Surface-enhanced Raman scattering of Rhodamine 123 in silver hydrosols andin Langmuir-Blodgett films on silver islands

Surface-enhanced Raman scattering(SERS) of the Rhodamine 123 (Rh 123) molec ule on ion-induced silver colloids has been studied. A time-dependent study of the SER spectra at a particular pH confirms charge transfer interaction between the probe molecule and the metal. The SER spectra of Rh 123 in Ag sol is compared with that of the molecules organized in a monolayer on silv er island films by the Langmuir-Blodgett (LB) technique. The origin of high SERS activity of Rh 123 molecules in a monolayer on a silver island film i s shown to be due to physisorption whereas in the ion-induced colloidal SER S both physisorption and chemisorption machanisms are involved. From these results, the contribution of charge transfer interaction to SERS in Ag sol has been estimated. In monolayer SERS, all the in-plane and out-of-plane (o f xanthene ring) modes are more or less equally enhanced, This indicates th at the xanthene plane of Rh 123 molecule organized in a LB film is oriented neither flat nor perpendicular to the silver island surface but is tilted. (C) 2001 Academic Press.