Effects of hyperthermia induced crystalline aggregation on properties of TiO₂ thin films

TiO₂ thin films were prepared on fused quartz by using the sol–gel dip coating method followed by annealing. The effects of annealing temperature on the phase transition, crystalline agglomeration, surface topography and optical properties of the TiO₂ films were studied. Activation energy of the phase transition from the anatase to rutile phase was estimated about 64 kJ mol⁻¹. Crystallite size did not vary significantly with the annealing temperature, but higher temperature led to the aggregation of nanocrystallines into large particles with wide size distribution due to the surface nucleation (SN) mode gradually replaced the interface nucleation (IN) mode. Both the optical transmittance and band gap of the TiO₂ thin films decrease as the annealing temperature increase. The highest optical transmittance over the visible wavelength region was obtained by the film annealed at 800 K, which was composed entirely of anatase phase.