ADSORBATE-INDUCED RECONSTRUCTION OF SURFACES - AN ATOMISTIC ALTERNATIVE TO MICROSCOPIC FACETING

There is increasing evidence that there exists a class of adsorbate-induced reconstructions of metal surfaces in which the outermost substrate layer (or layers) and the adsorbed species adopt an almost identical geometry on surfaces of several different orientations of the same substrate; on one orientation this involves little or no substrate distortion, but on the others, major reconstruction is required. There is also evidence that the adsorption structure on the unreconstructed orientation surface may have a particularly low surface free energy. This type of reconstruction therefore appears to offer an atomistic alternative to the more microscopic phenomenon of adsorbate-induced faceting. By reviewing the existing structural information concerning the adsorbate structures of S on Ni, Cu and Pt, C and N on Ni and Cu and O on Cu, the evidence for this idea, and for some complementary patterns of adsorbate-induced reconstruction, are discussed. These data on the long-range-ordered phases on the (100), (111) and (110) faces of these materials are compared with the limited data available on the influence of the adsorbates on the anisotropy of the surface free energy, or gamma-plot.