Methods and Applications of UV Photoelectron Microscopy in Heterogeneous Catalysis

Abstract

A newly designed photoemission electron microscope (PEEM), based on electrostatic electron optics and fully compatible with UHV conditions, has been applied for the investigation of spatio-temporal pattern evolution associated with the oscillatory catalytic CO oxidation on platinum single crystal surfaces. The design of the instrument will be described by W. Engel in detail. The oscillations can be understood on the basis of an adsorbate induced (CO) structural change of the surface, which modulates the catalytic activity via the sticking coeffizient of O2. The mentioned spatio-temporal pattern evolution during CO-oxidation on Pt (100) has been previously observed by scannig photoemission microscopy (SPM), but time resolution was in this case restricted to about 1 min. Work function differences of about 0.3 eV between the oxygen and the CO covered Pt (110) surface give rise to the sufficent contrast of the images taken by the SPM as well as by the PEEM. The new instrument allows real time observation, storing the images by a video system still enables 20 ms time resolution. Imaging of the much faster reactions of CO and O2 with a Pt (110) surface has therefore become possible. For the first time “live” pictures of the spatial patterns on the (110) surface during these fast oscillations (period ˜ 1 s), including period doubling and transitions to chaotic behavior, have been observed.