Multiscale Simulations of Irradiation Effects of Bilayer Graphene Induced by Swift Heavy Ions

The damage production induced by swift heavy ion irradiation in bilayer graphene (BLG) is investigated. The radial dose distributions of delta rays produced by bismuth ions are calculated by Monte Carlo simulation. The radial dose rapidly decreases with increasing the distance from the path center. An unusual phenomenon is found that the velocity effect is not suitable for BLG the same as in the single layer graphene (SLG). The energy deposited into the lattice due to electron-phonon coupling is simulated by molecular dynamics method. By given energy to a cylindrical region, the carbon chains even nanoholes can be produced, which depends on the electronic energy loss (dE/dx). For BLG, the threshold electronic energy loss is lower than 6.5 keV/nm, which is lower than for SLG of 8 keV/nm. Through the calculation of density changes, a low density core and a high density shell structure can be seen while the tracks radii are obtained. With increasing dE/dx values, the track radius is first increasing and then saturates. At the end, the analysis of defects indicates that only a small part of the defects can be recombined and the radiation damage in BLG is less severe than in SLG.