The interaction of alkali atoms with oxygen on W(110) as studied by UPS and metastable impact electron spectroscopy: II. K and Cs

Abstract

UPS and metastable impact electron spectroscopy (MIES) were employed to study the interaction between oxygen and K (Cs) in the coverage range up to one monolayer on W(110) (in units of the first complete adlayer at room temperature) at room temperature. For small alkali coverages below 0.5 ML the oxygen molecules are dissociated at the reactive W(110) surface and adsorbed atomically on two different adsorption sites for all oxygen exposures. In the coverage range between 0.6 and 1 ML efficient charge transfer from the alkali s Orbitals to the impinging oxygen takes place as long as the s orbital is filled. Molecules are then incorporated into the alkali adlayer as O q− 2 ( q ⩽ 1) ions. Beyond the work function minimum (induced by the oxygen coadsorption) most of the adsorbed oxygen is dissociated; the oxygen atoms are then bound at the same two adsorption sites as for the oxidation below 0.5 ML alkali precoverage. The results are compared with previous results for the oxygenation of Li and Na layers on W(110) and for the oxidation of Cs films. A coadsorption diagram is constructed which allows the prediction of the oxidation stage of the surface as a function of the exposures to K (Cs) and oxygen.