Speaker
Description
Control of optical properties of single molecules by plasmonic nanostructures is an important issue in nanoplasmonics and nanophotonics, particularly valuable for the development of molecular plasmonic devices and ultrasensitive high-resolution microscopic techniques. The nanocavity defined by the coinage-metal tip and substrate in a scanning tunneling microscope (STM) can provide highly localized and dramatically enhanced electrical fields upon appropriate plasmonic resonant tuning, which can modify the excitation and emission of a single molecule inside and produce interesting new optoelectronic phenomena. In this talk, I shall demonstrate two STM-based phenomena related to single-molecule optical spectroscopy. The first is single-molecule Raman scattering. The spatial resolution of tip enhanced Raman spectromicroscopy has been driven down to sub-nanometer scale for a single porphyrin molecule. I shall demonstrate further applications of this technique to chemically distinguish different adjacent molecules on a surface, from relatively large porphyrin molecules to small DNA-base molecules. The second phenomenon is single-molecule electroluminescence. I shall first demonstrate the realization of electrically driven single-photon emission from a well-defined isolated single molecule. Then, by using STM manipulation to construct a molecular dimer, I shall demonstrate the visualization of coherent intermolecular dipole-dipole coupling in real space through sub-nanometer resolved electroluminescence imaging, together with a demonstration of single-photon superradiance in artificially constructed oligomers. These findings provide unprecedented spatial details about the coherent dipole-dipole coupling in molecular systems, which may open up new research avenues to study molecular interactions and enable rational engineering of light harvesting structures and quantum light sources.
