Angle dependence of the O K edge absorption spectra of TiO 2 thin films with preferential texture

Abstract

O K and Ti L 2,3 edge X-ray absorption spectra have been recorded for TiO 2 thin films (∼100 nm thickness) prepared by ion beam induced CVD at room temperature. The as prepared films were amorphous but they crystallize into the anatase structure of TiO 2 after annealing at T>650 K. In the amorphous films, the magnitude of the crystal field, determined from the evaluation of the spectra, was smaller than in the well crystallized anatase samples. In these latter samples the O K edge spectra show a strong dependence on the angle of incidence of the radiation with respect to the sample surface. This dependence rises some concerns about the use of the O K edge spectra of oxide materials for a universal “fingerprint” characterization of thin films. A preliminary theoretical evaluation of the evolution of the t 2g/e g intensity ratio with the relative orientation of the electric field of the radiation and the surface normal of the samples is carried out. For this evaluation, the texture of the thin film (i.e. the preferential growth of certain crystallographic planes parallel to the surface) and the existence of surface modifications of the environment around the Ti are taken into account.