Correlation between bonding structure and microstructure in fullerene-like carbon nitride thin films

The bonding structure of highly ordered fullerene-like (FL) carbon nitride (CNx) thin films have been assessed by x-ray absorption near edge spectroscopy (XANES). In particular, samples with different degree of FL character (in terms of graphene plane alignment, extension, and cross-linking) have been analyzed to discern spectral signatures of the microstructure formation. The XANES spectra of FL-CNx films resemble that of graphitic CNx, indicating a sp2 character for C and N atoms. However, the evolution of the FL structure is promoted with the dominance of three-fold N over pyridine-like and cyanide-like bonding environments. In addition, the p*/s* ratio at the C(1s) edge is constant, independent of the change in FL character, while it decreases ~40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp3 hybrids with the development of FL structures and, additionally, that a different spatial localization of p electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could as such explain the outstanding elastic properties of FL-CNx.