Molecular nano junctions formed with different metal electrodes

Conductance of nanoscale junctions consisting of molecular monolayer contacted by different metal electrodes is studied. The characteristic energy scales are determined from the temperature dependence of conductance and from the non-linear current-voltage characteristics. Conductance measured at small bias follows the Arrhenius law. The determined activation energies are dependent on the metal contacts. All the energies, typically in the range of 5-150 meV, are small compared to the expected molecular level spacing. The nature of the low-energy states is yet unclear, however the doping of the molecular layer by the metal atoms can be excluded. Depending on the metals, the energies extracted from the onset of the non-linearity do or do not correspond to the low-bias energies. These differences are likely caused by the mutual topography of metal electrodes imposing dissimilar effective conducting paths through the molecular layer.