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O: Fachverband Oberflächenphysik
O 42: Poster Session II (Nanostructures at surfaces: arrays; Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: Other; Nanostructures at surfaces: Wires, tubes; Metal substrates: Adsorption of O and/or H; Metal substrates: Clean surfaces; Metal substrates: Adsorption of organic/bio moledules; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsorption of inorganic molecules; Metal substrates: Epitaxy and growth; Heterogeneous catalysis; Surface chemical reactions; Ab-initio approaches to excitations in condensed matter; Organic, polymeric, biomolecular films– also with adsorbates; Particles and clusters)
O 42.30: Poster
Mittwoch, 25. März 2009, 17:45–20:30, P2
Suppression of phase transition by doping: atomic Pb chains on Si(557) — Marcin Czubanowski, •Melani Gauch, Christoph Tegenkamp, and Herbert Pfnür — Leibniz Universität Hannover, Festkörperphysik, Abteilung Oberfächen
The adsorption of Pb on Si(557) substrate leads to the formation of anisotropic metallic structures as reveal by conductivity measurements, SPA-LEED and ARPES. The annealing of at least 1.3ML Pb at 640K forms atomic chain structure within a (223) facet, which shows below Tc=78K a metallic conductance along the wires, whereas the perpendicular direction is insulating. As revealed by ARPES and LEED, the interplay between the filling of the surface bands, determined by the Pb coverage, and the reciprocal lattice vector, defined by the inter-chain spacing, results below Tc in a perfect nesting condition. Due to a temperature driven refaceting transition, the system switches into a 2d regime, where conductivity is seen in both direction. In our recent experiments, the influence of additional Pb atoms on the phase transition at Tc has been investigated by means of SPA-LEED. The electronically stabilized system at 1.3ML has been doped by a small amount of addition Pb (in steps of 0.01ML). The structural phase transition is gradually suppressed as the coverage reaches 1.5ML. As judged from SPA-LEED the excess coverage starts to decorate the steps, obviously changing the filling factors of the surface states.