Scientists from Helmholtz-Zentrum Berlin (HZB) observed exotic behaviour from beryllium oxide (BeO) when they bombarded it with high-speed heavy ions: After being shot in this way, the electrons in the BeO appeared "confused", and seemed to completely forget the material properties of their environment. The researchers' measurements show changes in the electronic structure that can be explained by extremely rapid melting around the firing line of the heavy ions. If this interpretation is correct, then this would have to be the fastest melting ever observed. The researchers are publishing their results in Physical Review Letters (DOI:10.1103/Phys.Rev.Lett.105, 187603 (2010)).
In his experiments, Prof. Dr. Gregor Schiwietz and his team irradiated a beryllium oxide film with high-speed heavy ions of such strong charge that they possessed maximum smashing power. Unlike most other methods, the energy of the heavy ions was chosen so that they would interact chiefly with their outer valence electrons. As heavy ions penetrate into a material, there are typically two effects that occur immediately around the fired ions: the electrons in the immediate surroundings heat up and the atoms become strongly charged. At this point, Auger electrons are emitted, whose energy levels are measurable and show up in a so-called line spectrum. The line spectrum is characteristic for each different material, and normally changes only slightly upon bombardment with heavy ions.
As a world's first, the HZB researchers have now bombarded an ion crystal (BeO), which has insulator properties, with very high-speed heavy ions (xenon ions), upon which they demonstrated a hitherto unknown effect: The line spectrum of the Auger electrons changed drastically it became "washed out", stretching into higher energies. Together with a team of physicists from Poland, Serbia and Brazil, the researchers observed distinctly metallic signatures from the Auger electrons emitted by
|Contact: Prof. Dr. Gregor Schiwietz|
Helmholtz Association of German Research Centres