Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 55: Poster Session III - MA 141/144 (Methods: Atomic and Electronic Structure; Particles and Clusters; Heterogeneous Catalysis; Semiconductor Substrates: Epitaxy and Growth+Adsorption+Clean Surfaces+Solid-Liquid Interfaces; Oxides and Insulators: Solid-Liquid Interfaces+Epitaxy and Growth; Phase Transitions; Metal Substrates: Adsorption of Inorganic Molecules+Epitaxy and Growth; Surface Chemical Reactions; Bimetallic Nanosystems: Tuning Physical and Chemical Properties; Oxides and insulators: Adsorption; Organic, polymeric, biomolecular films; etc.)
O 55.45: Poster
Mittwoch, 27. Februar 2008, 18:30–19:30, Poster F
Water adsorption on stepped and flat Pt(111) surfaces – combined TDS and STM measurements — •Alexander Picolin1, Alex Redinger1, Carsten Busse1, Markus Morgenstern2, and Thomas Michely1 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2II. Physikalisches Institut B, RWTH Aachen, Germany
An extensive insight into the water-metal-bonds and a deeper understanding of corrosion and catalytic reactions require knowledge about the behaviour of water molecules on metallic surfaces. Therefore, adsorption mechanism, resulting phases, and preferred bonds of the ice double layer on Pt(111) are investigated with thermal desorption spectroscopy (TDS) and scanning tunneling microscopy (STM).
After adsorption of water at 120 K on a flat Pt(111) surface, TDS measurements only show the well-known multilayer (at 150-160 K) and monolayer desorption peaks (∼168 K). When the sample is prepared by 5 keV Ar+ ions (fluence 1017 ions/cm2) under grazing incidence (83∘ against surface normal) a rippled morphology with a high step density (∼5% of adsorption sites) results. Subsequent TDS on this surface shows a shift in temperature of the monolayer peak as well as two further desorption peaks at 180 K and 195 K. These two additional peaks are absent, if a small amount of CO is adsorbed at 400 K prior to H2O adsorption. As CO binds preferentially to steps, the two additional H2O desorption peaks from the clean surface are attributed to molecules bound to {100} and {111}-microfacetted steps. Binding energies and the order of desorption for step edges are determined. The preference of step edge occupation is also observed in STM images.