Effects of gating and contact geometry on current through conjugated molecules covalently bonded to electrodes

TL;DR

This study investigates how gating and contact geometry influence electrical current in conjugated molecules attached to gold electrodes, revealing significant variations based on molecular orientation and binding site, with implications for molecular electronics.

Contribution

It provides new insights into how contact geometry and gating affect conductance in conjugated molecules, highlighting the importance of molecular orientation and binding site in electron transport.

Findings

Current varies by over an order of magnitude with molecular orientation.

Gating effects are stronger for molecules on less coordinated sites.

Hollow site binding leads to ohmic current-voltage behavior.

Abstract

We study the effects of gating and contact geometry on current through self-assembled monolayers of conjugated molecules strongly coupled to gold electrodes by sulfur ``anchor groups''. The current changes by more than an order of magnitude depending on the angle between the axis of the benzene-dithiolate molecules and the normal to the electrode on the less coordinated ``top site'' position. The effect of gating is also much stronger in this case compared to higher coordinated ``hollow site'' binding of the molecule on a Au(111) surface. The large hybridization of the molecular states with electrode states for the hollow site leads to practically ohmic current-voltage characteristics. Changes in molecule-electrode geometry accompanying the gating of the SAM may be the reason for strong changes of the conductance observed by Schoen et al. in the ``slot'' geometry.