Asymmetric behavior in the excitation of plasmons by ions entering or leaving a material in an oblique trajectory

In this work we analyze the production of bulk and surface plasmons by fast ions entering or leaving a material at different incidence angles. In the framework of a semi classical dielectric formulation, we study the different contributions to the induced potential, mainly in the vicinity of the surface, analyzing the differences and similarities that arise when in and out trajectories are compared. In particular, we find some novel oscillatory structures for both perpendicular and oblique trajectories