Atomic layer deposition of epitaxial TiO2 II on c-sapphire

Using atomic layer deposition technique, epitaxial titania polymorph TiO2 II was grown on α-Al2O3(0 0 1) (c-sapphire) substrates. TiCl4 and H2O served as precursors. The growth temperature ranged from 350 to 680 °C. Raman scattering and high-resolution x-ray diffraction and reflection measurements were applied to characterize the films. It appeared that the films contained, in addition to TiO2 II, anatase and/or rutile phase. The dependence of the film properties on the growth temperature and the film thickness was explored. The growth of the TiO2 II phase was shown to be controlled by the α-Al2O3 substrate orientation. This phase did not grow when the substrate was (0 1 2) oriented (r-sapphire). The epitaxial relationship was determined to be (1 0 0)[0 1¯ 0]TiO2 II ∥ (0 0 1)[1 2 0]sapphire, (1 0 0)[0 0 1]TiO2 II ∥ (0 0 1)[1 0 0]sapphire.