Microscopic observations of metallic inclusions generated along the path of MeV clusters in CaF2

Fluorite (CaF2) crystals were irradiated at 300 K with MeV cluster (Au-4, C-10, C-60) ions at normal incidence. After irradiation, the samples were observed in a transmission electron microscope. During observations, the samples were kept at low temperature (approximate to 100 K) in order to avoid the formation of metallic inclusions due to electron irradiation. The cluster ions are shown to create intermittent tracks which are stable under the electron beam. The tracks consist of aligned faceted anion voids, which can also be viewed as calcium inclusions. These inclusions appear as having fully developed {1 0 0} faces, indicating that there is always a good epitaxy with the surrounding fluorite lattice. After irradiation with 30 MeV C-60 the typical dimension of these metallic inclusions is of about 10 nm. Furthermore, surface contrasts associated to sputtering are sometimes observed at the track entrance and exit. (C) 1998 Elsevier Science B.V. All rights reserved.