Sol-gel derived epitaxial MgTiO₃ thin films

MgTiO₃ thin films have been successfully grown on a sapphire crystal by the sol-gel process. Epitaxial growth of MgTiO₃ thin films was obtained using magnesium acetylacetonate and titanium isopropoxide in the sol-gel process. In nonhydrolytic conditions, the c-axis oriented ilmenite structure of MgTiO₃ thin films developed at the crystallization temperatures 650-800 °C with a 3-fold axis symmetry in the c-plane. These epitaxial MgTiO₃ thin films had extremely fine features in morphology, i.e., a fine grain size of 10-20 nm and a very smooth surface of 0.9 nm rms roughness. The epitaxial MgTiO₃ thin films exhibited a UV absorption edge at 280 nm and were transparent in the wavelength range of 400-1100 nm. The ordinary refractive index of the epitaxially grown MgTiO₃ thin films was 2.305, very close to the value of single-crystal MgTiO₃. This suggests that the epitaxially grown MgTiO₃ thin films are well crystallized and sufficiently strain-relaxed due to the small lattice mismatch with Al₂O₃ substrate.