Formation of dislocations in LiF irradiated with 3He and 4He ions

Abstract

Influence of the irradiation with 13.5 MeV 3 He and 5MeV 4 He ions on the micro-structure and mechanical properties of LiF single crystals was studied. The depth profiles of nanoindentation, dislocation mobility, selective chemical etching and photoluminescence served for the characterization of damage. Strong ion-induced increase of hardness and decrease in dislocation mobility at the stage of track overlapping due to accumulation of dislocations and other extended defects was observed. At high fluences (10 15 ions/cm 2) the hardness saturates at about 3.5 GPa (twofold increase in comparison to a virgin crystal) thus confirming high efficiency of light projectiles in modifications of structure and properties. The depth profiles of hardness indicate on a notable contribution of elastic collision mechanism in the damage production at the end-ofrange region. The effects of ion-induced increase of hardness and decrease of dislocation mobility are observed also beyond the ion range and possible mechanisms of such damage are discussed. Highlights  The depth profiles of damage in LiF irradiated with 3 He and 4 He ions were studied.  High-fluence irradiation creates dislocation-rich structure and induces strong hardening.  Changes of LiF structure and properties were observed also beyond the ion range.  Mechanisms of damage beyond the ion range are discussed.