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A.S. El-Said, W. Meissl, M. Simon, J.R. Crespo López-Urrutia, C. Lemell, J. Burgdörfer, I. Gebeshuber, Hp. Winter, J. Ullrich, C. Trautmann, M. Toulemonde, F. Aumayr:
"Potential energy threshold for nano-hillock formation by impact of slow highly charged ions on a CaF₂(111) surface";
Nuclear Instruments & Methods in Physics Research Section B, 258 (2007), 167 - 171.

We investigate the formation of nano-sized hillocks on the (111) surface of CaF2 single crystals by impact of slow highly charged ions.
Atomic force microscopy reveals a surprisingly sharp and well-defined threshold of potential energy carried into the collision of about
14 keV for hillock formation. Estimates of the energy density deposited suggest that the threshold is linked to a solid-liquid phase transition
(``melting´´) on the nanoscale. With increasing potential energy, both the basal diameter and the height of the hillocks increase. The
present results reveal a remarkable similarity between the present predominantly potential energy driven process and track formation by
the thermal spike of swift ( GeV) heavy ions.
2007 Elsevier B.V. All rights reserved.
PACS: 34.50.Dy; 79.20.Rf; 61.80.Jh

http://dx.doi.org/10.1016/j.nimb.2006.12.142