Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 18: Poster Session I - MA 141/144 (Atomic Wires; Size-Selected Clusters; Nanostructures; Metal Substrates: Clean Surfaces+Adsorption of Organic / Bio Molecules+Solid-Liquid Interfaces+Adsorption of O and/or H; Surface or Interface Magnetism; Oxides and Insulators: Clean Surfaces)
O 18.4: Poster
Montag, 25. Februar 2008, 18:30–19:30, Poster F
Atomic Nanowires of Self-Organized Pt on Ge(001) -- Structural Elements and Electronic Properties — •Marc Wisniewski1, Jörg Schäfer1, Sebastian Meyer1, Andrei Stekolnikov2, Ralph Claessen1, and Friedhelm Bechstedt2 — 1Physikal. Institut, Universität Würzburg, D-97074 Würzburg — 2Inst. f. Festkörpertheorie u. -optik, Universität Jena, D-07743 Jena
A special class of nanowires is formed by Pt on the Ge(001) surface. Its low-energy electron states have been explored by scanning tunneling microscopy (STM). A dimerization along the chains is observed at high bias, which might suggest a charge density wave. However, dimer elements also exist with sideways orientation, thus being inconsistent with such picture and instead indicating dimerized back-bonding. Most significantly, for states near the Fermi level, such dimerization along the nanowires is no longer observed. Here a spatially rather uniform charge density is detected. The nanowires can be imaged down to the millivolt regime, indicating metallic character, and tunneling spectroscopy shows finite zero-bias conductivity at room temperature. Ab-initio simulation of the structure has been performed, and a model for the reconstruction at 0.25 ML coverage has been derived. It well reproduces the STM data for various biases. We find that Pt-Ge bonds are favored over Pt-Pt bonds. The prominent dimers along the chain are explained by Ge dimers, while a row of alternating Pt and Ge atoms is identified next to them. This novel tetramer-dimer-chain model consistently explains the wire geometry and its subtle asymmetry. It also accounts for the differential conductivity near the Fermi level.