Nickel Oxide Films Research Articles

Study on structural, morphological, optical, and luminescence properties of nickel oxide thin-film synthesized by dip-coating technique

Nickel oxide is one of the best materials for fabricating optical devices. The Dip-coating technique was used to deposit nickel oxide thin films on a glass substrate. Nickel acetate tetrahydrate Ni (Ac) 2·H2O was used as starting precursor and monoethanolamine (MEA) was added as a catalyst. These fabricated films were pre-heated at 150 °C for 10 min and then annealed in the air at 400–700 °C temperatures. XRD, UV–Vis-NIR, FESEM, EDAX, and photoluminescence techniques are used for analyzing the fabricated films. FESEM and EDAX studies confirmed the surface and the elemental analysis of the prepared films. X-ray diffraction studies confirmed the structure of the Nickel oxide film. The UV–Vis-NIR spectrometer was used to analyze the transmission and absorption spectra of the films.

Design and Fabrication of Nanostructure TiO2 Doped NiO as A Gas Sensor for NO2 Detection

In this paper, thin films of undoped and nickel oxide (NiO) doped titanium dioxide (TiO2) were prepared using the chemical spray pyrolysis deposition (CSP) technique, with different concentrations of nickel oxide (NiO) in the range (3-9) wt%. The morphological, structural, electrical, and sensing properties of a gas of the prepared thin films were examined. XRD measurements showed that TiO2 films have a polycrystalline structure. AFM analysis showed that these films have a regular structure both before and after doping . The roughness of these films decreased after adding impurities but then the opposite of that took place. The electrical and gas sensing properties of titanium dioxide was also affected after doping. The highest sensitivity value was obtained at doping concentration of 5wt% and working temperature 473ºK.

Effect of Selective Lateral Chromium Doping by RF Magnetron Sputtering on the Structural, and Opto-Electrical Properties of Nickel Oxide

In this study, chromium (Cr)-doped nickel oxide (NiO) thin films were deposited by employing selective lateral doping of Cr in NiO by radio-frequency magnetron sputtering at different doping times ranging from 0 s (undoped) to 80 s. The structural, optical, and electrical properties of the resulting Cr-doped NiO thin films were investigated. Structural investigation from XRD patterns indicated that the grown Cr-doped NiO layer crystallized in a cubic phase. Broadening of the diffraction peak with increasing doping time from 0 s to 80 s led to a reduction in the crystallite size that varied from 23.52 nm to 14.65 nm. Compared with the undoped NiO, the diffraction peak along the (200) plane shifted from left to right as a function of doping time. This result indicated that Cr+3 could easily enter the NiO lattice. Results from the Hall-effect study disclosed that electrical properties of Cr-doped NiO was highly dependent on doping time. The conductivity of NiO was increased with doping time, and the highest conductivity (8.73 × 10−2 Scm−1) was achieved at a doping time of 80 s. Finally, optical investigations revealed that as doping time increased, the optical bandgap of Cr-doped NiO films dropped from 3.43 eV to 3.28 eV. The highest Urbach energy at higher doping time indicated that crystallinity became poorer, and the degree of defects increased with increasing doping time.

Fabrication of Metal (Cu and Cr) Incorporated Nickel Oxide Films for Electrochemical Oxidation of Methanol

Methanol electrochemical oxidation in a direct methanol fuel cell (DMFC) is considered to be an efficient pathway for generating renewable energy with low pollutant emissions. NiO−CuO and Ni0.95Cr0.05O2+δ thin films were synthesized using a simple dip-coating method and tested for the electro-oxidation of methanol. These synthesized electrocatalysts were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Different electrochemical techniques were used to investigate the catalytic activity of these prepared electrocatalysts for methanol oxidation, including linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). In the presence of 0.3 M methanol, the current densities of NiO−CuO and Ni0.95Cr0.05O2+δ thin films were found to be 12.2 mA·cm−2 and 6.5 mA·cm−2, respectively. The enhanced catalytic activity of NiO−CuO and Ni0.95Cr0.05O2+δ thin films may be a result of the synergistic effect between different metal oxides. The Chronoamperometry (CA) results of the mixed metal oxide thin films confirmed their stability in basic media. Furthermore, the findings of electrochemical impedance spectroscopy (EIS) of mixed metal oxide thin films demonstrated a lower charge transfer resistance as compared to the pure NiO, CuO, and Cr2O3 thin films.

