The Optical, Electrical and Surface Differences between As-Deposited and Annealed NiO Films Produced by Ultrasonic Spray Pyrolysis (original) (raw)
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Study of Physical Properties of Nanocrystalline NiO Thin Films Prepared by Spray Pyrolysis Technique
Volume 5,Issue 1,2019, 2019
In this paper a systematic study has been carried out on the influence of thickness on the physical properties of nanocrystalline nickel oxide (NiO) thin films prepared on glass substrate by spray pyrolysis method. The prepared nanocrystalline NiO films were characterized using X-ray diffraction technique (XRD), field emission scanning electron microscopy (FESEM) and optical measurement techniques. XRD patterns reveal the cubic structure for all the samples and the crystallite size varies with the thickness. FESEM images confirmed that all the films are homogeneous, without any crack, dense and exhibit almost complete coverage of the substrate. The optical parameters such as transmittance, absorption coefficient and energy band gap of the films as a function of film thickness was investigated by UV-Vis spectrophotometer. The band gap of the films is found to be direct allowed transition and the variation of band gap values of nanocrystalline NiO thin films were found to be in the range of 3.48 eV to 3.53 eV.
Effect of Substrate Temperature on Properties of Nickel Oxide (NiO) Thin Films by Spray Pyrolysis
Journal of ELECTRONIC MATERIALS, 2019
NiO thin films were deposited on a glass substrate and investigated for the physical properties optimized through substrate temperature (350-390°C) using a spray pyrolysis technique. The effect of substrate temperature on deposited NiO thin film was studied by thermogravimetric analysis and differential thermal analysis, X-diffraction (XRD), field electron scanning electron microscopy, optical absorption and electrical measurement techniques. XRD analysis indicates that NiO thin films are of a polycrystalline cubic structure. Optical properties are calculated with help of transmittance and absorbance data in the wavelength range between 200 nm and 900 nm. The optical band gap energy values increased from 3.1 eV to 4.0 eV with substrate temperature. Further, the extinction coefficient, refractive index, and real and imaginary parts of dielectric constant and optical conductivities of NiO thin films were calculated. The electrical resistivity measurement shows conductivity of the NiO thin film increased with increase in substrate temperature.
A simple and inexpensive spray pyrolysis technique was employed to deposit nickel oxide (NiO) thin films from hydrated nickel chloride salt solution onto amorphous glass substrate. The as-deposited films were transparent, uniform and well adherent to the glass substrate. The effect of the substrate temperature, the volume and the concentration of the sprayed solution on the structural, optical and electrical properties was studied using X-ray diffraction, optical transmittance, four point probe, scanning electron microscopy and atomic force microscopy. The structural analyses show that all the samples have a cubic structure. It was found that the increase in the volume of sprayed solution leads to an increment in the crystallite size of NiO and improves the homogeneity of the film. Optical measurements have shown that an increase in the thickness of the layer results in a decrease in the optical transmission, but it remains higher than 70 % even if the thickness exceeds 600 nm. At the same time, the optical gap decreases from 3.7 to 3.55 eV when the thickness increases from 133 to 620 nm. Low values of the electrical resistivity (less than 10 Ω.cm) were obtained for thin films with thicknesses less than about 240 nm, but for higher thicknesses the resistivity increases linearly to reach about 170 Ω.cm for a thickness of 620 nm.
Solar Energy Materials and Solar Cells, 2006
NiO thin films have been deposited by chemical spray pyrolysis from nickel chloride hexahydrate (NiCl 2 Á 6H 2 O) solution in water. The substrate temperature during deposition is around 350 1C. The solution flow rate was 10 ml/min. The nickel chloride concentration in the solvent has been used as parameter. It varies from 0.05 to 0.5 M. It is shown that the NiO film properties depend strongly on the nickel chloride concentration. Below 0.3 M, the final thickness of a film deposited using 50 ml of solution is around 0.5 mm. From 0.3 to 0.5 M the thickness is around 3 mm. There is a threshold value for the different film properties when the precursor concentration varies between C ¼ 0:2 and 0:3 M. The oxygen concentration present in the films decreases from 1, in the case of small molar concentration, to 0.86 for 0.3 M and more. In the X-ray diffraction diagram, the more intense contribution is systematically the (1 1 1) peak, while the (2 0 0) diffraction peak is small. This last peak increases slowly up to 0.3 M with the NiCl 2 concentration, and then it stabilizes. Also, the conductivity decreases when the molar concentration of NiCl 2 increases, to stabilize at around 0.3 M. Moreover, while, as expected, the films are p-type when the molar concentration is smaller than 0.3 M, they becomes n-type for higher concentrations.
