Investigation of Electronic and Vibrational Properties of Single-Walled Carbon Nanotubes Functionalized with Diazonium Salts

Single-walled carbon nanotube films functionalized with 4-chlorophenyl and 4-nitrophenyl diazonium groups were studied by resonant Raman and optical absorption spectroscopies. Samples with different degrees of functionalization, from 0.24 to 4.1% of functional groups in relation to the number of carbon atoms in the nanotube, were used in the experiments. The effects of the functional groups on the electronic and phonon structures were addressed by a resonant Raman investigation using several different laser excitation energies. A dependence of the optical excitation energies on the nanotube functionalization is reported. A shift in the optical transition energies as well as a broadening in the resonance Raman profiles are observed for the functionalized samples, caused by the charge transfer between the nanotube and the functional group. Comparison between Raman and optical absorption results reveals a dependence of the functionalization with the nanotube diameter. The absolute dependence of the ratio between the dispersive D-band and G-band intensities, a metric commonly used to benchmark functionalization in these systems, on the excitation energy is reported, allowing for objective comparison between ratios measured at different wavelengths.