Modification and densification of sol-gel derived silica films at low temperatures

Relatively new modification methods for densification of sol-gel derived silica films using electronic excitations and water vapor were investigated. Dried silica gel films were found to be densified by vacuum ultraviolet irradiation and He⁺ ion implantation. The densification is deduced to be ascribed to dehydration and cleavage of the strained bonds through electronic excitations induced by the irradiations. The structure of the irradiated silica films is similar to that of silica glass densified under a high pressure. The exposure to water vapor at 80° -180°C is also effective in densification and dehydration of sol-gel silica films. These methods are expected to be valuable for fabrication of dense silica films at low temperatures. However, the silica films densified by the irradiations and the exposure are suggested to contain a strained network because a subsequent annealing above 300°C induced structural changes through a thermal relaxation.