Surface Structure of TiO2 Rutile (011) Exposed to Liquid Water

J. Balajka, U. Aschauer, S. Mertens, A. Selloni, M. Schmid, U. Diebold

Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria
Department of Chemistry and Biochemistry, University of Bern, CH-3012, Bern, Switzerland
Department of Chemistry, Princeton University, Frick Laboratory, Princeton, New Jersey 08544, U. S. A.

J. Phys. Chem. C 121 (2017) 26424-26431

The rutile TiO2(011) surface exhibits a (2 × 1) reconstruction when prepared by standard techniques in ultra-high vacuum (UHV). Here we report that a restructuring occurs upon exposing the surface to liquid water at room temperature. The experiment was performed in a dedicated UHV system, equipped for direct and clean transfer of samples between UHV and liquid environment. After exposure to liquid water, an overlayer with a (2 × 1) symmetry was observed containing two dissociated water molecules per unit cell. The two OH groups yield an apparent "c(2 × 1)" symmetry in scanning tunneling microscopy (STM) images. On the basis of STM analysis and density functional theory (DFT) calculations, this overlayer is attributed to dissociated water on top of the unreconstructed (1 × 1) surface. Investigation of possible adsorption structures and analysis of the domain boundaries in this structure provide strong evidence that the original (2 × 1) reconstruction is lifted. Unlike the (2 × 1) reconstruction, the (1 × 1) surface has an appropriate density and symmetry of adsorption sites. The possibility of contaminant-induced restructuring was excluded based on X-ray photoelectron spectroscopy (XPS) and low-energy He+ ion scattering (LEIS) measurements.

Corresponding author: Ulrike Diebold (diebold at iap_tuwien_ac_at).

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