||Wenhui Yang, Tomokazu Yamamoto, Kohei Aso, Flora Somidin Kazuhiro Nogita, Syo Matsumura,, Atom locations in a Ni doped η-(Cu,Ni)6Sn5 intermetallic compound, Scripta Materialia, 10.1016/j.scriptamat.2018.08.020, 158, 1, 1-5, 2019.01, The present study has succeeded in direct determination of the location of dopant Ni atoms in η-(Cu,Ni)6Sn5 by aberration-corrected scanning transmission electron microscopy (STEM) including atomic-resolution imaging as well as elemental mapping by X-ray energy-dispersive spectroscopy (XEDS). The three sublattices of Sn, Cu1 and Cu2 were distinguished in atomic-resolution images observed along the [2 -1 -1 0] direction. Atomic-resolution XEDS maps have verified for the first time that the dopant Ni atoms located at the Cu2 sites in η-(Cu,Ni)6Sn5, taking advantage of the Poisson non-local principal component analysis (NLPCA) processing and the lattice-averaging procedure..
||Takeshi Watanabe, SatoruYoshioka, TomokazuYamamoto, Hossein Sepehri-Amin, Tadakatsu Ohkubo, Syo Matsumura, Yasuaki Einaga, The local structure in heavily boron-doped diamond and the effect this has on its electrochemical properties, Carbon, 10.1016/j.carbon.2018.05.026, 137, 333-342, 2018.05, Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS), and ﬁrst principles calculations of EEL spectra were utilized to elucidate the relationship between the microscopic structure and the electrochemical properties of heavily boron-doped diamond (h-BDD). The electro-chemical properties of h-BDD containing 1 at.% and 3 at.% boron are very different. TEM observations showed that 1 at.% h-BDD consists of small densely packed diamond crystallites, while 3 at.% h-BDDcontains small voids and a graphite phase partly along the grain boundaries. The EEL spectrum of the grain interior in 1 at.% h-BDD and comparison of this with a theoretical spectrum shows that the boron atoms are mostly dispersed as single isolated substitutional atoms on diamond lattice sites in the grain interior and that only a small amount of sp2-bonded carbon is present. In contrast, in the grain interior of 3 at.% h-BDD, the boron atoms are mostly associated with nearest neighbor boron pairs, and consequently sp2-bonded carbon is formed. Thus, the local structure has a signiﬁcant effect on the amount of sp2-bonded carbon. The quite different electrochemical properties of the samples are ascribed to the amount of sp2-bonding arising from the different local structures..
||Quan Zhang, Kohei Kusada, Dongshuang Wu, Tomokazu Yamamoto, Takaaki Toriyama, Syo Matsumura, Shogo Kawaguchi, Yoshiki Kubota & Hiroshi Kitagawa, Selective control of fcc and hcp crystal structures in Au–Ru solid-solution alloy nanoparticles, Nature Communications, 10.1038/s41467-018-02933-6, 9, Article number: 510, 1-9, 2018.02, Binary solid-solution alloys generally adopt one of three principal crystal lattices—body-centred cubic (bcc), hexagonal close-packed (hcp) or face-centred cubic (fcc) structures—in which the structure is dominated by constituent elements and compositions. Therefore, it is a significant challenge to selectively control the crystal structure in alloys with a certain composition. Here, we propose an approach for the selective control of the crystal structure in solid-solution alloys by using a chemical reduction method. By precisely tuning the reduction speed of the metal precursors, we selectively control the crystal structure of alloy nanoparticles, and are able to selectively synthesize fcc and hcp AuRu<sub>3</sub> alloy nanoparticles at ambient conditions. This approach enables us to design alloy nanomaterials with the desired crystal structures to create innovative chemical and physical properties..
||Kohei Aso, Koji Shigematsu, Tomokazu Yamamoto, Syo Matsumura, Detection of picometer-order atomic displacements in drift-compensated HAADF-STEM images of gold nanorods, Microscopy, 10.1093/jmicro/dfw018, 65, 5, 391-399, 2016.09.
