Identification of structural changes in carbon–nitrogen alloys by studying the dependence of the plasmon energy on nitrogen concentration

The effect of nitrogen on the valence-electron plasmon energy in amorphous carbon–nitrogen alloys $\mathrm{(a-}{\mathrm{C}}_{\text{1−x}}{\mathrm{N}}_x)$ is used to identify structural changes in the material. The samples were prepared by dual-ion-beam-assisted deposition and studied in situ by x-ray photoemission spectroscopy. The plasmon energy of the alloy goes through a maximum above 15–20 at.% nitrogen concentration. This behavior is correlated with structural changes obtained in a semiempirical quantum chemical calculation on graphite-like carbon clusters, randomly substituted by nitrogen. At that concentration, the geometry optimization shows that the graphite-like conformation is unstable against the buckling of the structure.