Epitaxial growth of titanium oxide thin films on c-cut and α-cut sapphire substrates

C-cut and α-cut sapphire substrates are used to grow epitaxial titanium oxide films by pulsed-laser deposition at 700 °C under a controlled oxygen pressure in the 10−1-10−5 mbar range. The rutile phase is evidenced in films whatever the substrate and the oxygen pressure while the anatase phase is only observed on c-cut sapphire substrate and for oxygen pressure down to 10−3 mbar. No other titanium oxide phases (i.e. TiO, Ti2O3 or Magneli phases) are identified despite the oxygen-deficiency observed in films grown at low oxygen pressure. According to asymmetric X-ray diffraction measurements performed on films, the main axis growth and the in-plane epitaxial relationships between titanium oxide films and sapphire substrates are found to be depending on the orientation of the sapphire basal plane and on the oxygen pressure. The anatase crystallites are highly oriented with the following epitaxial relationship (004)[110]A//(00.1)[11¯.0]c-S. The rutile phase is (2 0 0) oriented on c-cut sapphire substrate and displays two distinct in-plane relationships: [010]R//[10.0]c-Sor[011]R//[11¯.0]c-S. The use of α-cut sapphire substrate leads to the growth of rutile crystallites (2 0 0) or (1 0 1) oriented. In these cases, the in-plane orientations are (200)[010]R//(11.0)[00.1]α-S,and(101)[101¯]R//(11.0)[11¯.0]α-S, respectively. For the two substrates used, schematic views of atomic arrangement of the different interfaces are proposed.