Effects of asymmetric contacts on single molecule conductances of HS(CH2)nCOOH in nano-electrical junctions

TL;DR

This study investigates how asymmetric contacts in single-molecule junctions affect electrical conductance, revealing that contact asymmetry decreases transmission and conductance, which is crucial for designing molecular electronic devices.

Contribution

The paper combines experimental measurements with theoretical modeling to show that contact asymmetry significantly reduces conductance in single-molecule junctions, a factor often overlooked.

Findings

Asymmetric contacts lower single-molecule conductance.

Contact asymmetry influences apparent contact resistance.

Theoretical models confirm experimental observations.

Abstract

A scanning tunnelling microscope has been used to determine the conductance of single molecular wires with the configuration X-bridge-X, X-bridge-Y and Y-bridge-Y (X = thiol terminus and Y = COOH). We find that for molecular wires with mixed functional groups (X-bridge-Y) the single molecule conductance decreases with respect to the comparable symmetric molecules. These differences are confirmed by theoretical computations based on a combination of density functional theory and the non-equilibrium Green functions formalism. This study demonstrates that the apparent contact resistance, as well as being highly sensitive to the type of the anchoring group is also strongly influenced by contact-asymmetry of the single molecular junction which in this case decreases the transmission. This highlights that contact asymmetry is a significant factor to be considered when evaluating nano-electrical junctions incorporating single molecules.