Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 62: Surface chemical reactions II

O 62.2: Vortrag

Freitag, 27. März 2009, 11:30–11:45, SCH A01

Structure Formation in Ultrathin V-Oxide films on Rh(111) under different Reaction Conditions — •Florian Lovis, Martin Hesse, and Ronald Imbihl — Institut für Physikalische Chemie und Elektrochemie, Leibniz-Universität Hannover, Callinstr.3-3a, D-30167 Hannover, Germany

As a model system for vanadium-oxide based catalysts we prepared ultrathin vanadium oxide films on a Rh(111) surface. At 400°C 0.1 and 0.25 ML of vanadium were evaporated in oxygen with p(O2)=2x10-7 mbar. After characterization with LEED and Auger electron spectroscopy the films were subjected to the O2 + H2 reaction using photoemission electron microscopy (PEEM). After evaporation a large variety of differently ordered Rh(111)/V/O phases were identified in LEED. The O2 + H2 reaction was studied in the 10-8 to 10-5 mbar range at temperatures between 400 and 500°C. With PEEM we observe that under reaction conditions the film is no longer homogeneous but reaction fronts and stationary Turing-like patterns develop. In the evaporated V-film we find partially ordered patterns consisting of large islands of about 0,05 mm diameter. These islands are very stable and change only very slowly after turning off the gases. Under different reaction conditions we find small islands of roughly 0,02 mm diameter which in contrast to the large islands are quite dynamic and vary in diameter depending on the reaction conditions. The patterns induced by the reaction are discussed in the context of the concept of reactive phase separation. It is suspected that the attraction between oxygen and vanadium is the driving force for the condensation process.