Effect of H2O Content on Structure and Optical Properties of TiO2 Thin Films Derived by Sol-Gel Dip-Coating Process at Low Temperature

Abstract

Pure TiO2 thin films were prepared on the glass substrates by sol–gel dip coating technique with titanium (IV) isopropoxide including simultaneously acetylacetone and acetic acid as stabilizing reagents. The effect of the amount of water in the sol on structural and optical properties of TiO2 thin films was investigated. The structural and optical properties of post- sintered films for 1 hour at 500°C in air were investigated By X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis spectroscopy and ellipsometry. The results showed a simultaneous appearance of the rutile and the anatase phases with different rutile / anatase proportions for all samples. The increase of the water content leads to the decrease of rutile / anatase proportion. The crystalline size varies from 7.94 to 24.84 nm for the anatase phase and from 17.70 to 22.31 nm for the rutile phase. The optical measurements showed that the structure was strongly influenced by the water / alcoxides molar ratios. In comparison with the bulk material, the TiO2 thin films prepared by this way exhibit low refractive index in the range of 2.15 and high band gap energy narrowing from 3.88 to 3.95 eV for direct allowed transition and from 3.09 to 3.39 eV for indirect allowed transition according to the cristallinity degree and the rutile /anatase weight fraction.