Characteristics of Nickel Oxide Modified Zr-Doped HfO2 High-k Thin Films

The high-k thin film can be used to replace SiO2 as the gate dielectric in nano MOS devices to improve the performance and reliability (1,2,3). The HfO2 high-k dielectric suffers from the low crystallization temperature, e.g., <600˚C (4,5). The Zr-doped HfO2 (ZrHfO) dielectric has a higher crystallization temperature and better properties than the undoped HfO2 film based on the same EOT (6-9). The sub 1 nm EOT ZrHfO gate dielectric has been demonstrated (6,10). There are reports that high-k dielectric properties could be improved by dispersing metal particles into the structure (11,12). In this work, the authors investigated changes of material and electrical properties of the ZrHfO gate dielectric by embedding nickel oxide (NiO) into the structure.The ZrHfO/NiO/ZrHfO dielectric stack was sputter deposited on a HF pre-cleaned p-type Si (100) wafer in one-pump down. The bottom and top ZrHfO films were deposited from a Hf/Zr target in Ar/O2 at 5 mTorr for 2 min and 10 min, separately. The NiO film was sputter deposited from a Ni target in Ar/O2 at 5 mTorr for 20s. The PDA was done at 800°C under N2 for 60 sec. The nanocrystalline NiO (nc-NiO) was formed in the dielectric layer, as shown in Figure 1. The gate electrode and backside ohmic contact were formed from the sputter deposited Al. The control sample, i.e., ZrHfO gate dielectric without the embedded NiO, was also prepared for comparison.Figure 2 shows C-V hysteresis curves of the control and nc-NiO embedded samples. All samples show counter-clockwise hysteresis. The control sample has a larger hysteresis than the nc-NO embedded sample has, i.e., 0.2V vs. < 0.02V. The large number of trapped charges in the control sample reflects the incomplete passivation of defects in the PDA step (13,14). The small amount of nc-NiO effectively reduced the oxygen deficiencies or vacancies in the film (13,15). The EOTs of the control and nc-NiO embedded samples are 8 nm and 7.7 nm, respectively. The embedded nc-NiO increase of bulk film’s permittivity due to its dipole moment (16). Similar phenomenon was observed in other nanoparticles embedded high-k stack (11,13).The stress-induced leakage current (SILC) of the capacitor was investigated. The leakage current was measured after stress with a negative gate voltage (-Vg ) for various periods. The leakage current increases with the increase of the stress time, which is attributed to the deterioration of the film (17,18). The nc-NiO embedded sample has a large leakage current than the control sample due to its conductive nature (19).More detailed results on the influence of nc-NiO on the breakdown mechanism using the ramp-relax method will be reported (20).This study was partially sponsored by NSF Grant 0926379. C.-H. Yang thanks Professor Way Kuo of City University of Hong Kong for his advice and support throughout this study. The International Technology Roadmap for Semiconductors. Semiconductor Industry Association, December (2003).C. Hu, Nanotech., 10, 113 (1999).J. J. Lee, X. Wang, W. Bai, N. Lu and D.-L. Kwong, IEEE Trans. Elec. Dev., 50, 2067 (2003).J. Robertson, J. Vac. Sci. Technol. B, 18, 1785 (2000).J. Lu, Y. Kuo, J. Yan and C.-H. Lin, Jpn. J. Appl. Phys., 45, L 901 (2006).Y. Kuo, J. Lu, S. Chatterjee, J. Yan, T. Yuan, H.-C. Kim, W. Luo, J. Peterson and M. Gardner, ECS. Trans., 1, 447 (2006).D. Triyoso, ECS Trans., 3, 463 (2006).Y. Kuo, ECS Trans., 3, 253 (2006).Y. Kuo, ECS Trans., 2, 13 (2006).J. Yan, Y. Kuo, and J. Lu, ECS Solid-State Lett., 10, H199 (2007).R. Ravindran, K. Gangopadhyay, S. Gangopadhyay, N. Mehta, and N. Biswas, Appl. Phys. Lett., 89, 263511 (2006).G. C. Vezzoli, M. F. Chen, and J. Caslavsky, Ceram. Int., 23, 105 (1997).C.-H. Lin and Y. Kuo, J. Electrochem. Soc., 158, G162 (2011).N. Zhan, M. C. Poon, C. W. Kok, K. L. Ng, and H. Wong, J. Electrochem. Soc., 150, F200 (2003).H. Sim, H. Chang, and H. Hwang, Jpn. J. Appl. Phys. Part 1, 42, 1596 (2003).S. C. Chung, S. Krüger, G. Pacchioni, and N. Rösch, J. Chem. Phys., 102, 3695 (1995).S. Chatterjee, Y. Kuo, J. Lu, J.-Y. Tewg, and P. Majhi, Microelec. Rel., 46, 69 (2006).S. Chatterjee, Y. Kuo, J. Lu, Microelec. Eng., 85, 202 (2008).J. Feinleib and D. Adler, Phys. Rev. Lett., 21(14), 1010 (1968).W. Luo, Y. Kuo and W. Kuo, IEEE Trans. Dev. Mat. Rel., 4, 488 (2004). Figure 1

