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

Abstract

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.

Acknowledgments

The authors are indebted to Y. Seri for some of the SFM measurements in experiment 4. The authors thank Dr C. Trautmann, Dr K. Schwartz and Dr R. Neumann, GSI, Darmstadt, and Dr M. Toulemonde, GANIL, Caen, for performing the ion irradiations. SAS acknowledges a grant by the European Community – Access to Research Infrastructure Action of the Improving Human Potential Programme – for a research visit to the Angström Laboratory, Uppsala, and thanks F. Ericson and J. Lu for their guidance. This research was supported by the Israel Science Foundation, grant 23/03.