Relaxation of Ni(111) Surface by Oxygen Adsorption

We have shown by displacement-sensitive high-energy He⁺-ion scattering that the clean Ni (111) surface has a bulklike structure with {~}20% enhancement of surface thermal vibration, and that the p(2×2) and (√3×√3)R30^∘ superstructures on the oxygen-adsorbed surface are accompanied by expansion of the first nickel layer by {~}0.15 {}. In addition, the absolute oxygen coverages for these two superstructures and at saturation were measured to be {~}{}, ~1/3, and {~}3 monolayers, respectively.