Figure 2: One of the most beautiful Raman spectra of sp2 nanocarbons found in the literature. They come from graphite whiskers obtained at three different laser wavelengths (excitation energies), as measured by Tan et al. [61]. Note that some phonon frequencies vary with and some do not. Above 1650 cm−1, the observed Raman features are all multiple-order combination modes and overtones, though some of the peaks observed below 1650 cm−1 are actually one phonon-bands activated by defects. The inset to (c) shows details of the peaks labeled by and , involving the acoustic iTA and LA branches, respectively, according to the double-resonance Raman scattering model.