ABSTRACT

Carbon onions are a member of the family of nanometer-scale graphite-like all-carbon allotropes, the emergence of which was catalyzed by the Nobel Prize-winning discovery of the first member, the fullerene, by Kroto et al. in 1985. It is the ability of carbon atoms to form covalent bonds with different orientations and bond strength that gives rise to the diverse range of all-carbon structures observed in nature. The transformation of carbon nanoparticles to carbon onions can be stimulated by exposure to an intense beam of electrons. The transformation of diamond to graphitic structures is perhaps not very surprising, because graphite is more thermodynamically stable than diamond under normal conditions. Thermal transformation of nanostructured soot results in the formation of carbon onions with large internal shells in comparison to using nanodiamonds (NDs) as the precursor. Carbon onions can serve as nanocapsules for a range of different materials.