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HL: Halbleiterphysik
HL 50: Nanodr
ähte
HL 50.9: Vortrag
Dienstag, 8. März 2005, 12:45–13:00, TU P-N201
Switching between one and two dimensions: conductivity of Pb–induced chain structures on Si(557) — •C. Tegenkamp, Z. Kallasy, H.-L. Günter, V. Zielasek, and H. Pfnür — Institut für Festkörperphysik, Abteilung Oberflächen, Appelstr. 2, 30167 Hannover, Germany
The conductivity of epitaxially grown Pb–structures on Si(557) has been measured. Different characteristic transport mechanisms have been found: For coverages above the percolation limit(0.6ML) up to 3ML the electronic transport in the annealed Pb–films is activated. Furthermore, the uniaxial symmetry of the Si(557) surface is reflected directly in a higher conductance in the parallel direction compared to the direction perpendicular to the steps. For coverages higher than 3ML a metallic behavior is found for both directions, i.e. the conductance decreases with increasing temperature. In contrast, already one ML, but annealed to 640K, leads to the formation of atomic wires, as seen by STM, with an extremely high and quasi one–dimensional surface state conductance along the wire direction. At a critical temperature of Tc=78K, the system switches from low to high conductance anisotropy, with a metal–insulator transition in the direction perpendicular to the chain structure, while in the direction along the chains conductance with a (1/T + const.) temperature dependence was found. STM has shown further, that the 1D/2D transition is associated with an order–disorder phase transition of a 10- fold superperiodicity along the Pb chains.