Charge dynamics in proton-irradiated aluminum sheets*

Materials capable of withstanding continual ion radiation are highly desirable in space and nuclear applications. A detailed understanding of the mechanisms leading to degradation of materials under ion bombardment would enable targeted development of radiation resistant materials. As an energetic charged particle penetrates a material's surface, it deposits energy and excites electrons, leading to secondary electron (SE) emission and localized charge within the material. Even when direct collisions with nuclei are rare, fs scale surface charge dynamics may cause Coulomb explosion, which would damage and erode the material surface. We use time-dependent density functional theory to characterize SE emission, surface charge dynamics, and atomic forces in few-layer aluminum sheets under proton irradiation. From first-principles, we compute exit-side and entrance-side SE yields, SE energy spectra, and time scales of charge equilibration within the material as the projectile velocity and material thickness are varied. We also estimate the momentum acquired by aluminum atoms near the impact point. These simulations provide unprecedented insight into the dynamical response of materials' surfaces to ion bombardment.