Direct evidence of the occupied valence states for adsorbed Cs atoms on the Si(111) surface

Metastable deexcitation spectroscopy (MDS) has been applied to detect occupied valence-band features for Cs atoms adsorbed on a Si(111) surface. The MDS spectrum exhibited a clear peak structure of the Cs 6s-derived level near the saturation coverage, which is contrary to the concept of full ionization of adsorbed alkali-metal atoms. Direct evidence of the valence-band charge redistribution as a function of Cs coverage is presented.