Nickel Oxide Thin Films Research Articles

Electron-Beam-Evaporated Nickel Oxide Thin Films for Application as a Hole Transport Layer in Photovoltaics

We present the growth of nickel oxide (NiO) thin films as a hole transport material in photovoltaic devices using the e-beam evaporation technique. The metal oxide layers were reactively deposited at a substrate temperature of 200 °C using an electron beam evaporator under an oxygen atmosphere. The oxide films reactively grown through electron-beam evaporation were optimized for carrier transport layers. Optical and structural characterizations were performed using ultraviolet–visible (UV–Vis) spectrometry, X-ray diffraction, contact angle measurements, scanning electron microscopy, and Hall effect measurements. The study of these films confirmed that the NiO layer is a suitable candidate for use as a hole transport layer based on Hall effect measurements. A morphological study using field-emission scanning electron microscopy confirmed the growth of compact, uniform, and defect-free metal oxide layers. Contact angle measurements revealed that the films possessed semi-hydrophilic properties, contributing to improved stability by repelling water from their surfaces. The stoichiometry of the films was influenced by the oxygen pressure during deposition, which affected both their morphological and optical features. The NiO films exhibited a transmittance exceeding 80% in the visible spectrum. These findings highlight the potential applications of such nickel oxide films as hole transport material layers.

Effect of thermal treatment on thin films of NiO:WO3 for optoelectronic applications

Nickel oxide (NiO), a semiconducting metal oxide, with its exceptional optical, electrical, and magnetic properties make it highly sought after for use in optical, optoelectronic, and electrochromic devices. Recent advancements in NiO-optical devices relies on the optical parameters like intrinsic optical nonlinearities. The current study involves the deposition of NiO:WO3 thin films utilizing radio frequency (RF) sputtering at various substrate temperature (Ts) of 100, 200, and 300 °C. An investigation was carried out to analyse the significance of Ts on the structural, optical, morphological, & vibrational characteristics. The X-ray diffraction investigation revealed the amorphous nature of the films. Scanning electron microscopy confirms the compact pinhole free surface of the films. The results of energy dispersive X-ray spectroscopy (EDS) spectra verified the existence of nickel (Ni), oxygen (O), and tungsten (W) components in the films. XPS analysis confirms the presence of both Ni2+ and Ni3+ states. The optical transmittance increased, and the band gap decreased with increase in Ts. The impact of Ts on various optical parameters such as refractive index, extinction co-efficient, dielectric constants, optical non-linear susceptibility, and dispersion energy parameters obtained by the Wemple-DiDomenico theory has been calculated and extensively investigated. The results indicate that NiO:WO3 films can be used to fabricate electrochromic and optoelectronic devices.

Impact of metal deposition on the optical and interface properties of NiO: growth and characterization of NiO/metal thin bilayer films

Abstract Since transparent conductive oxides (TCOs) provide electrical conductivity together with optical transparency, they have found wide applications in optoelectronic devices and photovoltaics. Among the TCOs, nickel oxide (NiO) is challenging due to its inherent trade-off between transparency and electrical conductivity. To address this challenge, one effective approach is to deposit a metal layer onto NiO thin films. In this work, NiO, NiO/Au, NiO/Ag, and NiO/Cu thin films are prepared by sputtering and thermal evaporation techniques on glass substrates and fully characterized finding the proper film for optoelectronic applications. The electrical and optical properties of the fabricated films are examined by four-point probe measurements and optical spectrometry. According to the obtained results, the NiO/Au, NiO/Ag, and NiO/Cu bilayers show sheet resistance of 200, 338, and 925 Ω sq−1 respectively while their optical bandgaps vary from 3.2 to 3.76 eV. These findings provide valuable insights into the performance of these films, making them potentially viable choices for various optoelectronic applications.

