Using atomistic computer simulations based on analytical potential and density-functional theory models, we study effects of ion irradiation on graphene. We identify the types and concentrations of defects which appear in graphene under impacts of various ions with energies ranging from tens of electron volts to megaelectron volts. For two-dimensional targets, defects beyond single and double vacancies are formed via inplane recoils. We demonstrate that the conventional approach based on binary-collision approximation and stochastic algorithms developed for bulk solids cannot be applied to graphene and other low-dimensional systems. Finally, taking into account the gas-holding capacity of graphene, we suggest the use of graphene as the ultimate membrane for ion-beam analysis of gases and other volatile systems which cannot be put in the high vacuum required for the operation of ion beams.

We report tensile failure experiments on paper sheets. The acoustic emission energy and the waiting times between acoustic events follow power-law distributions. This remains true while the strain rate is varied by more than two orders of magnitude. The energy statistics has the exponent β ∼ 1.25 ± 0.10 and the waiting times the exponent τ ∼ 1.0 ± 0.1, in particular for the energy roughly independent of the strain rate. These results do not compare well with fracture models, for (brittle) disordered media, which as such exhibit criticality. One reason may be residual stresses, neglected in most theories.

Double and single vacancies differently affect the conductance of carbon nanotubes [G. Gómez-Navarro et al., Nat. Mater. 4, 534 (2005)], so that the exact knowledge of the abundance of these defects is mandatory for an unambiguous interpretation of irradiation-induced changes in nanotube conductance. We calculate concentrations of defects produced by Ar ions using the molecular dynamics method combined with kinetic Monte Carlo simulations. Carefully taking into account the annealing of defects, we show that the ratio of single to double vacancies has a minimum at ion energies of about 0.5keV and that the ratio saturates toward a constant value at high ion energies.