Thickness dependence of structural, optical and morphological properties of sol-gel derived TiO2 thin film

Abstract

In this research, Titanium dioxide (TiO2) thin films with different thicknesses were deposited on glass substrate by the sol - gel technique. Formation of TiO2 thin films was confirmed by EDAX spectra. The effect of thin film thickness on the structural, optical and morphological properties of the thin films was respectively analyzed by x-ray diffraction (XRD), UV–vis spectroscopy and atomic force microscopy (AFM). XRD measurements reveal the amorphous structure of the thin films before thermal treatment, while the thin films have crystalline phases after annealing at 600 °C. The XRD patterns also showed the dominant anatase phase in thin films structure. Moreover, peaks that belong to the Brookite phase appear as the thin film thickness increases. Brookite is the rare phase which is hardly gained and is suitable for photo catalytic applications. Crystalline transformation from anatse to anatas- brookite is attributed to grain size increase as increase of thin film thickness. Increase of grain size as a result of thin film thickness increase affect on the structural, optical and morphological properties. In addition, the weight fraction of brookite, grain size, lattice parameter and dislocation density were computed. The direct allowed band gap of TiO2 thin films with thickness of 50 nm to 150 nm was found to reduce in the range of 3.788 eV to 3.687 eV. The extinction coefficient, refractive index, susceptibility and porosity of the thin films were measured at the wavelength of 550 nm. Root mean square (RMS) roughness of the thin films increases as the thin film thickness increases.