Optical and microstructural properties of sol–gel derived titania/organically modified silane thin films

Waveguide thin films with thickness more than one and a half micron were prepared by the sol–gel spin coating technique and low temperature heat treatment from relatively high titanium content organically modified silanes (ORMOSIL). The films were analyzed by X-ray diffraction (XRD), ellipsometry, atomic force microscopy (AFM), thermal gravimetric analysis (TGA), UV-visible spectroscopy (UV-vis), and Fourier transform infrared spectroscopy (FTIR) to study their optical and microstructural properties. It was observed that the film becomes thinner as the titanium content increases. A change of the refractive index through the range 1.44–1.55 at the optical wavelength of 633 nm was achieved by varying the molar ratio between ORMOSIL and titanium. UV-vis transmission spectroscopy and AFM results showed that macro-pore free and high transparency (in the visible range) waveguide films could be obtained at both low and high temperatures. While at low temperatures, our simpler recipe produced as good films as previously reported, it was noted that purely inorganic and crack-free silica-titania films with a thickness of about 0.5 μm could also be obtained when the film was baked at a temperature of 500°C or higher. Meanwhile, our films obtained after a high temperature heat treatment showed a hardness that is dependent on the heat treatment temperature. A hardness as high as 10.0 GP was achieved at a heat treatment temperature of 1000°C and we believe that this is a result of the formation of TiC structure.