Electron Transport Across Plasmonic Molecular Nanogaps Interrogated with Surface-Enhanced Raman Scattering

Charge transport plays an important role in defining both far-field and near-field optical response of a plasmonic nanostructure with an ultrasmall built-in nanogap. As the gap size of a gold core–shell nanomatryoshka approaches the sub-nanometer length scale, charge transport may occur and strongly alter the near-field enhancement within the molecule-filled nanogap. In this work, we utilize ultrasensitive surface-enhanced Raman spectroscopy (SERS) to investigate the plasmonic near-field variation induced by the molecular junction conductance-assisted electron transport in gold nanomatryoshkas, termed gap-enhanced Raman tags (GERTs). The GERTs, with interior gaps from 0.7 to 2 nm, are prepared with a wet chemistry method. Our experimental and theoretical studies suggest that the electron transport through the molecular junction influences both far-field and near-field optical properties of the GERTs. In the far-field extinction response, the low-energy gap mode predicted by a classical electromagnetic mod...