Does local disorder influence secondary ion formation

The ionization probabilities of particles sputtered from a clean metallic single crystal surface bombarded under self-sputtering conditions (i.e. with projectiles of the same atomic species as the target material) are calculated using a hybrid computer simulation model based on a combination of molecular dynamics and excitation dynamics. The simulations reveal an apparent correlation between the ionization probability of a sputtered particle and the local lattice disorder at the point in space and time when it is being emitted from the surface. By examining cross correlations between emission time, local order and the local surface electron temperature, however, we find that particles exhibiting the highest ionization probability are being emitted in an early stage of the collision cascade, where the surface is still practically intact. Atoms emitted at later stages of the cascade can in principle benefit from an effective excitation energy confinement induced by the local disorder; the resulting ionization probability, however, is too low to significantly contribute to secondary ion formation. Copyright © 2014 John Wiley & Sons, Ltd.