Radiation defects in lithium fluoride induced by heavy ions

Single crystals of lithium fluoride were irradiated with various species of heavy ions in the energy regime between 1 and 30 MeV/u. The induced radiat ion damage was studied with techniques such as optical absorption spectrosc opy, small-angle X-ray scattering, chemical etching and profilometry, compl emented by annealing experiments. Clear evidence is given for a complex tra ck structure and defect morphology. Single defects such as F-centers are pr oduced in a large halo of several tens of nanometers around the ion traject ory. The defect creation in this zone is similar to that under conventional radiation. For heavy ions above a critical energy loss of 10 keV/nm, new e ffects occur within a very small core region of 2-4 nm in diameter. The dam age in this zone is responsible for chemical etching and for a characterist ic anisotropic X-ray scattering. It is assumed that in this core, complex d efect aggregates (e.g., cluster of color centers, molecular anions and vaca ncies) are created. Their formation is only slightly influenced by the irra diation temperature and takes place even at 15K where diffusion processes o f primary defects are frozen. Furthermore, irradiation with heavy ions lead s to pronounced swelling effects which can be related to an intermediate zo ne of around 10 nm around the ion path. (C) 1998 Elsevier Science B.V. All rights reserved.