Ion Channeling and High-Energy Shadowing

Abstract

Ion-induced electron emission from a crystal target is influenced by ion channeling and related effects because of the restricted impact parameters in the ion—atom collisions in the crystal. In this chapter the concept of the ion-beam shadowing effect, which is familiar for keV-energy ions, is extended to MeV or higher-energy ions and is consistently linked to ion channeling. To do this, we discuss ion—atom elastic scattering over a wide energy range of the ions in a unified manner, on a classical as well as a quantum-mechanical basis. At low ion energies the ion-beam shadowing effect is directly related to the shadow of an individual atom, while at high ion energies it essentially corresponds to ion channeling near the surface, which can generally be understood by Lindhard’s standard continuum model of channeling. Such a viewpoint is essential to understand electron emission under channeling incidence conditions.