Transition voltage spectroscopy analysis of charge transport through molecular nanojunctions

Probing the position of frontier molecular orbitals (the highest occupied molecular orbital, HOMO or the lowest unoccupied molecular orbital, LUMO) with respect to the Fermi levels of the electrodes in the molecular junctions is of crucial importance to understand the charge transport behavior and realize the functions of the molecular junctions. Recently, transition voltage spectroscopy (TVS) has been presented to provide insight into the energy offset between the contact Fermi level and the nearest frontier molecular orbital energy responsible for molecular charge transport; this is accomplished by measuring the transition voltage required to generate the inflection behavior of a Fowler–Nordheim plot, i.e., the corresponding analysis of ln(I/V2) against 1/V for I(V) characteristics. One of the key advantages of the TVS is that it requires lower electric fields, which accordingly can avoid the breakdown of the junctions (due to very large electric fields reaching “resonant” condition). This review describes theoretical interpretations of TVS, and then covers the major advances regarding TVS as a promising spectroscopic tool for charge transport experiments in molecular-scale junctions.