DENSIFICATION OF SOL-GEL THIN-FILMS BY ULTRAVIOLET AND VACUUM-ULTRAVIOLET IRRADIATIONS

Structural changes in SiO2 and TiO2 gel films were investigated using ultraviolet (UV) and vacuum ultraviolet (VUV) irradiations. A signific ant compaction with dehydration of SiO2 gel films was induced by irrad iation of photons in the range of 9-18 eV. The refractive index and th e shrinkage of the irradiated SiO2 gel films were comparable to those obtained by sintering at 1000 degrees C. Densification of TiO2 gel fil ms was also observed with irradiation of 5-14 eV photons. However, eff ects of the irradiation on TiO2 gel were smaller that those on SiO2 ge l. The structural changes in the gel films are attributed to electroni c excitations which are induced by irradiation with photons having hig her energies than the bandgap of the oxides. The photo-induced effects are presumed to depend on the optical properties and structure of the gels.