Surface Finishing Method Using Plasma Chemical Vaporization Machining for Narrow Channel Walls of X-Ray Crystal Monochromators

Takashi Hirano; Yuki Morioka; Shotaro Matsumura; Yasuhisa Sano; Taito Osaka; Satoshi Matsuyama; Makina Yabashi; Kazuto Yamauchi

doi:10.20965/ijat.2019.p0246

Special Issue on Precision Surface Finishing

Surface Finishing Method Using Plasma Chemical Vaporization Machining for Narrow Channel Walls of X-Ray Crystal Monochromators

Takashi Hirano, Yuki Morioka, Shotaro Matsumura, Yasuhisa Sano, Taito Osaka, Satoshi Matsuyama, Makina Yabashi, Kazuto Yamauchi

Author information

Takashi Hirano
Department of Precision Science and Technology, Graduate School of Engineering, Osaka University
Yuki Morioka
Department of Precision Science and Technology, Graduate School of Engineering, Osaka University
Shotaro Matsumura
Department of Precision Science and Technology, Graduate School of Engineering, Osaka University
Yasuhisa Sano
Department of Precision Science and Technology, Graduate School of Engineering, Osaka University
Taito Osaka
SPring-8 Center, RIKEN
Satoshi Matsuyama
Department of Precision Science and Technology, Graduate School of Engineering, Osaka University
Makina Yabashi
SPring-8 Center, RIKEN
Kazuto Yamauchi
Department of Precision Science and Technology, Graduate School of Engineering, Osaka University

Keywords: X-ray optical device, channel-cut crystal, X-ray free-electron laser, atmospheric-pressure plasma, damage-free etching

JOURNAL OPEN ACCESS

2019 Volume 13 Issue 2 Pages 246-253

DOI https://member-cnki-net-s-1416.res.gxlib.org.cn:443/rwt/1416/https/MSYXTLUQPJUB/10.20965/ijat.2019.p0246

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Abstract

Channel-cut Si crystals are useful optical devices for providing monochromatic X-ray beams with extreme angular stability. Owing to difficulties in the high-precision surface finishing of narrow-channel inner walls of the crystals, typical channel-cut crystals have considerable residual subsurface crystal damage and/or roughness on their channel-wall reflection surfaces that decrease intensity and distort the wavefronts of the reflected X-rays. This paper proposes a high-precision surface finishing method for the narrow-channel inner walls based on plasma chemical vaporization machining, which is a local etching technique using atmospheric-pressure plasma. Cylinder- and nozzle-shaped electrodes were designed for channel widths of more than 5 and 3 mm, respectively. We optimized process conditions for each electrode using commercial Si wafers, and obtained a removal depth of 10 μm with a surface flatness and roughness of less than 1 μm and 1 nmRMS, respectively, which should allow the damaged layers to be fully removed while maintaining the wavefront of coherent X-rays.

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