Substitution of Titanium for Magnesium Ions at the Surface of Mg-Doped Rutile

The surface structure of Mg-doped rutile TiO2 (011) surfaces is determined by combining the core-level or valence band photoemission and photoelectron diffraction (PED) measurements with evolutionary algorithm, density functional theory (DFT), and multiple scattering calculations. Upon annealing the reduced crystal above 620 K, Mg segregates by substitution to the Ti atoms from the TiO2 lattice while retaining the known reconstruction of the Mg-free surface. Since the band gap states are totally healed by the Mg segregation, the charge compensation is provided by the O vacancies as formally expressed by the Kroger and Vink notation. Full support of these findings comes from DFT calculations based on the findings from evolutionary algorithm calculations, which demonstrate that a combination of four surface structures nicely accounts for the observed experimental Ti 3s and Mg 2s patterns. These model structures only involve Mg in the substitutional position and O vacancies, and neither interstitial atoms nor excess electrons were experimentally detected.