COVERAGE-DEPENDENT ELECTRONIC-STRUCTURE OF NA ON CU(111)

The electronic states of Na on Cu(111) have been studied by high-resol ution two-photon photoemission. Image states which are well separated from alkali states are observed at all coverages. An abrupt change of the occupancy of the alkali state is observed at coverages between 0.4 0 and 0.45 ML. We interpret this as the transition from a more ionic b onding of alkali atoms on the surface to the metallic bond in alkali i slands. Other alkali metals on close-packed surfaces show a very simil ar electronic structure as a function of alkali coverage.