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Osaka T., Inoue I., Yamada J., et al. Hard x-ray intensity autocorrelation using direct two-photon absorption. Physical Review Research, 4, 1, L012035. https://doi.org/10.1103/PhysRevResearch.4.L012035., An intensity autocorrelation measurement is demonstrated to characterize a pulse duration of 9-keV x-ray free-electron laser (XFEL) pulses from a split-delay optical (SDO) system with four-bounce silicon 220 reflections in each branch. XFEL pulse replicas with variable time delays are generated by the SDO system itself. High intensity of >2×1016W/cm2 achieved in a self-seeding operation and careful data analysis allow the measurement with direct two-photon absorption. The autocorrelation trace gave a duration of 7.6±0.8fs in full width at half maximum for a Gaussian assumption. Furthermore, the trace shows good agreement with a simulation of the XFEL pulse shape propagating through the SDO system, irrespective of spectral chirps in the original XFEL pulses. Our results open the door toward direct temporal characterization of narrowband XFELs at the hard x-ray regime, such as self-seeded and future cavity-based XFELs, and indicate a solid way for temporal tailoring of ultrafast x-ray pulses with perfect crystals.

Osaka T., Inoue I., Yamada J., et al. Hard x-ray intensity autocorrelation using direct two-photon absorption. Physical Review Research, 4, 1, L012035. https://doi.org/10.1103/PhysRevResearch.4.L012035., An intensity autocorrelation measurement is demonstrated to characterize a pulse duration of 9-keV x-ray free-electron laser (XFEL) pulses from a split-delay optical (SDO) system with four-bounce silicon 220 reflections in each branch. XFEL pulse replicas with variable time delays are generated by the SDO system itself. High intensity of >2×1016W/cm2 achieved in a self-seeding operation and careful data analysis allow the measurement with direct two-photon absorption. The autocorrelation trace gave a duration of 7.6±0.8fs in full width at half maximum for a Gaussian assumption. Furthermore, the trace shows good agreement with a simulation of the XFEL pulse shape propagating through the SDO system, irrespective of spectral chirps in the original XFEL pulses. Our results open the door toward direct temporal characterization of narrowband XFELs at the hard x-ray regime, such as self-seeded and future cavity-based XFELs, and indicate a solid way for temporal tailoring of ultrafast x-ray pulses with perfect crystals.

Daisetsu Toh, Pho Van Bui, Kazuto Yamauchi, and Yasuhisa Sano, “Photoelectrochemical Oxidation Assisted Catalyst-Referred Etching for SiC (0001) Surface,” Int. J. Automation Technol., Vol.15, No.1, pp. 74-79, 2021., In a previous study, we developed an abrasive-free polishing method named catalyst-referred etching (CARE) and used it for the planarization of silicon carbide (SiC) (0001). In this method, Si atoms at step edges are preferentially removed through a catalytically assisted hydrolysis reaction to obtain an atomically smooth and crystallographically well-ordered surface. However, the removal rate is low (

Takato Inoue, Yuka Nishioka, Satoshi Matsuyama, Junki Sonoyama, Kazuteru Akiyama, Hiroki Nakamori, Yoshio Ichii, Yasuhisa Sano, Xianbo Shi, Deming Shu, Max D. Wyman, Ross Harder, Yoshiki Kohmura, Makina Yabashi, Lahsen Assoufid, Tetsuya Ishikawa, and Kazuto Yamauchi, "Optimal deformation procedure for hybrid adaptive x-ray mirror based on mechanical and piezo-driven bending system", Review of Scientific Instruments 92, 123706 (2021), https://doi.org/10.1063/5.0070465., A hybrid deformable x-ray mirror consisting of a mechanical bender and a bimorph deformable mirror has been developed to realize adaptive optical systems, such as zoom condenser optics, for synchrotron-radiation-based x-ray microscopy. In the developed system, both bending mechanisms comprehensively contribute to the formation of the target mirror shape and can narrow the role of piezoelectric actuators, thereby enabling a more stable operation. In this study, the behavior of the bimorph mirror under the clamped condition was investigated, and the sharing of the deformation amount for each bending mechanism was optimized to minimize the amplitude of the voltage distribution of the bimorph mirror.

