Thickness Dependence of Infrared Optical Properties of LaNiO₃ Thin Films Prepared on Platinized Silicon Substrates

Using infrared spectroscopic ellipsometry (IRSE), the infrared optical properties of LaNiO₃ thin films with different film thicknesses on Pt/Ti/SiO₂/Si substrates prepared by a modified metal-organic deposition technique have been investigated in the wavelength range of 2.5-12.6 μm. By fitting the measured ellipsometric parameter (ψ and δ) data with a three-phase model (Air/LaNiO₃/Pt) and the classical Drude dispersion relation for the LaNiO₃ thin films, the optical constants and thicknesses of the films have been obtained. The infrared optical constants (refractive index n and extinction coefficient κ) of the LaNiO ₃ films decrease with increasing thickness in the measured wavelength range. It is closely associated with the crystallinity of the thin films, the crystalline size effect and the influence of the interface layer. An obvious break has been observed between the 49.2-nm thick film and the 70.2-nm thick film for the infrared optical constants. LaNiO₃ has a relative large absorption coefficient and the absorption coefficient monotonously decreases with increasing thickness in the entirely measured wavelength range.