Molecular Dynamics Simulation Studies Of Displacement Cascade In Gold Nanowires And Nanotubes

Displacement cascade in gold nanowires and gold nanotubes was studied using molecular dynamics computer simulations.Primary knock-on atoms(PKAs)with different kinetic energies were initiated either at the surface or at the center of the gold nanowires.And nanowires with different diameters were implemented in the simulations.We found three kinds of defects that were induced by the cascade,including point defects,stacking faults and crater at the surface.The starting points of PKAs influence the number of residual point defects.In the first case,PKAs were started at the center.Under this circumstance,the final number of self-interstitial atoms is dependent on the diameter of the nanowire,nevertheless the final number of vacancies does not show a clear trend when diameters of nanowires are changed.In the second case,PKAs were started at the surface.Under this condition,due to that the influence of surface is the donimant factor which determines the evolution of point defects,the residual number of point defects in nanowires with different diameters are nearly the same.Formation of stacking faults that expanded the whole cross-section of gold nanowires was observed when the PKA's kinetic energy was higher than 5 ke V.The mechanism of the formation process has been fully analysed.Increasing the PKA's kinetic energy up to more than 10 ke V may lead to the formation of crater at the surface of nanowires due to microexplosion of hot atoms.All these factors,namely initial positions of PKAs,formation of stacking faults as well as the craters induced by higher energy irradiation,would influence the ability of radiation resistance of gold nanowires.Gold nanotubes with different external and internal diameters are investigated.PKAs with kinetic energy of 1 ke V were initiated at the surface of all the nanotubes.With increasing the internal diameters of the nanotubes while the external diameter is fixed,the increased area of the internal surface of the nanotubes leads to more point defects are absorbed by the surface.And consequently the residual number of point defect left inside the nanotubes are decreased.However,with increasing the internal diameters of the nanotubes,more HCP atoms are observed in the nanotubes at the end of the simulations.Furthermore the possibilities of formation of relative stable stacking faults are higher due to the HCP atomic layers are more easily to expand in nanotubes with smaller internal diameters.