Dresden 2009 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 3: Focus Session: Interactions of Molecules with Dielectric Surfaces

DF 3.6: Topical Talk

Monday, March 23, 2009, 16:40–17:00, WIL A317

Determination of Molecule Orientation on Oxide Surfaces by Near-Edge X-ray Absorption Spectroscopy — •Alexei Nefedov, Mikhail Naboka, and Christof Wöll — Ruhr Universität Bochum, Germany

Recently, the formation of molecular networks on metals has attracted considerable attention [1]. When replacing the supporting metals by their oxides the situation becomes more complex because the interaction with the ionic centers on the substrate will compete with the molecule-molecule interaction. Since most techniques employed to study adsorption on metals are difficult to apply to oxides because of the insulating nature of these substrates only few works focusing on such systems have been reported so far. Recently, Tekiel et al. [2] studied the adsorption of TPA on TiO₂(110) and an upright orientation was reported, which is incompatible with the formation of a two-dimensional network. We have carried out a systematic investigation on the orientation of the TPA-molecules on a rutile TiO₂(110) substrate using near-edge x-ray absorption spectroscopy. We have investigated a series of coverages, extending from a few percent of monolayer to saturation corresponding to 1 ML. We find a planar adsorption geometry of TPA molecules up to ∼ 0.3 ML, while when saturation coverage is reached the TPA molecules are adsorbed in an upright position. The latter adsorption geometry implies that one of the carboxyl groups binds to the surface as a bidentate carboxylate.

[1] S. Stepanow et al, J. Phys. Chem. B. 108, 19392, (2004).

[2] A. Tekiel et al, J. Phys. Chem. C, 112, 12606, (2008).