Optical Emission Study of RF Thermal Plasma During Fullerene Synthesis

Results on studies of molecular spectra emitted in the initial stages of fullerene synthesis during processing of graphite powder in RF thermal plasma conditions are presented in this work. CN—usually present in carbon plasmas—and C₂ were found as dominant molecular species. The role of CN radicals on the fullerene formation was discussed in detail. Intensities of CN and C₂ lines were studied against the composition of gas phase and the feed rate of graphite powder. The rotational-vibrational temperatures of CN species were calculated by fitting the experimental spectra to the simulated ones. It was concluded that in the plasma region CN radicals could be formed by the reaction of C₂ with atomic nitrogen at smaller loads. This reaction lowered the yield of fullerenes. At larger loads, C₂ formation was decreased due to lower temperature of the particles compared to smaller load. The CN radicals were produced by the surface reaction of the hot carbon particles with nitrogen atoms. Results confirmed that for effective fullerene synthesis, the nitrogen content of the precursors and the plasma gases should be minimized.