Low-energy ion induced sputtering of pre-patterned fused silica surfaces
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1181-DD13-15
Low-energy ion beam sputtering of pre-patterned fused silica surfaces
J. Völlner, B. Ziberi, F. Frost, B. Rauschenbach Leibniz-Institut für Oberflächenmodifizierung e.V. (IOM) Permoserstr. 15, D-04318 Leipzig, Germany E-mail: [email protected]
ABSTRACT Ripple formation and smoothing of pre-patterned fused silica surfaces by low-energy ion beam erosion have been investigated. As pre-pattern ripple surfaces produced by low-energy Ar+ ion beam erosion were used. In addition to the enhanced ripple formation on the pre-patterned surfaces also the smoothing characteristics of surface is changed. Due to the anisotropic surface roughness of the ripple pattern the irradiation direction with respect to the pre-pattern becomes important. It is suggested that all of these effects are related to surface gradient dependent sputtering and therefore it is an important mechanisms also in the low-energy ion beam erosion of fused silica surfaces.
INTRODUCTION In 1962, Navez et al. observed the first ripple structures on glass surface induced by ion beam erosion [1]. Since then a diversity of surface pattern topographies such as well ordered dot and ripple structures were found for nearly all material classes and have been discussed extensively. Different roughening and smoothing processes were discussed which contribute to surface patterning and smoothing by energetic ion beams [2-4]. Nevertheless, the experimental and theoretical work in the area of self-organized ion beam patterning of glasses such as fused silica is less investigated. As a potential optical material with notable physical and chemical properties fused silica is nearly irreplaceable as a material for lenses or light deliveries especially in the deep ultraviolet spectral range (DUV). The evolution of surface features on fused silica [5] and glass [6] was investigated depending on, e. g. the ion incidence angle, ion energy or fluence. Although, the Bradley-Harper model [7] predicts the ripple orientation successfully, the ripple coarsening over time is not explained yet. In general, former investigations of the evolution of fused silica during ion beam erosion were focused on initially smooth surfaces. Recently it was shown for Si and Ag surfaces that the initial surface topography can strongly affects the ion induced ripple formation [8,9]. Therefore, in the present study surface smoothing and ripple formation on pre-patterned fused silica surfaces were investigated. As pre-pattern ripple surfaces produced by low-energy Ar+ ion beam erosion at oblique ion incidence angles were used. The rippled surface also offers a model system to study the influence on a non-isotropic surface roughness on the ripple formation and surface smoothing.
EXPERIMENTAL METHODS For the experiments described below a custom-built ion beam etching system with a base pressure below 2 × 10-6 mbar was used. The samples were mounted on a water-cooled sample holder that offers the possibility of rotating around its axis with about 12 rotations per minute. Additionally,
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