Photoemission of Cs Valence Electrons from a Cs Monolayer on Si(111) 2×1

Abstract
The adsorption of Cs atoms on the Si(111) 2×1 surface has been studied by photoelectron spectroscopy using synchrotron radiation. A photoemission peak due to Cs 6s valence electrons is clearly observed at full monolayer coverage by tuning photon energy at around 50 eV over an available energy range from 30 to 130 eV. The peak appears at almost the same initial energy (-1 eV) as that of the surface state of the clean Si(111) 2×1 surface. It is shown that the insulator-metal transition in the Cs monolayer takes place with increasing coverage.