Influence of annealing temperature of nickel oxide as hole transport layer applied for inverted perovskite solar cells

Nickel oxide (NiO) has recently attracted great attention for its use as a hole transport layer (HTL) of inverted perovskite solar cells (PSCs). In this paper, NiO films are fabricated on a silicon wafer and fluorine-doped tin oxide by plasma-enhanced atomic layer deposition (PEALD) with nickelocene as the metal precursor and oxygen plasma as the coreactant. The effects of the annealing treatment on the film properties at different annealing temperatures are analyzed. The experimental results show that the PEALD-NiO films have a high thickness uniformity and low surface roughness as evaluated by atomic force microscopy measurements. All the PEALD-NiO films have a wide bandgap and high transmittance of ∼80%–85% in the visible light range. The postannealing treatment induces a reduced electrical resistivity owing to crystal structure repair and surface defect reduction. This treatment also leads to a significantly enhanced wettability of the NiO films, facilitating perovskite layer deposition in subsequent device fabrication. Finally, the inverted PSCs based on the NiO HTL with different annealing temperatures demonstrate an enhanced performance of the device as compared to that with unannealed NiO HTL. The 400 °C-annealed PEALD-NiO HTL yields the best cell conversion efficiency, improving from 15.38% for unannealed NiO to 17.31%, demonstrating the potential of PEALD-NiO compact films for applications in inverted PSCs.

Hydrothermally synthesized nickel oxide (NiO) nano petals

P-type semiconductor NiO is a wide bandgap, cost-effective and promising material as a counter electrode in the DSSC (dye-sensitized solar cells). In a solar cell device, a counter electrode helps in allowing holes to pass through the electrolyte towards the load and blocking the electrons to pass through it. In the present work, a thin film of NiO has been synthesized on an FTO substrate via hydrothermal technique in the ammonia evaporated environment. FESEM images show nano petals, porous like structures grown on the thin film of NiO which provides well absorption of the electrolyte on it which acts as a redox mediator. Diffraction peaks in the XRD plot confirm the synthesized thin film is NiO. The Calculated bandgap of the synthesized thin film of NiO is found to be 4.01 eV. Cyclic voltammetry (CV) helps in analysing the conductivity of synthesized NiO thin film which can be used in the application of solar cells.

Electrochromic characteristics of porous nanosheet-structured nickel oxide films with cobalt and zinc dopants

Porous nanosheet-structured nickel oxide (NiO) films were directly prepared on conductive oxide substrates using a cost-effective and simple one-pot solution method. By incorporating cobalt (Co) dopant, the growth of vertically aligned nanosheet was promoted. However, zinc (Zn)-doped NiO film had the loose-packed nanosheet-structure with relatively low coverage on the surface of the substrate compared to the NiO and Co-NiO films. All the NiO films exhibited electrochromic properties. In the colored state, the NiO, Co-NiO, and Zn-NiO films were dark brown, black, and brown, respectively. In the bleached state, the NiO, Co-NiO, and Zn-NiO films were pale gray, pale yellow, and transparent, respectively. The switching time of the Co-NiO film (tc ~ 2 s, tb ~ 6 s) was slightly slower than those of the NiO (tc ~ 1 s, tb ~ 1 s) and Zn-NiO (tc ~ 1 s, tb ~ 2 s) films. However, it had better transmittance modulation (~58% at 700 nm) with excellent memory durability (increased by ~2% after 3,000 s) than the NiO and Zn-NiO films. Dopants could easily and effectively modify the electrochromic performance of NiO films.

