Electronic structure of epitaxial anatase TiO2 films: Angle-resolved photoelectron spectroscopy study

Synchrotron-radiation angle-resolved photoelectron spectroscopy has been utilized to examine the bulk valence-band structure of anatase TiO2(001) thin films fabricated on LaAlO3(100) by pulsed laser deposition. The energy-momentum dispersion relation of O 2p-derived nonbonding, O 2p-Ti 3d sigma bonding and several pi bonding states is determined experimentally. The nonbonding state at the top of the valence band is located at 4.3 eV at the center of the bulk Brillouin zone, and it shifts towards the shallower energies to 3.8 eV at the zone boundary. No other states with binding energies smaller than 3.8 eV are found on any other high-symmetry axes and points. Thus the valence-band maximum is located at the zone boundary. Our finding proves that anatase is an indirect-band-gap semiconductor.