Raman studies of rhodamine 6G and crystal violet sub-monolayers on electrochemically roughened silver substrates: Do dye molecules adsorb preferentially on highly SERS-active sites?

The enhancement factors in surface-enhanced Raman scattering (SERS) are significantly different for molecules adsorbed on different sites. We show that on electrochemically roughened silver substrates dye molecules preferentially adsorb at highly SERS-active sites (probably slits between metal nanoparticles). Our results suggest that even such large molecules as rhodamine 6G and crystal violet can locate themselves into highly SERS-active sites not only during rearrangement of the metal nanoparticles (this mechanism is likely for metallic sols) but can also diffuse into already existing highly SERS-active sites. The number of such sites is small, however, they provide very high surface enhancement.