Yasuhisa Sano, Ken Nishida, Ryohei Asada, Shinya Okayama, Daisetsu Toh, Satoshi Matsuyama, and Kazuto Yamauchi, "High-throughput deterministic plasma etching using array-type plasma generator system", Review of Scientific Instruments 92, 125107 (2021), https://doi.org/10.1063/5.0071623., A deterministic processing method is a high-precision finishing method, where the to-be-removed amount of material at each point of the work surface is calculated based on an accurately measured present surface shape and is removed precisely using a numerically controlled (NC) processing system. Although this method has achieved nanometer-scale accuracy, the method requires considerable time to scan the work surface, leading to low productivity. Therefore, using an individual on-off controllable array-type plasma generator covering the entire work surface, enabling simultaneous NC plasma processing is proposed herein. A novel intermittent gas flow system was constructed using cyclic on-off control of the gas supply and exhaust valves instead of the commonly used continuous gas flow to achieve uniform in-plane plasma etching. It was found that uniform removal could be achieved by combining it with a pulse-modulated high-frequency power supply and setting the plasma generation time in one cycle to be sufficiently short. Furthermore, a power control approach was developed for maintaining a constant plasma state, even while varying the plasma-generating array elements, which resulted in a demonstration experiment of NC plasma etching that successfully reduced the thickness variation of a silicon substrate.

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Satoshi Matsuyama, Kazuto Yamauchi, and Yasuhisa Sano, "An abrasive-free chemical polishing method assisted by nickel catalyst generated by in situ electrochemical plating", Review of Scientific Instruments 91, 045108 (2020), https://doi.org/10.1063/1.5141381., An abrasive-free polishing method using water and a Pt catalyst, called catalyst-referred etching (CARE), has been developed for the finishing of optical and semiconductor surfaces. This method realizes well-ordered surfaces with a smoothness of several tens of picometers without crystallographic disturbance. In this study, we propose a new CARE method using a Ni catalyst with in situ electrochemical plating and dissolution, which enable enhancing the catalytic capability of Ni. This method has advantages to realize more than ten times higher removal rate and better stability compared with the conventional CARE method.

Minami O., Ito R., Hosoo K., et al. Improvements in graphene growth on 4H-SiC(0001) using plasma induced surface oxidation. Journal of Applied Physics, 126, 6, 065301. https://doi.org/10.1063/1.5092336., A Si-face 4H-SiC surface was modified by plasma oxidation followed by HF etching. The resulting surface was covered with a carbon overlayer composed of C-C bonded clusters and Si-O-C bonding from Si4C4O4 and Si4C4-xO2 (x < 2), as evidenced by photoemission spectroscopy measurements and wetting properties. A trend was observed in which the thickness of the carbon overlayer was proportional to the SiO2 thickness after plasma oxidation, indicating that the former could be controlled on the subnanometer scale by adjusting plasma conditions. After a subsequent annealing under ultrahigh vacuum, we found that graphene grew on the modified SiC surface without the formation of a pitting morphology, which is in contrast to the case using an untreated SiC substrate. Raman spectroscopy revealed that the former graphene includes fewer defects than the latter graphene. We discuss the microscopic mechanism by which reaction products composed of C-C and Si-O-C bonds form in the SiO2 film near the SiO2/SiC interface via plasma oxidation as well as their influence on the subsequent growth of graphene.

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Naotaka Kidani, Satoshi Matsuyama, Yasuhisa Sano, Yoshitada Morikawa, and Kazuto Yamauchi, "Catalyzed chemical polishing of SiO2 glasses in pure water", Review of Scientific Instruments 90, 045115 (2019), https://doi.org/10.1063/1.5090320., A catalytically assisted etching system was developed for the ultra-precision fabrication of optical components, such as X-ray mirrors and extreme-ultraviolet mask blanks. This study demonstrates that an atomically smooth surface with a sub-Angstrom root-mean-square roughness could be achieved on a SiO2 glass substrate using pure water and Pt as the etching solution and catalyst, respectively. Density functional theory calculations confirmed that the mechanistic pathway was involved in catalyzed hydrolysis. The significant roles of the catalyst were clarified to be the dissociation of water molecules and the stabilization of a meta-stable state, in which a hypervalent silicate state is induced, and the Si-O backbond is elongated and loosened. To confirm the role of the catalyst, the Pt metal was replaced by Au, and the observed drastic difference in the removal rate was attributed to the degree of stabilization of the metastable state.

Pho Van Bui, Yasuhisa Sano, Yoshitada Morikawa, and Kazuto Yamauchi, “Characteristics and Mechanism of Catalyst-Referred Etching Method: Application to 4H-SiC,” Int. J. Automation Technol., Vol.12, No.2, pp. 154-159, 2018., A novel abrasive-free planarization method named catalyst-referred etching (CARE) was developed. A polishing pad is coated with a catalytic material to promote chemical etching of the work substrate. During processing, the topmost areas of the work substrate, which are in contact with the catalyst surface, are selectively etched off. Atomically highly ordered surfaces are obtained for many types of work substrates. In this paper, the removal characteristics and mechanism of CARE for single crystalline 4H-SiC are reviewed.

