Sims and flash filament study of the interaction of polycrystalline nickel with oxygen

Abstract

The interaction of oxygen (exposure up to 100 L) with a polycrystalline nickel surface was observed at 300 K. Four different stages considering the secondary ion emission, depending on the oxygen exposure dose could be distinguished. A comparison between our measurements and corresponding LEED, AES, XPS, Δφ ISS, etc. experiments allowed the assignment of the stages observed in SI emission to states of O 2 adsorption mentioned in literature. Chemisorption of oxygen on Ni could be correlated with a rapid increase of Ni +, Ni 2 +, O − emission, resulting from a strong dipole moment in the initial stage of adsorption. Increasing oxygen exposure results in NiO island growth, that finally leads to the formation of a closed NiO layer. This is indicated by a relatively high emission of NiO specific secondary ions (NiO −, NiO 2 −, e.g.). Furthermore, we were able to detect adsorbed oxygen on top of the NiO layer indicated by characteristic secondary ion emission and flash signals. Further characterization of and transitions between the different stages could be established by heating, ion bombardment and isotope experiments. Finally, we studied the influence of bulk-solved oxygen during oxygen exposure from the gas phase.