Optical Properties Of NiO Research Articles

Investigation of deep defects and their effects on the properties of NiO/β-Ga2O3 heterojuncion diodes

In this study, the effect of rapid thermal annealing (RTA) on the electrical and optical properties of NiO/ β-Ga2O3 heterojunction diodes was investigated using capacitance-voltage, current-voltage, Deep Level Transient Spectroscopy (DLTS), Laplace DLTS, photoluminescence and micro-Raman spectroscopy techniques, and SILVACO-TCAD numerical simulator. The NiO is designed to be lowly-doped, allowing for the NiO full depletion at zero bias and the study of properties of β-Ga2O3 and its interface with NiO. Micro-Raman results revealed good agreement with the theoretical and experimental results reported in the literature. The photoluminescence intensity of the sample after RTA is five times higher than the fresh sample due to a rise in the density of gallium and oxygen vacancies (VGa + VO) in the annealed β-Ga2O3 samples. The current-voltage characteristics showed that annealed devices exhibited a lower ideality factor at room temperature and higher barrier height compared with fresh samples. The DLTS measurements demonstrated that the number of electrically active traps were different for the two samples. In particular, three and one electron traps were detected in fresh samples and annealed samples, respectively. SILVACO-TCAD was used to understand the distribution of the detected electron E2 trap (Ec-0.15 eV) in the fresh sample and the dominant transport mechanisms. A fairly good agreement between simulation and measurements was achieved considering a surface NiO acceptor density of about 1 × 1019 cm−3 and E2 trap depth into the surface of β-Ga2O3 layer of about 0.220 µm and the effect of the most observed Ec-0.75 eV trap level in β-Ga2O3. These results unveil comprehensive physics in NiO/β-Ga2O3heterojunction and suggest that RTA is an essential process for realizing high-performance NiO/β-Ga2O3devices.

Lu doping nickel oxide thin films using sol-gel spin coated and density functional theory: optoelectronic and magnetic properties

For the first time, sol-gel spin coating was used to fabricate thin films of NiO doped with lutetium. The films were characterized to determine their crystalline structure, surface morphology, and optical properties as a function of Lu doping concentration. The investigations revealed that the Lu-doped NiO films consisted of nano-polycrystalline particles with a cubic bunsenite structure and (200) preferential orientation. Optical studies indicated that the optical band gap of pure NiO widened with low levels of Lu incorporation before narrowing with higher concentrations. The Urbach energy value for pure NiO initially decreased with 1 at. % Lu-content, from 224 meV to 190 meV, and then continuously increased to 380 meV with more Lu-level. To investigate the effects of Lu doping on the electronics, magnetic, and optical properties of NiO, first-principle computations were performed. The results showed that bulk magnetization underwent significant modifications due to a high hybridization between the Lu-f/d and Ni-d states. This study suggests that NiO doped with lutetium could be used for spin-polarized transport devices and other spin-dependent applications.

Structural and optical properties of NiO and Mn doped NiO nanparticles

Ni1-xMnxO (x = 0.0 - 0.05) nanoparticles were successfully prepared by precipitation method at room temperature Prepared samples were characterized by structural, optical, microstructure and magnetic properties. X-ray diffraction analysis confirmed that Mn ions substitution of NiO lattice with FCC structure. The average crystalline size found to decrease from 42 to 34 nm. Optical analysis show increase in band from 4 -3.8 eV by strong quantum confinement effect with blue shift in the absorption spectra range of 325 – 290 nm. FTIR spectra confirmed the formation of Ni-Mn-O.

Fabrication and study of self-assembled NiO surface networks assisted by Sn doping

Complex patterning of surfaces commonly requires a significant effort in terms of time, cost, and advanced post-fabrication treatments design, which could be overcome by self-organization mechanisms avoiding damage to the surface materials and enhancing properties of interest. In the present work, grid self-assembled NiO complex surfaces have been fabricated assisted by Sn incorporation during growth, following thermal treatments at 1400 °C under a controlled Ar flow. The singular morphologies achieved enable the fabrication of robust high surface to volume ratio surfaces with a wide range of surface properties and functionalities. Based on the research performed by a set of complementary techniques, the mechanisms involved in the formation of these textured surfaces have been discussed and some of the fundamental electronic and optical properties of NiO have been analyzed, both aspects necessary to head up the potential development of applications based on this p-type material which is arousing growing attention. These singular micro- and nanostructures present high luminescence and tunable performance unusual to bulk NiO samples, which can broaden the applicability of this material to light-emitting devices. Moreover, the surface evolution depends on a controllable way on the preferential state of charge of the incorporated Sn, which could be selected through the convenient Sn-based precursor, its ratio to the metallic Ni starting precursor, and the atmosphere and duration of the fabrication treatment. Finally, in order to assess the dependence of some potential NiO-based applications on the insights achieved on the surface characterization, the gas-sensing response to ethanol from the Sn doped NiO samples was also evaluated. The study of the processes and mechanisms involved in the growth of these grid-patterned surfaces can be extended to similar oxide-based systems.

