Fabrication and characterization of a CeO₂ buffer layer on c-plane and tilt-c-plane sapphire substrates

We have examined in-plane orientation of CeO₂ buffer layers on c-plane and tilt-c-plane sapphire substrates. The tilt angles are 5°, 10° and 15°, which are defined as the angles between the c-plane and the surface planes of the sapphire substrates (called 5°, 10°, 15° tilt-c-plane substrates). The films were prepared by inductively coupled plasma sputtering. The in-plane orientation of the films was measured using X-ray φ-scan. φ-scan peaks of films fabricated on c-plane substrates appeared every nπ/6 or nπ/12 (n: integer), showing 12-fold or 24-fold symmetry. The in-plane orientation is influenced by the hexagonal symmetry of the sapphire c-plane. The degree of film orientation depends on the substrate temperature during preparation. On the other hand, we found weak 4-fold symmetry for films fabricated on 10° and 15° tilt-c-plane substrates. This suggests that we can obtain CeO₂ films with perfect 4-fold symmetry on tilt-c-plane sapphire substrates.