Surface enhanced Raman scattering of single 1,4-Benzenedithiol molecular junction

Abstract

Here, we present simultaneous electronic and optical measurements of a single 1,4-benzenedithiol (BDT) molecular junctions to investigate the electronic and structural details in the molecular junction and to understand the charge transport property at the single molecular scale. The electronic property was investigated by DC conductance measurement while structural property was characterized using surface enhanced Raman scattering (SERS) measurement. The single BDT junctions sandwiched between Au nanogap-electrodes were prepared by the mechanically controllable break junction method at ambient conditions. The simultaneous conductance and SERS measurements demonstrate that ring deformation mode coupled to C–S stretching mode, ring breathing mode, and C=C stretching mode are detectable for the single BDT molecular junctions with electronic conductance of [Formula: see text] [Formula: see text]. The single molecule origin is supported by the characteristic variability of SERS within samples. Time evolution of the conductance and SERS signals indicated that the molecular conductance and the vibrational energy of the ring breathing mode exhibits anti-correlated relationship. This relationship can be mediated by time evolution of structural change in the single molecular junction and corresponding change in strength of metal–molecular coupling. The larger metal–molecular coupling causes higher electronic conductance of the molecular junction while charge transfer effect leads to weakening of molecular bonds and thus a resulting decrease in the vibration energy of the ring breathing mode.