In recent years ion beam erosion with energetic particles becomes a promising technique for large area nanostructuring of surfaces. Due to self-organization processes caused by low-energy ion beam erosion, well ordered ripple and dot patterns can evolve on different semiconductor materials [1-3]. This pattern formation is related to the complex interplay between curvature dependent sputtering and different surface relaxation mechanisms. It is well known that the evolution of ripple and dot patterns depends on sputtering conditions like ion energy, ion incidence angle and ion fluence. For example by varying the ion incidence angle a dot-ripple-dot transition is observed [4].
In this contribution results for the evolution of ripple and dot nanostructures on Si and Ge surfaces with sizes below 100 nm, using Xe+ ions (ion energy ≤ 2000 eV) for oblique ion incidence without sample rotation at room temperature, are presented. In this context, it will be shown that the settings of the multiaperture two-grid ion optical system of the Kaufman-type broad beam ion source used in the experiments also influence the evolution of patterns. These settings, neglected up to now in many studies, influence the angular distribution of ions within the ion beam and the beam divergence. One of the ion optical parameters is the voltage Uacc applied on the second grid called acceleration grid. This parameter is crucial not only for the evolution of patterns on the surface but also for their lateral ordering. For the given experimental setup of the ion source an increase of Uacc leads to an increase of angular distribution and beam divergence and the opposite for decreasing values. Additionally by varying the beam divergence a topographical transition, for example, from ripples to dots is observed on Si and Ge surfaces. Further, by choosing appropriate values of Uacc and the ion incidence angle an almost perfect array of dot patterns covering the whole sample area is observed.
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[5] B. Ziberi, et. al., Appl. Phys. Lett. 88, 173115 (2006). |