Coadsorption of cesium and oxygen on Ni(100): II. Cesium enhanced chemisorption and oxidation

The effects of adsorbed Cs atoms on the chemisorption and oxidation of Ni(100) surfaces have been studied with low energy electron diffraction and work function measurements. In addition to the c(2×2) structure of O on clean Ni(100), the preadsorption of Cs caused the formation of a (3×3) and a c(4×2) structure. The experimental results suggest that these new structures were due to ordered arrays of chemisorbed O atoms underneath the Cs layer, with O densities higher than that of c(2×2). It is found that a Cs overlayer increased drastically the rate of O chemisorption and NiO formation. Depending on the initial Cs coverage, the NiO formed in the (100) and (111) crystallographic rientations. During the enhanced oxidation the Cs layer remained on top of the oxide.