DYNAMIC STUDIES OF SURFACE-REACTIONS WITH MICROSCOPIC TECHNIQUES

Work function changes which are combined with surface processes can be investigated and used to characterize adsorption states during heterogeneous catalytic reactions. The oscillatory behaviour of the CO-oxidation was studied on palladium and platinum single crystal surfaces as well as on platinum field emitter tips. On macroscopic crystals the reaction was simultaneously characterized by mass spectrometric analysis and by work function measurements via a Kelvin probe with an area of almost-equal-to 30 mm2 being probed. In a second series of experiments photoelectron emission microscopy (PEEM) was applied to follow surface processes with a spatial resolution of almost-equal-to 1 mum. Finally, Pt surfaces were investigated with a lateral resolution of almost-equal-to 20 angstrom by using field emission microscopy (FEM). Gas phase coupling of oscillations as demonstrated by the simultaneous oscillations of two separated macroscopic crystals, was missing at small areas of a field emitter. The PEEM registers local oscillations under conditions where the Kelvin probe fails to register dynamic processes. FEM-data showed that critical radii for nucleation could be as small as few angstrom.