Enhancing energy storage with binder-free nickel oxide cathodes in flexible hybrid asymmetric solid-state supercapacitors

The need for flexible electrode materials for the development of flexible supercapacitors has drawn scientific interest recently. We present the successful synthesis of nickel oxide thin films using the successive ionic layer adsorption and reaction (SILAR) method, with the use of three different cationic precursors. This paper provides comprehensive details on the synthesized nickel oxide structure, morphology, and elemental analysis in addition to its electrochemical characteristics, which include specific capacitance (SCs), charge transfer resistance, etc. The produced nickel oxide electrodes achieved specific capacity as 120 C g−1, 517 C g−1, and 1147 C g−1 with different nickel precursors such as nickel chloride, nickel nitrate, and nickel sulfate respectively, at a 1 mA cm−2 current density. A flexible hybrid asymmetric solid-state supercapacitor (FHASS) (S:NiO//PVA-KOH//CuS) device delivered SCs of 165 Fg−1 at a 0.5 mA cm−2 current density, with a maximum SE of 58.87 Wh kg−1 at SP 347 W kg−1. FHASS device exhibits capacitive retention and coulombic efficiency of between 79 % and 96 % after 5000 successful GCD cycles. Also, the device retained an outstanding 97 % of its capacitance at a 175º bending angle. Furthermore, to illustrate its real-world applicability, the constructed device underwent 30 s of charging to a lightning LED table lamp for 90 s. The fabricated device is bringing a new era of broad integration of device-grade applications.

Fabrication and Characterization of Aluminum-Doped Nickel Oxide Thin Films for Optoelectronic Applications using the SILAR Method

Study’s Excerpt The effect of varying annealing times on 10% Aluminum-doped Nickel Oxide (ANO) thin films, deposited via the SILAR technique is presented. SEM and RBS analyses were used for detailed correlation between annealing time and the film's microstructural improvements. ANO thin films could be used for advanced technological applications. Full Abstract The effect of varying the annealing time of %10 aluminium-doped Nickel Oxide thin film was studied to understand the possible effect on the optical, structural, and electrical properties of %10 aluminium-doped Nickel Oxide (ANO) for possible application. The thin films were deposited on glass substrates using the successive ionic layer adsorption reaction (SILAR) deposition technique. The samples formed were annealed at 3000C, and the annealing time varied at 1.35 hrs., 1.45 hrs., 1.55 hrs., and 2 hrs, respectively. The deposited films were characterized to obtain the optical, electrical, and structural characteristics and the compositional constituent of the film using the double beam photo spectrometer, Four-Point Probe, Scanned electron Microscope, Energy Dispersion Spectroscopy, and X-ray Diffractometer. The films were observed to have low absorbance in the range of 0.1 to 0.01 and high % transmittance within the range of 80% - 98% in the visible region of the spectrum. The reflectance of the film was observed to decrease with an increase in annealing time in the range of 10% - 2.5%, all in the visible region of the spectrum. The crystallite size of the deposited films decreased with increased annealing time with the structural formation of simple cubic phase NiO thin film. SEM micrograph of the thin films reveals that an increase in annealing time improved the crystallinity of the films with the grain size evenly distributed. The EDS result of the deposited films revealed the presence of nickel, aluminum and Oxygen as the major constituent of the deposited films. The Ruther Ford Backscattering (RBS) analysis of the thickness of the films shows an increase in the thickness with an increase in annealing time. Clearer compositions of the films were also seen from the RBS analysis. Their electrical properties revealed that the films formed had low electrical resistivity and high conductivity, so they could be useful in making optoelectronics devices and corrosion resistance.

Improved transparency and charge matching of electrochromic devices with Ce-doped NiO counter electrode

The quest for cost-effective and efficient electrochromic electrodes, featuring high color contrast and rapid response times, has sparked increasing interest in research of metal oxides for electrochromic applications. In this study, nickel oxide thin films with various cerium dopant concentrations are synthesized, with the optimized doping concentration identified as 1 at%. X-ray diffraction analysis confirmed that the dopant successfully reduces crystal size and alters the preferred orientation to (111). The 1 % Ce:NiO thin film exhibits enhanced electrochromic performance, with a transmittance modulation increase of 27.4 % at 633 nm, a 27.1 % rise in coloration efficiency and faster response time (tb=9.64 s and tc=6.76 s) compare to the undoped NiO. Importantly, the charge density of 1 % Ce:NiO thin film increases from 4.86 to 8.14 mC cm−2, representing a 67.5 % improvement, which becomes a better charge matching with WO3 in electrochromic devices. The incorporation of Ce into the NiO thin films not only leads to increased transmittance in the bleached state and optical modulation in the electrochromic devices but also contributes to a rise in the optical band gap of the NiO thin films and improved charge balance matching. These results underscore the positive impact of cerium doping on microstructure and electrochromic performance, indicating a promising future for electrochromic devices.

