Ion Induced Surface Patterning - The Role of Surface Currents


Ion Induced Surface Patterning - The Role of Surface Currents

Facsko, S.; Liedke, B.; Ou, X.; Heinig, K. H.

The formation of these periodic surface patterns during ion irradiation is generally ascribed to the interplay of a sur- face instability, i.e. ion induced roughening, and smoothing mechanisms [2]. Different mechanisms have been proposed for surface roughening: The Bradley-Harper (BH) mecha- nism describes the curvature dependent sputtering whereas the Carter-Vishnyakov (CV) mechanism accounts for mass drift by momentum transfer from the incoming ions. Sur- face smoothing is accomplished by surface diffusion, and surface viscous flow [2].
2.2. ReverseEpitaxy
At temperature above the dynamic recrystallization temper- ature of the material a new kind of pattern is formed on the surface during ion irradiation [3]. At these conditions the surface remains crystalline and an additional surface in- stability appears due to the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms or vacancies to cross terrace steps. The symmetry of the pattern is now given by the crystalline symmetry of the surface. In Figure 1 patterns on different crystalline Ge surfaces irradiated with 1 keV Ar+ at normal incidence are shown: a checkerboard pattern with four-fold symmetry on the Ge(100) surface ori- ented along h100i crystal directions is visible in the atomic force microscopy (AFM) in Fig. 1a). On the Ge(111) sur- face a pattern with three-fold symmetry is formed by ion irradiation (Fig. 2b).

Keywords: ion irradiation; self-organized patterning; ripples

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