Density functional theory study of the effect of Vanadium doping on electronic and optical properties of NiO

The effect of Vanadium (V) doping on electronic and optical properties of NiO is discussed. Electronic and optical properties of a 32-atom supercell of V[Formula: see text]Ni[Formula: see text]O [Formula: see text] obtained from first-principles calculations, performed within density functional theory (DFT), using the generalized gradient approximation (GGA) with the Hubbard potential [Formula: see text] were studied and compared to those of a 32-atom supercell of pure NiO. From the electronic structure and complex dielectric function analysis, the V doping causes the reduction of the bandgap by inducing the localized V [Formula: see text] state in the NiO bandgap region, and the first optical transition for V-doped NiO occurs at a lower frequency than the one for the intrinsic NiO. The bandgap shrinkage to about 2 eV makes NiO when doped with V a potential candidate for visible light range application in photocatalytic applications. The resulting effects on refractive index, reflectivity, absorption, optical conductivity and loss function for V-doped NiO are compared to those of pristine NiO.

Hydrothermal synthesis of p-type nanocrystalline NiO nanoplates for high response and low concentration hydrogen gas sensor application

High quality nanocrystalline NiO nanoplates were synthesized using surfactant and template free hydrothermal route. The gas sensing properties of NiO nanoplates were investigated. The nanoplates morphology of NiO with average thickness ~ 20 nm and diameter ~ 100 nm has been confirmed by FE-SEM and TEM. Crystalline quality of NiO has been studied using HRTEM and SAED techniques. Structural properties and elemental compositions have been analyzed by XRD and energy dispersive spectrometer (EDS) respectively. The detailed investigation of structural parameters has been carried out. The optical properties of NiO were analyzed from UV–Visible and photoluminescence spectra. NiO nanoplates have good selectivity towards hydrogen (H2) gas. The lowest H2 response of 3% was observed at 2 ppm, whereas 90% response was noted for 100 ppm at optimized temperature of 200 °C with response time 180 s. The H2 responses as functions of different operating temperature as well as gas concentrations have been studied along with sensor stability. The hydrogen sensing mechanism was also elucidated.

Structural, Electrical and Optical Properties of NiO Nanostructured Growth Using Thermal Wet and Dry Oxidation of Nickel Metal Thin Film

Structural, Electrical and Optical Properties of NiO Nanostructured Growth Using Thermal Wet and Dry Oxidation of Nickel Metal Thin Film

Ab initio study of oxygen vacancy effects on electronic and optical properties of NiO

ABSTRACTDensity Functional Theory calculations of electronic and optical properties of NiO, with and without O vacancies, are the focus of this work. Two bands, one fully occupied and the other unoccupied, induced by an O vacancy, are found in the gap. These energy levels are identified and analyzed by means of a local density of states (LDOS) calculation, and notable crystal field splitting can be seen. The real and imaginary parts of the dielectric function are calculated, and an additional optical transition can be seen at lower energy, which can be attributed to the O vacancy induced state in the band gap.

Effect of annealing conditions on the structural, electrical and optical properties of Li-doped NiO thin films

Transparent conductive oxide (TCO) p-type Li-doped NiO thin films were deposited on the (0001) sapphire substrates by magnetron sputtering technique with a high purity NiO:Li2O ceramic target. We systematically investigated the structural, electrical and optical properties of NiO:Li thin films annealed in different conditions. We found that annealing in different conditions greatly affects the physical properties of NiO:Li thin films. Compared with the NiO:Li thin film annealed in oxygen, the hole concentration of NiO:Li thin film annealed in nitrogen at the same processing temperature is obviously lower. Annealed in oxygen at 500 °C, NiO:Li films show excellent crystal quality with single (111) orientation, high hole concentrations. When the annealing temperature increased, the transmittance of NiO:Li thin films become better for wavelength range from ultraviolet (UV) to visible with a significant absorption edge near 350 nm.

