Effects of titanium content on sol-gel hard optical films prepared in an organic-inorganic hybrid system

Sol-gel derived SiO₂-TiO₂ hard optical films from acid catalyzed solutions of GLYMO and MTES mixed with TPOT were studied. A single-layer film with a thickness of more than 0.6 μm was prepared on solid silicon substrate by single spin coating and a heat treatment temperature of 500 °C. The effects of the titanium content and heat treatment temperature on the optical structural properties of the fims were characterized by TGA, UV-VIS, FTIR, and Raman spectroscopy. The results show that carbon exists in all films heated at the temperature of 800°C. The hardness and Young's modulus of the films as characterized by a nanoindenter show a linear dependence on the titanium content. Hardness as high as 6.60 GPa was obtained in a 0.5 M titanium content film and heat treated at 800°C. The high hardness of the film was related to the existence of carbon phase in the film.