High-resolution transmission electron microscopy and energetics of flattened carbon nanoshells

When examined under a high-resolution transmission electron microscope. carbon soot produced alongside buckytubes in an arc-discharge is found to contain a small percentage of flattened carbon shells. These objects are shown to be small graphite flakes which have eliminated their dangling bonds by terminating their edges with highly curved junctions. Ideal models for these structures are presented and their energies estimated. The calculations show that the establishment of highly curved junctions is energetically favourable for a graphite flake in an inert atmosphere. Flattened shells also appear more stable than their 'inflated' counterparts (fullerene 'onions' and buckytubes) when the shell dimensions obey specific criteria. (C) 1997 Elsevier Science B.V.