Effects of Cu-Doping on Optical Properties of NiO

This work presents the effect of Cu-doping on some optical properties of Cu:NiO thin film prepared by spray pyrolysis technique. UV-Visible spectrophotometer in the range 380-900 nm used to determine the absorbance spectra for various Cu-doping of Cu:NiO thin film. The transmittance and energy gap are decreased with increasing Cu-doping in the prepared films, while absorption coefficient, extinction coefficient, and skin depth are increased with increasing Cu-doping.

Effects of Cu-Doping on Optical Properties of NiO

This work presents the effect of Cu-doping on some optical properties of Cu:NiO thin film prepared by spray pyrolysis technique. UV-Visible spectrophotometer in the range 380-900 nm used to determine the absorbance spectra for various Cu-doping of Cu:NiO thin film. The transmittance and energy gap are decreased with increasing Cu-doping in the prepared films, while absorption coefficient, extinction coefficient, and skin depth are increased with increasing Cu-doping.

Synthesis, characterization and optical properties of NiO:Cs thin film

Transition metal oxides have shown an encouragement for industrial applications especially in lithium-ion batteries, electrochromic windows, and fuel cell films. The kinetic of addition of group I elements into transition metal oxides resulted in an improvement in their physical properties. Here, we reported the influence of doping of cesium on the electrochromic and crystalline structure of nickel oxide films. The results showed that a small amount of cesium (1wt%) made a disorder of the NiO cubic structure. This disordered structure resulted in an improvement in the amount of Coulomb's charge by a factor of 2 as compared to NiO alone. A higher contrast ratio accounting for improved electrochromic performances was also observed for Cs doped NiO thin film as compared to NiO film. This novel structure is a promising candidate for industrial applications in renewable energy devices.

Effect of film thickness on the optical constants and optical absorption properties of NiO x thin films

NiO x ( x>1) thin films were deposited by reactive DC-magnetron sputtering from a nickel metal target in Ar+O 2 with the relative O 2 content 5%. The reflectivity and transmission of the films were measured from 350 to 700 nm. The films coated to thicknesses of 17, 27 and 34 nm had the same absorption mechanism which is a direct allowed transition. The refractive index n and extinction coefficient k of the films were calculated from the measured reflectivity and transmission of these films, and the relationship of the optical band gap with variation in film thickness was studied as well. All results showed that the optical properties of NiO x thin films depended on the film thickness.

Spray deposition and characterization of nanostructured Li doped NiO thin films forapplication in dye-sensitized solar cells

Transparent conducting Li (0–5 wt%) doped NiO thin films with preferentialgrowth along the (111) plane were deposited onto glass substrates bypyrolytic decomposition of nickel nitrate and lithium chloride precursors at500 °C in air. The effect of Li concentration on the structural, optical and transport properties ofNiO thin films was studied by x-ray diffraction (XRD), scanning electron microscopy(SEM), atomic force microscopy (AFM), spectral transmittance, photoluminescence andlinear four-probe resistivity. Activation energies as a function of Li concentration werededuced from the temperature dependent resistivity data measured in the range 300–448 K.The figure of merit was deduced by combining the spectral transmittance and sheetresistance values. The variation in properties of NiO thin film due to Li doping arediscussed based on the above results. A dye-sensitized solar cell has also beenfabricated for the optimized Li doped NiO thin film and the results are presented.

Optical Properties of NiO and CoO

The optical reflectance spectra of the transition-metal oxides NiO and CoO have been measured over the energy range from 1 to 26 eV. The optical constants have been derived by means of a Kramers-Kr\"onig analysis of their reflectance spectra. Structure in reflectance is found at 4.0, 4.8, 5.9, 7.2, 8.25, 12.8, 13.6, and 17.8 eV in NiO, and at 5.5, 7.5, 12.6, and 17.5 eV in CoO. The positions of high-energy structure in their absorption coefficients is consistent with maxima in their respective optical densities of states determined from photoemission data. Two alternative interpretations are given for the structure in NiO between 4.0 and 9.0 eV. One interpretation involves oxygen $p$ and nickel $d$ states in localized excitations, and the other involves the nickel $d$ states and the "$4s$" band. Distinction between models on the basis of presently available photoconductivity data is found to be questionable.