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 (a-C1-xNx) 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. (C) 1998 American Institute of Physics. [S0003-6951(98)02050-6].