Formation and decay of spherical concentric-shell carbon clusters

The influence of the kinetic energy of the electrons, E, on the formation rate and size distribution of concentric-shell carbon clusters (''bucky onions'') by in-situ electron irradiation of various carbon modifications was studied by transmission electron microscopy. In the energy range of 100 less than or equal to E less than or equal to 1250 keV the irradiation dose required for the complete transformation of an amorphous carbon film decreased with increasing E,indicating that neither heating nor electronic excitations provide the main driving force for the transformation of the starting material into onions. The instability of the onions at or near room temperature both during and after the electron irradiation shows that the onions are not an energetically favoured carbon modification and demonstrates that they must be looked upon as a dissipative structure. Their decay rate after irradiation is enforced by an amorphous environment.