Properties of structurally excellent N-doped TiO2 rutile

We have used plasma-assisted molecular beam epitaxy to synthesize structurally near-perfect crystalline films of TiO2−xNx rutile for the first time. These materials allow the properties of TiO2−xNx to be elucidated without the interfering effects of bulk substoichiometric defects that have characterized previous investigations. In the absence of such defects, the extent of N incorporation in the lattice is limited to ∼2 ± 1 at.% of the anions. Substitutional N (NO) exhibits a −3 formal charge due to charge transfer from shallow-donor interstitial Ti(III), which forms during epitaxial growth. Hybridization between NO and adjacent lattice Ti ions occurs, resulting in new states at the top of the rutile valence band and an apparent band gap reduction of ∼0.6 eV.