X-ray analysis and optical properties of nickel oxide thin films

Nanoparticles of NiO were prepared by a homogeneous precipitation method with an aqueous solution of nickel nitrate hexahydrate and citric acid. The microstructure and surface morphology of NiO powder were characterized by thermogravimetric (TGA) analysis, differential scanning calorimeter (DSC), X-ray diffraction (XRD), and infrared (IR) spectroscopy. Different thicknesses of nickel oxide (NiO) thin films were deposited onto highly cleaned glass substrates by the electron beam technique. Their structural characteristics were studied by X-ray diffraction (XRD) and scan electron microscope (SEM). The XRD investigation shows that NiO films are polycrystalline with an cubic type structure. The microstructure parameters, e.g., crystallite size and microstrain were calculated. The optical constants (n, k) and film thicknesses of NiO thin films were obtained by fitting the ellipsometric parameters (psi and Delta) data using three layer model systems in the wavelength range 300-1100 nm. It is found that the refractive index, n increases with the increase of the film thickness. The possible optical transition in these films is found to be allowed direct transitions. The direct energy gaps increase with increasing of the film thickness. (C) 2014 Elsevier B.V. All rights reserved.