Relaxation of Ni(111) Surface by Oxygen Adsorption

Abstract

We have shown by displacement-sensitive high-energy ${\mathrm{He}}^{+}$-ion scattering that the clean Ni (111) surface has a bulklike structure with \ensuremath{\sim}20% enhancement of surface thermal vibration, and that the $p(2\ifmmode\times\else\texttimes\fi{}2)$ and $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ superstructures on the oxygen-adsorbed surface are accompanied by expansion of the first nickel layer by \ensuremath{\sim}0.15 \AA{}. In addition, the absolute oxygen coverages for these two superstructures and at saturation were measured to be \ensuremath{\sim}\textonequarter{}, $\ensuremath{\sim}\frac{1}{3}$, and \ensuremath{\sim}3 monolayers, respectively.