CuO Thin Films Research Articles

Cu2O thin films grown by magnetron sputtering as solar cell absorber layers

In the present work, Cu2O thin films were deposited by reactive magnetron sputtering at different substrate temperatures ranging from 300 to 673 K. The structural, optical and electrical properties of Cu2O films have been studied for their potential use as solar cell absorber layers. X-ray diffraction and Raman studies confirmed the cubic phase of Cu2O. X-ray photoelectron spectroscopy shows the presence of minority CuO phase at the surface. The surface morphology at different substrate temperatures has been studied using the scanning electron microscopy and atomic force microscopy. The optical property of Cu2O thin films has been evaluated with the help of transmittance spectroscopy, photoluminescence spectroscopy and spectroscopic ellipsometry. The optical band gap obtained from the transmittance spectroscopy is found to be in the range of 1.82–2.07 eV. All the films exhibit p-type conductivity with a typical carrier concentration of ∼1014 cm−3.

Influence of substrate temperature and solution molarity on CuO thin films' properties prepared by spray pyrolysis

Influence of substrate temperature and solution molarity on CuO thin films' properties prepared by spray pyrolysis

Mg-doped Cu2O thin films with enhanced functional properties grown by magnetron sputtering under optimized pressure conditions

Cu2O appears as a promising material for synthesizing p-type transparent semiconducting oxides with low electrical resistivity and high optical transmittance. We report on an exhaustive study of magnesium-doped cuprous oxide layers deposited by radio frequency magnetron sputtering. We present the characterization of the structural and optoelectronic properties of Mg:Cu2O thin films deposited at room temperature with varied argon plasma pressure. As a result, we found that by adjusting the Ar plasma pressure, Mg-doped Cu2O layers with high crystallinity combined with optimal electrical and optical properties can be synthesized. Using a plasma pressure of 13 mTorr, we obtained a transparent p-type material with crystallite size of 15 nm, electrical resistivity of 10.2 Ωcm, and optical band gap of 2.55 eV.

Flexible nanostructured CuO thin film: A promising candidate for wearable real-time sweat rate monitoring devices

Hydration level monitoring ensures clinically convenient instructions for preventive medicine and disease diagnostics. This paper aims to develop a wearable metal-oxide based sensor for monitoring hydration levels using flexible nanostructured copper oxide (CuO) thin film. Nanostructured CuO thin films were designed and fabricated on flexible cellulose acetate (CA) substrates via the successive ionic layer adsorption and reaction (SILAR) method. The obtained CuO films vigorously adhered to the CA substrate, and the resulting coated substrates were efficiently flexible to be used as wearable hydration level monitoring systems to realize big data collection of human health. The sensing response of the CuO-based flexible sensors is heavily improved by optimizing the growth process.

High responsivity n-ZnO/p-CuO heterojunction thin film synthesised by low-cost SILAR method for photodiode applications

In this report, we have prepared n-ZnO/p-CuO heterojunction thin film by low-cost SILAR method and made a comparative study with physical properties of ZnO and CuO thin film photodetectors. The prepared heterojunction film is exhibit mixture of hexagonal structure of ZnO and monoclinic structure of CuO. All the films have uniform surface morphology without any voids and ensured that the presence of used elements like Zn, Cu, and O. The optical absorption spectrum declared that comparatively high photon absorption in the range of 2–6% occurred in 365 nm of UV light. The photoluminescence spectrum notices that different kind of point defects are present in the prepared heterojunction film. The photo sensing results announce that the ZnO/CuO heterojunction film exist a good photodiode characteristic behavior with good responsivity of 43.69 × 10−2 A/W.

Hydrothermally formed copper oxide (CuO) thin films for resistive switching memory devices

This work presents the preliminary research on Metal-Insulator-Metal (MIM) structures containing copper oxide (CuO) layers for memory applications. Structural and optical investigations of fabricated materials have shown distinct differences in chemical compositions of ‘as grown’ and thermally annealed CuO, i.e., ‘HT + RTP’ film. Those differences strongly influence the electrical behavior of fabricated MIM structures. The examined electrical performance of fabricated devices revealed stability and repeatability of the HRS/LRS ratio over time. The presented results have demonstrated the possible application of CuO thin films in low-power and high-speed Resistive Random-Access Memory (RRAM) devices.

