Molecular Dynamics Simulations of Coulomb Explosion

摘要

A swift ion creates a track of electronic excitations in the target material. A net repulsion inside the track can cause a 'Coulomb Explosion', which can lead to damage and sputtering of the material. Here we report results from molecular-dynamics (MD) simulations of Coulomb explosion for a cylindrical track as a function of charge density and neutralization/quenching time,(tau). Screening by the free electrons is accounted for using a screened Coulomb potential for the interaction among charges. The yield exhibits a prompt component from the track core and a component, which dominates at higher excitation density, from the heated region produced. For the cases studied, the number of atoms ejected per incident ion, i.e. the sputtering yield Y, is quadratic with charge density along the track as suggested by simple models. Y((tau)= 0.2 Debye periods) is nearly 20% of the yield when there is no neutralization ((tau)(yields)(infinity)). The connections between 'Coulomb explosions', thermal spikes and measurements of electronic sputtering are discussed.