Dresden 2006 – scientific programme

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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

Monday, March 27, 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 Küppers^1,4 — ¹Experimentalphysik 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.