Resonant transport and electrostatic effects in single-molecule electrical junctions

TL;DR

This paper demonstrates how structural modifications in single-molecule junctions influence resonant transport, revealing electrostatic effects that enable control over conductance and potential applications in molecular electronics and switching.

Contribution

It introduces a method to control transport resonances in metal-molecule-metal junctions through molecular length variation, linking electrostatic effects to conductance behavior.

Findings

Resonance sharpens and shifts closer to Fermi energy with increasing n

Conductance decay with molecular length is very shallow

Electrostatic effects at the interface explain the observed transport behavior

Abstract

In this contribution we demonstrate structural control over a transport resonance in HS(CH$_{2}$)$_{n}$[1,4 - C$_{6}$H$_{4}$](CH$_{2}$)$_{n}$SH (n = 1, 3, 4, 6) metal - molecule - metal junctions, fabricated and tested using the scanning tunnelling microscopy-based $I(z)$ method. The Breit-Wigner resonance originates from one of the arene $\pi$-bonding orbitals, which sharpens and moves closer to the contact Fermi energy as $n$ increases. Varying the number of methylene groups thus leads to a very shallow decay of the conductance with the length of the molecule. We demonstrate that the electrical behaviour observed here can be straightforwardly rationalized by analyzing the effects caused by the electrostatic balance created at the metal-molecule interface. Such resonances offer future prospects in molecular electronics in terms of controlling charge transport over longer distances, and also in single molecule conductance switching if the resonances can be externally gated.