CuO Thin Films Research Articles

Investigating the role of film thickness on the physical properties of sol-gel coated CuO thin films: Discussing its potentiality in optoelectronic applications

In the present study, Cupric oxide thin films with varying thicknesses were successfully fabricated on a glass substrate at room temperature via dip coating technique. Highly crystalline CuO films with monoclinic symmetry were examined from XRD which was further confirmed with the help of Raman spectra. FESEM results showed a uniform coating surface with nano-sized grains without any agglomerations. The elemental composition of Cu and O atoms is in a 1:1 stoichiometric ratio for samples having higher thickness values. Strong absorption in the visible and nearby IR region makes the sample a viable choice in the field of photovoltaics. The estimated band gap values from the Tauc plot ranges from 1.10 eV to 1.26 eV. All the samples exhibited a p-type nature and their uniformity of resistance over the film surface was examined by resistance mapping. Hall measurements indicated the direct proportionality of sample resistivity with thickness.

Electrical properties of vertical Cu2O/β-Ga2O3 (001) p–n diodes

In this work, p-type cuprous oxide (Cu2O) films grown on beta gallium oxide (β-Ga2O3) substrates by magnetron sputtering were reported. The resulting vertical Cu2O/β-Ga2O3 heterojunction p–n diodes demonstrated superior performance compared to devices fabricated with polycrystalline Cu2O thin films. Meanwhile, analysis of the discrepancies between the built-in potential and turn-on voltage revealed diverse carrier transport mechanisms in the fabricated devices. Numerical fitting of the forward J–V characteristics further discerned that distinct carrier transport mechanisms dominated under various bias voltages or temperature conditions. At 300 K, trap-assisted tunneling dominates the regime because of the presence of defects in β-Ga2O3 or Cu2O. While the bias voltage is low, the polycrystalline nature of the films formed at room temperature leads to the prevalence of grain boundaries as the primary source of interface-type defects at the Cu2O/β-Ga2O3 interface. Consequently, the dominant mechanism governing carrier transport is interface recombination. As the temperature increases, however, thermionic emission becomes more important. This study presents an opportunity for further investigation into the epitaxial growth of Cu2O and provides insights into the carrier transport mechanism of β-Ga2O3-based heterojunctions.

Tuning the phase structure and surface morphology of Cr2O3:CuO thin film by annealing for enhanced ammonia sensing performance at room temperature

Driven by global environmental concerns, there is currently a strong need to identify real-time sensing materials for sensor devices. In this work, we mainly report the observation of an annealing-induced enhancement in room temperature ammonia sensing performance of binary composite metal oxide thin films of Cr2O3:CuO by tuning the phase structure and surface morphology. The activation energy of Cr2O3:CuO film was estimated from the Arrhenius plot and its magnitudes varied between 0.182 eV and 0.186 eV upon the variation of annealing temperature from 300 to 1000 °C. X-ray diffraction patterns of annealed Cr2O3:CuO film showed the existence of two different phases such as tetragonal CuCr2O4 and orthogonal CuCrO4. Fascinatingly, the CuCr2O4/CuCrO4 thin film prepared on quartz substrate exhibits a clearly visible cumin seed-like morphology with clear boundaries, which support the observed improvement in gas sensing performance. The sensitivity and detection limit (DL) of CuCr2O4/CuCrO4 thin film for ammonia gas were measured to be 5.77 and 1.9 ppm, respectively. The CuCr2O4/CuCrO4 film shows good response to different concentrations of NH3 and the film has a competence to retort for very low NH3 level (1 ppm). In addition, the prepared film retains 95 % of its initial response to ammonia even after 1-year duration. The observed results provide a probe for designing good and reliable room temperature sensor for ammonia gas at room temperature.

CuO-ZnO nanocomposites-based thin films: Characterization, physical properties and sunlight photocatalytic degradation of organic pollutants

