MeV-energy Xe ion-induced damage in LiF: The contribution of electronic and nuclear stopping mechanisms

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The contribution of electronic and nuclear damage mechanisms in the modification of structure and micromechanical properties of LiF crystals irradiated with 52, 224, and 450 MeV Xe ions at fluences 1010–1014 ions cm−2 has been studied. The ion-induced formation of dislocations and hardening in LiF at fluences above 1010 ions cm−2 has been observed. The depth profiles of nanoindentation show a joint contribution of electronic excitation and nuclear (impact) mechanisms to the ion-induced hardening. The electronic excitation mechanism dominates in the major part of the ion range while the impact mechanism prevails in a narrow zone at the end of the ion range. The efficiency of hardening produced by electronic excitations is by one order of magnitude higher than that produced by the impact mechanism. Ion-induced prismatic dislocation loops are the main cause of the hardening. At an electronic energy loss above the threshold of 10 keV nm−1, an ordered dislocation structure is created. HRXRD measurements on heavily irradiated LiF crystals (at fluences above 1012 Xe cm−2) reveal a mosaic type substructure composed of nanosize domains tilted under low angles.