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29 July 2010 Thin gold layer in NiCo and Ni electroforming process: optical surface characterization
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Mandrel replication by NiCo electroforming is an upgrade of the well-suited X-ray mirrors manufacturing process with pure Nickel. In this process, a Gold layer deposited on the mandrel acts as release agent and, at the same time, as reflective coating. To increase the optical performances of X-ray mirrors, the replicated optical surface is meant to reproduce the smooth topography of the mandrel: a surface degradation is commonly observed, indeed. A factor leading to surface smoothness worsening can be the spontaneous roughness growth of the Gold layer itself; therefore, the optical quality of the reflecting surface might be improved by optimizing the Gold layer thickness. A preliminary study, aimed at investigating the effects of Gold thickness reduction (< 100 nm Vs. the usual 200 nm), had already been dealt in the spectral range 0.02-1000 μm: measurements performed on flat electroformed samples showed that the Gold thickness reduction chiefly affects the roughness around 1 μm. Here we presents a study of the effectiveness of a Gold layer with reduced (< 100 nm) thickness in the NiCo X-ray mirrors electroforming, aimed at surface micro-roughness mitigation. The characterization, in the spectral range 0.02-1000 μm, of 3 X-ray mirrors manufactured utilizing Gold layers with different thickness values from a flight mandrel is reported. The performed investigation is organized as follows: (a) characterization of the flight mandrel; (b) dependence of the micro-roughness from different Gold layers thicknesses supported by XRD study; (c) comparison of the micro-roughness of mirrors manufactured in NiCo in Ni, with the same Gold layer thickness. As a conclusive remark the effects of the Gold layer thinning on the angular degradation at high energy are reported.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
G. Sironi, D. Spiga, L. Raimondi, G. Pareschi, A. Orlandi, G. Borghi, N. Missaglia, and B. Negri "Thin gold layer in NiCo and Ni electroforming process: optical surface characterization", Proc. SPIE 7732, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, 77322R (29 July 2010);


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