Variable incidence infrared absorption spectroscopy of gel-derived silica and titania films

Abstract

SiO2, TiO2 and mixed SiO2–TiO2 thin films were prepared, via sol-gel processing, by spin-coating on silicon wafer substrates. They were either dried at room temperature, or subjected to different heat treatments, from 600 °C up to 950 °C. Infrared spectroscopy was performed on these films, in transmission mode, using variable incidence, light, either natural or polarized. The longitudinal optical (LO) components of the rocking and asymmetric stretching Si–O–Si vibrations become more visible and the position can be more accurately determinated, respectively, with increasing incidence angles away from normal. These peak positions shift to higher frequencies with thermal treatment, as the films undergo a transition from the gel to the glassy state. In titania films, the detection of LO vibrations is less evident than in silica based-films, even at oblique incidence. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)