Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 41: Poster Session I (Semiconductor Substrates: Epitaxy and growth; Semiconductor Substrates: Adsorbtion; Semiconductor Substrates: Solid-liquid interfaces; Semiconductor Substrates: Clean surfaces; Oxides and insulators: Epitaxy and growth; Oxides and insulators: Adsorption; Oxides and insulators: Clean surfaces; Organic, polymeric and biomolecular films - also with adsorbates; Organic electronics and photovoltaics, Surface chemical reactions; Heterogeneous catalysis; Phase transitions; Particles and clusters; Surface dynamics; Surface or interface magnetism; Electron and spin dynamics; Spin-Orbit Interaction at Surfaces; Electronic structure; Nanotribology; Solid/liquid interfaces; Graphene; Others)
O 41.23: Poster
Dienstag, 23. März 2010, 18:30–21:00, Poster B1
Change of adsorption kinetics of CH4 in the presence of O− centers on MgO: a TPD study — •Philipp Giese1, Harald Kirsch1, Christian Frischkorn1,2, and Martin Wolf1,2 — 1Institut für Experimentalphysik, FU Berlin, Arnimallee 14, 14195 Berlin — 2Fritz-Haber-Institut, Abt. Physikalische Chemie, Faradayweg 4-6, 14195 Berlin
In order to obtain a deeper understanding of the interaction between localized holes and adsorbed CH4, its adsorption kinetics are studied on in-situ prepared MgO/Ag(001). Different methods to increase the amount of localized holes or more specifically O− sites on MgO-surfaces were examined. The detection method is temperature programmed desorption (TPD). After running several cycles of photoinduced N2O reduction on MgO, the monolayer of CH4 is slightly more strongly bound (increase of desorption temperature by ∼ 5 K) compared to CH4 adsorbed on untreated MgO. Furthermore, the whole TPD spectrum is broadened and its intensity is smaller. We conclude that the CH4 adsorbate rearranges itself after subsequent reduction of N2O on MgO. This behaviour cannot be induced by direct UV irradiation, so the interaction between a localized hole and CH4 is much less favourable than the recombination of excited electron-hole pairs, in contrast to the activation of the N2O bond in photoinduced N2O reduction. As these localized holes reduce the activation barrier of the C-H abstraction to 0.7 eV, the aforementioned adsorbed state can be interpreted as a precursor in the process of the oxidative coupling of CH4 on oxide surfaces.