6. Evolution of Topography Under Low-Energy Ion Bombardment

The sputtering of the surface by low-energy ion irradiation presented in the last chapter leads directly to roughening of the surface. The behavior can be described by relations of dynamic scaling theory and stochastic growth equations. The surface after ion irradiation with ion energies above the displacement energy is initially characterized by the formation of vacancies, interstitial sites, and adatoms, some of which coalesce into clusters. The kinetics of growth of surface defects in the early stages of ion irradiation is influenced primarily by two factors, the ion energy and the temperature during bombardment. In the specific case of a high nuclear energy loss, carters are created. As ion irradiation progresses, increasingly extended defects form on the surface, whereby a distinction must be made between intra- and Inter-crystalline surface defects. The evolution of individual defects such as cones, pyramids, etch pits, facets, etc. is discussed in detail as a function of the irradiation parameters. The theoretical description of ion beam-induced surface evolution is based on the assumption that the sputtering yield is exclusively a function of the local surface curvature and higher spatial derivatives of the local surface height. This assumption allows the surface evolution to be considered spatially and temporally as a moving wavefront and to apply geometrical methods developed in optics. Finally, secondary ion beam-induced mechanisms, such as grazing incidence ion reflection, re-deposition, shadowing, surface diffusion, non-uniform bombardment, viscous flow, and swelling are presented, which can have an additional significant effect on the topography evolution.