Nucleation, growth mechanism, and bifunctional electrochromic supercapacitive properties of NiO thin films

Bifunctional devices combining display and energy storage capabilities are crucial for next-generation optoelectronic technology. This study investigates the application of nickel oxide (NiO) thin films for bifunctional electrochromic energy storage systems. The amorphous Ni(OH)2 thin films were electrodeposited with a focus on their time-dependent properties. The Scharifker-Hills model revealed a mixed nucleation process during the electrodeposition. The deposited thin films were examined for their physicochemical properties using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron Spectroscopy (XPS), and morphological studies. Rietveld refinement of the XRD pattern confirmed a cubic NiO polycrystalline phase, while XPS identified Ni3+ as the dominant oxidation state. Significant morphological changes were observed with the varying deposition time. The NiO electrode deposited for 120 minute exhibited optimal characteristics including the highest areal capacitance of 161.77 mF/cm2, along with excellent cyclic stability of 96.54 % even after 2000 cyclic voltammetry cycles. The electrochromic study demonstrated optical modulation ranging within 55–82 % at 532 nm, with a maximum coloration efficiency of 86.90 cm2/C. This research demonstrates the viability of NiO thin films as bifunctional electrochromic energy storage systems and the advancement of optoelectronic devices that integrate display and energy storage functionalities.

Fast-switching electrochromic smart windows based on WO3 doped NiO thin films

Nickel oxide (NiO) is a very promising material for the counter electrode in electrochromic devices (ECDs). In the current research, WO3 incorporated NiO thin films were fabricated via RF sputtering to enhance the electrochromic performance of NiO thin films. An XRD analysis revealed that the addition of WO3 to the cubic NiO thin film disrupts its long-range crystalline structure, resulting in an amorphous state. FESEM revealed the formation of columnar structure which favours ECDs. XPS analysis revealed that the addition of WO3 into NiO enhanced the hole concentration by creating nickel vacancies (nickel defects). Compared to pristine NiO, WO3 mixed NiO thin films showed enhanced optical modulation (66 %) with rapid switching speed (0.6 s/1.0 s for bleaching/colouring). This is mainly because the defect- induced amorphous structure of the nickel tungsten oxide thin film can provide large number of diffusion channels which facilitates the rapid ion intercalation process, and can accommodate large number of ions, and hence enhances the electrochromic performance. This advancement might have a substantial impact on the development of nickel tungsten oxide as a potential counter electrode in high-performance energy saving smart windows.

Post-growth annealing effect of Li-doped NiO thin films grown by mist chemical vapor deposition

Nickel oxide (NiO) thin films were grown by mist chemical vapor deposition (mist CVD) with various amounts of Li dopant in the precursor (0–15%). As the Li dopant readily decomposed under the high temperature above 700 °C, the post-growth annealing was conducted at 600–800 °C. The crystal quality of the undoped and Li-doped NiO films was improved by thermal annealing due to the crystal reconstruction. The optical transmittance of NiO films was decreased with increasing the amounts of Li dopants, whereas it was increased with thermal annealing. The bandgap of the NiO films was slightly red-shifted with increased amounts of Li dopants, whereas it was blue-shifted with increasing annealing temperature. The resistivity of as-grown NiO films ranged from 25–75 Ω·cm with Li doping. Electrical properties abruptly decreased under a high annealing temperature of 700 °C. Hence, an appropriate combination of Li doping and post-growth annealing might improve the structural properties of the NiO thin films while retaining the p-type conductivity.

Effect of Iron Doping in Ordered Nickel Oxide Thin Film Catalyst for the Oxygen Evolution Reaction.

