Origin of dispersive effects of the Raman D band in carbon materials

The origin and dispersion of the anomalous disorder-induced Raman band (D band) observed in all sp(2) hybridized disordered carbon materials near 1350 cm(-1) is investigated as a function of incident laser energy. This effect is explained in terms of the coupling between electrons and phonons with the same wave vector near the K point of the Brillouin zone. The high dispersion is ascribed to the coupling between the optic phonons associated with the D band and the transverse acoustic branch. The large Raman cross section is due to the breathing motion of these particular phonons near the K point. Our model challenges the idea that the Raman D peak is due to laser-energy-independent features in the phonon density of states, but rather is due to a resonant Raman process. [S0163-1829(99)50110-4].