2004
Nickel oxide films have been deposited from nickel chloride solution by spray pyrolysis technique onto glass substrates at different substrate temperatures ''T sub ''. X-ray diffraction (XRD) analysis showed that, at low T sub ; amorphous films have been obtained, while at higher T sub > 275 C; crystalline NiO with preferential growth along (1 1 1) plane. From measurements of spectral transmittance and reflectance, and on the basis of Murmann's exact equations, the optical constants have been computed over the spectral range 300-2500 nm. Analysis of the spectral absorption confirmed direct and indirect transitions with values markedly affected by T sub due to structure and offstoichiometry changes of the formed films. The dark electrical resistivity drops with three orders of magnitude for films deposited at higher substrate temperature due to improvement in crystallinity. The results have been interpreted by assuming two-phase model. Infrared spectral reflectance showed presence of nickel chloride in films formed at T sub p225 C; which is consistence with XRD findings and claiming incomplete pyrolytic reaction.
Behavior of NiO thin films sprayed at different annealing time
Optical and Quantum Electronics, 2016
Nickel oxide thin films were prepared by spray pyrolysis, using nickel chloride as precursor at the concentration of 0.05 M, deposited on ordinary glass substrates. The conditions of preparation were fixed except the annealing time, which is described through optical and electrical characterizations. The films exhibit a cubic structure, with a preferential orientation along (111) revealed by X-ray diffraction (XRD). The optical data measured by Lambda 900 UV/VIS/NIR spectrometer showing a transmission below 60 %. The refractive index n ðkÞ, extinction coefficient (k) and dielectric constants are calculated in the range of (300 and 1000 nm), besides Urbach and the gap energies. The electrical characterization using 4-point probe indicated that the sample with the highest annealing time is less resistive.
Tin-doped nickel oxide thin films have been successfully prepared by spray pyrolysis technique on glass substrates at 460°C. The effects of tin doping on structural, optical, and electrical properties were investigated. X-ray diffraction pattern reveals that all prepared thin films have cubic structure with (111) preferred orientation. The surface topography of these films was performed by atomic force microscopy. Optical measurements show a high transparency in the visible range around 95%. The optical band gap Eg decreases with Sn content from 3.633 to 3.54 eV. PL measurements show some bands transition which shift irregularly with Sn doping. Finally, the electric conductivity of NiO thin film was investigated through the impedance spectroscopy measurements in the frequency range 5 Hz-13 MHz at various temperatures. These measurements show a thermally activation of the electric. AC conductivity of NiO thin films is investigated through Jonscher law. Also, from these measurements, dielectric parameters were calculated.
Nickel oxide thin films were prepared by chemical bath deposition (CBD) and by chemical spray pyrolysis from the same precursor onto glass substrate. The sprayed NiO thin films are polycrystalline in cubic phase structure with (111) preferred orientation. While the chemical bath deposited as a nickel hydroxide phase and transfer to polycrystalline NiO with annealing. The annealed CBD-films are polycrystalline NiO with cubic phase structure and preferred orientation (200). Sprayed and CBD-NiO films have optical transmittance in the visible region 70 and 46 %, respectively. Sprayed and CBD-NiO thin films have optical band gap 3.54 and 3.62 eV, respectively. Sprayed NiO thin films can be used as transparent materials in invisible electronics applications.
Effect of precursor solutions on the structural and optical properties of sprayed NiO thin films
Nickel oxide thin films were deposited by a simple and low-cost spray pyrolysis technique using three different precursors: nickel nitrate, nickel chloride, and nickel acetate on corning glass substrates. X-ray diffraction show that the NiO films are polycrystalline and have a cubic crystal structure, although predominantly with a preferred 111-orientation in the growth direction and a random in-plane orientation. The deconvolution of the Ni 2p and O 1s core level X-ray photoelectron-spectra of nickel oxides produced by using different precursors indicates a shift of the binding energies. The sprayed NiO deposited from nickel nitrate has an optical transmittance in the range of 60-65% in the visible region. The optical band gap energies of the sprayed NiO films deposited from nickel nitrate, nickel chloride and nickel acetate are 3.5, 3.2 and 3.43 eV respectively. Also, the extinction coefficient and refractive index of NiO films have been calculated from transmittance and reflectance measurements. The average value of refractive index for sprayed films by nickel nitrate, nickel chloride and nickel acetate are 2.1, 1.6 and 1.85 respectively. It is revealed that the band gap and refractive index of NiO films by using nickel nitrate corresponds to the commonly reported values. We attribute the observed behavior in the optical band gap and optical constants as due to the change of the Ni/O ratio.