Pronounced nonlinear behavior of atomic collision sequences induced by keV-energy heavy ions in solids and molecules

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Abstract
When an energetic ion hits a target consisting of atoms lighter than the projectile, the target configuration seen by the ion along its trajectory may differ significantly from the initial state. This nonlinear effect, which originates in rapidly moving recoil atoms, has been investigated by molecular-dynamics simulation mainly for the simple case where the target is a diatomic molecule. Nonlinear behavior has been distinguished from linear behavior by, respectively, switching on and off the interaction between target particles. Pronounced nonlinear effects have been found in energy loss and scattering angle of the ion; they have been classified roughly as clearing-the-way and blocking-the-way effects, depending on whether nonlinear behavior results in a low or high scattering probability. Effects on stopping power appear small for the small systems investigated. For ion-molecule collisions, the important conclusion is made that binary-scattering behavior need not be indicative of a spectator collision but may, if the ion mass exceeds the target mass, originate in the (nonlinear) clearing-the-way effect. The paper ends with a few results and tentative conclusions on ion-surface scattering with heavy ions.