Formation of Dislocation Structure in LiF Crystals Irradiated with Swift Heavy Ions under Oblique Incidence

The structural modifications of LiF irradiated with swift heavy ions under oblique angles have been investigated using AFM, SEM, chemical etching, nanoindentation and optical absorption spectroscopy. LiF crystals were irradiated under incidence angles of 30 and 70 degrees with 2.2 GeV Au (fluence 5 × $10^{11}$ ions $cm^{-2}$) and 150 MeV Kr ions (fluence $10^{12}-10^{14}$ ions $cm^{-2}$). Structural study on sample cross-sections shows that two damage regions, (1) nanostructured zone and (2) dislocation rich zone, which are typical for irradiations at normal incidence, appear also in samples irradiated under oblique angles. However in the latter case a more complex structure is formed that leads to stronger ion-induced hardening.