Structure determination of Ag(111)(root 3X root 3)R30 degrees-Sb by low-energy electron diffraction

A quantitative structure determination of the Ag(111)(root 3 x root 3)R30 d egrees-Sb surface has been performed using low energy electron diffraction. Six possible structural models were tested: Sb overlayers with four differ ent adsorption sites and a substitutional alloy surface layer, with or with out a stacking fault relative to the underlying substrate. The results clea rly favor the faulted alloy surface model with all outermost layer Sb and A g atoms occupying hcp hollow sites, in agreement with a recent x-ray diffra ction study of this surface phase and both x-ray diffraction and medium ene rgy ion scattering studies of the related Cu(111)(root 3 x root 3)R30 degre es-Sb surface.