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A.S. El-Said, R. Heller, W. Meissl, R. Ritter, S. Facsko, C. Lemell, B. Solleder, I. Gebeshuber, G. Betz, M. Toulemonde, W. Möller, J. Burgdörfer, F. Aumayr:
"Creation of Nanohillocks on CaF₂ Surfaces by Single Slow Highly Charged Ions";
Physical Review Letters, 100 (2008), 2376011 - 2376014.

Upon impact on a solid surface, the potential energy stored in slow highly charged ions is primarily
deposited into the electronic system of the target. By decelerating the projectile ions to kinetic energies as
low as 150 q eV, we find first unambiguous experimental evidence that potential energy alone is
sufficient to cause permanent nanosized hillocks on the (111) surface of a CaF2 single crystal. Our
investigations reveal a surprisingly sharp and well-defined threshold of potential energy for hillock
formation which can be linked to a solid-liquid phase transition.