EVIDENCE OF CHARGE-TRANSFER FROM NA ADATOMS TO THE CS SUBSTRATE - A COLLISIONALLY EXCITED AUTOIONIZATION ELECTRON-EMISSION STUDY

Na adsorption on a bulk Cs substrate at 20 K has been studied with col lisionally excited autoionization electron spectroscopy using 1 keV Ne + ion impact. Our results show a slight decrease in the surface work f unction and a quite small Ne 2p(4)3s(2) D-1-to-P-3 conversion rate at very low coverages, suggesting that, in contrast to the expectation ba sed on the electronegativity consideration, a partial charge transfer occurs from Na adatoms to the more electropositive Cs substrate. We at tribute this to the shift and broadening of the valence level of Na ad atoms to overlap with the substrate conduction band.