Paper SE-WeM4
The Substrate Effect on the TiO2 Photocatalytic Thin Films

Wednesday, October 17, 2007, 9:00 am, Room 617

Titanium dioxide thin films were deposited on two different substrates of p-typed Si (100) and LaAlO3 (001) single-crystal in a pulsed laser deposition system via KrF excimer laser ablation of a pure titania target of 99.95% purity. The substrate temperature and oxygen partial pressure were varied at 400-600?C and 0-9.3 Pa, respectively. The mismatch of lattice constant between anatase TiO2 and LaAlO3 (001) is less than 0.2%, but that between anatase TiO2 and Si (100) is much larger. TiO2 films deposited on LaAlO3 have much better crystallinity than those deposited on Si. The films on LaAlO3 also revealed strong preferred orientation, but the films on Si did not. At all substrate temperatures the films on LaAlO3 compose of only a single anatase phase, while the film on Si composes of mixed phases of anatase and rutile at 600?C, but the crystallinity of the films on both substrates increases with rising substrate temperature. For the surface morphology, the films on LaAlO3 show mosaic structures of epitaxial growth, but the films on Si are polycrystalline in nature with smaller random grains. The photocatalytic performance is determined by the relative amounts of precipitated silver aggregates on the deposited films from AgNO3 aqueous solution under illumination of ultraviolet or visible light. The most precipitated silver aggregates were found at the steps or grain edges on the film surfaces. At lower substrate temperatures, the film deposited on Si has better catalytic performance than those deposited on LaAlO3. It may be due to much more grain edges of the films on Si. At higher substrate temperatures, however, the film deposited on LaAlO3 has better performance than the film on Si, which may be due to pure anatase phase with better crystallinity in the film on LaAlO3.