FORMATION OF STABLE, 2-DIMENSIONAL ALLOY-SURFACE PHASES - SN ON CU(111), NI(111), AND PT(111)

Results are summarized of ion-scattering analysis of the surface structure obtained following deposition and annealing of ultrathin layers of Sn on Cu(111), Ni(111), and Pt(111). It is found that on each substrate, annealing to about 0.4 of the substrate melting temperature gives rise to a stable structure characterized by a p(square-root 3 X square-root 3)-R 30-degrees low-energy electron diffraction pattern and 1/3 monolayer coverage. The surfaces are isostructural and correspond to rippled surface alloy which is a single layer thick. The measured rippling, in which Sn atoms protrude outward from neighboring substrate atoms, is found to be linearly related to the substrate lattice constant suggesting that rippling provides lateral strain relief within the layer. Issues of the depth distribution, the thermal stability, the preferential formation of the p(square-root 3 X square-root 3)-R 30-degrees ordering, and the measured rippling are discussed in light of the ion-scattering results and theoretical studies of surface alloys.