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O: Fachverband Oberflächenphysik

O 42: Poster Session II (Nanostructures at surfaces: arrays; Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: Other; Nanostructures at surfaces: Wires, tubes; Metal substrates: Adsorption of O and/or H; Metal substrates: Clean surfaces; Metal substrates: Adsorption of organic/bio moledules; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsorption of inorganic molecules; Metal substrates: Epitaxy and growth; Heterogeneous catalysis; Surface chemical reactions; Ab-initio approaches to excitations in condensed matter; Organic, polymeric, biomolecular films– also with adsorbates; Particles and clusters)

O 42.96: Poster

Mittwoch, 25. März 2009, 17:45–20:30, P2

The interaction of HCOOH with oxygen-terminated ZnO(000-1) — •Hengshan Qiu, Yuemin Wang, and Christof Wöll — Physical Chemistry I, Ruhr-University Bochum, 44780 Bochum, Germany

Zinc oxide is one of the most important metal oxide due to its electrical, optical and catalytical properties as well as potential applications [1]. The clean, adsorbate-frei polar O-terminated ZnO(000-1) surface is electrostatically unstable due to uncompensated surface charges and adopts a (1x3) structure with an abundance of oxygen vacancies [1]. It has been proposed that these vacancy sites exhibit high catalytic activity toward methanol synthesis and formate species could be one of the important intermediates in this process. In this work, the interaction of HCOOH with O-ZnO(000-1) has been studied by high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). Exposing ZnO(000-1) surface to HCOOH at 100 K leads to the formation of physisorbed multilayers, chemisorbed monolayer and bidentate formate species. The latter can only be formed at oxygen vacancies through a dissociative adsorption of HCOOH with the ionized H diffusing into the bulk. Heating the sample to higher temperatures induces a thermally activated conversion from the bidentate to a monodentate formate species. At 550 K further decomposition occurs releasing CO, CO2 and H2. In addition, an adsorbate-induced Zn desorption was also observed along with the formate dissociation. [1] Ch. Wöll, Prog. Surf. Sci. 82 (2007) 55.