N. J. Hartley, N. Ozaki, T. Matsuoka, B. Albertazzi, A. Faenov, Y. Fujimoto, H. Habara, M. Harmand, Y. Inubushi, T. Katayama, M. Koenig, A. Krygier, P. Mabey, Y. Matsumura, S. Matsuyama, E. E. McBride, K. Miyanishi, G. Morard, T. Okuchi, T. Pikuz, O. Sakata, Y. Sano, T. Sato, T. Sekine, Y. Seto, K. Takahashi, K. A. Tanaka, Y. Tange, T. Togashi, Y. Umeda, T. Vinci, M. Yabashi, T. Yabuuchi, K. Yamauchi, and R. Kodama , "Ultrafast observation of lattice dynamics in laser-irradiated gold foils", Appl. Phys. Lett. 110, 071905 (2017) https://doi.org/10.1063/1.4976541., We have observed the lattice expansion before the onset of compression in an optical-laser-driven target, using diffraction of femtosecond X-ray beams generated by the SPring-8 Angstrom Compact Free-electron Laser. The change in diffraction angle provides a direct measure of the lattice spacing, allowing the density to be calculated with a precision of ±1%. From the known equation of state relations, this allows an estimation of the temperature responsible for the expansion as <1000 K. The subsequent ablation-driven compression was observed with a clear rise in density at later times. This demonstrates the feasibility of studying the dynamics of preheating and shock formation with unprecedented detail.

Ai Isohashi, P. V. Bui, D. Toh, S. Matsuyama, Y. Sano, K. Inagaki, Y. Morikawa, and K. Yamauchi, "Chemical etching of silicon carbide in pure water by using platinum catalyst", Appl. Phys. Lett. 110, 201601 (2017) https://doi.org/10.1063/1.4983206., Chemical etching of SiC was found to proceed in pure water with the assistance of a Pt catalyst. A 4H-SiC (0001) wafer was placed and slid on a polishing pad in pure water, on which a thin Pt film was deposited to give a catalytic nature. Etching of the wafer surface was observed to remove protrusions preferentially by interacting with the Pt film more frequently, thus flattening the surface. In the case of an on-axis wafer, a crystallographically ordered surface was obtained with a straight step-and-terrace structure, the height of which corresponds to that of an atomic bilayer of Si and C. The etching rate depended upon the electrochemical potential of Pt. The vicinal surface was observed at the potential at which the Pt surface was bare. The primary etching mechanism was hydrolysis with the assistance of a Pt catalyst. This method can, therefore, be used as an environmentally friendly and sustainable technology.

Jumpei Yamada, Satoshi Matsuyama, Shuhei Yasuda, Yasuhisa Sano, Yoshiki Kohmura, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi "Development of concave-convex imaging mirror system for a compact and achromatic full-field x-ray microscope", Proc. SPIE 10386, Advances in X-Ray/EUV Optics and Components XII, 103860C (6 September 2017); https://doi.org/10.1117/12.2272904.

Yasuhisa SANO, Kousuke SHIOZAWA, Toshiro DOI, Syuhei KUROKAWA, Hideo AIDA, Tadakazu MIYASHITA, Kazuto YAMAUCHI, High-efficiency planarization method combining mechanical polishing and atmospheric-pressure plasma etching for hard-to-machine semiconductor substrates, Mechanical Engineering Journal, 2016, 3(1), 15-00527, https://doi.org/10.1299/mej.15-00527., A high-efficiency planarization technique for preprocessing before final polishing is needed for hard-to-machine wide-band-gap semiconductors, such as silicon carbide (SiC), gallium nitride, and diamond. We proposed a novel planarization method that combines chemical mechanical polishing (CMP) and atmospheric-pressure plasma etching (plasma chemical vaporization machining [P-CVM]) and developed a prototype of the basic type CMP/P-CVM combined processing system. This prototype has a mechanical polishing part for introducing a damaged layer on the convex part of the sample surface and a P-CVM part for efficient etching of the damaged layer. Process conditions for plasma generation were determined in order to minimize the optical emission intensity ratio of nitrogen to helium because nitrogen comes from circumstance air and should not exist in the plasma region. Process conditions for mechanical polishing were determined in order to efficiently generate a damaged layer only on the convex part of the sample surface. The combined process was performed using a SiC substrate on which the mesa structure was fabricated as a sample. As a result, we found that the convex parts of the mesa structure were preferentially removed and the surface of the sample was planarized. We also found that the decreasing rate of the peak-to-valley value of the mesa structure obtained by CMP/P-CVM combined processing was approximately seven times greater than that during mechanical polishing.

T. Goto, S. Matsuyama, H. Nakamori, H. Hayashi, Y. Sano, Y. Kohmura, M. Yabashi, T. Ishikawa, and K. Yamauchi "Size-changeable x-ray beam collimation using an adaptive x-ray optical system based on four deformable mirrors", Proc. SPIE 9965, Adaptive X-Ray Optics IV, 996502 (27 October 2016); https://doi.org/10.1117/12.2238794.

