Electromagnetic Enhancement Factor of Surface-enhanced Raman Scattering of Rh6G Molecules on Au Nanoparticles

Surface-enhanced Raman spectroscopy (SERS) of molecules on nanometals has been intensively studied for technical application of bio-chemical sensing. Among physical origins of SERS enhancement, the electromagnetic effect is the most fundamental contribution of SERS enhancement. Relevant REF of C-C stretching mode of Rh6G near 1511 cm$^{-1}$ was shown two-order enhancement with 5-nm Au colloidal nanoparticles. The REF was greatly enhanced up to $\sim $six orders with $\sim $35 nm Au particles, and was enhanced $\sim $five orders with 40-nm Au nanoparticles. The reduction of REF with smaller sizes is possibly due to the scattering of conduction electrons on particles surfaces; that with larger sizes is probably due to tips or complex structures. This work at Hampton University was supported by the National Science Foundation (HRD-0734635, HRD-0630372, and ESI-0426328/002) and the U.S. Army Research Office (W911NF-07-1-0608).