Coadsorption of cesium and oxygen on Ni(100): I. Cesium probing of NiO bonding

Low energy electron diffraction (LEED) and work function measurements have been used to study the interaction of Cs and O on (100) surfaces of Ni. Deposition of Cs on oxygen-chemisorbed Ni(100) changed the structure of the O array. The work function of this surface showed a minimum at 0.14 monolayer of Cs coverage and a maximum at 0.29 monolayer. On the other hand, Cs on oxidized Ni(100) could not change the oxygen arrangement at all, and the work function remained constant after reaching a minimum value. These two types of behavior of Cs can be used to probe the bonding states of O on metal surfaces. Our results suggest that the c(2×2) structure of O on Ni(100) is simple chemisorption rather than reconstruction and that the c(2×2) coexists with regions of disordered NiO on Ni(100). While LEED intensity variations detect primarily the chemisorbed c(2×2), other measurements like work function, ion neutralization and sticking coefficient should detect both kinds of NiO bonding.