H. Takei, S. Kurio, S. Matsuyama, K. Yamauchi, and Y. Sano, "Development of array-type atmospheric-pressure RF plasma generator with electric on–off control for high-throughput numerically controlled processes", Review of Scientific Instruments 87, 105121 (2016) https://doi.org/10.1063/1.4964656., An array-type atmospheric-pressure radio-frequency (RF) plasma generator is proposed for high-precision and high-throughput numerically controlled (NC) processes. We propose the use of a metal-oxide-semiconductor field-effect transistor (MOSFET) circuit for direct RF switching to achieve plasma on-off control. We confirmed that this type of circuit works correctly using a MOSFET with a small parasitic capacitance between its source and gate. We examined the design method for the distance between adjacent electrodes, which corresponds to the parasitic capacitance between adjacent electrodes and is very important in the individual on-off control of each electrode. We developed a prototype array-type plasma generator apparatus with 19 electrodes and the same number of MOSFET circuits; we then confirmed that each electrode could control its plasma on-off state individually. We also demonstrated that the thickness uniformity of the surface Si layer of a silicon-on-insulator wafer could be processed to less than 1 nm peak to valley by the NC sacrificial oxidation method using the apparatus.

Takumi Goto, Hiroki Nakamori, Takashi Kimura, Yasuhisa Sano, Yoshiki Kohmura, Kenji Tamasaku, Makina Yabashi, Tetsuya Ishikawa, Kazuto Yamauchi, and Satoshi Matsuyama, "Hard X-ray nanofocusing using adaptive focusing optics based on piezoelectric deformable mirrors", Review of Scientific Instruments 86, 043102 (2015) https://doi.org/10.1063/1.4916617., An adaptive Kirkpatrick-Baez mirror focusing optics based on piezoelectric deformable mirrors was constructed at SPring-8 and its focusing performance characteristics were demonstrated. By adjusting the voltages applied to the deformable mirrors, the shape errors (compared to a target elliptical shape) were finely corrected on the basis of the mirror shape determined using the pencil-beam method, which is a type of at-wavelength figure metrology in the X-ray region. The mirror shapes were controlled with a peak-to-valley height accuracy of 2.5 nm. A focused beam with an intensity profile having a full width at half maximum of 110 × 65 nm (V × H) was achieved at an X-ray energy of 10 keV.

P. V. Bui, A. Isohashi, H. Kizaki, Y. Sano, K. Yamauchi, Y. Morikawa, and K. Inagaki, "Study on the mechanism of platinum-assisted hydrofluoric acid etching of SiC using density functional theory calculations", Appl. Phys. Lett. 107, 201601 (2015) https://doi.org/10.1063/1.4935832., Hydrofluoric acid (HF) etching of the SiC surface assisted by Pt as a catalyst is investigated using density functional theory. Etching is initiated by the dissociative adsorption of HF on step-edge Si, forming a five-fold coordinated Si moiety as a metastable state. This is followed by breaking of the Si-C back-bond by a H-transfer process. The gross activation barrier strongly correlates with the stability of the metastable state and is reduced by the formation of Pt-O chemical bonds, leading to an enhancement of the etching reaction.

Taito Osaka, Takashi Hirano, Makina Yabashi, Yasuhisa Sano, Kensuke Tono, Yuichi Inubushi, Takahiro Sato, Kanade Ogawa, Satoshi Matsuyama, Tetsuya Ishikawa, and Kazuto Yamauchi "Development of split-delay x-ray optics using Si(220) crystals at SACLA", Proc. SPIE 9210, X-Ray Free-Electron Lasers: Beam Diagnostics, Beamline Instrumentation, and Applications II, 921009 (8 October 2014); https://doi.org/10.1117/12.2060238.

T. Goto, S. Matsuyama, H. Nakamori, T. Kimura, Y. Sano, Y. Kohmura, K. Tamasaku, M. Yabashi, T. Ishikawa, and K. Yamauchi "Development of a one-dimensional two-stage focusing system with two deformable mirrors", Proc. SPIE 9208, Adaptive X-Ray Optics III, 920802 (3 October 2014); https://doi.org/10.1117/12.2061821.

Yasuhisa Sano, Toshiro K. Doi, Syuhei Kurokawa, Hideo Aida, Osamu Ohnishi, Michio Uneda, Kousuke Shiozawa, Yu Okada and Kazuto Yamauchi, Dependence of GaN Removal Rate of Plasma Chemical Vaporization Machining on Mechanically Introduced Damage, Sens. Mater., Vol. 26, No. 6, 2014, p. 429-434., A high-efficiency planarization method combining atmospheric-pressure plasma etching [plasma chemical vaporization machining (PCVM)] and mechanical polishing is proposed. The convex part of a substrate surface, considered to be affected by mechanical action, is removed preferentially by PCVM. However, it is not evident whether the PCVM removal rate of the damaged layer of a gallium nitride (GaN) substrate increases. In this study, the dependence of removal rate on removal depth is investigated using a GaN substrate with a damaged layer. As a result, the removal rate of the damaged layer is observed to be three or four times greater than that of deep undamaged layers.

