Effects of titanium content on properties of sol-gel silica-titania films via organically modified silane precursors

The effects of titanium content on the properties of silica-titania films by the sol-gel method using γ-glycidoxypropyltrimethoxysilane (GLYMO), tetraethoxysilane (TEOS) and tetrapropylorthotitanate (TPOT) as the starting materials have been investigated. Atomic force microscopy (AFM), ellipsometry, thermal gravimetric analysis (TGA), UV-visible spectroscopy (UV-VIS), Fourier transform infrared (FT-IR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy have been used to investigate the optical and structural properties of the films. These results showed that crack-free and high transparency (in the visible and near infrared range) silica-titania films with a thickness of 0.75 μm could be obtained by a single spin-coating process after a heat treatment at 500°C. The hardness and Young's modulus of the films were also characterized by a nanoindenter and showed a linear dependence on the titanium content. Hardness as high as 9.0 GPa was achieved in a high titanium content film at a heat treatment temperature of 800°C.