FAIR, Facility for Antiproton and Ion Research, is a new international accelerator facility for the research with antiprotons and ions. It will be built in cooperation of an international community of countries and scientists.Fundamental questions of the evolution of the universe, the structure of matter and its building blocks will be approached with the physics at FAIR.

Materials modification by Swift Heavy Ions

Ions with energies in the keV energy range are regularly used in the semiconductor industry for device fabrication. Irradiation at higher energies can also induce favourable structural changes in the irradiated sample. The irradiation effects of the so-called Swift Heavy Ions (SHIs), ions with specific energies in the range of 1 MeV / amu range, are of a particular interest.

SHIs induce a cylindrical region of structural transformation known as ion track. Ion tracks in SiO2 can be used to change its refractive index or as a mean to induce anisotropy for etching. Furthermore, it was recently found out that ion irradiation can be used to induce a shape transformation in metal nanocrystals (NCs) that are embedded in silica. Spherical NCs elongate along the ion beam direction and are shaped into nanorods or prolate spheroids.

TEM images initially spherical (left) and elongated nanocrystals (right) in silica after irradiation

This phenomenon can be exploited to produce large arrays of equally aligned nanocrystals, which is difficult to achieve otherwise. The mechanism by which this transformation occurs is unclear. The effects of SHIs impacts in materials are poorly understood on the atomic scale and a predictive theory is essential for the controllability of the SHI-induced structural changes.The simulations help us to explain and provide an insight into the fundamentals of ion-solid interactions. The modelling of SHIs is very challenging as, contrary to the ions with lower energies, they induce intense electronic excitations. Incorporating the excitations is especially difficult in insulators, and the methods have not yet been fully established.