Jangwoo Kim, Takahisa Koyama, Hirokatsu Yumoto, Ayaka Nagahira, Satoshi Matsuyama, Yasuhisa Sano, Makina Yabashi, Haruhiko Ohashi, Tetsuya Ishikawa, and Kazuto Yamauchi "Damage characteristics of platinum/carbon multilayers under x-ray free-electron laser irradiation", Proc. SPIE 8848, Advances in X-Ray/EUV Optics and Components VIII, 88480S (27 September 2013); https://doi.org/10.1117/12.2022735.

S. Matsuyama, Y. Emi, H. Kino, Y. Sano, Y. Kohmura, K. Tamasaku, M. Yabashi, T. Ishikawa, and K. Yamauchi "Development of achromatic full-field x-ray microscopy with compact imaging mirror system", Proc. SPIE 8851, X-Ray Nanoimaging: Instruments and Methods, 885107 (26 September 2013); https://doi.org/10.1117/12.2023152.

Taito Osaka, Makina Yabashi, Yasuhisa Sano, Kensuke Tono, Yuichi Inubushi, Takahiro Sato, Kanade Ogawa, Satoshi Matsuyama, Tetsuya Ishikawa, and Kazuto Yamauchi "Thin crystal development and applications for hard x-ray free-electron lasers", Proc. SPIE 8848, Advances in X-Ray/EUV Optics and Components VIII, 884804 (27 September 2013); https://doi.org/10.1117/12.2023465.

Hiroki Nakamori, Satoshi Matsuyama, Shota Imai, Takashi Kimura, Yasuhisa Sano, Yoshiki Kohmura, Kenji Tamasaku, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi, "Experimental and simulation study of undesirable short-period deformation in piezoelectric deformable x-ray mirrors", Review of Scientific Instruments 83(5), 053701 (2012) https://doi.org/10.1063/1.4709499., To construct adaptive x-ray focusing optics whose optical parameters can be varied while performing wavefront correction, ultraprecise piezoelectric deformable mirrors have been developed. We computationally and experimentally investigated undesirable short-period deformation caused by piezoelectric actuators adhered to the substrate during mirror deformation. Based on the results of finite element method analysis, shape measurements, and the observation of x-ray reflection images, a guideline is developed for designing deformable mirrors that do not have short-period deformation errors. © 2012 American Institute of Physics.

S. Matsuyama, T. Wakioka, H. Mimura, T. Kimura, N. Kidani, Y. Sano, Y. Nishino, K. Tamasaku, M. Yabashi, T. Ishikawa, and K. Yamauchi "Development of a one-dimensional Wolter mirror for an advanced Kirkpatrick-Baez mirror", Proc. SPIE 7802, Advances in X-Ray/EUV Optics and Components V, 780202 (27 August 2010); https://doi.org/10.1117/12.860405., SPIE Optical Engineering + Applications, 2010, San Diego, California, United States, To realize achromatic full-field hard X-ray microscopy with a resolution better than 100 nm, we studied an imaging system consisting of an elliptical mirror and a hyperbolic mirror. The figure accuracies of the elliptical and hyperbolic mirrors required to obtain diffraction-limited resolution were investigated using a wave-optical simulator, and then elliptical and hyperbolic mirrors were precisely fabricated, following the criterion of the figure accuracies. Experiments to form a demagnified image of a one-dimensional slit installed 45 m upstream were conducted using the imaging system at an X-ray energy of 11.5 keV at BL29XUL of SPring-8. The system could form a demagnified image with the best resolution of 78 nm. In addition, the field of view to obtain a resolution better than 200 nm was 4.2 micron. © 2010 SPIE.

Takashi Kimura, Hidekazu Mimura, Soichiro Handa, Hirokatsu Yumoto, Hikaru Yokoyama, Shota Imai, Satoshi Matsuyama, Yasuhisa Sano, Kenji Tamasaku, Yoshiki Komura, Yoshinori Nishino, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi , "Wavefield characterization of nearly diffraction-limited focused hard x-ray beam with size less than 10 nm", Review of Scientific Instruments 81(12), 123704 (2010) https://doi.org/10.1063/1.3509384., In situ wavefront compensation is a promising method to realize a focus size of only a few nanometers for x-ray beams. However, precise compensation requires evaluation of the wavefront with an accuracy much shorter than the wavelength. Here, we characterized a one-dimensionally focused beam with a width of 7 nm at 20 keV using a multilayer mirror. We demonstrate that the wavefront can be determined precisely from multiple intensity profiles measured around the beamwaist. We compare the phase profiles recovered from intensity profiles measured under the same mirror condition but with three different aperture sizes and find that the accuracy of phase retrieval is as small as 12. © 2010 American Institute of Physics.

