IRRADIATION EFFECTS INDUCED BY REACTIVE AND NONREACTIVE LOW-ENERGY ION IRRADIATION OF GRAPHITE - AN ELECTRON-SPECTROSCOPY STUDY

The effect of low energy Ar+ and N2+ irradiation of highly oriented pyrolytic graphite (HOPG) has been investigated by AES and XPS. Based on measurements of the C(KVV) Auger line shape before and after irradiation it has been found that a high degree of structural disorder is induced in the near-surface region of HOPG. The production of defects induced by the irradiation process was established by the appearance of a shoulder at the high energy side of the C(KVV) Auger line. After Ar+ irradiation the shoulder is well defined and clearly visible in the Auger spectrum. However, after N2+ irradiation this shoulder is broader and its intensity is smaller than that observed after Ar+ irradiation. It is suggested that the defects created during the N2+ irradiation process are partly compensated by chemical bonding between implanted nitrogen and displaced carbon atoms. XPS measurements confirmed the existence of chemical bonds formed between the implanted nitrogen and carbon atoms. The effect of thermal annealing of the irradiated graphite was investigated up to 500-degrees-C. At temperatures as low as 100-degrees-C a decrease of the shoulder intensity was observed, whereas the desorption of the implanted Ar occurs at 300-400-degrees-C only. These results suggest that the defects created by Ar+ irradiation are partially annealed. For N2+ irradiation, some nitrogen desorption occurs accompanied by a broadening and splitting of the N(1s) core-level line. Also in this case, the shoulder intensity decreases with increasing the annealing temperature. It is suggested that partial annealing of the nitrogen-implanted layer takes place. These results are of relevance for the understanding of the basic processes occuring during deposition of carbon nitride thin films by ion beam-assisted methods.