Incorporation of nonmetal impurities at the anatase TiO₂(001)- (1×4) surface

We use first principles calculations to investigate the adsorption and incorporation of nonmetal impurities (N, C) at the anatase TiO ₂(001)-(1×4) reconstructed surface. We analyze in detail the influence of the surface structure and local strain on the impurity binding sites and incorporation pathways and identify important intermediates that facilitate impurity incorporation. We find various subsurface interstitial binding sites and corresponding surface → subsurface penetration pathways on the reconstructed surface. This surface also favors the presence of subsurface oxygen vacancies, to which adsorbed species can migrate to form substitutional impurities. Most notably, we show that the nonexposed oxygen sites just below the surface have a key role in the incorporation of nitrogen and carbon in TiO₂(001).