End group effect on electrical transport through individual molecules: A microscopic study

TL;DR

This study investigates how different chemical end groups on a benzene molecule influence electron transport in molecular devices, revealing significant conductance variation and bias voltage distribution depending on the end groups.

Contribution

It demonstrates how chemical modifications at the metal-molecule interface affect transport mechanisms and conductance in molecular junctions using first-principles calculations.

Findings

Transport mode depends on end group chemistry.

Conductance varies over two orders of magnitude.

Bias voltage distribution depends on potential landscape.

Abstract

The effect on molecular transport due to chemical modification of the metal-molecule interface is investigated, using as an example the prototypical molecular device formed by attaching a p-disubstituted benzene molecule onto two gold electrodes through chemically different end groups. Using a first-principles based self-consistent matrix Green's function method, we find that depending on the end group, transport through the molecule can be mediated by either near-resonant-tunneling or off-resonant-tunneling and the conductance of the molecule varies over more than two orders of magnitude. Despite the symmetric device structure of all the molecules studied, the applied bias voltage can be dropped either equally between the two metal-molecule contacts or mostly across the source (electron-injecting) contact depending on the potential landscape across the molecular junction at equilibrium.