Dan Ward

Fri, Dec 17, 2010, 3:00 pm to 4:00 pm
Jadwin 303
Speaker: Dan Ward Affiliation: Rice Title: Electrical and Optical Characterization of Molecular Nanojunctions Abstract: Electrical conduction at the single molecule scale has been studied extensively with molecular nanojunctions. However, our understanding is hindered by a lack of methods for simultaneous local imaging or spectroscopy to determine the conformation and local environment of the molecule of interest. Plasmon based surface-enhanced spectroscopies are one method of probing the conformation and environment of a molecule. Using a combination of simultaneous electrical and optical measurements we have successfully demonstrated that nanojunctions are excellent surface-enhanced Raman spectroscopy substrates that can have single molecule sensitivity. In this talk I will discuss two recent experimental results, including an investigation into optically driven currents in bare nanojunctions. The resulting photocurrent is due to rectification of the enhanced optical electric field in the nanogap. From low frequency electrical measurements we are able to infer the magnitude of the enhanced electric field, with inferred enhancements exceeding 1000. I will also discuss electrical and optical heating in molecular nanojunctions. Our measurements show that molecular vibrations and conduction electrons in nanojunctions, under electrical bias or laser illumination, can be driven from equilibrium to effective temperatures exceeding 600 K. We observe that individual vibrations are not in thermal equilibrium with one another, the conduction electrons, or the substrate.