Optical and Material Characteristics of MoS2/Cu2O Sensor for Detection of Lung Cancer Cell Types in Hydroplegia

In this study, n-type MoS2 monolayer flakes are grown through chemical vapor deposition (CVD), and a p-type Cu2O thin film is grown via electrochemical deposition. The crystal structure of the grown MoS2 flakes is analyzed through transmission electron microscopy. The monolayer structure of the MoS2 flakes is verified with Raman spectroscopy, multiphoton excitation microscopy, atomic force microscopy, and photoluminescence (PL) measurements. After the preliminary processing of the grown MoS2 flakes, the sample is then transferred onto a Cu2O thin film to complete a p-n heterogeneous structure. Data are confirmed via scanning electron microscopy, SHG, and Raman mapping measurements. The luminous energy gap between the two materials is examined through PL measurements. Results reveal that the thickness of the single-layer MoS2 film is 0.7 nm. PL mapping shows a micro signal generated at the 627 nm wavelength, which belongs to the B2 excitons of MoS2 and tends to increase gradually when it approaches 670 nm. Finally, the biosensor is used to detect lung cancer cell types in hydroplegia significantly reducing the current busy procedures and longer waiting time for detection. The results suggest that the fabricated sensor is highly sensitive to the change in the photocurrent with the number of each cell, the linear regression of the three cell types is as high as 99%. By measuring the slope of the photocurrent, we can identify the type of cells and the number of cells.

Improved electrocatalytic activity of copper (I) oxide electrodeposited on graphite carbon

Due to its abundance and low cost, Cu2O is an attractive electrocatalyst for the water treatment. The electrodeposition is an attractive technique, because of its simplicity, low cost and possibility of making large area as thin homogeneous film of Cu2O with good quality of nanoparticles. This study reports the electrode position of Cu2O thin uniform film which offers the advantages of precise stoichiometry and thickness control (δ = 5.11 μm). The uniform and well-adhered Cu2O red thin film electrodeposited on graphite carbon is used for the electrodegradation of the crystal violet dye (CVD). The gap value is equivalent to 2.02 eV calculated from spectral UV-visible, this value agrees with the red color and indicates semi-conductive properties. A potential Efb equal to 0.43 V and acceptors density of 1.14. 2019 cm-3 and p-type conductivity were determined by the Mott- Schottky measurement. This fact makes Cu2O a good candidate for electrocatalytic activity, pH =7, 25°C temperature, 1.6 V applied voltage and 180 min electrolysis. Cu2O was used to degrade CVD (10 mg /L) via an electrochemical technique. Pseudo-first order kinetics governed the electrochemical decomposition.

Influence of Cr Ion Implantation on Physical Properties of CuO Thin Films.

Cupric oxide is a semiconductor with applications in sensors, solar cells, and solar thermal absorbers. To improve its properties, the oxide was doped with a metallic element. No studies were previously performed on Cr-doping using the ion implantation technique. The research goal of these studies is to investigate how Cr ion implantation impacts the properties of the oxide thin films. CuO thin films were deposited using magnetron sputtering, and then chromium ions with different energies and doses were implanted. Structural, optical, and vibrational properties of the samples were studied using X-ray diffraction, X-ray reflectivity, infra-red spectroscopy, Raman spectroscopy, and spectrophotometry. The surface morphology and topography were studied with ellipsometry, atomic force microscopy, and scanning electron microscopy. A simulation of the range of ions in the materials was performed. Ion implantation had an impact on the properties of thin films that could be used to tailor the optical properties of the cupric oxide and possibly also its electrical properties. A study considering the influence of ion implantation on electrical properties is proposed as further research on ion-implanted CuO thin films.

Hydrothermally-synthesized CuO nanoparticles decorated on CuO sputtered thin-film for nitrite sensing application

Herein, CuO nanoparticles were prepared on an ITO/glass substrate to fabricate NO2‒ sensors. The morphology of the CuO nanoparticles was controlled by varying the concentration of the precursor solution. Among all the samples, the CuO grown using a 15 mM precursor solution resulted in nano-sized CuO particles with more voids and gaps between the particles after packing. A larger surface area provides more reaction sites, which is beneficial for NO2‒ sensing. A sputtered thin film of CuO deposited before drop-coating enhanced the crystallinity and adhesion of the nanoparticles. The working electrode fabricated with CuO nanoparticles stacked onto the CuO thin film exhibited a high sensitivity of 402.89 μAmM−1cm−2. The NO2‒ sensing ability was significantly improved by the addition of the CuO thin film. The sensing material used in this study can be applied to the detection of industrial residuals and pollutants.

