AGGREGATES OF CHEMISORBED COPPER ON THE (110) AND (100) SURFACES OF TUNGSTEN - ELECTRONIC-STRUCTURE

In a certain range of temperature and coverage, copper atoms chemisorb ed on low-index facets of a thermally annealed tungsten field emitter aggregate to form stable islands surrounded by regions of extremely lo w adsorbate density, yielding a spatially inhomogeneous overlayer. Spa tially resolved field emission and photofield emission measurements of the surface density of electronic states have been carried out for co pper aggregates on the (110) and (100) facets. Features detected in th e surface density of states near the centre of an aggregate yield clue s to its structure. On the (110) facet, the measurements reveal striki ng differences between the surface density of states near the edge of an aggregate and that near the centre. It is argued that the adsorbate configuration in the region between the aggregates might approximate single-atom adsorption.