The incorporation of nitrogen impurities in the anatase TiO 2(101) surface is investigated by first principles density functional theory calculations. Several substitutional and interstitial configurations and different concentrations for the N impurities in the surface and subsurface layers are considered, as well as their interactions with oxygen vacancies in the TiO 2 lattice. The stability of the various investigated systems is compared on the basis of their formation energy as a function of the oxygen chemical potential, which determines whether the system is in an oxidizing or reducing environment. Under oxygen-rich conditions, N bound to a surface O is preferred, whereas, under oxygen-poor conditions, substitutional N together with oxygen vacancies is favored, as previously found for bulk TiO 2. The cost of formation of a surface oxygen vacancy is almost cancelled in the presence of N impurities in subsurface layers. The incorporation of nitrogen in the lattice modifies the electronic structure by introducing localized states in the band gap, consistent with the experimentally observed absorption of N-doped anatase samples in the visible region. Also, these N impurity states are excellent traps for the Ti 3+ electrons deriving from surface oxygens vacancies. STM images for the various N-doped anatase (101) surface models have been computed to provide a reference to future experimental studies of this surface.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films