Interpretation of Raman spectra of disordered and amorphous carbon

The model and theoretical understanding of the Raman spectra in disordered and amorphous carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of pi states and the long-range polarizability of pi bonding. Visible Raman data on disordered, amorphous, and diamond like carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the sp(2) sites in sp(2)-bonded clusters. In cases where the sp(2) clustering is controlled by the sp(3) fraction, such as in as-deposited tetrahedral amorphous carbon (ta-C) or hydrogenated amorphous carbon (a-C:H) films, the visible Raman parameters can be used to derive the sp(3) fraction.