Two-Phonon Combination Raman Modes in Covalently Functionalized Single-Wall Carbon Nanotubes

Single-wall carbon nanotubes covalently functionalized with chloro-phenyl groups were investigated by Raman spectroscopy. We examine the features observed in the spectral ranges 350−1200, 1650−2000, and 2400−3200 cm −1 . The Raman modes associated with the presence of defects, strongly enhanced by the functionalization are clearly distinguished from those defect independent. We indicate that some features highly enhanced by the electron−phonon coupling are very sensitive to charge transfers between the nanotubes and functional groups. A feature at ∼2900 cm −1 is observed in the spectra of functionalized nanotubes, and its origin is explained here as a combination of two disorder-induced modes.