Hideyuki Hara, Yoshitada Morikawa, Yasuhisa Sano, and Kazuto Yamauchi Phys. Rev. B 79, 153306 (2009)., We study the effect of adsorbates on the relative stability of hexagonal and cubic stacking sequences at the topmost SiC bilayers of 4H-SiC (0001) -1×1 surfaces using first-principles calculations. We investigate F-terminated, OH-terminated, H-terminated, and clean surfaces, and in all cases, the cubic structure is more stable than the hexagonal structure. The energy difference between the two structures, however, significantly depends on adsorbates and is largest on the clean surface while it is smallest on the H-terminated surface. Stabilization of the cubic structure at F-terminated and OH-terminated surfaces is in contradiction to a simple argument based on the electrostatic interaction and we attribute it to orbital hybridization between occupied states of adsorbates and unoccupied states of the substrate surface. The present results suggest a possible means of controlling step bunching and the SiC stacking sequence by surface adsorbates. © 2009 The American Physical Society.

Hidekazu Mimura, Hirokatsu Yumoto, Satoshi Matsuyama, Soichiro Handa, Takashi Kimura, Yasuhisa Sano, Makina Yabashi, Yoshinori Nishino, Kenji Tamasaku, Tetsuya Ishikawa, and Kazuto Yamauchi Phys. Rev. A 77, 015812 (2008)., We present a remarkably accurate method for determining the wave field of an x-ray nanobeam. The intensity profile of a beam was directly measured over a range of three orders of magnitude while its phase distribution was successfully recovered using an iterative algorithm. The evolution of the wave field along the beam propagation direction was precisely simulated, and there was good agreement with the experimental results.

Yasuhisa Sano, Kazuya Yamamura, Hidekazu Mimura, Kazuto Yamauchi, and Yuzo Mori, "Fabrication of ultrathin and highly uniform silicon on insulator by numerically controlled plasma chemical vaporization machining", Review of Scientific Instruments 78(8), 086102 (2007) https://doi.org/10.1063/1.2766836., Metal-oxide semiconductor field-effect transistors fabricated on a silicon-on-insulator (SOI) wafer operate faster and at a lower power than those fabricated on a bulk silicon wafer. Scaling down, which improves their performances, demands thinner SOI wafers. In this article, improvement on the thinning of SOI wafers by numerically controlled plasma chemical vaporization machining (PCVM) is described. PCVM is a gas-phase chemical etching method in which reactive species generated in atmospheric-pressure plasma are used. Some factors affecting uniformity are investigated and methods for improvements are presented. As a result of thinning a commercial 8 in. SOI wafer, the initial SOI layer thickness of 97.5±4.7 nm was successfully thinned and made uniform at 7.5±1.5 nm. © 2007 American Institute of Physics.

Hidekazu Mimura, Hirokatsu Yumoto, et al. "Efficient focusing of hard x rays to 25nm by a total reflection mirror", Appl. Phys. Lett. 90(5), 051903 (2007) https://doi.org/10.1063/1.2436469., Nanofocused x rays are indispensable because they can provide high spatial resolution and high sensitivity for x-ray nanoscopy/spectroscopy. A focusing system using total reflection mirrors is one of the most promising methods for producing nanofocused x rays due to its high efficiency and energy-tunable focusing. The authors have developed a fabrication system for hard x-ray mirrors by developing elastic emission machining, microstitching interferometry, and relative angle determinable stitching interferometry. By using an ultraprecisely figured mirror, they realized hard x-ray line focusing with a beam width of 25 nm at 15 keV. The focusing test was performed at the 1-km -long beamline of SPring-8. © 2007 American Institute of Physics.

Kenta Arima, Hideyuki Hara, et al. "Atomic-scale flattening of SiC surfaces by electroless chemical etching in HF solution with Pt catalyst", Appl. Phys. Lett. 90(20), 202106 (2007) https://doi.org/10.1063/1.2739084., The authors present a method for flattening SiC surfaces with Pt as a catalyst in HF solution. The mechanism for flattening SiC surfaces is discussed. The flattened 4H-SiC (0001) surface is composed of alternating wide and narrow terraces with single-bilayer-height steps, which are induced by the rate difference of the catalytic reactions between adjacent terraces. Scanning tunneling microscopy images reveal a 1×1 phase on the terraces. The 1×1 phase is composed of coexisting of F- and OH-terminated Si atoms, which originate from the polarization of the underlying Si-C bonds. © 2007 American Institute of Physics.

