Structure, defects, and impurities at the rutile TiO2(011)-(2x1) surface: A scanning tunneling microscopy study

O. Dulub, C. D. Valentin, A. Selloni, U. Diebold

Department of Physics, Tulane University, New Orleans, Louisiana 70118, U.S.A.
Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Milano, Italy
Department of Chemistry, Princeton University, Princeton, NJ 08544, U.S.A.

Surf. Sci. 600 (2006) 4407-4417

The titanium dioxide rutile (011) [equivalent to (101)] surface reconstructs to a stable (2 × 1) structure upon sputtering and annealing in ultrahigh vacuum. A previously proposed model [T.J. Beck, A. Klust, M. Batzill, U. Diebold, C. Di Valentin, A. Selloni, Phys. Rev. Lett. 93 (2004) 036104] containing onefold coordinated oxygen atoms (titanyl groups, TiO) is supported by Scanning Tunneling Microscopy (STM) measurements. These TiO sites are imaged bright in empty-states STM. A few percent of these terminal oxygen atoms are missing at vacuum-annealed surfaces of bulk-reduced samples. These O vacancies are imaged as dark spots. Their number density depends on the reduction state of the bulk. Double vacancies are the most commonly observed defect configuration; single vacancies and vacancies involving several O atoms are present as well. Formation of oxygen vacancies can be suppressed by annealing a sputtered surface first in vacuum and then in oxygen; annealing a sputtered surface in oxygen results in surface restructuring and a (3 × 1) phase. Anti-phase domain boundaries in the (2 × 1) structure are active adsorption sites. Segregation of calcium impurities from the bulk results in an ordered overlayer that exhibits domains with a centered (2 × 1) periodicity in STM.

Reprints available from U. Diebold (diebold at iap_tuwien_ac_at).

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