SYNTHESIS OF CARBON NITRIDE

In 1990, Liu and Cohen presented a pseudopotential study of the structural and electronic properties of beta-C3N4, a hypothetical compound. The calculated properties of beta-C3N4, including bulk modulus and velocity of sound, were found to be comparable to that of diamond suggesting high values for hardness and for thermal conductivity. In this paper, the held of experimental efforts to produce carbon nitride is reviewed. Synthesis of beta-C3N4 has been claimed on the basis of diffraction data. However, the overall composition of the materials obtained in these as in most other experiments is not stoichiometric; the N-to-C concentration ratio attained in most cases is [N]/[C] < 1. The likely reasons for this and the dependence of the nitrogen content and bonding on deposition conditions are discussed. The determination of the carbon and nitrogen contents and, more importantly, their contents in specific bonding states is a complex problem to which a significant part of this paper is devoted. Most of the experimental work to date, including those claiming success, applied deposition methods using energetic particles. Among these methods, ion beam deposition (IBD) stands out for its ability to control deposition conditions. We discuss in particular detail our work based on IBD. On the basis of results from electron spectroscopies and computer simulations, a film growth model that includes surface deposition, subplantation and preferential sputtering of nitrogen has been developed. Some future possibilities for the deposition of C-N films are discussed on the basis of this model.