Transparent TiO2 films attract attention as anti-reflection and photo-catalytic coatings for self-cleaning, antifogging and heat mirror windows for architectural and automotive applications. High transparency and well-defined wavelength dispersion of refractive index is required to engineer multilayered structures with specially designed stop band optical spectra (photonic crystals). We report optical properties of series of TiO2 films with various thicknesses deposited by laser ablation on glass substrates at different temperatures. Wavelength dependencies of refractive index and absorption coefficient were obtained by fitting experimental transmission spectra in the wavelength range of 435 - 2630 nm to the Swanepoel formula. Theoretical modeling took into account film roughness measured by profilometer. Optical properties correlate with the microcrystalline structure (ratio of anatase and rutile phases) controlled by X-ray diffraction and tailored by post-annealing of the TiO2 films. Photocatalytic activity of the grown TiO2 films is discussed as well.
This work was supported by the Svenska Institutet (Dnr: 01199/382/2006) and the Kyushu Industrial Technology Center.