We have performed conductance measurements with a self-assembled metal-molecule-metal junction . The gap between the electrodes could be adapted in situ to the molecule's length employing the mechanically controlled break junction technique. The organic sample molecules were designed to form a stable chemical bridge between the electrodes. Both molecules, which differed essentially by their spatial symmetry, showed discrete stable conductance patterns. While the asymmetric molecule always generated asymmetric current-voltage relations (IVs), the symmetric molecules often showed symmetric IVs. This allows clearly to identify the IVs as transport through our sample molecules. The body of our data strongly suggests that each stable junction is related to current through only one single molecule, connected to both metal electrodes. Considerable differences between subsequently manipulated junctions, i.e. sample-to-sample fluctuations are attributed mainly to varying microscopic contact realisations. This is clearly demonstrated by intentionally inducing different asymmetric IVs with the symmetric molecule upon tuning the electrode distance.
Heiko B. Weber
Forschungszentrum Karlsruhe, Institute of Nanotechnology
P.O.Box 3640 Karlsruhe 76021 GERMANY
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