Public Release:  Nano-hillocks: Of mountains and craters

Helmholtz Association


IMAGE: Following bombardment with highly charged ions, nano-hillocks have formed in an area of localized melting. This is an atomic force microscope image. view more

Credit: Picture: HZDR



Charge instead of speed

"If the goal is to deposit a maximum amount of energy on a tiny spot on the surface, it is of comparatively little use to simply bombard the surface with fast atoms," explains Prof. Friedrich Aumayr of the TU Vienna's Institute of Applied Physics. "Fast particles penetrate deep into the material thereby depositing their energy over a wide range." If, however, you first strip a large number of electrons from individual atoms and then allow these highly charged ions to collide with the material surface, the effects you get are quite dramatic as the energy that was previously required to ionize the atoms is now being released within a very small area of a few nanometers in diameter, and within an ultrashort time.

This can lead to melting of a very small volume of the material, loss of its orderly atomic structure, and, finally, its expansion. The large number of electronic excitations that result from the ion's interactions with the surface has a strong impact on the material and ultimately leads to the atoms being bumped out of position. The end-result is nano-hillock formation - the appearance of tiny protrusions on the material's surface. If the energy required to initiate melting of the material is insufficient, small holes or defects will form on or below the surface instead.

Elaborate experiments at the HZDR facility for highly charged ions were just as important to obtaining a detailed picture of the processes that take place at the material's surface as were computer simulations and extensive theoretical work. "At our new HZDR facility, we have the capabilities for deliberately forming nano-hillocks and nano-craters on surfaces. In close collaboration with the groups of our colleagues Friedrich Aumayr and Joachim Burgdörfer at the TU Vienna we succeeded to grasp the underlying physical mechanisms in more detail", explains Dr. Stefan Facsko. Egyptian physicist Dr. Ayman El-Said, who spent two years as a Humboldt Foundation fellow conducting research at HZDR, made substantial contributions to the current body of research in this field.

Assumptions confirmed



Publication: A.S. El-Said, R.A. Wilhelm, R. Heller, S. Facsko, C. Lemell, G. Wachter, J. Burgdörfer, R. Ritter, F. Aumayr: "Phase diagram for nanostructuring CaF2 surfaces by slow highly charged ions", in Physical Review Letters 109 (2012), 117602,, DOI-Link: 10.1103/PhysRevLett.109.117602

Further Information

Dr. René Heller
Institute of Ion Beam Physics and Materials Research at HZDR
Phone: +49 351 260-3617

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The HZDR has been a member of the Helmholtz Association (the largest scientific organization in Germany) since January 2011. It has four locations in Dresden, Leipzig, Freiberg and Grenoble, and employs around 900 people - approx. 400 of these being scientists and doctoral candidates.
