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DS: Fachverband Dünne Schichten

DS 36: Postersession I

DS 36.32: Poster

Mittwoch, 22. März 2017, 17:00–19:00, P2-EG

Effect of a moderating etching front in reactive ion beam figuring of optical aluminium surfaces — •Jens Bauer, Frank Frost, and Thomas Arnold — Leibniz-Institut für Oberflächenmodifizierung, Permoserstraße 15, D-04318 Leipzig, Germany

Shape-adapted mirror optics are highly interesting for short-wavelength applications. Ion beam figuring is an established method in high-end optical surface manufacturing. But the direct machining of optical Al surfaces failed up to now, since the surface roughness increases drastically as a result of structural, crystallographic and chemical matrix irregularities. Our contribution focuses RIBE figuring of RSA Al6061 and Al905 with O₂ and N₂ containing process gas. In contrast to the classical RIBE scheme, no volatile process products are generated, but the machined surface is determinately chemically modified. A very stable and non-hazardous etch mechanism is obtained. The etch behaviour is analysed by WLI, AFM, and TOF-SIMS. Supplemented by Monte Carlo simulations a phenomenological model is presented. In particular, due to the impact of the energetic reactive ions a homogeneous and temporally stable surface oxide or nidride layer is formed. This layer results from a quasi-stationary equilibrium between ion implantation and sputter erosion. The surface layer acts as an etching front moderating the inhomogeneous structural conditions of the aluminium bulk material. Thus, the surface roughness is preserved almost in its initial state. Deterministic narrow ion beam operation via a dwell-time approach is now qualified for ultra-precision figure error correction of high-quality Al mirror optics.