S. Matsuyama, H. Mimura, et al. "Development of mirror manipulator for hard-x-ray nanofocusing at sub-50-nm level", Review of Scientific Instruments 77(9), 093107 (2006) https://doi.org/10.1063/1.2349594, X-ray focusing using Kirkpatrick-Baez (KB) mirrors is promising owing to their capability of highly efficient and energy-tunable focusing. We report the development of a mirror manipulator which enables KB mirror alignment with a high degree of accuracy. Mirror alignment tolerances were estimated using two types of simulators. On the basis of the simulation results, the mirror manipulator was developed to achieve an optimum KB mirror setup. As a result of focusing tests at BL29XUL of SPring-8, the beam size of 48 × 36 nm 2 (V×H) was achieved in the full width at half maximum at an x-ray energy of 15 keV. Spatial resolution tests showed that a scanning x-ray microscope equipped with the KB focusing system could resolve line-and-space patterns of 80 nm linewidth in a high visibility of 60%. © 2006 American Institute of Physics.

S. Matsuyama, H. Mimura, et al. "Development of scanning x-ray fluorescence microscope with spatial resolution of 30nm using Kirkpatrick-Baez mirror optics", Review of Scientific Instruments 77(10), 103102 (2006) https://doi.org/10.1063/1.2358699., We developed a high-spatial-resolution scanning x-ray fluorescence microscope (SXFM) using Kirkpatrick-Baez mirrors. As a result of two-dimensional focusing tests at BL29XUL of SPring-8, the full width at half maximum of the focused beam was achieved to be 50×30 nm2 (V×H) under the best focusing conditions. The measured beam profiles were in good agreement with simulated results. Moreover, beam size was controllable within the wide range of 30-1400 nm by changing the virtual source size, although photon flux and size were in a trade-off relationship. To demonstrate SXFM performance, a fine test chart fabricated using focused ion beam system was observed to determine the best spatial resolution. The element distribution inside a logo mark of SPring-8 in the test chart, which has a minimum linewidth of approximately 50-60 nm, was visualized with a spatial resolution better than 30 nm using the smallest focused x-ray beam. © 2006 American Institute of Physics.

Hirokatsu Yumoto, Hidekazu Mimura, Satoshi Matsuyama, Soichiro Handa, Akihiko Shibatani, Keiko Katagishi, Yasuhisa Sano, Makina Yabashi, Yoshinori Nishino, Kenji Tamasaku, Tetsuya Ishikawa, and Kazuto Yamauchi "At-wavelength figure metrology of total reflection mirrors in hard x-ray region", Proc. SPIE 6317, Advances in X-Ray/EUV Optics, Components, and Applications, 631709 (29 August 2006); https://doi.org/10.1117/12.681587.

Yumoto H., Mimura H., Matsuyama S., et al. At-wavelength figure metrology of hard x-ray focusing mirrors. Review of Scientific Instruments, 77, 6, 063712 (2006) https://doi.org/10.1063/1.2216870, We have developed an at-wavelength wave-front metrology of a grazing-incidence focusing optical systems in the hard x-ray region. The metrology is based on numerical retrieval from the intensity profile around the focal point. We demonstrated the at-wavelength metrology and estimated the surface figure error on a test mirror. An experiment for measuring the focusing intensity profile was performed at the 1-km-long beamline (BL29XUL) of SPring-8. The obtained results were compared with the profile measured using an optical interferometer and were confirmed to be in good agreement with it. This technique is a potential method of characterizing wave-front aberrations on elliptical mirrors for sub-10-nm focusing. © 2006 American Institute of Physics.

Hirokatsu Yumoto, Hidekazu Mimura, Satoshi Matsuyama, Hideyuki Hara, Kazuya Yamamura, Yasuhisa Sano Kazumasa Ueno, Katsuyoshi Endo Yuzo Mori, Makina Yabashi, Yoshinori Nishino, Kenji Tamasaku, Tetsuya Ishikawa and Kazuto Yamauchi, "Fabrication of elliptically figured mirror for focusing hard x rays to size less than 50nm", Review of Scientific Instruments 76(6), 063708 (2005) https://doi.org/10.1063/1.1922827., In this study, we designed, fabricated, and evaluated a hard x-ray focusing mirror having an ideally focused beam with a full width at half maximum in the intensity profile of 36 nm at an x-ray energy of 15 keV. The designed elliptically curved shape was fabricated by a computer-controlled fabrication system using plasma chemical vaporization machining and elastic emission machining, on the basis of surface profiles accurately measured by combining microstitching interferometry with relative angle determinable stitching interferometry. A platinum-coated surface was employed for hard x-ray focusing with a large numerical aperture. Line-focusing tests on the fabricated elliptical mirror are carried out at the 1-km -long beamline of SPring-8. A full width at half maximum of 40 nm was achieved in the focused beam intensity profile under the best focus conditions. © 2005 American Institute of Physics.

