Self-organized dot patterns on Si surfaces during noble gas ion beam erosion B. Ziberi * , F. Frost, B. Rauschenbach Leibniz-Institut fu ¨ r Oberfla ¨ chenmodifizierung e.V., Permoserstrasse 15, 04318 Leipzig, Germany Available online 17 April 2006 Abstract The erosion of target materials with energetic ions can lead to the formation of patterns on the surface. During low-energy (62000 eV) noble gas (Ne + , Ar + , Kr + , Xe + ) ion beam erosion of silicon surfaces dot patterns evolve on the surface. Dot structures form at oblique ion incidence of 75° with respect to surface normal, with simultaneous sample rotation, at room temperature. The lateral ordering of dots increases while the dot size remains constant with ion fluence, leading to very well ordered dot patterns for prolonged sputtering. Depending on ion beam parameters, dot nanostructures have a mean size from 25 nm up to 50 nm, and a mean height up to 15 nm. The formation of dot patterns depends on the ion/target mass ratio and on the ion energy. The temporal evolution and the lateral order- ing of these nanostructures is studied using scanning force microscopy (AFM). Ó 2006 Elsevier B.V. All rights reserved. Keywords: Sputtering; Silicon; Dot pattern; Atomic force microscopy; Self-organization 1. Introduction Self-organized spontaneous pattern formation during low-energy ion beam erosion is a cost-efficient ‘bottom up’ approach for the fabrication of large-area nanostruc- tures. Such nanostructures are promising candidates e.g. for the deposition of functional thin films or for the gener- ation of sub-wavelength nano-optic components. The formation of these patterns can be observed on various materials and is attributed to a surface instability between curvature dependent sputtering that roughens the surface and smoothing by different surface relaxation mechanisms [1–6]. For the technological important material silicon dot patterns are reported after Ar + ion beam erosion at normal ion incidence [7]. The dots have a marginal lateral ordering and a very small aspect ratio. Recently, it was reported about the possibility to form dot patterns on Si surfaces after low-energy Ar + ion beam erosion, at oblique ion inci- dence with simultaneous sample rotation [8]. The dot nano- structures show a very high lateral ordering with particular domains showing hexagonal arrangement of dots. In these work dot pattern formation due to low-energy (62000 eV) noble gas (Ne + , Ar + , Kr + , Xe + ) ion beam ero- sion of silicon surfaces at oblique ion incidence a ion = 75° with sample rotation at room temperature are analyzed. The formation of patterns depends on the kinematics between the incoming ions and the target atoms. While dot patterns are observed for ion energies up to E ion = 1000 eV with Ar + ions, for Kr + and Xe + ions dot patterns form for ion energies up to E ion = 2000 eV. Depending on ion beam parameters, i.e. ion energy, ion fluence the dots show a very high lateral ordering with size varying from 25 nm up to 50 nm. 2. Experimental details Samples used in this work were commercially available epi-polished Si(1 0 0) substrates (p-type, 0.01–0.02 X cm), with a root-mean-square (rms) roughness of 0.2 nm. The samples were mounted on a water-cooled substrate holder capable of revolving specimens about their axes. 0039-6028/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2005.12.072 * Corresponding author. Tel.: +49 341 235 3309; fax: +49 341 235 2595. E-mail address: bashkim.ziberi@iom-leipzig.de (B. Ziberi). www.elsevier.com/locate/susc Surface Science 600 (2006) 3757–3761