Correlation between bonding structure and microstructure in fullerenelike carbon nitride thin films

The bonding structure of highly ordered fullerenelike (FL) carbon nitride (CNₓ) thin films has been assessed by x-ray absorption near-edge spectroscopy (XANES). Samples with different degrees of FL character have been analyzed to discern spectral signatures related to the FL microstructure. The XANES spectra of FL-CNₓ films resemble that of graphitic CNₓ, evidencing the sp² hybridization of both C and N atoms. The FL structure is achieved with the promotion of N in threefold positions over pyridinelike and cyanidelike bonding environments. In addition, the relative π*∕σ* XANES intensity ratio at the C(1s) edge is independent of the 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 π 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.