The initial decrease of the work function caused by the oxygen adsorption o
n a Cs-monolayer-covered Si(100) is explained on the basis of the dipole th
eory. It is shown that the negative oxygen ions sitting on the cesium overl
ayer induce the extra polarization of Cs+ ions, which results in the reduct
ion of the system work function. (C) 1999 Elsevier Science B.V. All rights
reserved.