Thin solid films appear most commonly in polycrystalline form, which means that they have highly constrained single-crystalline grains. Polycrystalline films are used in a large variety of  devices, such as magnetic storage media, catalytic and thermal elements, protective coatings.  It is thus desirable to extend to polycrystalline films, the approaches which have been developed for the self-organized formation of nanostructures on single-crystalline metal substrates [1].

We report on the formation of periodic metal nanostructures induced by self-organized sputtering processes of polycrystalline metal films supported on dielectric substrates. These results qualitatively agree with the behaviour reported for off–normal sputtering experiments on single-crystal metals where periodic ripples endowed with wavelengths in the 10 nm range are observed [2].

At variance with the latter case, we found that a non-singular starting surface morphology does plays a critical role in guiding self-organization during the early stages, where the hierarchical distribution of polycrystalline grains imposes a non-stochastic spatial modulation of the ion impact sites.

We also discuss the role of grain boundaries in this self-organization process: although providing an additional bias for diffusion of mobile defects ona 100 nm scale, they do not limit the propagation of nanoscale ripples which extend for several micrometers across the individual grains .

[1] U. Valbusa et al., J. Phys. Condens. Matter 14 (2002) 8153

[2]A. Toma, D. Chiappe, B. Šetina Batič, M. Godec, M. Jenko,  F. Buatier de Mongeot, submitted

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1. Single Molecule Magnets On Metallic Surfaces
2. Self-organized metal nanowire arrays with plasmonic functionality and tunable optical anisotropy