Atomic and electronic structure of a surface alloy - comparison with the bulk alloy

A low-energy electron diffraction intensity analysis of the c(2 × 2) structure formed by 1 2 monolayer of Au on a clean Cu {0 0 1} surface reveals a single mixed-layer structure which can be properly called an ordered surface alloy. The layer is buckled, with the Au atoms located 0.1 A outwards from the Cu atoms and the distance between the latter and the second (all Cu) layer expanded by 4.2% with respect to the bulk. This structure of the surface alloy is the same, except for the smaller lattice constant, as that of the first two layers of a {0 0 1} surface of Cu3Au. The third atomic layer is shown to have no ordered Au content. Photoemission experiments with synchrotron light show that the d band of the surface alloy is noticeably narrower than the d band of the bulk-plus-surface Cu3Au alloy. © 1987.