| AVS 60th International Symposium and Exhibition | |
| Surface Science | Monday Sessions |
| Session SS-MoA |
| Session: | Metal Oxides: Reactivity and Catalysis |
| Presenter: | M.H. Farstad, Norwegian University of Science and Technology, Norway |
| Authors: | M.H. Farstad, Norwegian University of Science and Technology, Norway D. Ragazzon, Uppsala University, Sweden A. Schaefer, University of Bremen, Germany L.E. Walle, Norwegian University of Science and Technology, Norway A. Borg, Norwegian University of Science and Technology, Norway A. Sandell, Uppsala University, Sweden |
| Correspondent: | Click to Email |
When TiOx (x ≤ 2) thin films are deposited onto various metal substrates different structures with unique properties may form. This method therefore offers the possibility for guided design of TiO2 structures, which can lead to new kinds of TiO2-based materials for heterogeneous catalysis, photocatalysis and solar cells [1]. Since water is an integral part of these applications a solid understanding of the interaction between water and novel, supported titania structures is essential.
In the present work, we present results on water adsorption on ordered TiOx structures on Au(111) grown in situ by chemical vapor deposition (CVD). Depending on the conditions during deposition four different ordered phases can be produced. These phases have previously been studied and characterized with high-resolution photoelectron spectroscopy (HR-PES), scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Two phases, denoted honeycomb (HC) and wagon wheel (WW), are monolayer thick, reduced and wet the surface. The other two phases, denoted Star and Ring, are different forms of stoichiometric TiO2. The Star phase is the thermodynamically stable form of titania on Au(111) and it grows in the form of islands that partially covers the surface. The Ring phase is a multi-domain structure that covers basically the whole surface. The analysis of the LEED pattern gives an oblique unit cell, strongly indicating the formation of TiO2-B [2], a phase which surface properties are largely unknown.
Upon water adsorption all four TiOx phases show evidence of dissociation. The maximum hydroxyl coverage for the 2x2 and Star phases is close to that formed on the rutile (110) surface [3], while the hydroxyl coverage on the Ring phase is significantly lower. On the defect free rutile (110) surface, nearly all hydroxyl groups are gone at 300 K. In contrast, the hydroxyls on the 2x2 and Star phases persists up to 500-600 K, that is, a temperature regime typically associated with recombination at defect sites. The Ring phase interacts weakly with water with little dissociation. The amount of dissociated water corresponds to an active site density of about 7%. The correlation between the water adsorption and dissociation behavior and the structural properties of the TiOx phases will be discussed.
[1] U. Diebold, Surf. Sci. Reports 48, 53 (2003).
[2] A. Vittadini, M. Casarin, A. Selloni, The Journal of Physical Chemistry C 113 (44), 18973–18977 (2009).
[3] L. E. Walle, A. Borg, P. Uvdal, A. Sandell, Phys. Rev. B 80, 235436 (2009).