Crystal phase control for titanium dioxide films by direct deposition in aqueous solutions

Crystalline titanium dioxide (TiO₂) was directly grown on a substrate via heterogeneous nucleation in aqueous solutions with titanyl sulfate at near room temperature. The crystal phase of TiO₂ films was essentially determined by the initial pH value and the Ti concentration of the precursor solutions. The rutile and anatase phases were produced in the solutions around their thermodynamic equilibrium conditions between Ti(IV) ionic species and the solid phases. The effect of the deposition rate on the crystal phases was not dominant in this system. On the other hand, the morphology of the TiO₂ products was influenced by the reaction rate controlled with the properties of anions as a ligand for titanium cations. Homogeneous rutile and anatase films consisting of highly oriented needlelike crystals were obtained with a relatively slow deposition rate.