Density-functional ab initio molecular dynamics is used to study the incorporation of nitrogen into carbon networks. The resulting networks were analyzed using a Wannier-function technique for producing a localized orbital picture that provided us with a means of identifying bonding types of the nitrogen and carbon atoms within the disordered structures. Addition of nitrogen was found to cause a decrease in the fraction of sp 3 -bonded carbon and this effect is most severe at high density. These changes to carbon bonding are not confined to carbon atoms in the immediate vicinity of a nitrogen atom. The structure, and elastic and electronic properties of the networks are examined and compared with existing simulations and experimental observations. We found that removing electrons from the networks caused structural changes that could explain the two-state conductivity in amorphous carbon nitride memory devices.

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Carbon nitride materials have been the focus of research efforts worldwide. Most materials studied have been amorphous, with only a few groups claiming to have found a crystalline material. We investigate the structure of amorphous carbon nitride solids produced by two different techniques: cathodic arc deposition and high dose nitrogen implantation of glassy carbon. Transmission electron microscopy, electron energy loss spectroscopy, energy filtered electron diffraction, Rutherford backscattering, infrared, and Raman spectroscopy are all used to derive structural information. It was found that the carbon nitride materials prepared by both techniques have similar structures and [N]/[C] ratios (0.3). The materials appear to have a primarily sp2 bonded carbon structure with a smaller bond length than found in amorphous carbon. This is explained by nitrogen substituting into ‘‘rings’’ to a saturation level of about one nitrogen per three carbon atoms. We have found no evidence for a C3N4 crystalline structure, nor any amorphous derivative of it.

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