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

Abstract

The bonding structure of highly ordered fullerenelike (FL) carbon nitride $(\mathrm{C}{\mathrm{N}}_{x})$ 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 $\mathrm{FL}\text{\ensuremath{-}}\mathrm{C}{\mathrm{N}}_{x}$ films resemble that of graphitic $\mathrm{C}{\mathrm{N}}_{x}$, evidencing the $s{p}^{2}$ 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 ${\ensuremath{\pi}}^{*}∕{\ensuremath{\sigma}}^{*}$ XANES intensity ratio at the $\mathrm{C}(1s)$ edge is independent of the FL character, while it decreases $\ensuremath{\sim}40%$ at the $\mathrm{N}(1s)$ edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of $\mathrm{C}\text{\ensuremath{-}}s{p}^{3}$ hybrids with the development of FL structures and, additionally, that a different spatial localization of $\ensuremath{\pi}$ 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 $\mathrm{FL}\text{\ensuremath{-}}\mathrm{C}{\mathrm{N}}_{x}$.