Molecular ordering at the interface between liquid water and rutile TiO2(110)

G. Serrano, B. Bonanni, M. Di Giovannantonio, T. Kosmala, M. Schmid, U. Diebold, A. Di Carlo, J. Cheng, J. VandeVondele, K. Wandelt, C. Goletti

Department of Physics and CNISM, Università degli Studi di Roma "Tor Vergata", Rome, Italy
Institut für Physikalische und Theoretische Chemie, University of Bonn, Bonn, Germany
Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria
Department of Electronic Engineering and CHOSE, Università degli Studi di Roma "Tor Vergata", Rome, Italy
Department of Chemistry, University of Aberdeen, Aberdeen, UK
Department of Materials, ETH Zürich, Zürich, Switzerland

Adv. Mater. Interf. 2 (2015) 1500246

The pivotal importance of TiO2 as a technological material involves most applications in an aqueous environment, but the single-crystal TiO2/bulk-water interfaces are almost completely unexplored, since up to date solid/liquid interfaces are more difficult to access than surfaces in ultrahigh vacuum (UHV). Only a few techniques (as scanning probe microscopy) offer the opportunity to explore these systems under realistic conditions. The rutile TiO2(110) surface immersed in high-purity water is studied by in situ scanning tunneling microscopy. The large-scale surface morphology as obtained after preparation under UHV conditions remains unchanged upon prolonged exposure to bulk water. Moreover, in contrast to UHV, atomically resolved images show a twofold periodicity along the [001] direction, indicative of an ordered structure resulting from the hydration layer. This is consistent with density-functional theory based molecular dynamics simulations where neighboring interfacial molecules of the first water layer in contact with the bulk liquid form dimers. By contrast, this dimerization is not observed for a single adsorbed water monolayer, i.e., in the absence of bulk water.

Corresponding author: Giulia Serrano. Reprints also available from Ulrike Diebold (diebold at iap_tuwien_ac_at).

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