Spillover of oxygen adatoms from Ir to Au on an Ir/Au{111} bimetallic surface

We have used Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) to investigate oxygen adsorption on an Ir/Au{111} bimetallic surface. Chemisorbed oxygen stabilises Ir above the Au substrate, when it would otherwise dissolve sub-surface. At sufficient temperature, however, Au can nevertheless replace Ir in the outermost layer(s) in the presence of oxygen. Atomic oxygen is then found to be chemisorbed on both Ir and Au regions of the outermost layer, giving rise to co-existence of Ir{111}-(2 × 1)-O and Au{111}-(√3 × √3)R30°-O LEED patterns. Since dissociative O2 adsorption does not occur directly on Au{111} at low pressures, we conclude that a spillover process occurs, involving O2 molecules dissociating on the Ir sites and migrating to adjoining Au sites.