Characteristics of titanium oxide films deposited by an activated reactive evaporation method

Titanium di- and sesquioxide films were epitaxially grown on the (001) surface of sapphire single-crystalline substrates by an activated reactive evaporation method. Formation range for each titanium oxide was determined as a function of oxygen pressure (Po₂) by means of x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Films prepared at Po₂ ≥ 2.0 × 10⁻⁴ Torr were stoichiometric (100)-oriented rutile of TiO₂, and with decreasing Po₂ they would accommodate more and more Ti³⁺ ions in the rutile structure. At Po₂ = 0.6 × 10⁻⁴ Torr, on the other hand, (001)-oriented Ti₂O₃ was formed and an electrical transition was clearly detected at about 400 K. However, the large lattice mismatch between the substrate and these films leads to a periodic introduction of misfit dislocations in the case of the TiO₂ films and a mixing of stacking sequences for the Ti₂O₃ films.