ENERGY-RESOLVED FIELD-ION SPECTROSCOPY OF SURFACE-REACTIONS - H-2 O-2AND H-2/H2O ON PLATINUM/

Applications of field ion mass and appearance energy spectroscopy on c atalytic surface reactions are reviewed. The investigations have been stimulated by in-situ FIM observations in the group of the late J.H. B lock suggesting that single, active sites can be visualized. We have e specially examined the energetics and kinetics of H-2-O-2 and H-2-H2O reactions on [001] oriented Pt-tips. For single surface sites field io n yields have been measured as a function of H-2 partial pressure show ing (different) hysteresis behavior for both reaction systems. For H-2 /O-2/Pt the results agree qualitatively with features earlier observed at field-free conditions. This finding and the different kinetics of the two reaction systems suggest a less pronounced influence of the ap plied electric field on the surface catalyzed H2O formation for H-2/O- 2/Pt. At distinct control parameter (pressures, temperature) dynamic p henomena, such as kinetic instabilities and oscillating reaction diffu sion fronts, were characterized by probe hole FIM combined with FIMS a nd FIAPS. For H-2/O-2/Pt comparative measurements have recently reveal ed a different behavior in FIM and FEM modes possibly caused by the di fferent facets contributing to FI and FE emission currents.