One of the most commonly employed techniques for boosting photocatalytic efficiency by separating photo-induced electrons and holes is the formation of heterojunctions. The photocatalytic activity of CuO-ZnO nanocomposites-based thin films was investigated in this work for the decomposition of a model pollutant, methylene blue (MB), under sunlight irradiation. The spray pyrolysis method was utilized to produce nano-sized pure CuO and ZnO thin films, as well as CuO-ZnO nanocomposite thin films with varied molar ratios (Cu:Zn 1:3, 1:1, and 3:1). The structural and optical properties of the prepared materials were carefully studied. Contact angle measurements were used to determine the samples' wetting properties. XRD and Raman spectra confirmed the hexagonal würtzite and cubic structures of ZnO and CuO crystals in the different heterostructures. SEM images demonstrated the growth and distribution of the grains, with some spherical or plate-like nanostructures. The composition of the synthesized nanocomposites is confirmed by EDX analysis. UV-Vis investigations indicate that the optical band gaps are considerably impacted by the composition of nanocomposites. PL measurements confirmed a large number of defects in the synthesized nanocatalysts. These data also reveal that the formation of p-n heterojunctions prevented photogenerated carriers from recombining. The photocatalytic activity of the prepared CuO-ZnO nanocomposites was found to be greater than that of individual semiconductors. A possible mechanism and involvement of radicals in photocatalytic dye degradation were also proposed. As a result, the produced nanocomposite thin films might be beneficial for environmentally friendly and energy-saving wastewater treatment.

Sputtered nanocrystalline samarium doped CuO photoelectrode for efficient photoelectrochemical water splitting

Copper oxide (CuO) is a promising photoelectrode for photoelectrochemical (PEC) energy generation because of its fascinating properties, including high earth availability and inexpensive. In this context, samarium (Sm)-doped CuO thin films are deposited on a glass substrate through the sputtering technique to serve as photocatalysts in PEC water splitting. The structural characterizations of sputtered films were performed with X-ray diffraction (XRD) spectroscopy, while the morphology and elemental composition of all films were studied with the help of field-emission scanning electron microscopy (FE-SEM) connected with a dispersive energy X-ray analyzer. XRD pattern has shown that all films are polycrystalline with a preferred orientation of (−111) crystallographic plane. FE-SEM images and ImageJ analysis showed that all deposited particles are uniformly distributed as disassembled particles over the substrate area. The optical energy band gap (Eg) was increased by adding the Sm contents in the CuO films. The photocurrent density for the photoelectrode was improved by Sm dopants as compared to the pure sample and recorded its maximum value of − 4.66 mA/cm2 at ∼ − 0.385 V vs. RHE which was about 4 times higher than that of the pure sample with feasible photostability retention. Additionally, the value of the charge transfer resistor for the CuO photocathode with the smallest amount of Sm ions was the lowest as compared to other photocathodes. These results offer a practical method for creating a brand-new fabrication technique for PEC devices with remarkable water-splitting efficiency.

Comprehensive experimental and theoretical studies on the synthesis and characterization of electrodeposited nanostructured Cu2O thin films

In this study, we present a comprehensive analysis of the morphology, microstructure, and optical properties of electrodeposited Cu2O thin films on SnO2:F (FTO) substrates. The films were synthesized using the galvanostatic method at varying pH levels (9 and 12) and temperatures (40, 45, 50, 55, 60, and 65 °C). Characterization techniques employed include scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman and UV-VIS spectroscopy, photoluminescence (PL), and electrochemical measurements. Additionally, a theoretical study based on Wulff's theorem was conducted to investigate the influence of the synthesis environment on the growth process. The obtained films exhibited uniformity, reproducibility, stability, purity (solely the Pn3m Cu2O phase), and crystallinity. Furthermore, we successfully achieved thin films with various morphologies (cubic and octahedron, truncated or not), growth orientations [111 or 100], with relative high density of cupper vacancies and charge carrier, making a significant contribution to the exploration of multifunctional semiconductor materials for applications in photocatalysis, photovoltaic cells, photoelectrochemistry, and others advanced technologies.

Harnessing the tunability of intrinsic defects in isovalent Zn doped spray deposited CuO thin films

Doping is a versatile tool for tailoring the properties of semiconductor thin films. This article investigates the influence of isovalent dopant, Zinc (Zn), on the electronic, optical and structural characteristics of copper oxide (CuO) thin films prepared by spray pyrolysis technique. Structural characterization from XRD and Raman studies confirms the successful incorporation of Zn atoms into the CuO lattice without altering monoclinic structure of the films. The absence of secondary phases like Cu2O and ZnO confirms the good quality of the prepared films. A significant variation in the morphology of the films was observed in FESEM images. The EDS analysis confirmed the incorporation of Zn atoms in CuO films and showed that the prepared films are oxygen rich in nature. The band gap of the films increased from 1.50 eV in pristine samples to 1.62 eV in 8 at% Zn-doped sample. Different defect related emissions were observed in PL spectra with the resultant emission in yellowish green region as obtained from chromaticity diagram. XPS analysis confirmed that both Cu and Zn are found in +2 oxidation state. The electrical conductivity and carrier concentration of CuO films improved with doping due to the enhanced oxygen interstitial defects. The carrier density increased from 2.17 × 1014 to 2.82 × 1015 cm−3 after 6 at %doping with the lowest resistivity of 708 Ω cm. Hence, the properties of CuO films can be effectively modified by Zn doping. Zn doping improved the electrical properties of the films without trading off the excellent optical properties of CuO thin films making them suitable in solar cell absorber layer applications.