S. Matsuyama, H. Mimura, et al. "Diffraction-limited two-dimensional hard-x-ray focusing at the 100nm level using a Kirkpatrick-Baez mirror arrangement", Review of Scientific Instruments 76(8), 083114 (2005) https://doi.org/10.1063/1.2005427., The spatial resolution of scanning x-ray microscopy depends on the beam size of focused x rays. Recently, nearly diffraction-limited line focusing has been achieved using elliptical mirror optics at the 100 nm level. To realize such focusing two-dimensionally in a Kirkpatrick-Baez system, the required accuracies of the mirror aligners in this system were estimated using optical simulators based on geometrical or wave-optical theories. A focusing unit fulfilling the required adjustment accuracies was constructed. The relationships between alignment errors and focused beam profiles were quantitatively examined at the 1 km long beamline (BL29XUL) of SPring-8 to be in good agreement with the simulation results. © 2005 American Institute of Physics.

Hidekazu Mimura, Hirokatsu Yumoto, Satoshi Matsuyama, Kazuya Yamamura, Yasuhisa Sano, Kazumasa Ueno, Katsuyoshi Endo, Yuzo Mori, Makina Yabashi, Kenji Tamasaku, Yoshinori Nishino, Tetsuya Ishikawa and Kazuto Yamauchi, "Relative angle determinable stitching interferometry for hard x-ray reflective optics", Review of Scientific Instruments 76(4), 045102 (2005) https://doi.org/10.1063/1.1868472, Metrology plays an important role in surface figuring with subnanometer accuracy. We have developed relative angle determinable stitching interferometry for the surface figuring of elliptical mirrors, in order to realize hard x-ray nanofocusing. In a stitching system, stitching angles are determined not by the general method using a common area between neighboring shots, but by the new method using the mirror's tilt angles measured at times when profile data are acquired. The high measurement accuracy of approximately 4 nm (peak-to-valley) was achieved in the measurement of a cylindrical surface having the same curvature as the elliptically designed shape to enable hard x-ray nanofocusing. © 2005 American Institute of Physics.

Satoshi Matsuyama, Hidekazu Mimura, Kazuya Yamamura, Hirokatsu Yumoto, Yasuhisa Sano, Katsuyoshi Endo, Yuzo Mori, Makina Yabashi, Kenji Tamasaku, Yoshinori Nishino, Tetsuya Ishikawa, and Kazuto Yamauchi "Wave-optical and ray-tracing analysis to establish a compact two-dimensional focusing unit using K-B mirror arrangement", Proc. SPIE 5533, Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications II, (18 October 2004); https://doi.org/10.1117/12.567515., Optical Science and Technology, the SPIE 49th Annual Meeting, 2004, Denver, Colorado, United States, The spatial resolution of the scanning X-ray microscopy apparently depends on the beam size of the focused X-ray. Recently, highly accurate elliptical mirrors were reported to be fabricated, and nearly diffraction-limited line focusing was achieved. In this study, to realize diffraction-limited and 2-dimentional focusing with such highly accurate mirrors, accuracies to be realized in mirror alignings, for example, adjusting the glancing angle and the in-plane rotation, were estimated by employing two types of simulators. They are appropriately based on geometrical or wave-optical theories. They are alternatively employed according to the degree of accuracy required in the mirror alignment. A focusing unit with the adjusting mechanism fulfilling the required alignment accuracies was constructed, and the relationships between the alignment errors and focused beam profiles were quantitatively examined at the 1km-long beamline (BL29XUL) of SPring-8. Obtained results were in good agreement with the calculated results. Additionally, the alignment accuracy to be realized in the K-B unit equipping mirrors of larger NA (numerical aperture) was calculated to realize sufficient performances in focusing.

Yuzo Mori, Kikuji Hirose, Kazuto Yamauchi, Hidekazu Goto, Kazuya Yamamura and Yasuhisa Sano, Ultraprecision Machining based on Physics and Chemistry, Sens. Mater., Vol. 15, No. 1, 2003, p. 1-19., The paper overviews research preformed at “Osaka University, Ultra Precision Machining Research Center.” It explains in detail the historical background, motivation of the research, and physical concepts of new ultraprecision machining methods; i.e., elastic emission machining (EEM), atmospheric pressure plasma chemical vaporization machining (P-CVM) and hydroxyl electrochemical machining (H-ECM).

Yamauchi, K., Yamamura, K., Mimura, H., Sano, Y., Saito, A., Souvorov, A., Yabashi, M., Tamasaku, K., Ishikawa, T. & Mori, Y. (2002). J. Synchrotron Rad. 9, 313-316., An elliptical mirror for X-ray microfocusing was manufactured using the new fabrication methods of elastic emission machining and plasma chemical vaporization machining. Surface profiles measured using stitching interferometry showed a maximum deviation around the ideal figure of 7 nm peak-to-valley. The mirror showed nearly diffraction-limited focusing performance, with a 200 nm line width at the focus. Wave-optical calculations, taking the measured surface profile into consideration, reproduced well the measured focusing properties both at and around the beam waist.