Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The dominating driving force for self-organisation of surface nanopattern during low-energy ion irradiation is still under discussion. Thus, so far continuum models cannot include 3D non-local processes of ion-solid interactions. On the other hand, till now atomistic simulations could not describe pattern dynamics on the spatiotemporal scale of experiments.
Combining collision cascades of ion impacts with continuum equations [1] is one approach to achieve a better understanding of mechanisms, like surface smoothing by an effective ‘downhill’ mass current which are neglected so far [2][3].
Here we present a novel program package, which unifies atomistic 3D simulations of the col-lision cascades with 3D kinetic Monte-Carlo simulations. Atom relocations were calculated with the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of ener-getic atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic lattice Monte Carlo program. Effects like ballistic mass drift or dependence of lo-cal morphology on sputtering yield are automatically included by this approach.
The mechanism of ripple formation induced by local surface currents is studied. The quantita-tive description of current vectors for different environmental parameters, and initial surface condition of sinusoidal structure, can be analized in time and space, following the local atomic drift. Different mechanisms can be distinguished. Without ion irradiation the mass current vec-tors parallel to the surface cause always surface smoothing by Mullins-Herring diffusion. Surface defects created by collsion cascades may inverse the surface mass currents, resulting in self-organization of nanopatterns.
Sputtering violates mass conservation of processes mentioned till now. The majority of pub-lished papers assume that sputtering is the dominating driving force for pattern formation. Here it will be shown that ripple patterns perpendicular to oblique ion impacts originate not from the sputtering process but from defect kinetics. Sputtering dominates only formation of ripple pat-terns parallel to the ion beam at grazing incidence.
[1] S. A. Norris and M. P. Brenner and M. J. Aziz J. Phys. Condens. Matter 21 (2009) 224017.
[2] G. Carter and V. Vishnyakov PRB 54 (1996) 17647.
[3] M. Moseler and P. Gumbsch and C. Casiraghi and A. C. Ferrari and J. Robertson Science 309 (2005) 1545.