Preferential formation of anatase in laser-ablated titanium dioxide films

Abstract This paper gives a guideline for preparation of anatase TiO 2 films by pulsed laser deposition (PLD) technique, and the mechanism of preferential formation of anatase is described. The TiO 2 films with different thicknesses, 50, 100 and 300 nm, were prepared on quartz-glass substrates by Nd:YAG pulsed laser deposition, and subsequently annealed in air at 500 and 1000 °C. Their structures and optical properties have been investigated. The as-deposited film with a thickness of 50 nm was a mixture of amorphous, anatase and rutile. Anatase still existed after annealing for 1 h at 1000 °C. In contrast, the anatase phase was not present in the 300 nm thick film and only the rutile phase was observed. In the film with a thickness of 100 nm, anatase was found only in the as-deposited state. It has been revealed experimentally that the anatase phase is formed when the as-deposited films have an amorphous structure. This is strongly supported by an additional experiment using a sapphire single-crystal substrate. A micromechanical calculation substantiates that the anatase formation from the amorphous phase is preferred in terms of the strain energy and Gibbs free energy.