Thin gold layer in NiCo and Ni electroforming process: optical surface characterization

G. Sironi; D. Spiga; L. Raimondi; G. Pareschi; A. Orlandi; G. Borghi; N. Missaglia; B. Negri

doi:10.1117/12.857195

29 July 2010 Thin gold layer in NiCo and Ni electroforming process: optical surface characterization

G. Sironi, D. Spiga, L. Raimondi, G. Pareschi, A. Orlandi, G. Borghi, N. Missaglia, B. Negri

Proceedings Volume 7732, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray; 77322R (2010) https://doi.org/10.1117/12.857195
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

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.

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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); https://doi.org/10.1117/12.857195

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