Kinetic electron emission from Cu induced by impact of slow Cs+ ions

We have studied kinetic energy distributions of electrons emitted from the surfaces of polycrystalline Cu bombarded by slow Cs+ ions below the classical threshold. The electron yields at Cs+ impact energies between 50 eV and 500 eV are presented as a function of the inverse Cs+ impact-velocities 1/v. We have analyzed the data in terms of a phenomenological model for a sub-threshold ion-induced kinetic electron emission.