PHYSICAL PROPERTIES OF NOVEL α-Fe2O3/NiO HETEROSTRUCTURES THROUGH IMMERSION/ SOL–GEL SPIN COATING METHOD: DIFFERENT DEPOSITION NUMBERS OF NiO LAYER

The novel hematite (α-Fe2O3)/nickel oxide (NiO) heterostructures were grown on fluorine-doped tin oxide (FTO) coated glass substrates at various deposited NiO of 3, 5, and 7 layers. The heterostructures were successfully synthesized using the immersion and sol–gel spin coating methods for α-Fe2O3 and NiO films, respectively. The field emission scanning electron microscopy analysis showed that each sample of α-Fe2O3/NiO heterostructures has a unique surface morphology when deposited with different NiO layers. The X-ray diffraction pattern shows that the number of NiO layers affected the diffraction peaks. The NiO diffraction peak intensity at (111) plane increased when the deposition number of NiO layer was increased. The crystallite sizes of NiO were 35.4, 33.6, and 38.0 nm for 3-, 5-, and 7-layer NiO, respectively. The interplanar spacing, lattice parameter, and unit cell volume indicate NiO with 3-layer as the highest, while 5- and 7-layer had the same values. Meanwhile, the strain and stress values show the compressive strain and tensile stress, respectively. The optical properties reveal that the highest transmittance and the lowest absorbance percentages were recorded for a 3-layer NiO sample. In contrast, the lowest transmittance and the highest absorbance percentages were obtained for the sample with 5-layer NiO. Different thicknesses and morphologies of heterostructures explained these situations. In addition, each unique heterostructure of α-Fe2O3/NiO with high visible light absorption nature is perceived to reduce the bandgap energy and has the potential to be used in sensor and solar cell applications.

Design of Novel InP/InGaAs Photodetectors With NiO Transparent p-Region and Electrode

In this study, we report a new type of InGaAs/InP photodetector (PD) with nickel oxide (NiO) transparent p-region and electrode. By applying the NiO film, the device does not require the highly doped p-contact layer and the opaque p-contact metal electrode such as the traditional p-i-n PD. The epitaxial layer of the PD is simplified. Meanwhile, the optical power loss caused by the additional absorption in the highly doped p-contact layer can be avoided. With the fully covered transparent p-contact electrode, the PD can be illuminated from the p-side at the same time. The numerical simulation results show that the new structure can improve the 3-dB bandwidth and the RF output power of the PD.

NiX Layered Double Hydroxide Nanowire Arrays (X = Co, Fe, and Mn) Coated with Nanometer-Thick Films of NiOOH and Then NiO as Electrodes for Supercapacitors

Owing to their low cost, transition metal layered double hydroxides (LDHs) have the potential to become the electrode material of choice for supercapacitors if they can provide good cyclic stability and high specific capacity. Herein, we introduce an approach for forming a high-quality, uniform thin film of nickel oxide (NiO) that can act as an auxiliary nickel oxyhydroxide (NiOOH) layer during redox cycling in an alkaline electrolyte. This approach leads to a core/double-shell NiCo-LDH/NiOOH/ALD-NiO electrode that exhibits an unprecedented specific capacity of 1420.2 C g–1 (even at 4 A g–1), retaining 93% of the capacity after 20,000 cycles. Even when combined with a simple anode of activated carbon, an asymmetric supercapacitor with this cathode provides an energy density of 72.6 W h kg–1 with exceptional durability (9.1% loss over 10,000 cycles). This extraordinary electrode when combined with an articulated anode in a supercapacitor is expected to meet or exceed the current energy density limit of lithium-ion batteries.

Fabrication Of p-NiO/n-ZnO:Ga heterostructures for a rectifier diode and a UV photodetector via RF magnetron sputtering and spray pyrolysis synthesis

In this paper, a p–n thin film NiO/ZnO heterojunction for a rectifier diode and a UV photodetector is prepared and characterized. Nickel oxide (NiO) and gallium-doped zinc oxide (ZnO:Ga) thin films are grown by RF magnetron sputtering and spray pyrolysis techniques, respectively. The crystal structure of the thin films is studied by the X-ray diffraction (XRD) method. The transmittance and reflectance are studied by UV–VIS spectroscopy. The p–n electrical parameters are estimated from current–voltage characteristics. The effects of duration of thermal annealing at 450oC on the characteristics of the NiO/ZnO:Ga device are evaluated. The non-annealed diode shows the best rectification coefficient of 105 at ±1 V. The p–n photodetection capability is studied under UV illumination. At a reverse bias of –3 V under 365-nm UV illumination, the device shows a current intensity of ~6.2 × 10-12 A. The observed increase in the reverse current intensity by about two orders of magnitude under a UV lamp with a spectral irradiance of 10 W m-2 μ m-1 indicates a promising application in UV light detection.

