Growth and modification of nanostructures with ion beams

Nanocluster ensembles and nanowires can be synthesised in surface layers of various substrates by high dose ion implantation. Atomistic computer simulations lead to a detailed understanding of ion deposition and subsequent precipitation [1]. Recently it has been demonstrated that ion beams can be also used to change properties of nanostructures drastically. Thus, at elevated temperatures, irradiation of nanocluster ensembles results in a narrowing of the size distribution, which can be described as “inverse Ostwald ripening” [2]. Irradiation of single-crystalline but chemically disordered nanostructures assists chemical ordering of alloys like FePt, which has a very high magnetic anisotropy in its well-ordered state and is, therefore, a favorite material for future magnetic recording [3]. And finally, metallic nano-spheres in SiO₂ can be shaped into rods or even wires by high-energy ion irradiation. This contribution will review theoretical studies and atomistic computer simulations on the phenomena listed above. It will be shown that all this phenomena have a common origin, the competition between two driving forces: (i) ion beam induced disordering (interface mixing, defect generation, …) which drives the system far from equilibrium and (ii) thermally activated processes like diffusion and phase separation which drives the system back towards the thermodynamic equilibrium.
[1] M. Strobel, K.-H. Heinig, W. Möller, Phys. Rev. B 64, 245422 (2001); T. Müller, K.H. Heinig, and W. Möller, Appl. Phys. Lett. 81, 2373 (2002); T. Müller, K.H. Heinig et al., Appl. Phys. Lett. 85, 2373 (2004).
[2] K.-H. Heinig et al., Appl. Phys. A 77, 17–25 (2003).
[3] H. Bernas, J.-Ph. Attane, K.-H. Heinig et al., Phys. Rev. Lett. 91, 077203 (2003).