Raman spectra of aerographite, graphite oxide, graphite flakes, and kish graphite were investigated with different laser excitation energies (wavelengths, λL), namely, 2.81 eV (442 nm), 2.41 eV (514 nm), 2.33 eV (532 nm), and 1.96 eV (633 nm). X-ray diffraction analysis showed that aerographite and graphite oxide are structurally disordered. The Raman spectra of both exhibit typical graphitic features, namely, G, D, D′, and 2D bands. The D and 2D bands exhibit a "blue-shift"with laser excitation energies, EL, while the G bands remain invariant. The intensity ratio between the D and G bands (ID/IG) ranges from 0.70 to 1.25 for aerographite and graphite oxide and from 0.04 to 0.24 for graphite flakes and kish graphite. The dependence of ID/IG on λL4 is linear for graphite flakes and kish graphite, while it saturates at the longest λL for aerographite and graphite oxide. A physical explanation of this unexpected saturation is proposed within the double resonant Raman scattering model, taking into account the disorder-induced changes of the phonon density of states.
