Investigation on the Unique Behavior of the Surface-Enhanced Raman Scattering at a Single-Molecule Junction.

Single-molecule junctions (SMJs) have attracted wide attention due to their unique electronic property originating from their structure, i.e. single molecule connected to the electrodes at both ends. Although the junction structure has significant effects on the electronic property of the SMJs, the experimental method to define the geometry of the bridged molecule is limited. Recently, we have succeeded in the observation of surface-enhanced Raman scattering (SERS) spectroscopy in combination with the current-voltage (IV) response measurement, revealing the junction structure of SMJs. The IV response obtained by the combination measurement provides the electronic structure of the molecule fluctuated by the connection to the metal electrodes, allowing the analysis of the effect of the charge transfer on the SERS spectra. The strong electronic coupling between metal and molecule enhances the charge transfer resonance and it triggered the excitation of the "Raman silent mode" in the bulk state. Therefore, we have detected the unique SERS spectra in SMJs and revealed the contribution of the charge transfer effects on the SERS spectra at the single-molecule level. [ABSTRACT FROM AUTHOR]