Impact of electrode density of states on transport through pyridine-linked single molecule junctions

TL;DR

This study investigates how the electronic structure of electrodes influences charge transport in pyridine-linked single-molecule junctions, revealing the role of metal-specific effects and local interactions in molecular conductance.

Contribution

It demonstrates the impact of electrode density of states on molecular junction conductance and highlights the complex factors affecting molecular level alignment beyond simple work function differences.

Findings

Au electrodes exhibit stronger coupling than Ag electrodes due to relativistic effects.

Molecular orbital alignment does not directly correlate with work function differences.

Electronic coupling and level alignment are governed by subtle local interactions.

Abstract

We study the impact of electrode band structure on transport through single-molecule junctions by measuring the conductance of pyridine-based molecules using Ag and Au electrodes. Our experiments are carried out using the scanning tunneling microscope based break-junction technique and are supported by density functional theory based calculations. We find from both experiments and calculations that the coupling of the dominant transport orbital to the metal is stronger for Au-based junctions when compared with Ag-based junctions. We attribute this difference to relativistic effects, which results in an enhanced density of d-states at the Fermi energy for Au compared with Ag. We further show that the alignment of the conducting orbital relative to the Fermi level does not follow the work function difference between two metals and is different for conjugated and saturated systems. We thus demonstrate that the details of the molecular level alignment and electronic coupling in metal-organic interfaces do not follow simple rules, but are rather the consequence of subtle local interactions.