Density functional characterization of B doping at rutile TiO2(110) surface

The geometric and electronic properties of various B doping defects in rutile TiO2 (1 1 0) surface are investigated in detail using first-principles density functional theory. Our results indicate that the implanted B impurity prefers forming strongly covalent bonds with O atoms in the lattice, which will result in significant structure distortion and surface rumpling. Moreover, the cost energy of the formation of a bridging oxygen vacancy is enlarged in the presence of B impurities in the surface layers. In all cases, the interstitial subsurface site, which forms a tetrahedral structure with four adjacent O atoms, is the most energetically favoured position. However, this case gives rise to large electron transition energy, and thereby leads to the experimentally observed blueshift. Our calculation results also demonstrate that only when the B-Ti bonds are formed can the incorporation of boron induce some localized states in the mid-band gap, and thus result in the redshift of adsorption spectra.