Benzene vapor sensing performance of different phases of copper oxide (CuxOy) thin films

Three different phases of copper oxide can be grown by thin-film deposition techniques, which differ in the oxidation state of copper. However, few studies have focused on comparing and considering sensing performance of these phases. The current study scrutinizes the benzene vapor sensing properties of various phases of copper oxide that can be used for the development of sensing device based on CuxOy thin films. RF reactive sputtering technique was employed, and different phases of copper oxide (CuO, Cu2O, and Cu4O3) were grown by tuning the sputtering power and reactive gas. The samples with phases of CuO, Cu2O, and CuO/Cu2O showed the response to benzene at different operating temperatures while the sample with the Cu4O3 phase was not sensitive to target vapor. The results demonstrated that the device based on CuO thin film can be a promising candidate to detect benzene vapor due to its remarkable sensitivity, selectivity, and stability.

Influence of Effective Surface Area on Gas Sensing Properties and Surface Morphology of Ag Doped Cu2O Thin Films by Cost Effective Method of M-SILAR Technique

Influence of Effective Surface Area on Gas Sensing Properties and Surface Morphology of Ag Doped Cu2O Thin Films by Cost Effective Method of M-SILAR Technique

Fabrication and Electrical Characterization of Cu1-xCrxO/n-Si Diodes by Sol Gel Spin Coating Method

Undoped and Cr-doped CuO thin films were deposited on n-Si substrates by sol gel spin coating method. These electrical properties of copper oxide-based heterojunction structures were examined as a function of Cr doping concentrations. The results show that a change in Cr concentration significantly affects the electrical properties of Ag/Cu1-xCrxO/n-Si diodes. The all diodes exhibit rectification behavior, as shown by their dark 𝐼−𝑉 characteristics. The crucial junction parameters such as series resistance (R𝑆), rectification ratio (𝑅𝑅), ideality factor (𝑛) and barrier height (Φ𝐵) were calculated by using 𝐼−𝑉 data. The calculated values for the ideality factor (n), which offered details about the performance of the diodes, range from 2.16 to 2.78. The highest 𝑅𝑅 value was obtained from Cu0.5Cr0.5O/n-Si diode. In addition, the capacitance-voltage (𝐶−𝑉) characteristics of the diodes were measured in the frequency range of 10 kHz and 1 MHz. The 𝐶−2−𝑉 graphs were employed to calculate the values of 𝑁𝑣, 𝐸𝑓, 𝐸𝑚𝑎𝑥, and Φ𝐵 (𝐶−𝑉). The results show that the electrical properties of Ag/Cu1-xCrxO/n-Si diodes can be controlled by various chromium doping concentration.

H2 gas sensing applications of undoped and Fe-doped CuO thin films grown by USP

H2 gas sensing applications of undoped and Fe-doped CuO thin films grown by USP

Fabrication of Polyvinyl Alcohol Doped CuO Thin Films for Improved Amperometric-Non Enzymatic Hydrogen Peroxide Sensing

Fabrication of Polyvinyl Alcohol Doped CuO Thin Films for Improved Amperometric-Non Enzymatic Hydrogen Peroxide Sensing

Unraveling the role of solvent type in the physical and chemiresistive gas sensing properties of nebulizer-sprayed CuO films

Copper oxide thin films were grown via a nebulizer spray pyrolysis technique using five different solvents. The XRD patterns revealed that the CuO films prepared with alcoholic solvents are more crystalline andRaman analysis confirmed the crystalline quality of the films. The sample was prepared with an ethanolic solvent, producing a hierarchical, fiber-like morphology. EDAX spectra confirmed the presence of copper and oxygen in CuO films. XPS analysis showed a significant reduction of oxygen species in ethanol compared to water as a solvent. The film deposited with an ethanolic solution showed the lowest bandgap of 1.7 eV. PL spectra showed strong emission at 628 nm. Lifetime studies suggest that the enhancement in the decay lifetime of CuO films can be advantageous for optoelectronic applications. CuO thin films deposited with alcoholic solvents exhibited lower resistance values. VOC detection was employed by the CuO-based gas sensors. i.e., acetone, ethanol, and toluene.

