Structure Study of Oxygen-Adsorbed Ni(111) Surface by High Energy Ion Scattering

摘要

Surface atomic structures of clean, oxygen-adsorbed, and oxidized (111) nickel have been studied quantitatively by using MeV ion scattering in combination with AES and MEED. We show that; the clean (111) nickel surface has the bulk-like structure with reconstruction or relaxation less than 0.02 A, the surface thermal vibration amplitude is enhanced by approx. 20% compared to the bulk value, adsorbed oxygen results in surface lattice expansion by approx. 0.15 A which is closely correlated to the p(2x2) or (sq root 3 times sq root 3)R30 degrees superstructure, and oxidation at room temperature saturates at a stage which incorporates approx 3 monolayers of nickel in a stoichiometric amorphous film of NiO whereas at temperatures higher than approx. 200C thicker oxide films are produced. Our study indicates that each oxygen atom adsorbed on the Ni(111) surface interacts with and relaxes three nearest neighbor nickel atoms, and after saturation of the relaxation, oxidation of three monolayers takes place abruptly after which the oxide layer on the surface apparently blocks further reaction.