COMPARATIVE-STUDIES ON FIELD-IONIZATION AT SURFACE SITES OF RH, AG AND AU - DIFFERENCES IN LOCAL ELECTRIC-FIELD ENHANCEMENT

Field ion imaging conditions were studied for clean Rh, and for Rh epi taxially covered with Ag and Au, respectively. Significant, metal-spec ific decreases of the image voltages have been observed. This is cause d by different enhancements of local fields in the vicinity of protrud ing Rh, Ag and Au atoms due to their different electronic structures. The interpretation is based on self-consistent calculations of local e lectrostatic field distributions in the vicinity of single atoms adsor bed on a metal surface. For different facets of a surface, a close cor relation between local field distributions and the degree of localizat ion of the field ionization process is established from the measured f ull width at half maximum (FWHM) of field ion energy distributions and is discussed in association with possible field ionization mechanisms .