition of Rhodamine B Dye Using Copper Oxide Nanoparticles Prepared from Copper Chalcone Complexes

Nanostructured CuO has been successfully synthesized via Thermal decomposition method at 700∘C. Prepared CuO was characterized using IR spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM). IR spectra confirm the metal–oxygen bonding in these nanoparticles. The XRD pattern confirms a single-phase crystalline nature of the nanoparticles. The synthesized CuO was demonstrated as an efficient catalyst in degradation of Rhodamine B in the presence of light through oxidation. More than 93% of the Rhodamine B dye was degraded after 150[Formula: see text]min. It was observed that photocatalytic degradation of dyes follows pseudo-first-order kinetics. A tentative mechanism has also been proposed for the photocatalytic degradation of dyes in the presence of copper oxide semiconductor.

New Photoelectrochemical Reactor for Hydrogen Generation: Experimental Investigation

In the scope of this study, a new photoelectrochemical (PEC) reactor, comprising a novel geometry for effective absorption of sunlight, is developed conceptually, and tested and assessed experimentally. The conic mesh structure of the photoelectrode offers maximizing the performance via passive tracking of solar light during daylight. In sequence, electrodeposition and sol–gel dip coating techniques are practiced, fabricating a copper oxide semiconductor as a working electrode and a titanium dioxide-coated electrode as the counter electrode. The new reactor concept is experimentally assessed for various conditions through electrochemical tests including open circuit potential, linear sweep voltammetry, cyclic voltammetry, and PWR potentiostatic tests. Energy and exergy efficiencies and hydrogen production rates are evaluated for various experimental conditions implying with and without light. The highest hydrogen production rate corresponding to 4.48 μg H2/s at near-atmospheric conditions (25 °C temperature and 101.3 kPa pressure) is obtained with the applied external bias of 2.25 V, where the reactor operates under artificial solar light with an intensity of 1000 W/m2. The produced photocurrent density is determined to be 1.81 mA/cm2, corresponding to a photo-conversion efficiency of 1.84%. For these operational conditions, the energetic and exergetic efficiencies of the reactor are evaluated as 0.866 and 0.878%, respectively. Without light case, the PEC reactor acting as an electrolyzer operates with energetic and exergetic electrolysis efficiencies of 56.51 and 54.38%, respectively.

Boosting visible-light photocatalytic degradation of polystyrene nanoplastics with immobilized CuxO obtained by anodization

Plastics composed mainly of polystyrene polymer have become widely used materials in different industries. The poor disposition of these products and their interaction with the environment has caused their fragmentation into particles that reach a nanometric scale (≤1 µm), called nanoplastics (NPs), considered pollutants due to their effects on human health and capacity to absorb toxic-bioaccumulative substances. Currently, advanced oxidation processes have shown efficiency in removing emerging pollutants, making them promising alternatives to treat NPs. This study proposes photocatalytic degradation with visible light irradiation to mitigate the contamination produced by polystyrene nanoplastics (PS-NPs). Therefore, PS particles of ~ 350 nm were degraded using immobilized copper oxide semiconductors grown by the anodizing process for the first time. The anodization process considered two growth media (NH4F and NaOH), obtaining immobilized Cu2O/CuO semiconductors with different morphologies and a bandgap between 1.6 and 2 eV. The degradation of the nanoplastics was examined using several analytical methods such as TOC, ATR-FTIR, turbidity, and gas chromatography showing the presence of intermediates compounds with the carbonyl group, confirming the degradation of PS-NPs. The results showed that photocatalysis in visible light with copper oxide semiconductors promotes polymer chain scissions and reduces the concentration of PS-NPs up to 23%, representing six times more than the reductions achieved by photolysis. In addition, mineralization of up to 15% was achieved. Although contamination by nanoplastics involves many challenges, this study provides the basis for an alternative process that allows the mitigation of these nanoplastics using visible light.

