Ion Tracks in Metals and Intermetallic Compounds

Abstract

When an energetic ion penetrates a target, it loses its energy via two nearly independent processes: (1) elastic collisions with the nuclei (nuclear-energy loss (dE/dx)n), which dominate the ion slowing down in the low energy range (i.e., in the stopping region); (2) electronic excitation and ionization (electronic-energy loss (dE/dx)e), which strongly overwhelm (dE/dx)n in the high energy range (typically above 1 MeV/nucleon). Until the 1980s, researchers considered that electronic-energy deposition could participate in damaging creation in many insulators, but the effects observed in bulk metals were solely ascribed to elastic nuclear collisions. This widely held opinion was due to the fact that in metallic systems the numerous very mobile conduction electrons allow a fast spreading of the deposited energy and an efficient screening of the space charge created in the projectile wake so that it seemed unreasonable to hope for damage creation or track formation in metallic targets following high levels of electronic-energy deposition.A particular case is the observation more than 30 years ago of damage in thin or discontinuous. metallic films after fission fragment irradiation or MeV heavy ion bombardment. The spreading of the deposited energy is then strongly limited by the close vicinity of surfaces and interfaces.