Quantifying Transition Voltage Spectroscopy of Molecular Junctions

TL;DR

This paper evaluates the effectiveness of transition voltage spectroscopy (TVS) in molecular junctions through extensive ab-initio calculations, highlighting the importance of electrode coupling asymmetries for accurate molecular energy probing.

Contribution

It provides a comprehensive assessment of TVS applicability in molecular junctions, emphasizing the role of electrode coupling asymmetries for quantitative analysis.

Findings

Proper consideration of electrode asymmetries improves TVS accuracy.

Transition voltage correlates well with molecular orbital energies when asymmetries are accounted for.

The relation between transition voltage and molecular energy follows a simple analytical model.

Abstract

Transition voltage spectroscopy (TVS) has recently been introduced as a spectroscopic tool for molecular junctions where it offers the possibility to probe molecular level energies at relatively low bias voltages. In this work we perform extensive ab-initio calculations of the non-linear current voltage relations for a broad class of single-molecule transport junctions in order to assess the applicability and limitations of TVS. We find, that in order to fully utilize TVS as a quantitative spectroscopic tool, it is important to consider asymmetries in the coupling of the molecule to the two electrodes. When this is taken properly into account, the relation between the transition voltage and the energy of the molecular orbital closest to the Fermi level closely follows the trend expected from a simple, analytical model.