Highly conductive single molecular junctions by direct binding of π-conjugated molecule to metal electrodes

We have investigated electrical conductance of the single C₆₀ and benzene molecules bridging between metal electrodes. The single C₆₀ and benzene molecular junctions were prepared in ultra high vacuum. The single molecular junctions showed the high conductance values (around 0.1–1 G₀: G₀ = 2e²/h), which were comparable to that of the metal atomic contact. The highly conductive single molecular junctions could be prepared by direct binding of the π-conjugated organic molecule to the metal electrodes without the use of anchoring groups. For comparison, the single 1,4-benzenediamine molecular junction was investigated in solution. The benzene molecule was bound to the Au electrodes via amine (anchoring group) for the single 1,4-benzenediamine molecular junction. The conductance of the single 1,4-benzenediamine molecular junction was 8 × 10⁻³G_0. It was suggested that the anchoring groups acted as resistive spacers between the molecule and metal.