Annealing effects on microstructural and optical properties of Nanostructured-TiO₂ thin films prepared by sol–gel technique

In this paper we report on the effect of annealing on the microsctructural and optoelectronic properties of titanium dioxide (TiO₂) thin films prepared using sol–gel method onto silicon (Si) (100) and quartz substrates. The annealing temperatures range from 200 to 1000 °C. The Microstructural properties of annealed thin films were investigated by Thermal gravimetric analyses (TGA), X-ray diffraction (XRD) and Raman Spectroscopy. The surface morphology of the film was examined using Atomic Force Microscopy (AFM) method. The optical properties of TiO₂ thin films were characterized using UV–VIS and Spectroscopic ellipsometry. The results have shown that the TiO₂ thin films persist in the anatase phase even after annealing at 800 °C. The phase transformation from anatase to rutile occurred only when the films were annealed at 1000 °C. AFM studies revealed nanocrystalline structure where their shape and density depend strongly on the annealing temperatures. The elaborated nanostructured-TiO₂ thin films present a high transparency in the visible range. Spectroscopic ellipsometry (SE) study was used to determine the effect of annealing temperature on the thickness and on the optical constant of TiO₂ thin films. Spectroscopic ellipsometry and UV–VIS shows that the band gap of TiO₂ thin films was found to decrease when the annealing temperature increases. The Anatase phase was find to show higher photocatalytic activity than the rutile one.