Anatase TiO2 thin films grown on lattice-matched LaAlO3 substrate by laser molecular-beam epitaxy

Epitaxial anatase thin films were fabricated on lattice-matched $\text{(−0.2\%)}$ ${\mathrm{LaAlO}}_{\mathrm{3}}$ (001) substrates in the layer-by-layer fashion by laser molecular-beam epitaxy. X-ray diffraction and transmission electron microscope show the films to exhibit high crystallinity and atomically defined interfaces. By virtue of the adoption of ${\mathrm{LaAlO}}_{\mathrm{3}}$ substrate, which is transparent to photoexcitation of ${\mathrm{TiO}}_{\mathrm{2}},$ optical band gaps could be determined to be 3.3 eV at room temperature. A photoluminescence band due to recombination of self-trapped excitons was observed at 5 K to give the peak maximum at 2.2 eV. As a result of the high degree of orientation of the epitaxial films, anisotropic optical absorption was clearly observed.