POSITRON STATES ON THE CS/CU(100) SURFACE

The attenuation of the Cu M2,3VV Auger peak with Cs coverage on Cu(100) was measured using positron-annihilation-induced Auger electron spectroscopy (PAES) and conventional (electron-induced) Auger electron spectroscopy. The data (obtained at both 303 and 163 K) indicate that below a critical coverage (approximately 0.7 monolayer) the positrons are trapped at the Cu/Cs interface in agreement with theoretical calculations. We observe a sharp (less than 0.02 monolayer wide) drop in the normalized PAES intensity at the critical coverage indicating a transition to another positron state in which the positrons are localized on the vacuum side of the Cs overlayer.