Low-frequency feature in the first-order Raman spectrum of amorphous carbon.

In the first-order Raman spectrum of amorphous carbon (a-C) there is a low-frequency feature in the 200—900-cm ' region. This feature is characteristic of the highly disordered amorphous-carbon materials. We note that the intensity of this feature is very sensitive to the thermal history of samples, thus suggesting that it is an important measure of the degree of disorder of the a-C materials. We also discuss the relationship between this feature and the phonon density of states of graphite.