Study of composition and bonding character of CN x films

Abstract

A series of samples were prepared by reactive laser ablation of a graphite target in nitrogen environment. The CN x 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 N 1s and C 1s regions are similar to those reported by other research groups. Small satellite peaks were observed in the N 1s and C 1s 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 sp 2-hybridized carbon orbital. Thereafter, the main N 1s and C 1s 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 C 2N 2. 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.