Dresden 2009 – wissenschaftliches Programm
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SYSO: Symposium Self-organizing Surfaces and Interfaces
SYSO 7: Self-Organizing Surfaces and Interfaces VI
SYSO 7.4: Vortrag
Donnerstag, 26. März 2009, 16:30–16:45, GÖR 226
STM bias dependent imaging of molecular double layer — •Christian Seifert1, Nikolai Severin1, Daria Skuridina1, Xi Dou2, Klaus Müllen2 und Jürgen P. Rabe1 — 1Department of Physics, Humboldt University Berlin, 12489 Berlin — 2Max-Planck-Institute for Polymer Research, 55128 Mainz
While Aviram and Ratner had proposed a molecular recifyer based on tunneling through donor and acceptor moieties linked by a spacer, it has been argued later that rectification may be also achieved with a single physisorbed donor or acceptor molecule located asymmetrically between two electrodes. The latter was attributed to the dependence of the potential at the position of the molecular orbitals in the tunneling gap on their relative position within the gap. However, it has been also claimed that the potential of a molecular adsorbate is not dependent on the tip- sample distance but rather equal to the substrate potential. Here we report in-situ scanning tunneling microscopy bias dependent imaging of bilayers of conjugated molecules self-assembled at the interface between an organic solution and the basal plane of graphite. The imaging revealed a dependence of the layers visibility on the applied bias as predicted by the model, which confirms that the electron potential drops gradually across the molecular adsorbate. The results indicate that resonance enhanced tunneling through physisorbed molecules between two biased metallic electrodes depends sensitively on the gap width and the relative position of the electronic orbitals within the gap, thereby providing a means to precisely control current-voltage characteristics through the geometry of the gap.