Preparing CuO, Cu2O thin films at various argon gas by using reactive dc magnetron sputtering method

Copper oxide (Cu2O, CuO) has been formed by dc reactive magnetron sputtering method of glass substrates, whereas pure target of the solid copper was sputtered with a mixture of plasma for argon gas and oxygen gas which are used form these films. Under vacuum chamber pressure on 1.2×10-5 Pa, Ar was varying from 5 to 15 sccm while other deposition parameters were fixed. X-ray photoelectron spectroscopy, XRD diffractions system, Atomic Force Microscopy (AFM), hall effect measurement system, and UV–VIS spectrophotometer were used to calculate the characteristic of the deposited thin films. Thin film at 5 sccm has investigated n-type of CuO thin film with direct band gap of 1.8eV and p-type of Cu2O at 15 sccm with direct band gap of 2.7eV. The influence of changing the Ar on the electrical and the optical properties was investigated in this study, furthermore in this study approved that the reactive dc magnetron sputtering method is suitable to prepare two type of semiconductors by change only one condition.

Impact of Surface Hydroxyl Groups on CuO Film Growth by Atomic Layer Deposition.

CuO-based nanostructures have been widely investigated in catalysis, sensing, and energy conversion and storage in recent years. The unique properties of these nanostructures are largely related to the morphology and crystallinity of CuO. The controlled deposition of conformal CuO thin films by atomic layer deposition (ALD) has remained challenging until now owing to the limited understanding of the nucleation behavior and growth process. Here, a novel ALD process for copper oxide was developed using copper(II) trifluoroacetylacetonate [Cu(tfacac)2] as the metal precursor. The nucleation and initial growth of a CuO film are strongly dependent on the surface OH concentration. A continuous particulate-like CuO film was grown on OH-abundant pristine SiO2 particles, whereas the surface of the annealed SiO2 particles (presenting mostly isolated OH groups) remained uncoated under the same growth conditions. Moreover, a uniform and conformal CuO film was grown on covalently functionalized CNTs under identical conditions as pristine SiO2 particles. This study provides a strategy for tailoring the structure and the properties of thin films via ALD, which is promising for designing well-tailored nanostructures for various applications.

Improved design and development of an automated jet nebulizer spray pyrolysis system for Ag/Zn: CuO/Si structured diode application

Zinc-doped Copper oxide (Zn:CuO) thin films are deposited via well-designed automated jet nebulizer spray pyrolysis (JNSP) system for developing Ag/Zn:CuO/n-Si structured diode. The system is fitted with a microcontroller-based spray nozzle with an up/down movement to enable thin film deposition in an automated way. Zn:CuO thin films are deposited via an automated JNSP system with 1%, 3%, and 5% doping concentration. The characteristics studies and analysis of Zn:CuO thin films are studied. XRD examination showed that all of the Zn:CuO thin films have a monoclinic crystal structure. Surface morphological analysis of an automated Zn:CuO thin films showed spherical-shaped small grains. It is found that particles are closely packed and well covered. Additionally, elementary composition analysis (EDS) is carried through to finalize the ‘Cu’, ‘O’, and ‘Zn’ atoms in the deposited Zn:CuO materials. The least energy band gap of 1.90 eV and the highest conductivity of 3.67 x 10-8 S/cm is obtained for 3% Zn doped CuO. Based on the characteristics analysis and studies of automated Zn:CuO thin films, Ag/Zn:CuO/Si structured diode have been developed. Various diode parameters have been evaluated under light and dark conditions.

Photocatalytic reduction of CO2 over Ni-CuxO thin films towards formic acid production

Copper oxide (CuO) is an abundant and low-cost material, which is active as a photocatalyst under visible light due to its narrow band gap (1.3 eV). In the present work, CuO thin films at different Ni doping amounts (5, 10, and 30 % mol) were prepared using two different techniques: dip-coating and electrodeposition of Cu precursors over glass and PET substrates. X-Ray analysis results indicate the presence of Cu2O, CuO and Cuo phases in PET substrate films, while only CuO phase in Glass-substrate films. Glass substrate films presented a higher formic acid production performance reaching 50,000 μmol/g·h using 5% Ni doping on CuO. This higher activity was associated with a lower ratio between the adsorbed oxygen and the oxygen located in the crystal lattice, attributing this to the oxygen species adsorbed over the surface that could hinder the active sites of the material. Finally, PET substrate samples present a higher ratio between adsorbed oxygen and lattice oxygen, however, the Cu2O phase presents less affinity to adsorb CO2 molecules than CuO monoclinic phase reducing the photoactivity of the CO2 photoreduction. Majority charge carrier mobility of 4 cm2/Vs and 35 cm2/Vs for Cu2O and CuO respectively, with the charge carrier concentration of ∼1 × 1019 order was achieved switching the conducting type.

