The interaction of oxygen with a clean Ni(100) surface at room temperature has been studied using the static mode of secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). The O- yield as a function of coverage shows a fast adsorption at low coverage followed by a slow oxygen uptake between ∼1 and 8 L due to the low sticking coefficient of oxygen in this region. Before the O- intensity reaches its maximum at ∼300 L, a second plateau between ∼40 L and 50 L appears.The p(2 × 2) and c(2 × 2) LEED structures can be associated with the two plateau regions. At saturation two states of oxygen are apparent since XPS spectra show a doublet O 1s structure with peaks at 529.7 and 531.3 eV (peak height ratio of 3) which are correlated with NiO and Ni2O3, "defect oxide", respectively. The Ni 2p 3 2 line with a binding energy of 852.8 eV is not altered by the adsorbed oxygen species, but strong changes are observed due to the formation of the NiO layer. Beside O- ions, the following secondary ions have been detected and investigated with SIMS: O2-, O+, O2+, Ni+, Ni2+, Ni3+, NiO-, NiO2-, Ni2O3-, NiO+, and Ni2O+. The dependence of Ni2+, and Ni3+, on the oxidation process yields evidence for the importance of the local atomic environment of the surface Ni atoms on the formation of these ions. Relatively high O2-, yields at low oxygen coverage suggest that O atoms do not migrate far from each other after chemisorption. NiO2-, and Ni2O+, are enhanced relative to NiO-, and NiO+, in the region when c(2 × 2) is formed. Ni2O3-, may be associated with the Ni2O3 defect oxide. Comparison of results to recent calculations of secondary particle emission supports both close proximity requirements and formation of the molecular clusters by formation above the surface plane.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Materials Chemistry