The mechanism of growth and decay of carbon nano-onions formed by ordering of amorphous particles

The phenomena occurring during electron–beam irradiation of amorphous carbon nanoparticles have been studied. 300 keV electrons cause first ordering of amorphous particles leading to an imperfect shell structure which can be followed by either growth or decay. Growth occurs by a process, similar to Frank–van der Merwe growth of crystals, through forming and coalescence of two-dimensional islands into graphene layers. Decay occurs by two mechanisms: void formation and opening to the surface, and a layer-by-layer detaching of graphene shells. These two mechanisms occur often simultaneously. Void formation is due to densification and ordering. Detachment of layers is due to defect-induced local curving of the outmost layers resulting in an increase in the spacing between outer shells to 0.35–0.50 nm. Growth and decay are competing processes and exact conditions for their stimulation or suppression could not be established so far.