Electronic and optical properties of electromigrated molecular junctions

Electromigrated nanoscale junctions have proven very useful for studying electronic transport at the single-molecule scale. However, confirming that conduction is through precisely the molecule of interest and not some contaminant or metal nanoparticle has remained a persistent challenge, typically requiring a statistical analysis of many devices. We review how transport mechanisms in both electronic and optical measurements can be used to infer information about the nanoscale junction configuration. The electronic response to optical excitation is particularly revealing. We briefly discuss surface-enhanced Raman spectroscopy on such junctions, and present new results showing that currents due to optical rectification can provide a means of estimating the local electric field at the junction due to illumination.