Growth Mechanism and Charge Transfer Properties of Biphase TiO₂ Thin Films

Biphase TiO2 outperforms its single-crystal polymorphs in the field of photocatalysis because of the homojunction effect. However, most studies of biphase TiO2 focused on nanoparticles or powders. Growth of biphase TiO2 thin films remains a substantial challenge. In this study, biphase TiO2 thin films were epitaxially grown on SrTiO3 (111) substrates by using pulsed laser deposition. Transmission electron microscopy observations revealed that the R–TiO2 grains possessed six variants with a rotation angle of 60° since the Sr–O and Ti-terminated surfaces had three epitaxial relationships with the R–TiO2 phase, respectively. The A–TiO2 grains nucleated at the steps of the substrate and formed three variants with a rotation angle of 120°. Charge transfer measurements revealed that the biphase TiO2 film was superior to the single-crystal A–TiO2 film. These results suggest that the epitaxial biphase TiO2 film can be directly grown on a SrTiO3 (111) substrate, which will be beneficial for its real applications.