Optical properties of nanostructured TiO₂ thin films

Nanostructured titanium dioxide (TiO₂) thin films were prepared with one and two layers on glass substrates (ITO) using sol gel-spin coating technique and annealed at temperature ranging from 300°C to 600°C. X-ray diffraction (XRD) and UV-Vis transmittance spectroscopy were used to study the effects of annealing temperature on the structural and optical properties. X-ray diffraction studies showed that the as-deposited films were amorphous and at first changed to anatase phase with increase of annealing temperature. Optical constants of these films were derived from the transmission and reflection spectra subjected to annealing at different temperatures. The results indicate that an anatase phase structure TiO₂ thin film with nanocrystallite size of about 10.72 nm can be observed at 400°C. The optical gap decreases from 3.82 eV to 3.74.eV for one layer and from 3.64 eV to 3.5 eV for two layers when the annealing temperature increases from 300 °C to 600°C. The refractive index is low compared to a pore free anatase TiO₂ and it increases contrary to the porosity which is reduced with the raising of the annealing temperature.