Formation of ion damage tracks

Abstract

The formation of damage tracks in insulators from the passage of energetic (MeV/amu) ions indicates that the energy lost by an ion to electronic excitation is partially transferred to atomic motion. It is known that a track consists of localized regions of extended defects that are separated by lengths that exhibit only point defects. The utility of tracks for selective detection of various types of ions arises because of preferential chemical etching along the track as compared to etching the bulk material. In this letter we propose a new model to explain both the localized damage regions and the preferential etching of damage tracks. The formation of each region of extended defects is initiated by the Auger decay of a vacancy produced in an inner electronic shell of an atom of the insulator by the incident ion. This decay produces an intense source of ionization within a small volume around the decaying atom, which causes decomposition of the material in a manner similar to that observed in pulsed laser irradiation. The resulting chemical or crystalline modification of the material is the latent track, which because of its changed structure can be preferentially etched.