Investigation on optical properties of NiMn2O4 films by spectroscopic ellipsometry

Two different thicknesses of NiMn2O4 thin films were prepared on Pt (111)/Ti/SiO2/Si substrate by chemical solution deposition method. The microstructure of NiMn2O4 films was characterized by x-ray diffraction and scanning electron microscopy. The optical properties of the films were studied by spectroscopic ellipsometry at room temperature in the spectral range of 300–1700 nm. Double Tauc–Lorentz dispersion function was successfully adopted to describe the optical properties of the NiMn2O4 films. The refractive index, extinction coefficient and absorption coefficient of NiMn2O4 thin films were obtained by fitting the experimental data in the entirely measured wavelength range. The variation of the optical properties for different thicknesses was discussed. It was mainly attributed to different oxidation states originate from grown process. The results are meaningful to the understanding and optoelectronic applications of NiMn2O4 films.