Levy flight of atoms in collision cascadesD. Simeone1, L. Luneville2 and J. P. Both3
1 CEA, DEN, SRMA, LAZM, Equipe Mixte MFE - F-91191 Gif-sur-Yvette, France, EU
2 CEA, DEN, SERMA, LLPR, Equipe Mixte MFE - F-91191 Gif-sur-Yvette, France, EU
3 CEA, LIST, SSTM, LPSS - F-91191 Gif-sur-Yvette, France, EU
received 13 May 2008; accepted in final form 11 July 2008; published September 2008
published online 20 August 2008
In this work we analyze the ballistic phase of displacement cascades. Monte Carlo simulations performed with realistic cross-sections were used to calculate the probability density function, pL(l), describing the length traveled by a particle between two successive collisions within the binary collision approximation framework. From the analysis of pL(l), this work shows that the trajectories set displays a bifractal behavior. The comparison of different MC simulations clearly shows that this bifractality is only due to the long tail of pL(l). The unusual form of pL(l) implies that atoms displaced in the collision cascade during irradiation follow a Levy flight. Since the Levy law is scale invariant, an anomalous diffusion of atoms at large distances is then expected under irradiation and may explain experimental results.
61.43.Hv - Fractals; macroscopic aggregates (including diffusion-limited aggregates).
05.60.-k - Transport processes.
85.40.Ry - Impurity doping, diffusion and ion implantation technology.
© EPLA 2008