Water splitting has emerged as a promising route for generating hydrogen as an alternative to conventional production methods. Finding affordable and scalable catalysts for the anodic half-reaction, the oxygen evolution reaction (OER), could help with its industrial widespread implementation. Iron-containing Ni-based catalysts have a competitive performance for the use in commercial alkaline electrolyzers. Due to the complexity of studying the catalysts at working conditions, the active phase and the role that iron exerts in conjunction with Ni are still a matter of investigation. Here, we study this topic with NiO(001) and Ni0.75Fe0.25O x (001) thin film model electrocatalysts employing surface-sensitive techniques. We show that iron constrains the growth of the oxyhydroxide phase formed on top of the Ni or NiFe oxide, which is considered the active phase for the OER. Besides, operando Raman and grazing incidence X-ray absorption spectroscopy experiments reveal that the presence of iron affects both, the disorder level of the active phase and the oxidative charge around Ni during OER. The observed compositional, structural, and electronic properties of each system have been correlated with their electrochemical performance.

Using femtosecond laser pulses to investigate the thickness-dependent nonlinear optical properties of nickel oxide thin films and their potential use as optical limiters

In this study, the Z-scan technique was used to investigate the nonlinear optical properties of nickel oxide (NiO) thin films of various thicknesses. Direct current (DC) sputtering was used to deposit single-phase NiO thin films with thicknesses of 280, 350, and 470 nm onto a soda-lime glass substrate. The film structure was measured using X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the linear optical properties were measured using a UV-Vis spectrophotometer. NiO thin films were irradiated with 100 fs laser pulses at various excitation wavelengths and excitation powers to determine the nonlinear absorption coefficient and nonlinear refractive index. The NiO films were found to have reverse saturable absorption and self-focusing behavior. As the thickness of the NiO film increases, both the nonlinear absorption coefficient and nonlinear refractive index decrease. Additionally, the investigation of the optical limitations of NiO thin films revealed a definite association with the thickness of the NiO thin film.

Investigation of diodic behavior in p-NiO/n-SnO2 bilayer heterojunctions fabricated via DC magnetron reactive sputtering

Tin oxide (SnOx) thin films at varying oxygen flow rates and Nickel oxide (NiO) thin films were deposited by reactive dc magnetron sputtering on glass substrates. Structural, chemical, morphological, optical and electrical properties of the deposited films were studied. XRD studies confirmed that the deposited films were polycrystalline in nature. SnOx thin films have shown two phases such as SnO and SnO2. AFM and SEM were used to analyse the morphology of the films and EDS confirmed the presence of Sn and Ni in the respective films. The examination of the x-ray photoelectron spectrum showed that the sputtered SnOx films contain both Sn2+ and Sn4+ oxidation states and NiO films contain Ni+2 and Ni+3 oxidation states. Photoluminescence study shows strong violet and weak red emission peaks for SnOx films and NiO showed strong emission peaks in the orange-red region. The optical results demonstrate that the films were transparent. The bandgap of SnOx and NiO samples were ∼3.3 eV and − 3.42 eV, respectively. Further we constructed a p-NiO/n-SnO2 heterojunction diode and its electrical characteristics were thoroughly assessed. Using dark current–voltage measurements, electrical characteristics such saturation current, ideality factor and barrier height were determined. The increase in oxygen flow rate led to reduction in the rectification of the devices. Our findings support the creation of high-performance metal oxide heterojunction for optoelectronic devices.

Preparation of tunable magnesium atom-doped nickel oxide films with short response time and high coloring efficiency by sol-gel method

Nickel oxide, a representative electrochromic material, is commonly employed in environmentally conscious optoelectronic devices, such as multifunctional smart windows. In this paper, novel electrochromic nickel oxide films doped with magnesium atoms were prepared on indium tin oxide (ITO) substrates by sol-gel spin-coating method, and the results of X-ray diffraction and scanning electron microscopy show that the spin-coating is unique in that the existence of a small number of cracks on the surface of the sample is conducive to the enhancement of the electrochemical properties. UV–visible spectrophotometer and electrochemical workstation were used to explore the effect of Mg-atom doping concentration on the electrochromic performance of the nickel oxide thin films, and the results showed that at an annealing temperature of 400 °C, the optical modulation amplitude of the samples with a doping concentration of 4 % reached 43.12 %, and the coloring time and the fading time were reduced to 4.0 s and 3.1 s, respectively, with an increase in the coloring efficiency to 42.25 cm2C−1. In conclusion, Mg doping has an important reference value for the study of electrochromic performance of NiO thin films, and has good prospects for electrochromic applications.

