CRYSTALLIZATION BEHAVIOR OF SIO2-TIO2 SOL-GEL THIN-FILMS

The aim of this work was to investigate the crystallization behavior o f thin films of SiO2-TiO2 made by the sol-gel process as function of d ie TiO2 content and the temperature and time of heat treatment. Precur sor solutions were prepared by hydrolysis of TEOS (tetraethoxysilane) and TPOT (titanium tetraisopropoxide). Multilayer films were spun on s ingle crystal silicon wafers. The compositions studied were (on a mola r percentage basis) 20TiO(2)-80SiO(2), 30TiO(2)-70SiO(2), 40TiO(2)-60S iO(2) and pure TiO2. The films were heat treated at different temperat ures between 300 degrees C and 1200 degrees C, for different periods o f time (30 s-90 h). The crystallization kinetics were followed by micr o-Raman spectrometry. Grazing incidence X-ray diffraction showed that the films crystallized into one or both of two crystalline phases of T iO2: anatase and rutile (for pure TiO2 only). The volume fractions of the crystalline phase varied from very low values (<1%), up to 100%, f or a TiO2 sample heat treated at 800 degrees C for 8 hours. The result s show that the volume fraction of crystalline phase is strongly influ enced by the heat treatment temperature and also, to a smaller extent, by the heat treatment time. The most important parameter, however, is the composition of the films: the higher their TiO2 concentration, th e lower is the crystallization temperature and the larger is the cryst allized fraction.