Charge transfer in copper oxide nanostructure

The deposition potential affects the structural, morphological, optical, and electrochemical impedance spectroscopy properties of cuprous oxide (Cu2O) thin films formed on copper (Cu) substrates adopting a three-electrode electrochemical deposition procedure. XRD data revealed that the deposited films have a cubic structure established with desired (111) growth orientation. Scanning electron microscopy (SEM) images reveal that Cu2O film has very well three-sided pyramid-shaped grains which are equally spread over the surface of the Cu substrates and change substantially when the plating potential is changed. The photo-current density of prepared Cu2O thin films was increased from -1.41×10-4 to -3.01×10-4 A/cm2 with increasing the deposition potential of -0.3 to -0.6V, respectively. Further, Cu2O thin films obtained at -0.6V have the minimum charge transfer resistance (Rct) than Cu2O thin films synthesized at -0.3 to -0.5V, suggesting that Cu2O thin films produced at -0.6V have the highest electron transfer efficiency.

Inverting electrodeposited nanostructured Cu2O thin films from n-type to p-type semiconductors and variation of their physical and photoelectrochemical properties for optoelectronic applications

Employing identical techniques to produce the semiconductor with n and p-type conductivity is one of the most important keys to fabricating higher performance optoelectronic devices. Therefore, here the electrodeposition technique was employed to grow nanostructured Cu2O thin films with different pH values ranging from 3.5 to 13 from the same precursors before starting the deposition process. The morphological, structural, optical, electrical, and photoelectrochemical properties of fabricated Cu2O thin films were investigated employing SEM, EDX, XRD, Raman, UV–Vis, PL, Photocurrent, Mott-Schottky, and electrochemical impedance spectroscopy (EIS) measurements. XRD results showed the formation of Cu, Cu2O, and CuO phases with low pH values, while only Cu2O phase is obtained with higher pH. Raman measurements proven phonon modes of nanostructured Cu2O thin films. The morphology varies with different shapes such as spherical, pyramids, and prisms according to pH values. The optical absorption edge has appeared between 475 nm and 575 nm which indicates the formation of Cu2O and the calculated band gap varies from 2 to 2.44 eV. PL measurements indicate two dominant peaks related to inter-band transitions and defects including copper interstitials. Photocurrent measurements denoted that samples with lower pH from 6 to 7.6 are n-type semiconductors, while higher ones from 8 to 13 are p-type semiconductors. Mott-Schottky measurements showed that the donor’s density declines from about 2 × 1017 cm− 3 to about 1.6 × 1016 cm− 3 as pH increases from 6 to 7.6 whereas the acceptor’s density rises from about 1.25 × 1017 cm− 3 to about 3 × 1018 cm− 3 as pH increases from 8 to 13. EIS results show that both p-type and n-type samples have higher separation and transfer of charge carriers. Our outcomes indicate that the electrodeposited nanostructured Cu2O thin films are appropriate materials for biosensors, solar cells, and supercapacitors applications.

Enhancing the absorption figure of merit on solution-based CuO thin films by Ni doping

We evaluated an absorbance effectiveness on the solar spectrum using an absorption figure of merit (a-FOM) for the conducting thin films. In particular, Ni-doped and un-doped CuO thin films were deposited by a facile and sustainable solution-processed synthesis, whose Ni doping concentration was varied to be 0.2, 0.6, 1, 2, 3, 4 wt%. We observed a change of smooth surface to an appearance of nanoparticles by Ni doping, which supported to form of a plasmonic mechanism for improving the light capture and retention. The absorption of long wavelengths was improved and extended to the near-infrared range. That is, the bandgap energy decreased from 2.10 to 1.88 eV with Ni doping. Also, we found that the absorption length decreased from 99.93 nm to 63.80 nm as the Ni doping increased. In addition, the CuO-based film with 4 wt% Ni doping showed a maximal value of a-FOM as high as 30.88 Ω−1cm−1, corresponding to a resistance of 2.07 MΩ/sq and an absorption length of 63.80 nm. Our finding suggested that Ni-doped CuO thin films can be considered as an excellent selection of absorbent conductive oxide layers for application in optoelectronic devices and solar cell systems.