Highly Porous Nanocluster TiO[sub 2] Films Deposited Using APCVD in an Excess of Water Vapor

This paper describes high-porosity titanium dioxide ( Ti O 2 ) films deposited via atmospheric pressure chemical vapor deposition using tetraisopropyl titanate at deposition temperatures ( T dep ) of 250 and 450 ° C in excess water vapor. Films deposited at low T dep exhibit a very low refractive index ( n film ) and high porosity ( φ ) , up to 87% of the bulk rutile phase. High-temperature sintering, performed at either 450 or 1000 ° 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 φ. The nanoporous nature of the films has significantly retarded the transformation from anatase to rutile, and after sintering for 6 h at 1000 ° C , the anatase fraction is still greater than 79%. Such Ti O 2 thin films with a high surface area to volume ratio are suitable for use in dye-sensitized solar cells and gas sensors.