Structure–property correlation in epitaxial (2 0 0) rutile films on sapphire substrates

We have investigated the influence of the deposition variables on photocatalytic properties of epitaxial rutile films. Despite a large lattice misfit of rutile with sapphire substrate, (2 0 0) epitaxial layers were grown on (0 0 0 1)sapphire by domain matching epitaxy paradigm. Using φ-scan XRD and cross section TEM, the epitaxial relationship was determined to be rutile(1 0 0)||sapphire(0 0 0 1), rutile(0 0 1)||sapphire(1 0 −1 0), and rutile(0 1 0)||sapphire(1 −2 1 0). Based on the XRD patterns, increasing the repetition rate introduced tensile stress along the film normal direction, which may arise as a result of trapped defects. Formation of such defects was studied by UV–VIS, PL, and XPS techniques. AFM studies showed that the film roughness increases with the repetition rate. Finally, photocatalytic performance of the layers was investigated through measuring decomposition rate of 4-chlorophenol on the films surface. The films grown at higher frequencies revealed higher photocatalytic efficiency. This behavior was mainly related to formation of point defects which enhance the charge separation.