We present a novel way to obtain heavily nitrogen doped anatase TiO 2 films by using a solid-state nitrogen source. Epitaxial growth of the films was realized by introducing one unit-cell seed layer, which was indicated by reflection high-energy electron diffraction as intensity oscillation. Results of x-ray diffraction and x-ray photoelectron spectroscopy confirmed that the films were in the anatase phase heavily doped with nitrogen of ∼15 at%. The films obtained exhibited considerable narrowing of the optical bandgap, resulting in an enhancement of absorption in the visible-light region.
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