Growth and structure of Ti2O3 and TiO2 thin films on (0001)α-Al2O3 substrates

Titanium oxide thin films were grown at different temperatures on (0001) alpha-Al2O3 substrates by molecular beam epitaxy (MBE). The films gown at room temperature were amorphous. Annealing at 1223K of 6 nm thick films led to the formation of TiO2 with an epitaxial orientation relationship (100)[001]TiO2 parallel to (0001)[<01(1)over bar 0>]Al2O3 with the substrate. However, on similar heat treatment, thicker 100 nm films formed polycrystalline TiO2. At a deposition temperature of 1223K epitaxial Ti2O3 films with orientation relationship (0001)[<2(11)over bar 0]Ti2O3 parallel to (0001)[<2(11)over bar 0>]Al2O3 were formed. The lattice mismatch between Ti2O3 and alpha-Al2O3 was accomodated by a regular arrangement of misfit dislocations at the Ti2O3/alpha-Al2O3 interface. By comparing the microstructural evolution of the annealed films with that of those films grown at high temperature, mechanisms governing grain growth in polycrystalline titanium oxide films were discussed.