MBE growth and characterization of epitaxial TiO2 and Nb-doped TiO2 films

Epitaxial TiO2 and Nb-doped TiO2 thin films have been grown on (110) TiO2 rutile substrates by molecular beam epitaxy using elemental Ti and Nb sources along with an electron cyclotron resonance oxygen plasma source. Film composition was measured by X-ray photoelectron spectroscopy. Reflection high-energy electron diffraction and low-energy electron diffraction patterns reveal excellent long-range crystallographic order and a rutile structure for both TiO2 and Nb-doped TiO2 films. The high degree of similarity in Ti and Nb core-level X-ray photoelectron diffraction angular distributions establishes that Nb is substitutionally incorporated in the rutile lattice. Analysis of the Nb 3d(5/2) core-level binding energy suggests an Nb4+ oxidation state.