Plasma-Enhanced Atomic Layer Deposition of p-Type Copper Oxide Semiconductors with Tunable Phase, Oxidation State, and Morphology

Metal oxide semiconductors are important due to their diverse set of applications in (opto)electronics including light-emitting diodes, solar cells, and thin film transistors (TFTs). However, compa...

(Invited) Elucidation of Activity of Copper and Copper Oxide Nanomaterials for Electrocatalytic and Photoelectrochemical Reduction of Carbon Dioxide

Copper and copper oxide based materials are, in principle, promising components (supports, reactive sites, and visible-light absorbing semiconductors) of electrocatalysts and photocathodes for reduction of carbon dioxide. Electrochemical and photoelectrochemical approaches are generally suitable for the low-temperature CO2-conversion to carbon-based simple organic fuels or utility chemicals.Different concepts of utilization, including nanostructuring, doping, admixing, preconditioning, modification or functionalization of various copper and copper oxide based systems for catalytic electroreduction and photoelectrochemical reduction of CO2 will be elucidated, as well as important strategies to enhance the systems’ overall activity and stability will be discussed. Our recent developments in the area of electrochemical and photoelectrochemical CO2R in aqueous electrolytes at copper-based catalysts and copper oxide-based p-type semiconductors (e.g., Cu2O and related mixed oxides) are focused on the preparation of stable efficient systems exhibiting possibly high activity and selectivity toward a single specific product. Obviously the binding strength (chemisorption) of CO2 and the CO-type reaction intermediates would be different at Cu and Cu-oxo species what translates to differences in activity and selectivity. We have also concentrated on intentional modification of copper and copper oxide electrodes by the addition of other metals, metal oxides, coordination compounds or even organic species to alter reaction pathways, stabilize certain reaction intermediates, and to enhance reactivity. For effective heterogeneous photoelectrochemical CO2R at copper oxide semiconductors, the improvement in stability through formation of the p-n junction and/or the interfacial modifications, e.g. by fabrication of robust, not-inhibiting over-layers having also the capability of controlling the adsorption energy and possible activation steps, is crucial. The potential gain coming from the photoelectrochemical approach concerns the ability of driving the CO2R at less negative potentials relative to what can be achieved in conventional electrocatalysis. For example, careful comparison of the data obtained during electrocatalytic and photoelectrochemical reduction of carbon dioxide at hierarchical bilayered films of copper(I) oxide decorated with tungsten(VI) oxide nanowires clearly implies that upon illumination with visible light the electroreduction of CO2 starts at ca. 0.3 V (vs. RHE) whereas under conventional electrochemical conditions, the reaction is driven below -0.2 V. Although methanol have been postulated as dominating product, the mechanisms of operation of both systems are different: while the reduced, mostly Cu0 sites, are catalytically active during electrochemical CO2R, the photoelectrochemical approach utilizes Cu2O semiconductor and long-lived charge carriers (electrons) photogenerated at the interface. The role of the WO3 over-layer can be summarized as follows: the heterojunction formed by p-type (Cu2O) and n-type (WO3) semiconductors improves the system’s overall stability, suppresses competitive hydrogen evolution, and it seems to minimize charge recombination effects. The advantage of driving CO2R at less negative potentials could be fundamentally useful for construction of water-splitting type electrolyzers for conversion of carbon dioxide. In such electrochemical reactor, the oxygen evolution (water oxidation) reaction proceeds at anode, whereas CO2 is supplied in the cathode compartment where it is electrochemically (rarely photoelectrochemically) reduced.

A Study on the Transition of Copper Oxide by the Incorporation of Nitrogen

In the present study, the effects of nitrogen incorporation on the transition of a p-type copper oxide semiconductor are investigated. The properties of sputtered copper oxide and nitrogen-incorporated copper oxide are evaluated and compared at various nitrogen gas flow rates. The results indicate that the addition of nitrogen results in an increased optical bandgap, accompanied by significantly reduced tail states compared to pristine copper oxide. In addition, X-ray diffraction and X-ray photoelectron spectroscopy reveal that the incorporation of nitrogen stimulates the transition from copper (II) oxide to copper (I) oxide.

