8. Low-Energy Ion Beam Bombardment-Induced Nanostructures

An attractive ion beam method is the possibility of spontaneous formation of ordered surface patterns in the form of nanodots/nanoholes or sinusoidal modulations of the surface (ripples) in the nanometer range. This method, based on self-organization, is characterized by the interplay of two low-energy processes induced by ion beams. The ion bombardment roughens the surface, while relaxation processes such as surface diffusion or/and beam-induced viscous flow smooth the surface. In this chapter, the formation of nanoripples with and without metallic contaminants is presented and the dependence of ripple formation on temperature, ion incidence angle, ion energy and co-deposited metal concentration is discussed. Bradley and Harper have proposed a continuum theory to describe the topography evolution and pattern formation. This theory is based on curvature-dependent sputtering, which is proportional to the locally deposited energy. In the following, it will be shown that, on the one hand, this theoretical concept can be extended by introducing nonlinear terms and, on the other hand, that the formation of surface patterns can be also explained by a directional redistribution of mass. Finally, the great application potential of this technology for effective, low-cost and scalable patterning of large areas of all materials is demonstrated.