Conductance properties of single-molecule junctions

We have performed conductance measurements with a gold–molecule–gold junction employing the mechanically controlled break-junction technique. The organic sample molecules form a stable covalent bridge between the electrodes. Two molecules, which differ essentially by their spatial symmetry, showed discrete stable conductance patterns (IVs), which reflect the symmetry/asymmetry of the sample molecules. A third molecule with an additional tunnel barrier in the central axis shows a strongly suppressed conductance. The correlation between these obvious properties of the molecules and the observed IVs unambigously shows that the junction is indeed formed of the sample molecules. Vice versa, these observations demonstrate that IV characteristics can be appropriately designed by a proper choice of molecules.