Enhancement mechanism of SERS from cyanine dyes adsorbed on Ag2O colloids

Surface enhancement mechanism of Raman scattering from molecules adsorbed on silver oxide colloids is reported. Absorption spectra and Raman spectra of the cyanine dye D266 and pyridine molecules adsorbed on Ag2O colloids, and the influences of S2O32- and OH- on the SERS are studied respectively. The results indicate that 'chemical' enhancement is dominant in Ag2O colloidal solution. Surface complexes of adsorbed molecules and small silver ion clusters Ag-n(+) as the SERS active sites make an important contribution to surface enhanced Raman scattering (SERS). At these active sites, charge transfer between the adsorbed molecules and the small silver ion clusters is the main enhancement origin. The enhancement factor of D266 adsorbed on Ag2O colloids is theoretically estimated with the excited-state charge transfer model, which is roughly in accordance with the experiments. (C) 1997 Elsevier Science B.V.