Papers by Author: Nobuyuki Zettsu

Abstract: The aspherical supermirror is among the most useful optics for focusing a neutron beam with a wide wavelength range. The improvement in surface roughness is essential for increasing the focusing gain. A highly efficient and high-precision fabrication process for the substrate of the aspherical mirror combining conventional precision grinding, numerically controlled local wet etching (NC-LWE) figuring, and low-pressure polishing was developed. Using this new fabrication process, plano-elliptical neutron-focusing mirror substrates were successfully fabricated with a figure error of submicrometer order and an rms surface roughness of less than 0.3 nm. In this report, the surface roughness of a quartz glass substrate for a neutron focusing supermirror was evaluated.

Abstract: Quartz resonator is a very important device to generate a clock frequency for information and telecommunication system. Improvement of the productivity of the quartz resonator is always required because huge amounts of resonator are demanded to install to various electronic devices. Resonance frequency of the quartz resonator is determined by the thickness of the quartz crystal wafer. Therefore it is essential to uniform the thickness distribution of the quartz crystal wafer with nanometric level. We propose the improvement process of the thickness distribution of the quartz crystal wafer by numerically controlled correction using atmospheric pressure plasma which is noncontact and chemical removal technique. We have already succeeded in obtaining a thickness uniformity of 33.1nm within 2 min in the thickness correction of an AT-cut quartz crystal wafer with an area of 24 mm × 24 mm. However, increase of removal rate and improvement of correction accuracy are required for industrial manufacturing. Heating effects of the quartz crystal wafer in the removal rate and the correction accuracy were investigated. The heating of the substrate and compensate of the scanning speed of the worktable in accordance with the variation of the surface temperature enabled an increase of 50% in removal rate and 10-nanometric-level accuracy in correction of the thickness distribution of the quartz crystal wafer.

Abstract: In the X-ray fluorescence analysis on sub-micron particle, application of the doubly curved crystal (DCC) spectrometer with Johansson-type geometry is effective to improve the lowest limit of detection because DCC makes it possible to focus and monochromatize an X-ray beam simultaneously. A strain-free crystal is essential for the high-performance focusing crystal spectrometer. We propose the application of the open-air type numerically controlled plasma chemical vaporization machining (NC-PCVM), which utilizes neutral reactive species generated by atmospheric pressure plasma, to fabricate the DCC substrate. By applying NC-PCVM technique, a curvature radius error of 0.08% was obtained, and there was no degradation of the crystallinity of the Si (111) substrate.

Abstract: Numerically controlled local wet etching (NC-LWE) is a novel technique to fabricate the ultraprecision optical components and/or finishing the functional materials. In this technique, a figuring is performed by controlling the dwelling time of the combination nozzle, which consists of a supply and a suction part of an etchant, on the workpiece. In this paper, we proposed fabrication process of millimeter-thick elliptical neutron focusing mirror substrate by applying NC-LWE figuring involving CeO2 slurry polishing. We fabricated a millimeter-thick elliptical neutron focusing mirror substrate with a figure error of less than 0.2 μm and obtained a surface roughness of less than 0.15 nm rms.

Abstract: A novel machining method combined with the irradiation of atmospheric pressure plasma was proposed for the finishing of difficult-to-machine materials. The irradiation of helium-based water vapor plasma efficiently oxidized the surface of single-crystal 4H-SiC (0001), and a ball-on-disc test using an alumina ceramic ball revealed that the wear rate of SiC, the surface of which was modified by the irradiation of water vapor plasma, is 20-fold higher than that of the surface without plasma irradiation. Plasma-assisted polishing using CeO2 abrasives enabled us to improve the surface roughness of SiC without introducing crystallographical subsurface damage, and a scratch-free surface with a roughness of less than 0.3 nm rms was obtained.

Abstract: We have developed numerically controlled local wet etching (NC-LWE) as a novel deterministic subaperture figuring and finishing technique, which is suitable for fabricating various optical components and finishing functional materials. In this technique, a chemical reaction between the etchant and the surface of the workpiece removes the surface without causing the degradation of the physical properties of the workpiece material. Furthermore, the processing properties of NC-LWE are insensitive to external disturbances, such as the vibration or thermal deformation of the machine or the workpiece, because of its noncontact removal mechanism. By applying the NC-LWE process using HF/HNO3 mixtures to etch the silicon, we corrected the thickness distribution of the bulk silicon wafer with a diameter of 200 mm and achieved the total thickness variation of less than 0.23 µm within the diameter of 190 mm.