Optical and structural properties of reactive ion beam sputter deposited CeO₂ films

Abstract

Optical and structural properties of reactive ion beam sputter deposited CeO₂ films as a function of oxygen partial pressures (Po₂) and substrate temperatures (T_s) have been investigated. The films deposited at ambient temperature with Po₂ of 0.01 Pa have shown a refractive index of 2.36 which increased to 2.44 at 400 °C. Refractive index and extinction coefficient are sensitive up to a T_s of ~ 200 °C. Raman spectroscopy and X-ray diffraction (XRD) have been used to characterise the structural properties. A preferential orientation of (220) was observed up to a T_s of 200 °C and it changed to (200) at 400 °C and above. Raman line broadening, peak shift and XRD broadening indicate the formation of nanocrystalline phase for the films deposited up to a substrate temperature of 300 °C. However, crystallinity of the films were better for T_s values above 300 °C. In general both optical and structural properties were unusual compared to the films deposited by conventional electron beam evaporation, but were similar in some aspects to those deposited by ion-assisted deposition. Apart from thermal effects, this behavior is also attributed to the bombardment of backscattered ions/neutrals on the growing film as well as the higher kinetic energy of the condensing species, together resulting in increased packing density.