||S. Takaki, kazuhiro Yasuda, Tomokazu Yamamoto, Syo Matsumura, Norito Ishikawa, Atomic structure of ion tracks in Ceria, Nuclear Instruments and Methods in Physics Research B, 10.1016/j.nimb.2013.10.077, 326, 140-144, 2014.05, We have investigated atomic structure of ion tracks in CeO2 irradiated with 200 MeV Xe ions by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). TEM observations under inclined conditions showed continuous ion tracks with diffraction and structure factor contrast, and the decrease in the atomic density of the ion tracks was evaluated to be about 10%. High resolution STEM with high-angle annular dark-field (HAADF) technique showed that the crystal structure of the Ce cation column is retained at the core region of ion tracks, although the signal intensity of the Ce cation lattice is reduced over a region 4–5 nm in size. Annular bright field (ABF) STEM observation has detected that the O anion column is preferentially distorted at the core region of ion tracks within a diameter of 4 nm. The core region of ion track in CeO2 is determined to contain a high concentration of vacancies or small vacancy clusters and to generate interstitials in surrounding regions..
||Nao Sumimoto, Koichiro Nakao, Tomokazu Yamamoto, Syo Matsumura, kazuhiro Yasuda, Yasuro Niidome, In situ observation of structural transformation of gold nanorods under pulsed laser irradiation in an HVEM , Microscopy, 10.1093/jmicro/dfu012, 63, 4, 261-268, 2014.04, A pulsed laser light illumination system was attached to a high-voltage electron microscope (HVEM) for in situ observation of light-induced behaviors of nano objects. The wavelength λ of emitted laser pulses was 1064, 532 or 266 nm, and the pulse duration was 6–8 ns. Using this combined HVEM system, we observed the deformation behavior of gold nanorods irradiated by a pulsed laser (λ = 1064 nm) at an intensity of 310 J m−2 pulse or higher. A single shot of pulsed laser reduced the aspect ratio of the gold nanorods from 5 to a much smaller value. The extent of the reduction increased at higher laser intensities. However, at 310 J m−2 pulse−1, additional pulsed shots induced limited further deformation. The mean aspect ratio approximated to 2.5 even after irradiation with 7 pulses (total fluence exceeding 2 MJ m−2). In situ high resolution transmission electron microscopy (HRTEM) observation revealed that deformation was accompanied by total atomic restructuring of the nanorod interiors..
||kazuhiro Yasuda, M. Etoh, K. Sawada, Tomokazu Yamamoto, Kazufumi Yasunaga, Syo Matsumura, Norito Ishikawa, Defect formation and accumulation in CeO2 irradiated with swift heavy ions, Nuclear Instruments and Methods in Physics Research B, 10.1016/j.nimb.2013.04.069, 314, 185-190, 2013.11, We have investigated microstructure evolution in CeO2 irradiated with 210 MeV Xe ions by using transmission electron microscopy to gain the fundamental knowledge on radiation damage induced by fission fragments in nuclear fuel and transmutation target. Analysis on the accumulation of ion tracks has revealed an influence region to recover pre-existing core damage regions of ion tracks to be 8.4 nm in radius. Cross section observations showed that high-density electronic excitation induces both ion tracks and dislocation loops. At high fluences of 1.5 × 1019 and 1 × 1020 ions m−2, depth-dependent microstructure was developed with radiation-induced defects of ion tracks, dislocation loops (dot-contrast) and line dislocations. Formation of sub-divided small grains was found at shallow depth at a fluence of 1 × 1020 ions m−2. The microstructure evolution was discussed in terms of the accumulation of interstitials due to significant overlap of high density electronic excitation..
||M. Timpel, N. Wanderka, R. Schlesiger, T. Yamamoto, N. Lazarev, D. Isheim, G. Schmitz, Syo Matsumura, J. Banhart, Sr–Al–Si co-segregated regions in eutectic Si phase of Sr-modified Al–10Si alloy, Ultramicroscopy, dx.doi.org/10.1016/j.ultramic.2012.10.006, 132, 216-221, 2013.09, The addition of 200 ppm strontium to an Al–10 wt% Si casting alloy changes the morphology of the eutectic silicon phase from coarse plate-like to fine fibrous networks. In order to clarify this modification mechanism the location of Sr within the eutectic Si phase has been investigated by a combination of high-resolution methods. Whereas three-dimensional atom probe tomography allows us to visualise the distribution of Sr on the atomic scale and to analyse its local enrichment, transmission electron microscopy yields information about the crystallographic nature of segregated regions. Segregations with two kinds of morphologies were found at the intersections of Si twin lamellae: Sr–Al–Si co-segregations of rod-like morphology and Al-rich regions of spherical morphology. Both are responsible for the formation of a high density of multiple twins and promote the anisotropic growth of the eutectic Si phase in specific crystallographic directions during solidification. The experimental findings are related to the previously postulated mechanism of “impurity induced twinning”..
