Elongation or flattening of metal and semiconductor nanoclusters inside an insulating substrate has recently been demonstrated on several materials under swift heavy ion irradiation. The effect has been shown to be related to swift heavy ion track formation properties of the substrate. In recent experiments, a previously unresolved fine structure in ion tracks in amorphous silica was found comprising a low-density core and a high-density shell, and was confirmed by molecular dynamics (MD) simulations [1].

The origin of the fine structure is a picosecond time scale pressure wave out of the track center, creating a temporary low-density region around the ion path in several materials, and the observed nanocluster shape transformations may be closely linked to the process.

We present large-scale MD simulations on amorphous silica, and systems with Au and Ge nanoclusters under swift heavy ion irradiation, showing how the dynamics of track formation in the substrate and nanocluster material and dimensions affect the cluster shape transformation. Longer time scale effects are studied with kinetic Monte Carlo simulations and compared to experiments.

[1] P. Kluth, C. S. Schnohr, O. H. Pakarinen, F. Djurabekova, D. J. Sprouster, R. Giulian, M. C. Ridgway, A. P. Byrne, C. Trautmann, D. J. Cookson, K. Nordlund, and M. Toulemonde, Phys. Rev. Lett. 101 (2008) 175503.