Phase separation in SiO2-TiO2 gel and glassy films studied by atomic forcemicroscopy and transmission electron microscopy

An investigation of phase separation phenomena in gel and glassy thin films of silica-titania, with TiO2 contents of 20 and 40 mol%, has been carried out by atomic force microscopy (AFM) and transmission electron microscopy ( TEM), The thin films were prepared by spin coating of a precursor sol on si licon wafers. Both the TEM measurements (carried out on scrapped thin film flakes) and the AFM measurements (carried out on films coated on the silico n substrates) for samples with different heat treatments suggest that spino dal-like structural inhomogeneities occur in these samples, unlike the corr esponding observations in pure silica films, which are known to be homogene ous. Changes in the microstructure of the films have been noticed with the thermal treatment, in agreement with earlier x-ray photoemission studies. T he finer characteristic dimensions of the phase separated regions reveal th at silica-titania samples prepared by sol-gel processing exhibit a more int imate mixing of the phases.