Anatase-to-rutile transition of titania thin films prepared by MOCVD

Phase transitions of TiO2 thin films prepared by MOCVD were investigated using X-ray diffraction, scanning electron microscope, transmission electron microscope, and secondary ion mass spectroscope. It was found that the insitu deposited thin films showed the onset of anatase-to-rutile transition at a much lower temperature of 400 °C. In order to reveal the mechanism responsible for the low temperature transition, the transition of titanium isopropoxide derived and titanium tetra-chloride derived powders were investigated. The onset temperatures of transition were 450 °C and 700 °C, respectively. It is therefore suggested that “source effect” is the main mechanism of low temperature transition. It is also suggested that the heterogeneous nucleation on the surface of substrate is responsible for the transition shown by in-situ deposited and post-annealed titania thin films being much faster than that Shown by titania powders.