Charge Transfer Enhancement in the SERS of a Single Molecule

We measured the surface-enhanced Raman scattering (SERS) of individual gold nanoparticle-4-aminobenzenethiol (ABT)-gold film junctions to investigate the charge-transfer (CT) enhancement of the SERS signals Despite the mild electromagnetic field enhancement (similar to 10(5)) and high surface density of the ABT-molecules (similar to 240 molecules/hotspot) at the junctions, we observed the clear spectral and temporal signatures of CT-enhanced single-molecule SERS (SM-SERS) The result reveals that only a small fraction of the molecules at the junction has a significant CT-enhancement of I 10(1)similar to 10(3), whereas the rest of the molecules are nearly CT-inactive Furthermore, the result also proves that overall (charge-transfer and electromagnetic) enhancement of 10(6)-10(8) is sufficient to observe the SM-SERS of an electronically off-resonant molecule, which disproves the widespread belief that a minimum enhancement of similar to 10(14) is required for SM-SERS