Structural change in sol-gel derived SiO₂ films using ultraviolet irradiation

Photo-induced changes in structure of sol-gel derived SiO₂ films were studied in order to explore a possibility of densification of sol-gel films at room temperature using energetic photons. Gel films which were produced on silicon substrates by dip-coating of sols prepared through hydrolysis of tetraethoxysilane were subjected to synchrotron radiation at room temperature. Structural changes of the gel films were investigated by ellipsometry and infrared spectroscopy. The radiation resulted in an increase in refractive index, a decrease in thickness of the films and a loss of OH groups. Increase in temperature of the films was less than 50 °C during the irradiation. The results indicate that ultraviolet lights induce densification of gel films through electronic excitation.