Fundamental processes of surface enhanced Raman scattering detected by transient reflecting grating spectroscopy

Ultrafast charge transfer (CT) between gold and crystal violet (CV) molecules in relation with the surface enhanced Raman scattering (SERS) activation was investigated using the transient reflecting grating (TRG) spectroscopic method. A charge transfer between gold and crystal violet was observed only for the SERS-active substrate and it occurred within 200 fs. Since the adsorbed dyes had electronic overlap with the metal substrate at the point of central carbon, considering the difference of the Raman spectra between adsorbed and free dyes, it was suggested that the charge transfer occurred through the central carbon of crystal violet. Furthermore, it was shown that the surface morphology of the substrates is in close correlation with the charge transfer process from its dependence on the preparation method of substrates.