Abstract
Surface-enhanced Raman scattering (SERS) is a surface-sensitive vibrational spectroscopy that allows Raman spectroscopy on a single molecular scale. Here, we present a review of SERS from molecular junctions, in which a single molecule or molecules are made to have contact from the top to the bottom of metal surfaces. The molecular junctions are nice platforms for SERS as well as transport measurement. Electronic characterization based on the transport measurements of molecular junctions has been extensively studied for the development of miniaturized electronic devices. Simultaneous SERS and transport measurement of the molecular junctions allow both structural (geometrical) and electronic information on the single molecule scale. The improvement of SERS measurement on molecular junctions open the door toward new nanoscience and nanotechnology in molecular electronics.
Highlights
Molecular junctions, where a small number of molecules bridge metal electrodes, have been envisioned as components for miniaturized electronic circuits since the 1970s
Aviram et al first proposed theoretically that electrical rectification was possible with a molecular junction where a donor π system is bound to an acceptor π system via a σ bonded tunneling bridge [1]
The shift of the Surface-enhanced Raman scattering (SERS) peaks was observed for the BPY single-molecular junction fabricated with the fishing-mode’ STM (FM-STM) [33]
Summary
Molecular junctions, where a small number of molecules bridge metal electrodes, have been envisioned as components for miniaturized electronic circuits since the 1970s. Theoretical study showed that the conductance of the BDT single-molecular junction depended on the adsorption geometries on Au electrodes. Vibrational spectroscopy is the most straightforward method to determine the atomic and electronic structure of the molecular junction because it provides a molecular fingerprint that can be used to identify the bridging molecule and molecular adsorption site. As the metal nano electrodes approach each other, the localized plasmon modes hybridize, resulting in a strong electric field between metal nano electrodes This enhanced field increases the Raman signal. The SERS enhancement factor can be as large as 1015 in the metal nanogap, which is sufficient to study Raman scattering of a single molecule [26,27,28,29]. The conductance of the junction provides the information about the molecular junction; gap size, the number of the bridging molecules in the junction, and so on. We discuss the SERS studies on the molecular junctions
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