Morphologies of latent and etched heavy-ion tracks in {111} CaF₂

Structure details of latent tracks created by U, Pb and Au ions (energies 6.9, 28.7 and 11.1 MeV/A, respectively) in {111} CaF2 have been extracted by means of scanning force microscopy and transmission electron microscopy. The revealed structure has assisted in the interpretation of the etching behaviour of tracks created in {111} CaF2 by 9.2 MeV/A Bi ions. In the latter experiments, irradiated fragments were immersed for short durations in a 3:1 10% HCl/96% H2SO4 solution and the morphology of the formed etch pits was derived by high-resolution scanning electron microscopy and scanning force microscopy. Three conclusions emerged. First, ion-induced surface hillocks exhibit no resistance against etchant attack. Second, the primary etching diameter of the track coincides with the nanometric width of the structurally altered track core. Third, the structure of the etch pits, 3-faced symmetric pyramidal depressions with {122} faces, indicates that etching across the track halo, a few tens of nanometers wide strained crystal, is dominated by surface energies of crystal faces.