A write-once-read-many-times memory based on a sol-gel derived copper oxide semiconductor

In this paper, we demonstrate the write-once-read-many-times (WORM) characteristics of the Al/CuxO/n+-Si memory device. The CuxO oxide semiconductor used as the resistive switching layer was fabricated using a sol-gel process. The device is initially in a high-resistance state (HRS) with a resistance of ∼107 Ω. The writing process only occurs in the positive voltage region regardless of the initial voltage sweep direction, followed by a resistance switching to a value of ∼103 Ω. Then the memory remains in the low-resistance state (LRS) in the following voltage cycles. The read-endurance and read-disturb tests were performed to the memory device. The memory window is 104 for 104 pulse cycles. The sol-gel CuxO thin film is verified and analyzed by ultraviolet–visible (UV–vis) spectroscopy and X-ray photoelectron spectroscopy (XPS). The resistive switching and carrier transport mechanisms are also investigated.

Localized Photoluminescence Imaging of Bi‐Layered Cuprous/Cupric Oxide Semiconductor Films by Synchrotron Radiation

To develop multi‐layered semiconductor film devices, like a solar cell device, effects of localized impurities and layered interface mismatches on photovoltaic properties should be understood quantitatively and controlled effectively. However, the research of localized photoluminescence on layered semiconductor film devices is delayed. This is because, unfortunately, a measurement method for photoluminescence properties with spatial resolution on the sub‐micron scale, which could provide much of the local photoluminescence properties in bulk multi‐layered film semiconductor devices, has not been developed. In this study, a mapping method for local photoluminescence properties has been developed by utilizing a focused synchrotron radiation beam to evaluate localized photoluminescence affected by microstructures in bi‐layered semiconductor films. Luminescence maps of copper oxide semiconductor film which varies in emission energy and position are successfully obtained under the conditions of a focused beam size of 5 μm in width and 300 nm in height. The possibility of investigation for localized photoluminescence related with the microstructure is strongly suggested. This technique will support and enhance the development of high‐performance multi‐layered semiconductor film devices.

Optical, structural and phase transition properties of Cu2O, CuO and Cu2O/CuO: Their photoelectrochemical sensor applications

Cu2O and CuO provide a unique possibility to tune the band gap into the middle of the efficiency maximum for photoelectrochemical (PEC) and solar cell applications. Photoactive materials containing Cu2O, CuO and Cu2O/CuO have been prepared with high quality and stability in various compositions by an economic, simple and reliable electrodeposition (ED) method. These materials based on copper oxide have been characterized and compared using XRD, SEM, EDX, UV–Vis, PL, FTIR, Raman spectroscopy and electrochemical techniques. Based on the electrochemical production conditions; phase changes of photoactive materials and, at which conditions which phase or phases are present, were evaluated in detail. It was carried out that a full phase change from single-phase Cu2O to single-phase CuO. The crystal dimensions expand as the cube-shaped Cu2O transforms into CuO, crystal surface areas increase, crystal shapes change and turn gradually into flower-shaped crystals. Here, the band gap of copper oxide material can be altered within a broad scale by adjusting the element ratios. The semiconductors have been found to have direct band gap that is more preferred for solar energy applications. PEC performances of the copper oxide electrodes containing a different phase structure were determined, and the changes of PEC activities were examined comparatively. Copper oxide semiconductors have p-type conductivity and they act as photocathodes.

The Phase Evolution and Physical Properties of Binary Copper Oxide Thin Films Prepared by Reactive Magnetron Sputtering.

