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

Crystallization in SiO2–TiO2 glassy films with 20 and 40 mol% TiO2 was investigated by atomic force microscopy (AFM). The films were prepared by sol–gel spin coating on single crystal silicon wafers and then heat-treated at different temperatures (900°C, 1000°C and 1100°C), for different periods of time (between 5 min and 40 h). Anatase (TiO2) crystals were found to nucleate at the surface, by means of the atomic force microscope observations, with a mean diameter from 5 to 10 nm, depending on the nucleation time and the titania content of the glass and, on subsequent heating, the crystals grew. Based on the atomic force microscope measurements, parameters of the crystallization process such as the nucleation and crystal growth rates were estimated. These were both found to be time dependent and have an induction period.