Graphitization of amorphous carbon and its transformation pathways

The graphitic ordering of the amorphous state of carbon has been a long-standing challenge. Whilst there are numerous transformation methodologies, including the high-temperature-pressure approach, there are still many unclear elements concerning the mechanism. By employing classical molecular dynamics simulations, the process of graphitization of amorphous carbon is modelled and analyzed. A systematic study of various schemes of loading conditions suggests that (1) axial strain is a vital ingredient in the transformation, and (2) there exists a close relationship between the mean layer atomic density of the amorphous carbon structure and the graphitization process. Furthermore, the non-simultaneity (i.e., in a delayed manner) of structure loading (by high-temperature annealing and straining) promotes a greater extent of graphitization, as compared to a concurrent means. More interestingly, edge and non-edge bonds behave dissimilarly in response to a change in the atomic density, and graphitization prevails at different stages of the fast and slow loading schemes. Virial pressure calculations validate the structural stability. (C) 2013 AIP Publishing LLC.