P-type binary copper oxide semiconductor films for various O2 flow rates and total pressures (Pt) were prepared using the reactive magnetron sputtering method. Their morphologies and structures were detected by X-ray diffraction, Raman spectrometry, and SEM. A phase diagram with Cu2O, Cu4O3, CuO, and their mixture was established. Moreover, based on Kelvin Probe Force Microscopy (KPFM) and conductive AFM (C-AFM), by measuring the contact potential difference (VCPD) and the field emission property, the work function and the carrier concentration were obtained, which can be used to distinguish the different types of copper oxide states. The band gaps of the Cu2O, Cu4O3, and CuO thin films were observed to be (2.51 ± 0.02) eV, (1.65 ± 0.1) eV, and (1.42 ± 0.01) eV, respectively. The resistivities of Cu2O, Cu4O3, and CuO thin films are (3.7 ± 0.3) × 103 Ω·cm, (1.1 ± 0.3) × 103 Ω·cm, and (1.6 ± 6) × 101 Ω·cm, respectively. All the measured results above are consistent.

Thermal and Surface Evaluation on The Process of Forming a Cu2O/CuO Semiconductor Photocatalyst on a Thin Copper Plate

This research aims to investigate the process of forming a multi-scale copper oxide semiconductor (CuO/Cu2O) through a process of calcining a copper plate. The changes that occur during the formation of the oxide are thermally and surface evaluated. Evaluation using Differential Thermal Analysis (DTA) obtained by surface change of copper plate happened at temperature 380°C. Calcination of oxide formation was carried out at temperature 380°C for 1 hour. Surface evaluation process by using Scanning Electron Microscope (SEM) surface and cross-section, to determine diffusion of oxide formation on copper plate. The material composition is monitored by XRF and XRD to explain the process of structural and physical changes of the copper oxide plate formed during the heating process. The thickness of Cu plates used is 200-250 μm. SEM analysis results, the oxygen atom interruption region is in the range of 20-30 μm, and diffuses deeper during thermal oxidation process. The maximum diffusion depth of oxygen atoms reaches 129 μm.

Assessment of a Sustainable Electrochemical Ammonia Production System Using Photoelectrochemically Produced Hydrogen under Concentrated Sunlight

Intensive fossil fuel usage in ammonia production is considered nonsustainable; hence, alternative ammonia synthesis options are under investigation. In this study, a comprehensive study on environmental impact assessment is performed to investigate the electrochemical synthesis of ammonia at ambient pressure using photoelectrochemically produced hydrogen under concentrated solar light. The photoelectrochemical reactor consists of a membrane electrode assembly with a copper oxide semiconductor on a stainless steel cathode plate. The electrolyte for ammonia synthesis is molten salt containing a eutectic mixture of NaOH and KOH. The electrodes and wires are made of nickel. The life cycle assessment of the concentrated light photoelectrochemical hydrogen production is initially performed and integrated to molten-salt-based electrochemical ammonia synthesis. The material and energy requirements of the life cycle assessment are taken from the experimental data. The results imply that electrochemical ammonia synthesis driven by solar energy can significantly reduce the total environmental impact, corresponding to about 50% of the current steam methane reforming based ammonia production.

Integration of P-CuO Thin Sputtered Layers onto Microsensor Platforms for Gas Sensing.

P-type semiconducting copper oxide (CuO) thin films deposited by radio-frequency (RF) sputtering were integrated onto microsensors using classical photolithography technologies. The integration of the 50-nm-thick layer could be successfully carried out using the lift-off process. The microsensors were tested with variable thermal sequences under carbon monoxide (CO), ammonia (NH3), acetaldehyde (C2H4O), and nitrogen dioxide (NO2) which are among the main pollutant gases measured by metal-oxide (MOS) gas sensors for air quality control systems in automotive cabins. Because the microheaters were designed on a membrane, it was then possible to generate very rapid temperature variations (from room temperature to 550 °C in only 50 ms) and a rapid temperature cycling mode could be applied. This measurement mode allowed a significant improvement of the sensor response under 2 and 5 ppm of acetaldehyde.

