Conductance and SERS Measurement of Benzenedithiol Molecules Bridging Between Au Electrodes

We have measured electric conductance and surface enhanced Raman scattering (SEAS) spectra for the benzenedithiol molecules bridging between Au nano gap electrodes at room temperature to investigate the electric and optical properties of the molecular junction. The current-voltage characteristic of the molecular junction was investigated based on the single level tunneling model considering that the Fermi distribution function got smeared out for finite temperature, which provided the information on the number of molecules bridging metal electrodes, energy difference between conduction orbital and Fermi level, strength of the molecule-metal coupling. The conductance measurements confirmed the interaction between molecule and Au electrodes. Due to the interaction between molecule and metal electrodes, we could observe the SEAS spectra characteristic of the molecular junction. The SERS measurement showed the disappearance of the SH modes and red shift of some internal vibration modes, which confirmed the molecular bridge between Au electrodes. For some molecular junctions, we observed the b(2) mode, which was not observed in the bulk crystal. The appearance of the b(2) mode could be explained by the photon-driven charge transfer from molecule to metal electrodes.