研究者詳細 - 佐々木　拓也

Reprint of: Automated geometric aberration correction for large-angle illumination STEM 査読有り国際誌

Ishikawa, R; Tanaka, R; Morishita, S; Kohno, Y; Sawada, H; Sasaki, T; Ichikawa, M; Hasegawa, M; Shibata, N; Ikuhara, Y

ULTRAMICROSCOPY 231 巻頁： 113410 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ultramicroscopy

Depth resolution in scanning transmission electron microscopy (STEM) is physically limited by the illumination angle. In recent notable progress on aberration correction technology, the illumination angle is significantly improved to be larger than 60 milliradians, which is 2 or 3 times larger than those in the previous generation. However, for three-dimensional depth sectioning with the large illumination angles, it is prerequisite to ultimately minimize lower orders of aberrations such as 2- and 3-fold astigmatisms and axial coma. Here, we demonstrate a live aberration correction using atomic-resolution STEM images rather than Ronchigram images. The present method could save the required time for aberration correction, and moreover, it is possible to build up a fully automated program. We demonstrate the method should be useful not only for axial depth sectioning but also phase imaging in STEM including differential phase-contrast imaging.

DOI： 10.1016/j.ultramic.2021.113410

Crystal and Electronic Structure of U7Te12-Type Tungsten Nitride Synthesized under High Pressure. 査読有り国際誌

Chang, CC; Sasaki, T; Gaida, NA; Niwa, K; Hasegawa, M

INORGANIC CHEMISTRY 60 巻 ( 17 ) 頁： 13278 - 13283 2021年9月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

Tungsten nitride continues to drive fundamental interests because of its potential as a functional compound, which combines features such as high hardness together with thermal, chemical, and wear resistance. Here, we report a novel tungsten nitride phase synthesized from MoC-type WN0.6 and molecular nitrogen after laser irradiation at P = 70 GPa in a diamond anvil cell. This novel phase is quenchable at ambient pressure and determined to be U7Te12-type tungsten nitride and crystallizes in the hexagonal space group (P6) having lattice parameters of a = 8.2398(3) Å, c = 2.94948(14) Å, and V = 173.423(13) Å3. Tungsten atoms are coordinated to eight and nine nitrogen atoms, higher than previously reported tungsten nitrides. The bulk modulus is determined to be K0 = 312 (5) GPa (K0′ = 4.0 fixed), and DFT calculations predict that U7Te12-type W7N12 has a metallic nature.

DOI： 10.1021/acs.inorgchem.1c01633

Phase relations and thermoelasticity of magnesium silicide at high pressure and temperature 査読有り国際誌

Gaida, NA; Niwa, K; Sasaki, T; Hasegawa, M

JOURNAL OF CHEMICAL PHYSICS 154 巻 ( 14 ) 頁： 144701 2021年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Chemical Physics

Within the exploration of sustainable and functional materials, narrow bandgap magnesium silicide semiconductors have gained growing interest. Intriguingly, squeezing silicides to extreme pressures and exposing them to non-ambient temperatures proves fruitful to study the structural behavior, tune the electronic structure, or discover novel phases. Herein, structural changes and thermoelastic characteristics of magnesium silicides were probed with synchrotron x-ray diffraction techniques using the laser-heated diamond anvil cell and large volume press at high pressure and temperature and temperature-dependent synchrotron powder diffraction. Probing the ambient phase of Mg2Si (anti-CaF2-type Mg2Si, space group: Fm3¯m) at static pressures of giga-Pascals possibly unveiled the transformation to metastable orthorhombic anti-PbCl2-type Mg2Si (Pnma). Interestingly, heating under pressures introduced the decomposition of Mg2Si to hexagonal Mg9Si5 (P63) and minor Mg. Using equations of state (EoS), which relate pressure to volume, the bulk moduli of anti-CaF2-type Mg2Si, anti-PbCl2-type Mg2Si, and Mg9Si5 were determined to be B0 = 47(2) GPa, B0 ≈ 72(5) GPa, and B0 = 58(3) GPa, respectively. Employing a high-temperature EoS to the P-V-T data of anti-CaF2-type Mg2Si provided its thermoelastic parameters: BT0 = 46(3) GPa, B′T0 = 6.1(8), and (∂BT0/∂T)P = -0.013(4) GPa K-1. At atmospheric pressure, anti-CaF2-type Mg2Si kept stable at T = 133-723 K, whereas Mg9Si5 transformed to anti-CaF2-type Mg2Si and Si above T ≥ 530 K. This temperature stability may indicate the potential of Mg9Si5 as a mid-temperature thermoelectric material, as suggested from previous first-principles calculations. Within this realm, thermal models were applied, yielding thermal expansion coefficients of both silicides together with estimations of their Grüneisen parameter and Debye temperature.

DOI： 10.1063/5.0044648

Automated geometric aberration correction for large-angle illumination STEM 査読有り国際誌

Ishikawa, R; Tanaka, R; Morishita, S; Kohno, Y; Sawada, H; Sasaki, T; Ichikawa, M; Hasegawa, M; Shibata, N; Ikuhara, Y

ULTRAMICROSCOPY 222 巻頁： 113215 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ultramicroscopy

DOI： 10.1016/j.ultramic.2021.113215

Nitriding synthesis and structural change of phosphorus nitrides at high pressures 査読有り国際誌

JOURNAL OF RAMAN SPECTROSCOPY 2021年2月

Elasticity of nanocrystalline kyanite at high pressure and temperature from ultrasonic and synchrotron X-ray techniques 国際共著国際誌

Gaida, NA; Gréaux, S; Kono, Y; Ohfuji, H; Kuwahara, H; Nishiyama, N; Beermann, O; Sasaki, T; Niwa, K; Hasegawa, M

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 104 巻 ( 1 ) 頁： 635 - 644 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the American Ceramic Society

Material properties, such as elasticity data at wide-ranging conditions of pressure and temperature, attract increasing attention for material and earth sciences. In particular, polycrystalline ceramics for next-generation photonic applications are nowadays fabricated by advanced syntheses techniques operating under elevated pressures and temperatures. Herein, the elastic properties of a synthetic transparent and reinforced aluminosilicate nanoceramic composed of triclinic kyanite with minor amounts of trigonal α-alumina crystals are investigated using in situ synchrotron X-ray diffraction and ultrasonic techniques at high-pressure (up to 11 GPa) and high-temperature (300-1500 K) conditions. This not only enables the determination of the equation of state (EoS) parameters by applying the pressure-volume-temperature (P-V-T) data to the high-temperature Birch-Murnaghan EoS but also yields the elastic moduli together with their P and T derivatives from the fit of the compressional and shear wave velocities to a finite strain EoS: K<inf>S</inf><inf>0,300</inf> = 186(2) GPa, K′<inf>S</inf><inf>0,300</inf> = 7.2(6), (∂K<inf>S</inf><inf>0,300</inf>/∂T)<inf>P</inf> = −0.023(2) GPa K<sup>−1</sup>, G<inf>0,300</inf> = 125(1) GPa G′<inf>0,300</inf> = 2.3(2), (∂G<inf>0,300</inf>/∂T)<inf>P</inf> = −0.017(1) GPa K<sup>−1</sup>. On the basis of our acquired results, we propose to predict the elastic moduli of aluminosilicate ceramics by a linear function of the ratio of AlO<inf>6</inf> octahedra and SiO<inf>4</inf> tetrahedra within the constituting phases.

DOI： 10.1111/jace.17464