Two-Color Sum-Frequency Generation Study of Single-Walled Carbon Nanotubes on Silver

We present the first measurement of the interfacial vibrational and electronic states of single-walled carbon nanotubes (SWCNTs) on a silver substrate by using two-color IR−visible sum frequency generation (SFG). With an input visible light of 532 nm, the G-bands of the SWCNTs deposited on silver were clearly observed, while they were absent on glass or silicone substrates. The observation of the G-band SFG signal shows the existence of coupling between the vibrational and electronic states at the SWCNTs/silver interface. The shape of the two-color SFG spectra of the SWCNTs showed remarkable dependence on the visible excitation wavelength of 470 to 640 nm. The dependence is ascribed to the resonance of the SFG photon energy with the electronic transition energy of the semiconducting SWCNTs.