Infrared spectroscopy study of titanium dioxide films

Disordered titanium dioxide films with anatase and rutile short-range order, grown on aluminum and silicon, are studied using infrared reflection-absorption (IRAS) spectroscopy. The experimental IRAS spectra are calculated using Fresnel reflection coefficients and an average dielectric function for the films. The latter is capable to take into account the disordered character of the films. A good agreement between experimental and calculated IRAS spectra is found. Absorption bands appear at frequencies of transverse optical (TO) but not longitudinal optical (LO) modes of anatase and rutile TiO₂ single crystals. The Berreman effect is observed but not in absorption bands appearing at frequencies of LO modes of anatase and rutile TiO₂ single crystals. These phenomena are correlated to the macroscopic response of the disordered character of the films to an infrared beam. Effects of substrate and film thickness and alternative expressions of the dielectric function of the disordered films are also discussed.