Contact Atomic Structure and Electron Transport Through Molecules

TL;DR

This study uses first-principles calculations to analyze how atomic-scale contact structures influence electron transport in molecular junctions, revealing significant conductance changes due to contact atom presence and separation variations.

Contribution

It provides detailed insights into how atomic-level contact modifications affect conductance and resonance features in molecular electronics, expanding understanding of contact effects.

Findings

Additional Au atoms increase conductance up to 100 times.

Presence of resonance peaks near Fermi energy affects conductance.

Molecule-lead separation impacts conductance variably.

Abstract

Using benzene sandwiched between two Au leads as a model system, we investigate from first principles the change in molecular conductance caused by different atomic structures around the metal-molecule contact. Our motivation is the variable situations that may arise in break junction experiments; our approach is a combined density functional theory and Green function technique. We focus on effects caused by (1) the presence of an additional Au atom at the contact and (2) possible changes in the molecule-lead separation. The effects of contact atomic relaxation and two different lead orientations are fully considered. We find that the presence of an additional Au atom at each of the two contacts will increase the equilibrium conductance by up to two orders of magnitude regardless of either the lead orientation or different group-VI anchoring atoms. This is due to a LUMO-like resonance peak near the Fermi energy. In the non-equilibrium properties, the resonance peak manifests itself in a large negative differential conductance. We find that the dependence of the equilibrium conductance on the molecule-lead separation can be quite subtle: either very weak or very strong depending on the separation regime.