Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 93: Surface Chemical Reactions

O 93.2: Vortrag

Freitag, 29. Februar 2008, 10:30–10:45, MA 043

Structure and Composition of the TiO₂(110) Surface: From UHV to Realistic Reaction Conditions — •Piotr Kowalski, Bernd Meyer, and Dominik Marx — Lehrstuhl fuer Theoretische Chemie, Ruhr-Universitaet, D-44780 Bochum, Germany

Using DFT-based ab-initio calculations in combination with a thermodynamic formalism we have calculated the relative stability of various structural models of the nonpolar, mixed-terminated TiO₂(110) surface in contact with a surrounding gas phase at finite temperature and pressure. Adsorption and desorption of hydrogen atoms and water molecules, as well as the formation of O vacancies were considered. Assuming thermodynamic equilibrium between the TiO₂ surface and an oxygen, hydrogen and water containing atmosphere, we constructed a phase diagram of the lowest free energy surface structures.

For a wide range of temperatures and pressures we find that water will be adsorbed at the surface. At full monolayer coverage, a molecular adsorption of water is preferential. The most stable adsorption site for hydrogen atoms is on-top of the bridging O atoms. Surprisingly, we find that in thermodynamic equilibrium the bridging O atoms can not be fully saturated which hydrogen, but only a maximum coverage of about 0.6 monolayer can be reached. The formation energy for O vacancies is found to be rather high so that O defects should only form at extreme oxygen poor conditions.