Effect of solution molarity on structural and optical properties of nickel oxide thin films prepared by chemical spray pyrolysis technique

In this work,NiO thin films at different molarities (0.05M, 0.1M, 0.15M and 0.2M)have been successfully deposited on glass substrates by chemical spray pyrolysis (CSP) technique at substrate temperature of (400 oC) and thickness of about 300 nm. The structural and optical properties of these films have been investigated using XRD, AFM, and UV-Visible spectroscopy. The XRD results showed that all films are polycrystalline in nature with cubic structure and preferred orientation along (111) plane. The crystallite size was calculated using Scherrer formula and it is found that the molarity 0.1M has maximum crystallite size (51.16nm). AFM images showed homogenous and smooth NiO thin films and the average grain size estimated from the AFM granularity report confirms the XRD results. The absorbance and transmittance spectra have been recorded in the wavelength range of (300-900) nm in order to study the optical properties.The optical energy gap for allowed direct electronic transition was calculated using Tauc equation. It is found that the band gap decreases when the molarity increases and the band gap values range between 3.71 eV and 3.59 eV for the preparedNiO thin films at different molarities. The Urbach energy increases as the molarity increases and the Urbach energy values range between 299 meV and 343 meV.The optical constants including (absorption coefficient, real and imaginary parts of dielectric constant) were also calculated as a function of photon energy. Refractive index and extinction coefficient for NiO thin films were estimated as a function of wavelength.