[Zurück]

F. Aumayr, A.S. El-Said, W. Meissl, R. Heller, R. Ritter, S. Facsko, C. Lemell, B. Solleder, I. Gebeshuber, G. Betz, W. Möller, J. Burgdörfer:
"Potential energy threshold for nano-hillock formation on CaF₂ by impact of very slow, highly charged ions";
Poster: 14th Intern. Conf. on the Physics of Highly Charged Ions (HCI-2008), University of Electro-Communications, Chofu, Tokyo/Japan; 02.09.2008; in: "Book of Abstracts, 14th Intern. Conf. on the Physics of Highly Charged Ions", (2008), S. 123.

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. We present experiments with very slow (down to
impact velocities as low as 0.03 a.u. or 30 eV/amu) highly charged xenon ions creating hillock-like
topographic nanostructures on the surface of CaF2(111) single crystals which are stable in air and
non erasable by AFM scanning [1]. Surprisingly, these nanostructures closely resemble those
created by swift heavy ions at a CaF2 surface, while leaving deeper layers of the target undamaged.
We find first unambiguous experimental evidence that potential energy alone is sufficient to cause
these nano-sized hillocks. The observed dependence of the feature size on the kinetic energy of the
projectile ions is very weak. A sharp and well-defined threshold of potential energy is required for
the onset of nano-hillock formation [1,2].

Simulations of the dissipation of potential energy into the target material on the basis of an extended
classical over-the-barrier model have been performed to facilitate the interpretation of the
experimental findings [3]. The experimentally observed threshold of potential energy for hillock
formation is linked to a solid-liquid phase transition.

This work has been supported by Austrian Science Foundation FWF (P17449-N02 and M894-N02)
and by the European Project RII3\#026015. Transnational access to the Rossendorf ion beam
facilities was provided through AIM (EU contract no. 025646). A. S. El-Said was on leave of
absence from Nuclear and Radiation Physics Lab., Physics Department, Mansoura University,
Egypt.