Microfluidic Processing of Ligand‐Engineered NiO Nanoparticles for Low‐Temperature Hole‐Transporting Layers in Perovskite Solar Cells

Nickel oxide (NiO) is used as a hole‐transporting layer (HTL) in perovskite solar cells (PSCs) because of its high optical transmittance, intrinsic p‐type doping, and suitable valence band energy level. However, fabricating high‐quality NiO films typically requires high‐temperature annealing, which limits their applicability for low‐temperature, printable PSCs. Herein, the need for such postprocessing steps is circumvented by coupling 4‐hydroxybenzoic acid (HBA) or trimethyloxonium tetrafluoroborate (Me3OBF4) ligand‐modified NiO nanoparticles (NPs) with a Tesla‐valve microfluidic mixer to deposit high‐quality NiO films at a temperature &lt;150 °C. The NP dispersions and the resulting thin films are thoroughly characterized using a combination of optical, structural, thermal, chemical, and electrical methods. While the optical and structural properties of the ligand‐exchanged NiO NPs remain comparable with those possessing the native long‐chained aliphatic ligands, the ligand‐modified NiO thin films exhibit dramatic reductions in surface energy and an increase in hole mobilities. These are correlated with concomitant and significant enhancements in performance and stability factors of PSCs when the ligand‐modified NiO NPs are used as HTL layers within p−i−n device architectures.

Tailorable infrared emission of microelectromechanical system-based thermal emitters with NiO films for gas sensing.

Infrared gas sensors hold great promise in the internet of things and artificial intelligence. Making infrared light sources with miniaturized size, reliable and tunable emission is essential but remains challenging. Herein, we present the tailorability of radiant power and the emergence of new emission wavelength of microelectromechanical system (MEMS)-based thermal emitters with nickel oxide (NiO) films. The coating of NiO on emitters increases top surface emissivity and induces the appearance of new wavelengths between 15 and 19 µm, all of which have been justified by spectroscopic methods. Furthermore, a sensor array is assembled for simultaneous monitoring of concentrations of carbon dioxide (CO2), methane (CH4), humidity, and temperature. The platform shows selective and sensitive detection at room temperature toward CO2 and CH4 with detection limits of around 50 and 1750 ppm, respectively, and also shows fast response/recovery and good recyclability. The demonstrated emission tailorability of MEMS emitters and their usage in sensor array provide novel insights for designing and fabricating optical sensors with good performance, which is promising for mass production and commercialization.

Enhanced Electrochromic Performance by Anodic Polarization in Nickel Oxide Films

Nickel oxide (NiO) is considered to be the best candidate for the compensatory layer of WO3-based smart windows. In this article, we demonstrate that a facile anodic polarization can dramatically improve the electrochromic performance. Unambiguous evidence of performance enhancement was demonstrated by both in situ optical response and cyclic voltammetry. Benefiting from this treatment, the quantity of voltammetric charge increased by ∼43.8% under the same test conditions, enhancing the corresponding electrochromic modulation by ∼17.6 %. The improved performance is due to the newly exposed high-valence Ni3+ ions during anion-dependent anodization. These results offer a novel strategy for the preparation of high-performance NiO films and provide valuable insights into the underlying mechanism in the electrochromic process.

Nickel oxide film with tertiary hierarchical porous structure and high electrochromic performance and stability

The NiO electrochromic (EC) film with hierarchical porous structure was prepared by hydrothermal method and heat treatment. X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM) and X-ray diffractometer (XRD) were employed to characterize the morphology, microstructure and component of the obtained films. The EC properties including transmittance, cyclic voltammetry (CV), electrochemical impedance, switch speed and cycle stability were examined. Results show that the NiO film has a tertiary hierarchical porous structure constructed by NiO nanoparticles, nanosheets and laminated thick slices step by step. The mesopores that appear in the nanosheets are formed by the surrounding of nanoparticles. Response times (tc < 3.00 s, and tb is about 0.60 s) are short. The control factors of charge transport changed with EC cycling. The stability of EC properties could be kept from the 1000th cycle to the 25000th cycle. The most noteworthy is that after 40,000 cycles the hierarchical structure did not change significantly. The reason (or mechanism) of the performance was discussed and suggested.

