Surface patterning by low energy ion sputtering

The morphology of surfaces after erosion by ion sputtering show very different char-acteristics depending on the ion beam parameters and the material properties. The surface exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns, like periodic rip-ples or hexagonally ordered dots [1,2]. The structures of these patterns have small sizes in the range of 10 to 100 nm and show a high degree of ordering. Therefore, they have attracted strong interest recently as templates for nanostructured thin film deposition [3]. On materials whose surface turns amorphous during the ion erosion the formation of the periodic patterns relies on at least two interplaying processes: roughening of the surface due to the local variation of sputtering yield and smoothing via diffusion processes. Therefore, the surface morphology depends strongly on the details of the energy deposition by the incoming ions and on the details of the surface diffusion.
At the atomic level, the atomic sputtering, the creation of surface defects, and the influence of the ion beam on surface diffusion processes play a decisive role for the morphology evolution. In the case of single charged ions, the energy deposition is dissipated mainly kinetically in a collision cascade which leads finally to the emission of the sputtered atoms and the creation of defects.

[1] A. Keller, S. Rossbach, S. Facsko and W. Möller, Nanotechnology 19, 135303 (2008).
[2] S. Facsko et al., Science 285, 1551 (1999), F. Frost et al., Phys. Rev. Lett. 85, 4116 (2000).
[3] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mucklich, S. Facsko and J. Fassbender