Dresden 2006 – wissenschaftliches Programm

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O: Oberflächenphysik

O 14: Poster session I (Adsorption, Epitaxy and growth, Phase transitions, Surface reactions, Organic films, Electronic structure, Methods) (sponsored by Omicron Nanotechnology GmbH)

O 14.37: Poster

Montag, 27. März 2006, 18:00–21:00, P2

CO oxidation on Ir(111) surfaces: consequences of anisotropic diffusion and noise — •Stefan Wehner1, Patrick Hoffmann2, Dieter Schmeisser2, Helmut R. Brand3, and Jürgen Küppers1,41Experimentalphysik III, Universität Bayreuth, 95440 Bayreuth, Germany — 2Angewandte Physik II, Brandenburgische Technische Universität Cottbus, 03013 Cottbus, Germany — 3Theoretische Physik III, Universität Bayreuth, 95440 Bayreuth, Germany — 4Max-Planck-Institut für Plasmaphysik (EURATOM Association), 85748 Garching, Germany

The CO oxidation reaction on Iridium(111) surfaces shows bistability in a limited range of the CO fraction of the reactant gas flux Y and a wide range of temperatures T. The two branches are characterized by their reactivity for CO2 formation. The upper rate (high CO2 formation) rate is related to high oxygen coverage on the surface, the lower rate (little CO2 formation) to high CO coverage.

Quadrupol mass spectroscopy and PEEM (photoelectron emission microscopy) was employed to study the influence of a noisy reactant gas flux composition on the spatio-temporal pattern development in the CO oxidation reaction on flat Ir(111) and stepped Ir(977) surfaces. PEEM shows nucleation and growth of few oxygen resp. CO islands at small noise amplitudes. Anisotropic diffusion of CO parallel and normal to the steps causes elliptic shapes of large islands. The long axes of the ellipses are aligned along the steps. At increased noise amplitudes the density of islands becomes larger.

2D modeling of the phenomena based on reaction-diffusion differential equations reproduces the experimental findings quite nicely.

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