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Polishability of thin electrolytic and electroless NiP layers

: Kinast, J.; Beier, M.; Gebhardt, A.; Risse, S.; Tünnermann, A.


Bentley, J.L. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optifab 2015 : 12-15 October 2015, Rochester, New York
Bellingham, WA: SPIE, 2015 (Proceedings of SPIE 9633)
ISBN: 978-1-62841-838-5
Paper 963311, 6 pp.
Conference "Optifab" <2015, Rochester/NY>
Conference Paper
Fraunhofer IOF ()

Ultra-precise metal optics are key components of sophisticated scientific instrumentation in astronomy and space applications, covering a wide spectral range. Especially for applications in the visible or ultra-violet spectral ranges, a low roughness of the optics is required. Therefore, a polishable surface is necessary. State of the art is an amorphous nickel-phosphorus (NiP) layer, which enables several polishing techniques achieving a roughness of <1 nm RMS. Typically, these layers are approximately 30 μm to 60 μm thick. Deposited on Al6061, the bimetallic effect leads to a restricted operational temperature, caused by different coefficients of thermal expansion of Al6061 and NiP. Thinner NiP layers reduce the bimetallic effect. Hence, the possible operating temperature range. A deterministic shape correction via Magnetorheological Finishing of the substrate Al6061 leads to low shape deviations prior to the NiP deposition. This allows for depositing thin NiP-layers, which are polishable via a chemical mechanical polishing technique aiming at ultra-precise metal optics. The present article shows deposition processes and polishability of electroless and electrolytic NiP layers with thicknesses between 1 μm and 10 μm.