Resonant Raman spectra of amorphous carbon nitrides: the G peak dispersion

A general model is presented for the interpretation of the Raman spectra of amorphous carbon nitrides measured at any excitation energy. The Raman spectra can be explained in terms of an amorphous carbon based model, without need of extra peaks due to CN, NN or NH modes. We classify amorphous carbon nitride films in four classes, according to the corresponding N-free film: a-C:N, a-C:H:N, ta-C:H:N and ta-C:N. In all cases, a multi-wavelength Raman study allows a direct correlation of the Raman parameters with the N content, which is not generally possible for single wavelength excitation. The G peak dispersion emerges as a most informative parameter for Raman analysis. UV Raman enhances the sp1 CN peak, which is usually too faint to be seen in visible excitation.