Alternative modification methods for sol-gel coatings of silica, titania and silica-titania using ultraviolet irradiation and water vapor

We investigated relatively new techniques for densification and crystalliza tion of sol-gel silica, titania and silica-titania coatings at relatively l ow temperatures. irradiation of ultraviolet photons above the band-gap ener gy was found to lead shrinkage of the sol-gel films through electronic exci tations. Crystallization of sol-gel titania coatings was achieved by irradi ation of ultraviolet laser (4.7 eV) beam. Exposure to water vapor was shown to be effective in rearrangement of sol-gel films causing densification of silica, crystallization of titania and phase separation of silica-titania around 100 degrees C. These techniques are useful for preparation of hard s ilica coatings and crystalline titania films on low-heat-resistant substrat es, such as polymer plates. (C) 1999 Elsevier Science S.A. All rights reser ved.