Adverse effects of asymmetric contacts on single molecule conductances ofHS(CH2)n COOH in nanoelectrical junctions

Abstract

A scanning tunnelling microscope has been used to determine the conductance of singlemolecular wires with the configuration X–bridge–X, X–bridge–Y and Y–bridge–Y(X = thiol terminusand Y = COOH). We find that for molecular wires with mixed functional groups (X–bridge–Y) the singlemolecule conductance decreases with respect to the comparable symmetric molecules.These differences are confirmed by theoretical computations based on a combination ofdensity functional theory and the non-equilibrium Green’s functions formalism.This study demonstrates that the apparent contact resistance, as well as beinghighly sensitive to the type of the anchoring group, is also strongly influenced bycontact-asymmetry of the single molecular junction which in this case decreases thetransmission. This highlights that contact-asymmetry is a significant factor to beconsidered when evaluating nanoelectrical junctions incorporating single molecules.