Novel modification method of sol-gel thin films - Densification of silica gel films with electronic excitation

Significant structural changes in silica gel films with synchrotron radiation (SR) and energetic He⁺ ions have been found. Irradiation with photons in the energy range higher than approximately 8 eV and 100-keV He⁺ ions induce an increase in refractive index and a decrease in thickness of silica gel films. Fourier transform infrared absorption spectra indicate that irradiation with the photons and the ions reduces the Si-OH content and the average Si-O-Si bridging angle. Electronic excitation with energetic photons is suggested to induce atomic rearrangement which causes densification of silica gel. Structural changes with He⁺ implantation is also tentatively ascribed to an electronic process. Electronic processes using SR and light ion implantation are anticipated to offer an alternative route to prepare dense thin films derived from sol-gel method.