Coadsorption of electropositive and electronegative elements: II. Cs and O2 on W (100)

The coadsorption of Cs and O₂ on W (100) surface has been studied systematically. The results were analogous to those of the CsH₂ system. Independent of the sequence of deposition, the adsorbates formed a double layer with the oxygen underneath the Cs layer. The presence of Cs caused a transformation of a(4 × 1) structure of O₂ to a c (2 × 2) structure. Cesium also caused submerged oxygen atoms in the crystal to diffuse to the surface. The initially adsorbed O₂ enabled an increase in saturation coverage of Cs. This effect was more drastic in the O₂ case than that found with preadsorbed hydrogen. The presence of oxygen caused an increase in the work function at the saturation coverage of the subsequently adsorbed Cs, and a shift of the Cs coverage at the work function minimum to lower values. But both of these changes were small compared to those found for the Cs + H₂ system. The sticking coefficient of O₂ on Cs covered W (100) was higher than that for O₂ on clean W. This was attributed to an active chemisorption of O₂ on the Cs film and a place exchange mechanism.