FACTORS AND MECHANISM OF CHANGES IN THE REFRACTIVE-INDEX OF SOL-GEL DERIVED 80TIO2.20SIO2 FILMS COATED ON SODA-LIME-SILICATE GLASS SUBSTRATES

The mechanism of the changes in the refractive index of sol-gel derived 80TiO2.20SiO2 films dip-coated on commercial soda-lime-silicate glass and silicon wafer has been investigated by the ellipsometry and X-ray photoelectron spectroscopy. As the drying time after coating increased, the refractive index increased along with the decrease in film thickness by the evaporation of ethanol and water which were produced by the hydrolysis and polycondensation reaction. The refractive index of films coated on glass substrate was markedly lower than that coated on silicon wafer. This was due to sodium ions in films, which diffused from glass substrate and induced Na2Ti2Ti6O16 phase formation in the film. The refractive index of thick films was higher than that of thin films because sodium ion took more time to diffuse through thick films. The increase in the refractive index along with the decrease in the thickness of films prepared by the fast heating process was due to the sudden collapse and fast shrinkage of gel film before polycondensation reaction and thus to the higher packing density of film.