Titanium dioxide (TiO2) films were grown on Ni-, Ta-, and Ti-coated glass substrates at temperatures between 200 and 500 degrees C by atomic layer deposition (ALD) from TiCl4 and H2O precursors. The as-deposited films were anatase crystalline at the deposition temperature of 200 degrees C and became rutile crystalline with the increase in deposition temperature. The temperature for the transition of anatase to rutile varied with the substrate material; the Ni-coated substrate has the highest anatase-to-rutile transition temperature, followed by the Ta-coated substrate, and then the Ti-coated substrate. The grain size of as-deposited films had a minimum with deposition temperature for each substrate due to the composite effects of nucleus density and grain coalescence with temperature. The photocatalytic activity of ALD TiO2 films for the decomposition of methylene blue was highly influenced by the growth characteristics and the underlying material. The 200 and 300 C deposited films on Ni-coated substrates possessed the highest photocatalytic activity among all experimental samples due to their pure anatase structure and the Schottky contact of Ni/TiO2. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3138723] All rights reserved.