EFFECT OF ANNEALING TEMPERATURE ON OPTICAL PROPERTIES OF TITANIUM DIOXIDE THIN FILMS PREPARED BY SOL-GEL METHOD

TiO2 thin films were deposited on glass substrates by sol-gel method. Nanocrystalline TiO2 thin films were prepared at ambient conditions and titanium tetraisopropoxide [C12H28O4Ti] was used as a Ti-precursor. The effect of annealing temperature on optical properties of nanocrystalline TiO2 thin films was studied. The as-deposited films were dried at 100 °C for 1 hr. The films formed were further heated in temperature between 200 and 500 °C for 1 hr. The films were characterized by different techniques: XRD, UV-visible spectroscopy, FTIR spectroscopy and FESEM. The characterization studies revealed that the films are crystallized as anatase phase and nano-structured with better optical properties α = 0.89 as compared to reported data. The optical measurement showed the indirect band gap between 3.31 and 3.35 eV with corresponding crystallite sizes between 8.9 and 3.7 nm. The FESEM image of film annealed at 400 °C showed spherical nanocrystalline structure of TiO2 particles. The crystallite sizes obtained from FESEM image are found to be between 30 and 100 nm. It is also observed that refractive index of the film increases with increasing the annealing temperature. The smaller crystallite size gives larger band gap due to quantum size effects.