Internal electron emission in metal-insulator-metal thin film tunnel devices bombarded with keV argon and gold-cluster projectiles

The kinetic excitation of a solid surface under bombardment with energetic ions is studied via internal electron emission in a metal-insulator-metal junction. Particular attention was focused on the dependence of the internal emission yield on the impact angle of the projectile ions, which was measured and compared to corresponding data for external emission. We find the internal and external yields to behave differently, therefore delivering complementary information regarding the depth distribution of the kinetic excitation profile. A first attempt to interpret the internal emission yield in terms of a simple electron emission model is described and shown not to be sufficient to explain the experimentally observed behavior. Besides atomic ions, measurements of the internal emission yield under bombardment with cluster projectiles were performed, which are shown to exhibit a nonlinear yield enhancement similar to that of the sputter yield. This finding constitutes a new case in the observation of 'vicinage effects' in cluster-initiated kinetic excitation, which is attributed to the transition from a linear collision cascade to a collisional spike.