Irradiation-induced stiffening of carbon nanotube bundles

Recent experiments have demonstrated that electron irradiation of bundles of single-walled carbon nanotubes resulted in dramatic increase of the bundle bending modulus at moderate irradiation doses, followed by a decrease in mechanical properties at higher doses. To understand such a behavior, we employ molecular dynamics simulations with empirical potentials and analytical approximations to calculate defect production rates and mechanical properties of the irradiated nanotubes. We show that the observed peak in the bending modulus originates from a trade-off between irradiation-induced bundle stiffening via inter-tube covalent bonds and a drop in the Young's modulus of individual nanotubes due to vacancies. (C) 2004 Elsevier B.V. All rights reserved.