Ion-beam-eroded semiconductor materials can generically show, depending on the experimental parameters and setup, a plethora of self-organized large-area surface patterns. However, as recently reported by Allmers et al. J. Vac. Sci. Technol. B 24, 582 (2006), localized structures such as islands covered with hexagonally arranged dots surrounded by a basically flat surface can also evolve. Extending a recently developed continuum approach for the evolution of surface morphologies by ion-beam erosion, we present two scenarios how such localized structures can be understood: (i) by ion-beam inhomogeneities or (ii) by finite localized initial surface perturbations.
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