Defect-induced carbon nanoscroll formation

Carbon nanoscrolls (CNSs), a graphitic structure formed by rolling of a graphene plane, must overcome an energy barrier in order to form. This energy barrier is the result of competing interactions between the van der Waals force, which wants to cause overlap of the graphene, and the torsional or bending force, which resists bending of the graphene plane. In this study we used molecular dynamics simulation to examine the effect of vacancies on the CNS formation dynamics. We found that the energy barrier, which must be overcome to obtain a stable scroll structure, can be lowered or completely eliminated by introducing vacancies. Individual vacancy and divacancy configurations are studied and found to reduce the torsional bending energy by allowing local stress relaxation around the defect site. A structural transition diagram is created in which we show the energy barrier height for a range of vacancy concentrations and CNS rolling widths. These results provide the theoretical backing for a new method of fabricating CNSs using a focused ion beam and shed new light on the self-rolling phenomenon in graphene. (C) 2015 Elsevier Ltd. All rights reserved.