Correlation of interfacial bonding mechanism and equilibrium conductance of molecular junctions

TL;DR

This study investigates how different interfacial bonding mechanisms in molecular junctions influence quantum transport, revealing that contact details critically affect conductance and must be carefully considered in molecular nanoelectronics.

Contribution

It identifies and characterizes two bonding mechanisms at the Au-S interface in molecular junctions and links these to conductance and mechanical properties, emphasizing the importance of interfacial details.

Findings

Hydrogen-bound Au/BDT/Au junctions are non-dissociative and match experimental conductance.

Covalent bonding in H-dissociated devices results in conductance over ten times higher.

Interfacial bonding configuration strongly correlates with junction conductance and mechanical strength.

Abstract

We report theoretical investigations on the role of interfacial bonding mechanism and its resulting structures to quantum transport in molecular wires. Two bonding mechanisms for the Au-S bond in an Au(111)/1,4-benzenedithiol(BDT)/Au(111) junction were identified by ab initio calculation, confirmed by a recent experiment, which, we showed, critically control charge conduction. It was found, for Au/ BDT/Au junctions, the hydrogen atom, bound by a dative bond to the Sulfur, is energetically non-dissociative after the interface formation. The calculated conductance and junction breakdown forces of H-non-dissociative Au/BDT/Au devices are consistent with the experimental values, while the H-dissociated devices, with the interface governed by typical covalent bonding, give conductance more than an order of magnitude larger. By examining the scattering states that traverse the junctions, we have revealed that mechanical and electric properties of a junction have strong correlation with the bonding configuration. This work clearly demonstrates that the interfacial details, rather than previously believed many-body effects, is of vital importance for correctly predicting equilibrium conductance of molecular junctions; and manifests that the interfacial contact must be carefully understood for investigating quantum transport properties of molecular nanoelectronics.