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. 38 Initially, carbon onions were observed by Iijima in 1980, 33 and were brought to popular attention by the experiments of Ugarte in 1992. 83 Structurally, they consist of concentric spherically closed carbon shells and receive their name from the close resemblance between their nanoscale structure and the more familiar concentric layered structure of an onion. Closely related to carbon onions is a class of material known as onion-like carbons (OLCs), which include polyhedral nanostructures such as ideal nested fullerenes. This material, rather than ideal spherical carbon onions, can be currently produced in macroscopic quantities, and, hence, be used for future applications.
