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Abstract

The photoemission electron microscope (PEEM), invented more than 60 years ago, began being utilized for imaging surface reactions less than 10 years ago to make observations of pattern formation during heterogeneous catalytic CO-oxidation on platinum. First investigations of adsorption and reaction of oxygen on a previously CO-covered Pt surface are discussed, showing the growth of isolated oxygen islands (O-islands) up to millimeter sizes. Features like plane wave-front propagation and a “memory effect” of islands have been observed. Next pattern formation during CO-oxidation on a Pt(110) surface is studied, where both of the reactants are supplied from the gas phase. By creating boundaries on the surface utilizing microlithography single spiral waves can be isolated. Here experiments with reactive boundaries of Pd are shown, where in addition to observations of common pattern formation with CO and oxygen on top of the surface, subsurface oxygen areas become an important feature. The latter also plays a dominant role for the oscillation cycles within a circular Pt(110) domain.