Atomic structure of the SbCu surface alloy: a surface X-ray diffraction study

The dissolution at 400 deg C of an antimony layer deposited at room temperature on a Cu(111) substrate leads to a surface alloy with a p(root 3xroot 3)R 30 deg superstructure and a Sb composition of 1/3.We present here a structural study of this Sb-Cu compound by surface X-ray diffraction (SXRD). The best agreement is obtained for a Cu sub 2 Sb surface layer with Sb atoms substituting 1/3 of the Cu atoms, over an essentially unperturbed Cu(111) plane. The largest relaxation is undergone by the Sb atoms which rise by 0.32 plus/minus 0.02 A over the mean plane of its Cu neighbours. No substantial in-plane relaxations were observed.