Electron emission during grazing impact of atoms on insulator and metal surfaces

Abstract

The coincident detection of projectile energy loss with the number of emitted electrons for the scattering of atoms from atomically clean and flat insulator and metal surfaces under grazing angles of incidence allows one to identify the relevant electron excitation and emission processes. From detailed studies for the scattering of H and He atoms from a LiF(001) as well as from an Al(111) surface we find evidence for clearly different interaction mechanisms. For not too high projectile velocities with respect to kinematic thresholds, electron emission for the insulator target is understood by an electronic promotion mechanism with the formation of H− ions as dominant precursor, whereas for the metal target electronic excitations are governed by direct energy transfer in binary collisions with the atomic projectiles. Based on these features we reveal a microscopic understanding for the well established, but so far poorly understood property that electron emission induced by atom or ion impact on insulator ...