A general framework for the interpretation of infrared and Raman spectra of amorphous carbon nitrides is presented. In the first part of this paper we examine the infrared spectra. The peaks around 1350 and 1550 cm Ϫ1 found in the infrared spectrum of amorphous carbon nitride or hydrogenated and hydrogen-free amorphous carbon are shown to originate from the large dynamic charge of the more delocalized bonding which occurs in more sp 2 bonded networks. The IR absorption decreases strongly when the bonding becomes localized, as in tetrahedral amorphous carbon. Isotopic substitution is used to assign the modes to CvC skeleton modes, even those modes around 1600 cm Ϫ1 which become strongly enhanced by the presence of hydrogen. The infrared spectrum of carbon nitride may resemble the Raman spectrum at some excitation energy, but the infrared activity does not primarily result from nitrogen breaking the symmetry. In the second part we examine the Raman spectra. 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. We analyze a wide variety of samples for the four classes and present the Raman spectra as a function of N content, sp 3 content, and band gap. In all cases, a multiwavelength 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 sp 1 CN peak, which is usually too faint to be seen in visible excitation. As for N-free samples, UV Raman also enhances the CC sp 3 bonds vibrations, allowing the sp 3 content to be quantified.

Grazing-angle x-ray reflectivity ͑XRR͒ is described as an efficient, nondestructive, parameter-free means to measure the mass density of various types of amorphous carbon films down to the nanometer thickness range. It is shown how XRR can also detect layering if it is present in the films, in which case the reflectivity profile must be modeled to derive the density. The mass density can also be derived from the valence electron density via the plasmon energy, which is measured by electron energy-loss spectroscopy ͑EELS͒. We formally define an interband effective electron mass m*, which accounts for the finite band gap. Comparison of XRR and EELS densities allows us to fit an average m*ϭ0.87m for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, m*ϭ͓1Ϫn(0) Ϫ2 ͔m, where n(0) is the refractive index at zero optical frequency. The fraction of sp 2 bonding is derived from the carbon K-edge EELS spectrum, and it is shown how a choice of ''magic'' incidence and collection angles in the scanning transmission electron microscope can give sp 2 fraction values that are independent of sample orientation or anisotropy. We thus give a general relationship between mass density and sp 3 content for carbon films.

Features in the Raman and infrared ͑IR͒ spectra of highly sp 3 bonded hydrogenated amorphous carbon nitride films are assigned. The Raman spectra show three main features all found in a-C itself, the G and D peaks at 1550 and 1350 cm Ϫ1 , respectively, and the L peak near 700 cm Ϫ1 . The intensity ratio of the D and G peaks, I(D)/I (G), is found to scale as ͑band gap͒ Ϫ2 , which confirms that nitrogen induces carbon to form sp 2 graphitic clusters. The intensity of the L mode is found to scale with the D mode, supporting its identification as an in-plane rotational mode of sixfold rings in graphitic clusters. A small feature at 2200 cm Ϫ1 due to CwN modes is seen, but otherwise the Raman spectra resembles that of a-C and shows no specific features due to N atoms. The hydrogen content is found to have a strong effect on the IR spectra at 1100-1600 cm Ϫ1 making this band asymmetric towards the 1600 cm Ϫ1 region.

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