Bonding in amorphous carbon nitride

The main objective of the research on carbon nitride has been on producing a crystalline super-hard phase composed of single or sp(3) carbon-nitrogen bonds. However, the experimental outcome suggests only the formation of an amorphous phase with a major fraction of double or sp(2) CN bonds. One of the main problems in planning future actions to obtain or discard the hypothetical C3N4 material is the correct identification of the chemical bonding. There is little to no agreement of the interpretation of the spectra obtained for a-CN's for any of the common tools used to study chemical bonding. Nuclear magnetic resonance (NMR) has been used only in the few occasions in which enough material could be obtained; the results suggest that high-nitrogen content films are preferentially sp(2) bonded. Electron energy loss spectroscopy (EELS) and near-edge X ray absorbance (NEXAFS) spectroscopy suggest a decrease in the C sp(3) bonding induced by the increase in the nitrogen content, i.e. at high N at.% the CN films are preferentially pi bonded. However, according to some interpretations of the X-ray photoelectron spectra, films with a high CN sp(3) bonding have been produced. Similarly, interpretations of infrared and Raman spectra in a-CN's films suggest the formation of single bonded CN phases. The former contradictions are a consequence of the difficulties associated with the interpretation of the different spectra. Thus, it is necessary to characterize a-CN films more carefully, using as many of the techniques available before claiming any conclusions. In the last years we have concentrated on unveiling details about the CN bonding regimes present in a-CN and therefore the effect of the deposition conditions on the film properties, bonding and stoichiometry. With this information we are able to propose an interpretation of the infrared and Raman spectra, presented here, on well-characterized CN films in good agreement with other film properties and the electron-energy loss spectra. (C) 2003 Elsevier B.V. All rights reserved.