Broad band optical characterization of sol–gel TiO2 thin film microstructure evolution with temperature

Titanium dioxide (TiO2) thin films have been produced by spin coating a titanium isopropoxide sol on silicon wafer substrates. The structural evolution of the thin films in terms of decomposition, crystallization and densification has been monitored as a function of annealing temperature from 100 to 700 °C using optical characterization and other techniques. The effect of annealing temperature on the refractive index and extinction coefficient of these TiO2 thin films was studied in the range of 0.62 to 4.96 eV photon energy (250–2000 nm wavelength) using spectroscopic ellipsometry. Thermal gravimetric analysis and atomic force microscopy support the ellipsometry data and provide information about structural transformations in the titania thin films with respect to different annealing temperatures. These data help construct a coherent picture of the decomposition of the sol–gel precursors and the creation of dense layers of TiO2. It was observed that the refractive index increased from 2.02 to 2.45 at 2.48 eV (500 nm) in sol–gel spin coated titania films for annealing temperatures from 100 °C to 700 °C.