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 states and the long-range polarizability of bonding. Visible Raman data on disordered, amorphous, and diamondlike 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.