Early stages of radiation damage in graphite and carbon nanostructures: A first-principles molecular dynamics study

Abstract

Understanding radiation-induced defect formation in carbon materials is crucial for nuclear technology and for the manufacturing of nanostructures with desired properties. Using first principles molecular dynamics, we perform a systematic study of the non-equilibrium processes of radiation damage in graphite. Our study reveals a rich variety of defect structures (vacancies, interstitials, intimate interstitial-vacancy pairs, and in-plane topological defects) with formation energies of 5-15 eV. We clarify the mechanisms underlying their creation and find unexpected preferences for particular structures. Possibilities of controlled defect-assisted engineering of nanostructures are analyzed. In particular, we conclude that the selective creation of two distinct low-energy intimate Frenkel pair defects can be achieved by using a 90-110 keV electron beam irradiation.

Stone-Wales-type transformations in carbon nanostructures driven by electron irradiation

“…We begin the presentation of our results with the description of experimental observations The above-presented result is in clear contrast with the earlier simulation results for graphite [18] where no SW (55-77) formation was observed for low θ. This discrepancy is caused by the neighboring graphene planes in the case of graphite: The displaced atom gets attached to the adjacent layer and does not therefore initiate a bond rotation.…”

“…Such changes are equally surprising, because the barrier for bond rotation is about 5 eV [6,17], which should exclude thermal activation as a cause for SW transformation at room temperature during experimentally relevant time scales. Regarding irradiation effects, previous simulations [18] showed that an energy of ∼ 30 eV must be transferred to a C atom in graphene in the in-plane direction for a bond rotation to occur. Also this cannot explain the frequently observed SW transformations under the usual TEM imaging conditions, since with typical acceleration voltages ( 300 kV) the transferred kinetic energy in the direction almost perpendicular to the electron beam will remain significantly below 10 eV.…”

Ion and electron irradiation-induced effects in nanostructured materials

“…However, such simulations should be feasible in the near future due to more and more powerful computers, as recent works 206,207 indicate. As DFT methods describe well the atomic structure of defects, the methods have successfully been used for simulations of the behavior of various defected systems.…”

Electron irradiation of nuclear graphite studied by transmission electron microscopy and electron energy loss spectroscopy

“…According to calculations by Thrower and Mayer [10] a 1 MeV electron and neutron produce an average of 1.6 and 500 atomic displacements respectively. It is generally understood that cascades of atomic displacements are the most common route for large scale structural disturbances and models have been developed to calculate the number of atoms involved in cascade events resulting from different incident energies [11].…”