Effect of substrate type, dopant and thermal treatment on physicochemical properties of TiO2-SnO2 sol-gel films

Thin nanocrystalline TiO2-SnO2 films (0-50 mol% SnO2) were prepared on quartz and stainless steel substrates by sol-gel coating method. The obtained films were investigated by XRD, Raman spectroscopy and XPS. The size of the nanocrystallites was determined by XRD-LB measurements. We ascertained that the increase of treatment temperature and concentration of SnO2 in the films favour the crystallization of rutile phase. The substrate type influences more substantially the phase composition of the TiO2-SnO2 films. It was established that a penetration of elements took place from the substrate into the films. TiO2 films deposited on quartz substrate include a Si which stabilizes anatase phase up to 600 A degrees C. The films which are deposited on stainless steel substrate and treated at 700 A degrees C show the presence of significant quantity of rutile phase. This phenomenon could be explained by the combined effect of Sn dopant as well as Fe and Cr, which also are penetrated in the films from the steel substrate. The titania films doped up to 10 mol% SnO2 on stainless steel possess only 12-17 nm anatase crystallites, whereas the TiO2-(10-50 mol%) SnO2 films contain very fine grain rutile phase (4 nm).