Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 84: Poster Focus Session: Structure and Chemistry of Metal-Oxide Surfaces

O 84.2: Poster

Mittwoch, 14. März 2018, 18:15–20:30, Poster A

Roughening prevention in reactive ion beam figuring of aluminium mirror surfaces — •Jens Bauer, Melanie Ulitschka, Frank Frost, and Thomas Arnold — Leibniz-Institut für Oberflächenmodifizierung, Permoserstraße 15, D-04318 Leipzig, Germany

Mirror optics for short-wavelength imaging applications demand superior optical surface properties, i.e. a high figure accuracy down to the atomic level as well as a low surface micro-roughness below 1 nm rms. Up to now it is not possible to meet those requirements by direct machining of optical Al surfaces made from technical alloy materials as AL6061 or AL905. Conventional machining technologies fail, since the surface roughness increases drastically as a result of structural, crystallographic and chemical matrix irregularities. Recently has been shown, that ultra-precision machining by reactive ion beams can be a promising approach for surface figuring without considerable increase of the surface roughness. Based on process investigations by WLI, AFM, and TOF-SIMS and supplemented by Monte Carlo simulations a phenomenological model is suggested. In particular, the usage of O₂ or N₂ containing process gas induces the formation of a homogeneous and temporally stable surface oxide or nidride layer, respectively. This layer results from a quasi-stationary equilibrium between ion implantation and sputter erosion due to the impact of the energetic reactive ions. The surface layer acts as an etching front moderating the inhomogeneous structural conditions of the aluminium bulk material. As a result, by use of reactive ion beams the surface roughness can now be preserved in its initial state during ultra-precision figure correction.