Regensburg 2013 – scientific programme

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DS: Fachverband Dünne Schichten

DS 2: Focus Session: Ion Beam Induced Surface Patterns I

DS 2.5: Invited Talk

Monday, March 11, 2013, 11:45–12:15, H32

Movement of a ripple pattern by ion beam irradiation — •Paul Alkemade — Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands

When a beam of energetic ions bombards a material, atoms are being sputtered from the material's surface. Even if the surface is initially smooth, the bombardment might induce surface roughness, often in a more or less regular pattern. These patterns can be a nuisance in sputter deposition or 3-dimensional materials analysis, but are also potentially beneficial, e.g. as anti-reflection layers.

Depending on the material's bulk and surface composition, the temperature, and the type, energy and angle of the ion beam different pattern types might evolve. A very common one is a ripple pattern, evolving under off-normal incidence on amorphous surfaces.

Various physical mechanisms can determine the pattern evolution. So far almost all experimental and theoretical studies address the growth or decay of the ripple amplitude. However, study of the lateral movement of the ripples can reveal crucial details of the mechanisms.

The angular dependence of the sputter rate predicts that at off-normal incidence ripples move against the ion beam direction, but recent experiments show otherwise. In this talk I will show that beam-driven viscous flow and relaxation of beam-induced stress can explain the observed direction of the moving ripples.