Surface-enhanced resonance Raman (SERR) spectra of methylene blue adsorbed on a silver electrode

The SERS and SERSS effects of methylene blue (MB) adsorbed on a silver electrode have been investigated. SER and SERR spectra at monolayer and multilayer conditions have shown experimental evidences for the monomer adsorption. Contrary to previous reports, the in situ SERR spectra of MB adsorbed on a silver electrode with MB in solution were observed using confocal Raman microscopy, which avoids the strong fluorescence background from MB in solution. It has been observed that the relative Raman intensities of the adsorbed species (monomer and dimer/aggregates) are wavelength dependent and also dependent on the characteristics of the film, multi- or monolayer film, and on the applied potential. The monolayer condition and exciting at resonance or close to it cause the enhancement of the monomer signal, characterized by the feature at similar to481 cm(-1). Models for monomer, dimer, or MB aggregates as adsorbed on the electrode surface have also been presented and used to discuss the effect of laser excitation on the monomer/dimer (or aggregates) equilibrium at the electrode surface.