Study of composition and bonding character of CNx films

A series of samples were prepared by reactive laser ablation of a graphite target in nitrogen environment. The CNx films were annealed from room temperature to 900 °C, and in situ analyzed by electron energy loss spectroscopy (EELS), Auger electron spectroscopy, X-ray photoelectron spectroscopy and temperature desorption spectroscopy (TDS). A [N]/[C] ratio of 0.43 was determined and decreases notoriously as the annealing temperature increases. The peak shapes and intensities in the N1s and C1s regions are similar to those reported by other research groups. Small satellite peaks were observed in the N1s and C1s regions, corresponding to first- and second-order inelastic energy losses of the main peaks. These losses were detected also by EELS with an energy of 4 eV and assigned to the π–π∗ plasmon. This resonance is distinctive of non-localized electrons in an sp2-hybridized carbon orbital. Thereafter, the main N1s and C1s peaks could be assigned to atoms in a six- and five-member rings. Moreover, the films were easily degraded by the thermal treatment and the main desorption product determined by TDS was found to be C2N2. We concluded that the most probable structure is one where N atoms dope graphite-like carbon layers by substitution, causing three-dimensional polymerization reactions, with chemical states similar to Upilex, Kapton and other polyimides.