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" (CE), which can lead to damage and sputtering of the material. Here we report results from molecular dynamics simulations of CEs for cylindrical tracks as a function of charge density and neutralization/quenching time, τ. 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 from the heated region produced, which dominates at higher excitation density. 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 does not depend greatly on τ for τ approx> τ_D (one Debye period), and even Y (τ = 0.2τ_D) is still nearly 20% of the yield when there is no neutralization (τ → ∞). The connections between 'CEs', thermal spikes and measurements of electronic sputtering are discussed.