Crystallization of SiO2-TiO2 glassy films studied by atomic force microscopy

Crystallization in SiO2-TiO2 glassy films with 20 and 40 mol% TiO2 was inve stigated by atomic force microscopy (AFM). The films were prepared by sol-g el spin coating on single crystal silicon wafers and then heat-treated at d ifferent temperatures (900 degrees C, 1000 degrees C and 1100 degrees C), f or different periods of time (between 5 min and 40 h). Anatase (TiO2) cryst als were found to nucleate at the surface, by means of the atomic force mic roscope observations, with a mean diameter from 5 to 10 nm, depending on th e nucleation time and the titania content of the glass and, on subsequent h eating, the crystals grew. Based on the atomic force microscope measurement s, parameters of the crystallization process such as the nucleation and cry stal growth rates were estimated. These were both found to be time dependen t and have an induction period. (C) 2000 Elsevier Science B.V. All rights r eserved.