Effect of annealing temperature on the structural, optical, magnetic and electrochemical properties of NiO thin films prepared by sol–gel spin coating

Abstract

The effect of annealing temperature on the structural, morphological, optical, magnetic and electrochemical properties of spin coated NiO thin films were studied. The XRD analysis shows that all the annealed NiO thin films are cubic structure with (200) preferred orientation. The XPS spectrum indicates that the main peak and satellite peaks of Ni (2P) and O (1S) show the presence of Ni2+ cation and O2− anions. Raman spectra show (1P) 1LO and (2P) 2LO modes for annealed NiO thin films. The SEM result shows that, increase in annealing temperature increases the grain size. UV–Visible spectrum exhibits high transmittance for annealed NiO thin films. The band gap energy decreases from 3.72 to 2.89 eV with increasing annealing temperature. The room temperature PL spectrum of NiO thin film has blue and violet emission in addition to UV emission. VSM studies revealed that a weak ferromagnetic behavior has shown by films annealed upto 400 °C and thereafter the magnetic behavior changes to paramagnetic nature. The NiO thin film annealed at 600 °C shows high specific capacitance by cyclic voltammetry analysis. Equivalent series resistance of NiO thin films were measured using electrochemical impedance spectrum and it decreases with increasing annealing temperature.