Conductance of single 1,4-benzenediamine molecule bridging between Au and Pt electrodes

We investigated the single 1,4-benzenediamine molecule bridging between Au or Pt electrodes. The conductances of the molecular junctions with the Au-NH2 and Pt-NH2 bonds (Au-NH2 and Pt-NH2 molecular junctions) were 1 x 10(-1) Go (2e(2)/h) and 5 x 10(-3) G(0), respectively. The stretching lengths of the Au-NH2 and Pt-NH2 molecular junctions were 0.03 and 0.07 nm, respectively. The conductance value of the Au-NH2 molecular junction was unexpectedly larger than the value evaluated with the density of states of the metal electrodes and the molecule-metal bond strength, which have been discussed before. The large conductance value could be explained by the small energy difference between metal and molecular orbitals (Delta E) and the high degree of pi-conjugation (P) of the Au-NH2 molecular junction, which would be unique characteristics of the Au-NH2 bond. The present Study showed the importance of these two factors (Delta E, P) in studying the conductance of the single molecualr junction.