Adsorption of antimony on Au(001).

Abstract

Antimony overlayers on a clean Au(001) surface were prepared by surface segregation on a sputtered and annealed, Sb-doped gold single crystal. Valence-band photoemission data, taken with photon energies between 35 and 150 eV, exhibit a Sb 5p contribution at the Fermi energy at the higher photon energies. Core-level photoemission data yield surface-atom shifts for the Au 4f core electrons of +0.44 and +0.90 eV, opposite in sign to that of the clean Au surface, and suggestive of loss of charge from the Au surface layer. Sb 4d core-level spectra have the asymmetric line shape associated with metallic screening with a many-body singularity index of 0.08. This value is significantly larger than that of bulk gold, and suggests screening by electrons in Sb-derived states at the Fermi level. All aspects of these measurements indicate that the Sb is strongly chemisorbed and probably forms an ordered surface alloy. The reconstruction of the Sb-covered surface was investigated by low-energy electron diffraction, and showed a compressed hexagonal layer with 4\ifmmode\times\else\texttimes\fi{}22 periodicity, which fits a modified (111) double layer of ${\mathrm{AuSb}}_{2}$ with a small number of additional reconstructed Au atoms.