Investigating the effect of La doped CuO thin film as absorber material for solar cell application

The main objective of the study is to analyze the properties of undoped and La doped CuO (LCO) thin films as potential absorber for photovoltaic application. Chemical spray pyrolysis technique has been used to prepare the undoped and LCO thin films with different wt% (2, 4, 6, 8 and 10). All the films exhibit polycrystalline monoclinic crystal structure and no peaks related to impurity phases are identified. The average crystallite size of the La doped films is decreased from 19.51 nm to 8.73 nm. From UV spectra, the La doped films exhibit high optical absorption and their band gap value decreases from 1.62 eV to 1.49 eV upto 6 wt%. The PL intensity of the CuO films decreases upto 6 wt% of La and then increases. The SEM image of La doped films show the uniform, homogenous and compact surface with decrease in grain size. From Hall measurement, the 6 wt% of LCO shows higher carrier concentration (4.68 × 1019 cm−3) and lower electrical resistivity (1.33 Ω cm). All the films exhibit ohmic behavior and 6 wt% of La shows higher dark current (1.41 mA) and photoresponse of 1.5 mA. The photovoltaic performance of undoped and 6 wt% of LCO solar cells is evaluated, and their power conversion efficiencies are 0.34% and 1.36% respectively. The above mentioned results determined that 6 wt% of LCO thin films can be used as an effective absorber material for solid state p-n junction solar cell.

A CuO thin film type sensor via inkjet printing technology with high reproducibility for ppb-level formaldehyde detection

High-performance gas sensors have huge application prospects and consumer demands in environmental monitoring, public security and other fields. Nevertheless, the conductive type metal oxide gas sensors prepared by traditional coating or dropping technology encounter challenges in low detection limit and excellent replication, hardly meeting the actual needs of trace harmful gas detection and mass production. Here, a uniform and high-quality CuO sensing film is formed quickly and efficiently by inkjet printing technology, which is expected to realize mass preparation of high-performance formaldehyde sensors. The CuO sensor can reach as low as 50 ppb formaldehyde detection limit, satisfying the monitor needs of the World Health Organization’s specified value 80 ppb. In addition, the gas sensors in each batch exhibit outstanding repeatability and stability with small deviation, and the relative mean deviations toward formaldehyde in the aspect of response, response and recovery times are all about only 5% between batches. The controllable micro-nano-level film thickness and uniform surface achieved by inkjet printing technology are the compelling reasons for low detection limit and superb reproducibility of gas sensors. Our work can offer a theoretical and experimental basis for large-scaled production of high-performance gas sensors from research to practical application.

Improving the p–type conductivity of Cu2O thin films by Ni doping and their heterojunction with n–ZnO

Cu2O is one of the few transition metal oxides which can exhibit p–type conductivity due to native acceptor defects. Further improvements in the p–type conductivity of Cu2O can be achieved via extrinsic doping and post–growth processing. In this work, we investigate the effects of Ni doping in Cu2O with Ni content up to ∼11%. A variety of analytical techniques were utilized to investigate the structural, optical and electrical properties of these alloy thin films. We find that the incorporation of Ni improves the p–type conductivity of the films without altering the Cu2O crystallographic structure and maintains a wide bandgap of ∼2.5 eV. X–ray photoelectron spectroscopy (XPS) measurements reveal that the Fermi level moves closer to the valence band with increasing x, in agreement with the increasing hole concentration. Significant improvement in the crystallinity as well as the p–type conductivity of the alloy films can be observed after rapid thermal annealing (RTA). In particular, alloys with x≥0.005 exhibit a high hole mobility µ∼12–22 cm2/V-s with low resistivity of ρ∼30–60 Ω-cm and free hole concentration N∼1×1016 cm-3 after RTA in air–N2 ambient at 700°C. Such improvement can be attributed to the formation of Cu vacancies which promotes Ni substitution in the presence of small amount O2 in the air–N2 annealing environment. Finally, we fabricated a transparent p–(NixCu1-x)2O/n–ZnO heterojunction and evaluated its junction performance. XPS measurements reveal a type II band offset of this heterojunction with valence band and conduction band offsets of 2.81 eV and 2.07 eV, respectively. The heterojunction exhibits both rectification and photovoltaic response, demonstrating its potential for p–n junction and photodetection devices.

