LOCAL ELECTROSTATIC POTENTIAL DETERMINATION OF CS CU(111) SURFACES BYNEGATIVE-ION SPECTROSCOPY/

The local electrostatic potential change of Cs-covered Cu(111) as a fu nction of Cs coverage has been studied with negative ion spectroscopy produced by low-energy Li+ ion impact. The results indicate that at lo w coverages, the valence electron of Cs is transferred to the substrat e, while a considerable occupancy of the alkali slate occurs at a cove rage greater than or equal to 0.35 ML. With higher coverages, the surf ace shows a laterally uniform electrostatic potential. The results dem onstrate that site-specific negative ion spectroscopy can provide dire ct information on atomic-scale changes in the surface electrostatic po tential.