Highly porous nanocluster TiO2 films deposited using APCVD in an excess of water vapor

This paper describes high-porosity titanium dioxide (TiO2) films deposited via atmospheric pressure chemical vapor deposition using tetraisopropyl titanate at deposition temperatures (T-dep) of 250 and 450 degrees C in excess water vapor. Films deposited at low T-dep exhibit a very low refractive index (n(film)) and high porosity (phi), up to 87% of the bulk rutile phase. High-temperature sintering, performed at either 450 or 1000 degrees C, can be used to tailor the films properties by crystallizing the nanoclusters into the anatase or rutile phase, while retaining a low n(film) and high phi. The nanoporous nature of the films has significantly retarded the transformation from anatase to rutile, and after sintering for 6 h at 1000 degrees C, the anatase fraction is still greater than 79%. Such TiO2 thin films with a high surface area to volume ratio are suitable for use in dye-sensitized solar cells and gas sensors. (c) 2005 The Electrochemical Society. All rights reserved.