INTERACTION OF OXYGEN WITH A CS-MONOLAYER-COVERED SI(100) SURFACE

Oxygen adsorption on a Cs-monolayer-covered Si(100) surface has been s tudied by Li- ion spectroscopy and normally emitted secondary electron emission (SEE) spectroscopy. It is clearly shown that the oxygen lies above and below the Cs atoms, respectively, at low and high O exposur es, disproving the dipole model for the work function change. The init ial O adsorption induces a shoulder at the low-energy edge of the SEE spectra, indicating the existence of patches of a lower work function on the surface. The patches are explained as due to the CsO complexes formed by nonadiabatic chemisorption.