Influence of the Resonant Electronic Transition on the Intensity of the Raman Radial Breathing Mode of Single Walled Carbon Nanotubes during Electrochemical Charging

In situ Raman spectroelectrochemistry has been used to probe the E 11 S and E 22 S electronic transitions of the semiconducting single walled carbon nanotube tube (6,5). These two transitions were investigated through the intensities of the radial breathing mode by using 1.16 and 2.18 eV laser excitation energies, respectively. The bleaching behavior of the (6,5) tube is similar for both laser excitation energies if the magnitude of the applied electrode potential is smaller than about ±0.5 V. At potentials outside the ±0.5 V window, the intensity/potential profile is steeper for the 1.16 eV laser excitation. But a significant bleaching of the Raman signal is observed also for the 2.18 eV laser excitation energy even at mild potentials. This behavior shows that the filling of the E 11 S electronic state has a strong impact also on the E 22 S electronic transition. Hence, we suggest that a broadening of the resonance profile of E 22 S is a major reason for the change of the resonance enhancement of the Raman spectra before the Fermi level reaches the energy of E 22 S transition.