Time-evolution of oxidation states at the Ni(111) surface: O2 incident translational energy dependence

Abstract

Metallic Ni is expected to be a substitution candidate for Pt and Pd in catalytic materials. Generally speaking, catalytic reactions take place on a metal oxide layer. In this study, therefore, the oxidation states of the Ni(111) surface, which were made by irradiation with a supersonic O2 molecular beam, were analyzed by soft x-ray photoemission spectroscopy with synchrotron radiation. The oxygen uptake curve and initial sticking rate were found to show remarkably strong dependence on the O2 incident energy for energies of up to 2.3 eV. The intermediate plateau seen in the oxygen uptake curve for low incident energies was found to disappear with increasing incident energy due to a change of the dissociative adsorption mechanism from a two-dimensional island growth model to a direct activated adsorption model. Due to this activated adsorption, the formation rate of NiO and peroxide nickel increased as compared to backfilling oxidation by O2 gas.