Environmental Control of Single-Molecule Junction Transport

The conductance of individual 1,4-benzenediamine
(BDA)
Au molecular junctions is measured in different solvent
environments using a scanning tunneling microscope based pointcontact technique. Solvents are found to increase the conductance
of these molecular junctions by as much as 50%. Using first
principles calculations, we explain this increase by showing that a
shift in the Au contact work function is induced by solvents binding
to undercoordinated Au sites around the junction. Increasing the
Au contact work function reduces the separation between the Au Fermi energy and the highest occupied molecular orbital of BDA in the
junction, increasing the measured conductance. We demonstrate that the solvent-induced shift in conductance depends on the affinity of
the solvent to Au binding sites and also on the induced dipole (relative to BDA) upon adsorption. Via this mechanism, molecular junction
level alignment and transport properties can be statistically altered by solvent molecule binding to the contact surface.