Study on NiO:Zn2+ films fabricated through dc magnetron reactive sputtering: substrate temperature-dependent microstructure pattern, optical and electrical properties

Nickel oxide (NiO) films have potential applications in optical coatings, ultraviolet detectors, gas sensors and perovskite solar cells. The great improvement in electrical conduction is still critical for NiO films so far. NiO films are usually p-type conductive because of the native Ni vacancies and interstitials O. These native point defects make n-type NiO difficult to prepare. Even that, n-type NiO films with improved electrical conduction still need to be prepared for n-NiO-based heterojunction devices. Herein the face-centered cubic NiO:Zn2+ films are magnetron reactively sputtered on the glass substrates at different substrate temperatures (Tsub). The introduction of Zn2+ to NiO leads to the transition in conduction from p to n at 400 °C Tsub. The films are almost improved in crystallization with increase in Tsub, thereby reducing the point defect content i.e. the free carrier concentration. The resulting films are also improved in optical transmittance with increase in Tsub. The film’s optical energy gap is tunable in the range of 3.6 eV through 3.8 eV with Tsub.

Enhanced performance of p-i-n perovskite solar cell via defect passivation of nickel oxide/perovskite interface with self-assembled monolayer

The thin film of nickel oxide (NiOx) nanoparticles was successfully applied as the hole transporting layer (HTL) in inverted (p-i-n) perovskite solar cells (PSCs), but inevitable surface defects and hydroxyl groups present on the NiOx surface are limiting of performance and stability improvements. For overcome these problems, we introduce 3-(Triethoxysilyl)propylamine (TSPA), self-assembly molecule, as an interfacial modifier between NiOx and perovskite film to attenuate the surface defect and prevent deterioration caused by direct contact of the hydroxyl groups and the perovskite. Self-assembled monolayer is formed by hydrogen-bond between amino group of TSPA and hydroxyl group on the surface of the NiOx, which passivate surface and reduce defect density. In addition, a positive dipole was formed by the TSPA monolayer, which resulted in deeper work function at the NiOx interface and improved energy level alignment in PSCs, improving charge extraction-transportation capabilities and reducing recombination of charge carriers at the interface. In consequence, PSCs based on NiOx with TSPA monolayer have boosted PCE by up to 20.21% and showed long-term stability over 60 days under ambient air and varying humidity condition. This approach is expected to be further advanced as one of the methods for the development of high-performance PSCs.

Transparent All-Oxide Hybrid NiO:N/TiO2 Heterostructure for Optoelectronic Applications

Nickel oxide (NiO) is a p-type oxide and nitrogen is one of the dopants used for modifying its properties. Until now, nitrogen-doped NiO has shown inferior optical and electrical properties than those of pure NiO. In this work, we present nitrogen-doped NiO (NiO:N) thin films with enhanced properties compared to those of the undoped NiO thin film. The NiO:N films were grown at room temperature by sputtering using a plasma containing 50% Ar and 50% (O2 + N2) gases. The undoped NiO film was oxygen-rich, single-phase cubic NiO, having a transmittance of less than 20%. Upon doping with nitrogen, the films became more transparent (around 65%), had a wide direct band gap (up to 3.67 eV) and showed clear evidence of indirect band gap, 2.50–2.72 eV, depending on %(O2-N2) in plasma. The changes in the properties of the films such as structural disorder, energy band gap, Urbach states and resistivity were correlated with the incorporation of nitrogen in their structure. The optimum NiO:N film was used to form a diode with spin-coated, mesoporous on top of a compact, TiO2 film. The hybrid NiO:N/TiO2 heterojunction was transparent showing good output characteristics, as deduced using both I-V and Cheung’s methods, which were further improved upon thermal treatment. Transparent NiO:N films can be realized for all-oxide flexible optoelectronic devices.

Coloration–decoloration properties and mechanisms of nickel oxide films

It has been reported that nickel oxide is colored by ozone irradiation. Herein, the colored and bleached states of nickel oxide films were investigated using ozone and heat treatments. This phenomenon is known as reversible chromism. X-ray photoelectron spectroscopy analysis revealed that the NiOOH or Ni2O3 state was predominant in the colored sample; this state decreased (the color became lighter) as the heating temperature increased. Furthermore, ozone irradiation caused a compressive strain of more than 0.01%. Two types of reactions, fast and slow, were observed during the bleaching process, both exhibiting Arrhenius behavior.