Transformation of Amorphous Carbon Clusters to Fullerenes

Transformation of amorphous carbon clusters into fullerenes under high temperature is studied using molecular dynamics simulations at microsecond times. On the basis of the analysis of both the structure and energy of the system, it is found that fullerene formation occurs in two stages. First, fast transformation of the initial amorphous structure into a hollow sp 2 shell with a few chains attached occurs with a considerable decrease of the potential energy and the number of atoms belonging to chains and to the amorphous domain. Then insertion of the remaining carbon chains into the sp 2 network takes place at the same time as the fullerene shell formation. Two types of defects remaining after the formation of the fullerene shell are revealed: seven-membered rings and single one-coordinated atoms. One of the fullerene structures obtained contains no defects at all, which demonstrates that defect-free carbon cages can be occasionally formed from amorphous precursors directly without defect healing. No structural changes are observed after the fullerene formation, suggesting that defect healing is a slow process in comparison with the fullerene shell formation. The schemes of the revealed reactions of chain atom insertion into the fullerene shell just before its completion are presented. The results of the performed simulations are summarized within the paradigm of fullerene formation due to self-organization of the carbon system.