Synthesis and Characterization of Un-Doped and Copper Doped Nickel Oxide Thin Films

Synthesis and Characterization of Un-Doped and Copper Doped Nickel Oxide Thin Films

Ultra-fast switching of energy efficient electrochromic nickel oxide thin films for smart window applications

In today's modern world, energy consumption continues to escalate. In such cases, smart windows play a crucial role in reducing energy consumption and enhancing the quality of life. Electrochromic devices (ECDs) -based smart windows rely profoundly on nickel oxide (NiO) thin films, which act as a counter electrode in ECDs. This work aims to fabricate NiO thin films, with the intention of achieving ultrafast ECD. Through the sputtering technique, energy-efficient ECD is obtained with the highest optical modulation of 60 % at a rapid switching speed of 0.55s for bleaching and 0.95s for coloration. We have also investigated the structural, morphological, vibrational, and optical properties of NiO thin films. XRD analysis revealed the less crystalline or near amorphous nature of NiO thin film. XPS, PL, and Raman studies confirm the existence of defects in the film. The favourable, less crystalline nature, along with the presence of defects, facilitates ultra-fast ion intercalation and de-intercalation process. We believe that prepared NiO film can be used as a promising anodic colourant in electrochromic smart windows with applications in energy-efficient buildings.

Study of the effects of heating on the physical, optical, and electrical properties of NiO thin films synthesized using a low-cost sol-gel method

Developments in low-cost techniques for growing high-quality nickel oxide thin films (NiOTFs) are critical enablers for the fabrication of NiO-based devices, particularly solar cells, light-emitting diodes, lasers, and many other applications. In this study, it has been demonstrated that the optical, electrical, and structural characteristics of NiOTFs coated on glass substrate employing a low-cost solution method are strongly influenced by post-thermal annealing treatments in ambient air. A comprehensive study was carried out on the characteristics of the deposited NiOTFs. X-ray diffraction (XRD) measurements indicate the enhancement of the crystal quality of films after annealing. There is a noticeable change and improvement in coated NiOTFs with heat treatment at 300 and 600 ℃ due to clear shifts in density. During the heating temperature increment, the energy of the band gap was shifted from 3.63 to 3.44 eV, and the electrical resistance of the NiOTFs varied from 1020 to 700 Ω-cm. Furthermore, the results indicate that the low-cost sol-gel (SG) deposition technique has a greater potential for producing high-quality p-type NiOTFs with minimal defects for electronic device applications.

Synthesis, characterization, and CO sensing properties of NiO thin film for commercial aircraft applications

Abstract The detection of combustion gases such as carbon monoxide (CO) and fuel leaks is a concern in regard to aeronautical safety and has led to the development of semiconductor sensors. The focus of this work is the detection of CO within commercial aircraft using a thin film of nickel oxide (NiO) as the sensing element. The NiO phase was synthesized using the sol-gel method using a modification of the procedures proposed by N. Talebian and B. Pejova. Microstructural characterization of the NiO thin film was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Optical analysis was carried out using diffuse reflectance (UV-VIS) spectroscopy. The results showed that the NiO thin film was homogeneous and composed of nodular nanoparticles with size between 10 and 15 nm and thickness of 75 nm. The band gap value was 3.3 eV, which is consistent with p-type semiconductors. The sensitivity of the devices was determined by means of the static environment method. The best operation temperature was 200°C for the device with 100-µm spacing between tracks, which gave a response time of 165 seconds and recovery time of 212 seconds according the results of a flow-through method. The device with this track spacing is ideal for CO detection at 50 ppm, at which the first symptoms of intoxication appear in humans inside commercial aircraft.