H<sub>2</sub>S dosimeter with controllable percolation threshold based on semi-conducting copper oxide thin films

Abstract. Copper oxides, such as CuO and Cu2O, are promising materials for H2S detection because of the reversible reaction with H2S to copper sulfides (CuS, Cu2S). Along with the phase change, the electrical conductance increases by several orders of magnitude. On CuOx films the H2S reaction causes the formation of statistically distributed CuxS islands. Continuous exposition to H2S leads to island growth and eventually to the formation of an electrical highly conductive path traversing the entire system: the so-called percolation path. The associated CuOx ∕ CuxS conversion ratio is referred to as the percolation threshold. This pronounced threshold causes a gas concentration dependent switch-like behaviour of the film conductance. However, to utilize this effect for the preparation of CuO-based H2S sensors, a profound understanding of the operational and morphological parameters influencing the CuS path evolution is needed.Thus, this article is focused on basic features of H2S detection by copper oxide films and the influence of structural parameters on the percolation threshold and switching behaviour. In particular, two important factors, namely the stoichiometry of copper oxides (CuO, Cu2O and Cu4O3) and surface morphology, are investigated in detail. CuOx thin films were synthesized by a radio frequency magnetron sputtering process which allows modification of these parameters. It could be shown that, for instance, the impact on the switching behaviour is dominated by morphology rather than stoichiometry of copper oxide.

Gas sensing properties of semiconducting copper oxide nanospheroids

Monosize spheroidal porous particles of copper oxide were produced by controlled calcination of the copper basic carbonate particles, synthesized by the urea-based homogeneous precipitation process. After characterization by various physical methods, such as SEM, XRD, and FTIR, the copper oxide particles were employed for the fabrication of the gas sensor. The latter was made up of a thick film of copper oxide on alumina plate, having printed interdigitated gold electrodes. Electrical properties of the sensor material were evaluated as a function of the temperature, which indicated its semiconductor behavior. On exposing to ammonia gas, the sensor responded in the form of a decrease in electrical resistance in a reproducible manner. Reproducibility in performance was attributed to the use of monodispersed particles of copper oxide in the fabrication of sensor.

Copper oxide based H2S dosimeters – Modeling of percolation and diffusion processes

Semiconducting copper oxide (CuO) gas sensing layers show a remarkable conductance behavior if exposed to hydrogen sulfide (H2S) gas at low operating temperature (180°C). At first conductance decreases as expected for a p-type semiconducting metal oxide offering reducing test gas. After a certain exposure time, however, a sudden steep increase in conductance can be observed.In a first approach this behavior is explained by the formation of metallic conducting copper sulfide (CuS, degenerate p-type semiconductor) clusters which eventually form conducting pathways across the sensing layers short-circuiting the remaining CuO phase. In the field of statistical physics such behavior can be described by the so-called percolation theory.Here we present a detailed experimental and theoretical analysis of the observed effect utilizing RF-magnetron-sputtered copper oxide films with different stoichiometry (CuO, Cu4O3 and Cu2O) as model systems. The layers are exposed to H2S for different time spans and analyzed with respect to their morphology (SEM, XRD) and chemical composition (XPS, ToF-SIMS). Analysis of the transient behavior of the conductance by means of a percolation model and comparison of the results to the experimental data allow the identification of different processes. For CuO samples first the formation of different non-CuS copper–sulfur–oxygen phases is observed followed by the percolation regime with the steep conductance increase. Afterwards diffusion processes superimposing the percolation leading to a slower conductance increase and eventually the process is dominated by diffusion of copper ions from the bulk. For oxides with other stoichiometry (Cu2O, Cu4O3) no percolation regime is observed which is attributed to higher diffusion rate of copper ions weakening the percolation effect in these samples.Based on these observations a model for the electronic conductance behavior of copper oxide gas sensors under exposure to hydrogen sulfide (H2S) at temperatures below 200°C is proposed. A better understanding of these systems will enable the preparation of reliable sensors with inherent thresholds.