Resonant second-order Raman spectra ofC60on Ag and In surfaces

Enhanced second-order Raman modes of ${\mathrm{C}}_{60}$ molecules adsorbed on Ag and In surfaces are reported. This unusual observation for the metal surfaces is believed to result from the unique surface-enhancement mechanism of the Raman spectrum of adsorbed ${\mathrm{C}}_{60}$ and from the high relative intensity of the second-order modes previously observed for bulk ${\mathrm{C}}_{60}$ samples. Differences in line shapes and a modified resonant behavior, relative to results for ${\mathrm{C}}_{60}$ single crystals, are attributed to interactions between the adsorbed ${\mathrm{C}}_{60}$ and the metal surfaces, which have been shown in previous studies to include charge transfer to ${\mathrm{C}}_{60}$.