PHASE-TRANSFORMATIONS IN TIO2/SIO2 SOL-GEL FILMS AS A FUNCTION OF COMPOSITION AND HEAT-TREATMENT

The refractive indices of titania/silica sol-gel films are known to vary over a wide range with composition. However, little work has been done to investigate the possible variations in refractive index that can be produced for one specific sol-gel composition by varying the heat-treatment time and temperature. In this study, three different titania/silica sol-gel compositions containing 40, 60 and 80 mol % titania were studied after thermal processing at temperatures from 175-1050-degrees-C for variable lengths of time. The refractive indices and thicknesses of the sol-gel films spin-coated on to silicon wafers were determined using a combined technique of ellipsometry and reflectance spectroscopy. The microstructural differences in the films were investigated using X-ray diffraction and transmission electron microscopy techniques.