Experimental and theoretical study of hole scattering in RF sputtered p-type Cu2O thin films

One of the key materials of interest for p-type oxide semiconductor thin film electronics is cuprous oxide (Cu2O), due to its relatively high hole mobility. In this work, we use experiments, analytical models, and density functional theory calculations to study the scattering mechanisms that determine Hall mobility in two Cu2O samples. First, we examine a polycrystalline Cu2O thin film deposited by RF magnetron sputtering, and second, a single-crystalline Cu2O bulk substrate. Temperature-dependent Hall measurements indicate that neutral impurity and grain boundary scattering are dominant for the polycrystalline Cu2O thin film, while phonon scattering is dominant for single-crystalline Cu2O. Our first-principles calculations show that the room-temperature intrinsic hole mobility of Cu2O is 106 cm2 V−1 s−1, indicating the great promise of the material for p-type electronic devices. This intrinsic mobility is limited by phonon scattering, with the most dominant scattering modes having phonon energies of 88.4 and 17.1 meV. These results indicate that the key pathways to increase the hole mobility in Cu2O thin films are by reducing the impurity concentration and by increasing grain size. Our work thus sets the stage for the future development of high performance Cu2O-based p-type thin film transistors.

Fabrication and Characterization of the Broccoli-like Structured CuO Thin Films Synthesized by a Facile Hydrothermal Method and Its Photoelectrochemical Water Splitting Application

CuO thin films with broccoli-like structure were prepared using a facile hydrothermal method to construct photocathodes for water-splitting application. The morphological, structural, and optical properties of thin films were characterized and measured using several techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and ultraviolet-visible spectroscopy (UV-Vis). The thickness, structure, and morphology of CuO thin films can be controlled by varying the precursor concentration (Cp) and reaction temperature (Tr), which are also discussed. Moreover, the electrical properties of CuO thin films were also measured in the three-electrode system. The photocurrent density of photocathodes, when synthesized by a 0.5 M solution at 150 °C for 12 h, was 0.5 mA/cm2 at −0.6 V vs. Ag/AgCl, which is 1.8 times higher than that of photocathodes synthesized in a 0.1 M solution at 100 °C with the same reaction time. In addition, increasing the reaction temperature and precursor concentration aided in the enhancement of the IPCE and APCE values, which peaked at a wavelength range of 330–400 nm.

Structural and Electrical Properties of Glucose Biosensors Based on ZnO and ZnO-CuO Nanostructures

Background: Nanostructured metal oxides have stimulated tremendous efforts for sightseeing glucose bio-sensing applications. They have been mostly investigated to fabricate highly sensitive, stabilized and ultrafast biosensors. Objective: Fabrication and characterization of glucose biosensors based on zinc oxide (ZnO) nanostructured thin films modified by copper oxide (CuO) nanostructures in order to obtain stabilized ZnO:CuO biosensors with high sensitivity and fast response time. Methods: The components of the investigated biosensors are synthesized using the hydrothermal solgel method by dip-coating the sensing layer on indium tin oxide-coated glass substrates (ITO). The structural and electrical properties of the fabricated biosensors are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and I-V characteristics. Results: SEM micrographs indicate that ZnO nanostructures exhibit an interconnected sheet-like patterns. These sheets are thin and distributed randomly on the ITO substrate. SEM images of ZnO:CuO reveal that the morphology of nanostructured thin films is composed of flower-like patterns. The XRD patterns of ZnO and modified ZnO:CuO thin films subjected to thermal annealing show that thin films exhibit a high degree of crystallinity with minor traces of impurity phases. The biosensors' key parameters are calculated and interpreted by measuring the I-V characteristics to elucidate the sensitivity and reproducibility of measurements performed for various glucose concentrations. Furthermore, the electric current response of ZnO and ZnO:CuO biosensors are found to be linear and quadratic as a function of glucose concentration, respectively. The introduction of CuO into ZnO thin films leads to the enhancement of the sensitivity of the synthesized glucose biosensors for a high degree of precision in measuring glucose levels. Conclusion: Both sensors exhibit average sensitivities in the range (from 1 to 10 μA mM−1 cm−2) with quite good reproducibility. The unique property of this sensor is its ability to measure glucose concentrations at neutral pH conditions (i.e. pH = 7) using a simple, low cost and novel sensor design.

