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Abstract:
Two new optical imaging methods with submonolayer surface sensitivity are applied together to investigate pattern formation of adsorbate concentrations on surfaces during heterogeneously catalysed reactions. Ellipso-microscopy for surface imaging (EMSI) is based on an ellipsometric effect, reflection anisotropy microscopy (RAM) on the polarising properties of surface anisotropies. For the CO oxidation reaction on a Pt(110) surface features like front propagation, target patterns and spiral waves are observed, similar as in prior investigations by photoemission electron microscopy (PEEM). By applying EMSI and RAM simultaneously and imaging the same spot of the surface, supplementary information is gained on the properties of the reaction diffusion fronts. When observing a reaction front by EMSI and RAM at temperatures between 330 and 420 K the image of the front in RAM trails behind its image in EMSI. EMSI seems to display changes in the coverage of adsorbates while RAM relates to variations in surface structure.