Development of nickel oxide thin film by chemical route for supercapacitor application

Development of nickel oxide thin film by chemical route for supercapacitor application

Impact of zinc concentration and annealing temperature on the structural, optical, and photoelectrochemical properties of nickel oxide thin films synthesized by electrodeposition method

In this study, Zinc (Zn)- doped nickel oxide (NiO) thin films were fabricated via the electrodeposition method. The synthesized films were created with different concentrations of Zn (2 %, 4 %, 6 %, and 8 %) after that annealed at two different temperatures (300 °C and 500 °C). The prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (RAM), UV–vis spectrophotometry, photocurrent (PC), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), Energy-Dispersive X-ray spectroscopy (EDX), photocurrent (PC), and Mott-Schottky (MS) analysis. XRD patterns indicate that Zn: NiO thin films have a cubic phase, with the (111) direction as the preferred orientation. Various structural parameters such as dislocation density, stacking fault, lattice strain, and crystallite size have been determined. The presence of Zn doping in NiO has been confirmed by EDX analysis. The EDX mapping of elements revealed the uniform distribution of Ni, Zn, and O in the sample. The optical transmittance and absorbance were analyzed using a UV–vis spectrophotometer. The lowest transmittance values were found for 8 % Zn: NiO thin films annealed at 300 °C and 500 °C. The absorption edge corresponding to pure NiO-300 °C and NiO-500 °C has been observed at 300 and 320 nm, respectively. The band gap energy (Eg) decreased to 3.88 eV for 8 %Zn: NiO (300 °C) and 3.71 eV for 8 %Zn: NiO (500 °C). The Raman analysis showed three distinct peaks at 590 cm−1, 705 cm−1, and 1172 cm−1, which correspond to the vibration of Ni—O bonds. The SEM results indicated that increasing the doping concentration and annealing temperature resulted in larger grain sizes in the manufactured samples. Furthermore, the PL spectra analysis of the synthesized films revealed two distinct emission peaks at around 400 and 490 nm. PC analysis confirmed the p-type conductivity of manufactured arrays. From MS measurements, the highest carrier concentration (NA) values of 8.81×1018 cm−3 and 9.41×1019 cm−3 were obtained for 8 %Zn: NiO (300 °C) and 8 %Zn: NiO (500 °C), respectively. EIS analysis confirmed the highest conductivity and enhanced electrochemical activity for 6 % Zn: NiO (500 °C) and 8 % Zn: NiO (300 °C). These results suggest that Zn-doped NiO is suitable for optoelectronic applications.

Optical properties of NiO films: Effect of nitrogen-doping, substrate temperature and band gap estimation using machine learning

In this study, nickel oxide (NiO) thin films were synthesized on glass substrates using RF magnetron sputtering with varying nitrogen (N) doping ratio and substrate temperatures to explore modifications in their structural, morphological, and optical properties. The films were prepared using a high-purity NiO target under controlled sputtering conditions. Structural analysis by X-ray diffraction revealed an improvement in crystallinity in the (200) direction with increasing N ratio. In contrast, higher N ratio led to the suppression of (111) and (220) peaks, indicating a significant influence of N on the crystal structure and orientation. The films’ thickness and morphology, examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, showed uniform and homogeneous growth with smooth surface topologies. Optical properties, assessed by UV–Vis-NIR spectrophotometry, demonstrated a decrease in transmittance and a redshift in the absorption edge with increased N doping, corresponding to a narrowing of the energy bandgap from 3.7 eV to 3.45 eV. This bandgap reduction is attributed to N incorporation substituting oxygen sites, introducing defect states within the band structure. Additionally, the impact of substrate temperature on film growth enhanced crystallinity and orientation along the (111) plane at higher temperatures, with a simultaneous reduction in film thickness due to increased adatom mobility and potential thermal decomposition. The evaluation of Kernel Ridge Regression (KRR) and Ridge Regression (RR) models revealed their effectiveness in predicting band gap values for thin films at varying substrate temperatures and thicknesses. While RR excelled in predicting a band gap of 3.6 eV for a film with a substrate temperature of 24 °C and a thickness of 112.7 nm, KRR outperformed in predicting a band gap of 3.65 eV for a film with a substrate temperature of 24 °C and a thickness of 107 nm. These findings elucidate the dual influence of N doping and substrate temperature on enhancing the functional properties of NiO thin films, promising for applications in optoelectronic devices and gas sensors.