Reduction of thermally grown single-phase CuO and Cu2O thin films by in-situ time-resolved XRD

Copper oxide is used as a catalyst or catalyst precursor in chemical reactions that involve hydrogen as a reactant or a product. Controlled reduction and therefore known reduction kinetics of well-defined Cu-oxides in hydrogen is a key issue for the activation of oxide catalysts as well as for other technological fields such as gas sensing. The kinetics and mechanisms of reduction of single-phase CuO and Cu2O films in 5 vol% H2/Ar were investigated by in-situ real time synchrotron-based X-ray diffraction measurements. To this end, the incubation time, the CuO → Cu2O and Cu2O → Cu phase transformation rates, as well as the microstructure and strain state of the evolving Cu, CuO and Cu2O phases were studied during the reduction. Highly porous Cu and Cu-oxides scaffolds were obtained by alternating oxidation and reduction steps, which can be envisaged for a wealth of applications in the fields of catalysis, batteries, water treatment and biomedical applications.

Studies on DC sputtered cuprous oxide thin films for solar cell absorber layers

Cuprous oxide (Cu2O) thin films are prepared on corning glass substrates by metallic sputtering of copper under an oxygen atmosphere. The flow rate of oxygen is varied from 4 SCCM to 7 SCCM and the properties of as-deposited films are reported in this work. The structural, phase confirmation, morphology, elemental composition, bonding, and optical characteristics of Cu2O thin films is studied using various characterization tools such as X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX), X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM) and UV–Visible Spectrometer. It is perceived that the flow rate plays a vital role in obtaining the single-phase Cu2O thin films. The bandgap of the deposited thin films is measured and is in the range of 2.29–2.37 eV, making it suitable for thin-film solar cell applications.

Effect of Annealing on Sensing Properties of ZnO: CuO Nanocomposite Thin Films by the Sol-gel Method

The zinc oxide (ZnO) - copper oxide (CuO) n-p junctions are a promising material for detecting ammonia gas. In this work, nanocomposite of ZnO: CuO thin films were deposited by using sol-gel spin coating method on a glass substrate. The search aimed to study the effect of annealing at 500oC on the physical properties and the effect of annealing on the sensing properties of the prepared films. The characterization of thin films before and after annealing treatment was studied by X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) for the morphology of the surface and grain size of particles also, UV-Visible analysis for optical properties. Sensing properties were also studied before and after annealing. The results showed the films were polycrystalline in nature with a monoclinic phase and the crystalline size was 5.4 nm and 9.9 nm before and after annealing. The results of SEM and AFM showed the surface uniformly and particle size was 25nm to 32 nm before and after annealing. The results of sensing properties for ammonia gas showed the sensitivity was enhancement after annealing treatment.

Insights into Cu2O thin film absorber via pulsed laser deposition

Cuprous oxide materials are of growing interest for optoelectronic devices and were produced by several chemical and physical methods. Here, we report on the structural, optical, and electrical properties of CuxO thin films prepared by the pulsed laser deposition technique. The substrate temperature, as well as the oxygen partial pressure in the deposition chamber, were varied to monitor the copper to oxygen ratio within the deposited films. The growth conditions were carefully optimized to provide the highest conductivity and mobility. Thus, 100 nm thick cuprous oxide films (Cu2O) deposited at 750 °C exhibited a resistivity of 16 Ω∙cm, high mobility of 30 cm2/(V∙s), and a bandgap of around 2 eV. The film deposited at the optimized deposition parameters on Nb:STO (001) substrate with Au top electrode showed a photovoltaic response with an open circuit voltage of 0.56 V. These results path the way to efficient solar cells made with Cu2O films via the pulsed laser deposition technique.