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Electronic structure of point defects in controlled self-doping of the TiO2(110) surface: Combined photoemission spectroscopy and density functional theory study

DOI: 10.1103/PhysRevB.77.235424 DOI Help

Authors: Michael Nolan (Tyndall National Institute) , Simon D. Elliott (Tyndall National Institute) , Mark Basham (University of Reading) , Paul Mulheran (University of Strathclyde) , James S. Mulley (University of Reading) , Roger A. Bennett (University of Reading)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 77 (23) , PAGES 235424

State: Published (Approved)
Published: June 2008

Abstract: Point defects in metal oxides such as TiO2 are key to their applications in numerous technologies. The investigation of thermally induced nonstoichiometry in TiO2 is complicated by the difficulties in preparing and determining a desired degree of nonstoichiometry. We study controlled self-doping of TiO2 by adsorption of 1/8 and 1/16 monolayer Ti at the 110 surface using a combination of experimental and computational approaches to unravel the details of the adsorption process and the oxidation state of Ti. Upon adsorption of Ti, x-ray and ultraviolet photoemission spectroscopy XPS and UPS show formation of reduced Ti. Comparison of pure density functional theory DFT with experiment shows that pure DFT provides an inconsistent escription of the electronic structure. To surmount this difficulty, we apply DFT corrected for on-site Coulomb interaction DFT+U to describe reduced Ti ions. The optimal value of U is 3 eV, determined from comparison of the computed Ti 3d electronic density of states with the U S data. DFT+U and UPS show the appearance of a Ti 3d adsorbate-induced state at 1.3 eV above the valence band and 1.0 eV below the conduction band. The computations show that the adsorbed Ti atom is oxidized to Ti2+ and a fivefold coordinated surface Tiatom is reduced to Ti3+, while the remaining electron is distributed among other surface Ti atoms. The UPS data are best fitted with reduced Ti2+ and Ti3+ ions. These results demonstrate that the complexity of doped metal oxides is best understood with a combination of experiment and appropriate computations.

Subject Areas: Physics, Materials


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