Phase Transformation Comparison of TiO2 Nanorods and TiO2 Thin Film After Annealing

This paper reports the degree of phase transformation of titanium dioxide (TiO2) thin film and TiO2 nanorods before and after annealing. TiO2 nanorods were synthesized with titanium isoproxide (TIP) in Oleic acid, having approximately 5 nm diameter and 30 nm length. TiO2 thin film was fabricated by sol-gel method using TIP, ethanol and hydrochloric acid. The characteristics of TiO2 nanorods and thin film were investigated with transmission electron microscope, atomic force microscope and x-ray diffraction patterns. Although the TiO2 thin film shows no crystallite peak, as-synthesized TiO2 nanorods show broad anatase phase diffraction peaks. After annealing the TiO2 nanorods at 850 degrees C for 3 h, only approximately 3.1% of crystallite phase was transformed from anatase phase to rutile phase. This slow phase transformation might be due to the small diameter of the nanorods, which is thermodynamically more stable than the anatase crystallite phase. However, although the film has small grains on the surface, approximately 59.5% of phase was transformed from anatase to rutile crystallite structure after the thin film annealing. This large amount of phase transformation might be due to the two dimensional structure of the thin film.