Ion bombardment induced atom redistribution in amorphous targets: MD versus BCA

Atom redistribution is an important mechanism of ion bombardment induced spontaneous pattern formation in amorphous or amorphized targets. It may be characterized by either molecular dynamics (MD) simulations or by Monte Carlo (MC) simulations based on the binary collision approximation (BCA). In this work we analyze problems of the BCA approach in predicting atom redistribution by comparing MC and MD simulations of recoil events in amorphized Si. We find that the MC results critically depend on the displacement energy used, on the choice of the free flight paths and maximum impact parameters, and on the construction of the trajectories. Moreover, the net atom redistribution as determined by MD is significantly larger for recoils starting near the surface than for bulk recoils. The effect is not reproduced by the MC simulations.