||Kazu Suenaga, Toshiya Okazaki, Eiji Okunishi, Syo Matsumura, Detection of photons emitted from single erbium atoms in energy-dispersive X-ray spectroscopy, Nature Photonics, 10.1038/nphoton.2012.148, 6, 8, 545-548, 2012.08, The detection of photons emitted from single quantum objects is highly desirable for the diagnosis of nanoscale devices using microscopes. An extremely tiny probe (∼0.1 nm) with high current recently became available for aberration-corrected scanning transmission electron microscopy, and it is possible for individual atoms in nanoscale devices to be excited using such a highly focused probe1–3. Here, we demonstrate the successful
detection of characteristic X-ray signals from single erbium atoms using energy-dispersive X-ray spectroscopy. The intensities of the erbium L and M lines from a single erbium atom were extremely weak in comparison to the N edge of electron energy-loss spectroscopy, demonstrating the intrinsic difficulty in sensing single atoms using X-ray spectroscopy.
Nevertheless, this work will certainly help in the advance towards obtaining X-ray spectra from single atoms and to evaluate the fluorescence yield on a single-atom basis..
||M. Timpel, N. Wanderka, R. Schlesiger, T. Yamamoto, N. Lazarev, D. Isheim, G. Schmitz, Syo Matsumura, J. Banhart, The role of strontium in modifying aluminium–silicon alloys
, Acta Materialia, http://dx.doi.org/10.1016/j.actamat.2012.03.031, 60, 9, 3920–3928, 2012.05, Small amounts of strontium can transform the morphology of the eutectic silicon phase present in Al–Si casting alloys from coarse plate-like to fine fibrous networks. In order to understand this industrially important but hitherto insufficiently understood effect, the strontium distribution was studied in atomic resolution by atom probe tomography and in nanometre resolution by transmission electron microscopy. The combined investigations indicate that Sr co-segregates with Al and Si within the eutectic Si phase. Two types of segregations were found: (i) nanometre-thin rod-like co-segregations of type I are responsible for the formation of multiple twins in a Si crystal and enable its growth in different crystallographic directions; (ii) type II segregations come as more extended structures, restrict growth of a Si crystal and control its branching. We show how Sr enables both kinds of mechanisms previously postulated in the literature, namely “impurity-induced twinning” (via type I) and growth restriction of eutectic Si phase (via type II)..
||H. Unno, Y. Sato, S. Toh, N. Yoshinaga, S. Matsumura, Microstructures and electrical properties of TiO2-doped Al2O3 ceramics, Journal of Electron Microscopy, Volume 59, Pages S107-S115, 2010.08.
||M. Shirai, K. Tsumori, M. Kutsuwada, K. Yasuda, S. Matsumura
, Morphological change in FePt nanogranular thin films induced by swift heavy ion irradiation, Nuclear Instruments and Methods in Physics Research Section B, Volume 267, Issue 10, Pages 1787-1791
||Kousuke Kimura, Satoshi Hata, Syo Matsumura and Takao Horiuchi, Dark-field transmission electron microscopy for a tilt series of ordering alloys: toward electron tomography, Journal of Electron Microscopy, 10.1093/jmicro/dfi060, 54, 4, 373-377, 54 , 373-377, (2005), 2005.12.
||K. Kaneko, S. Matsumura, K. Ikematsu, Y. Kato, Y. Tomokiyo, M. Watanabe, T. Masumoto, Quantitative electron microscopy of FePt nano-crystallites in amorphous Al2O3 matrix, Scripta Materialia, 10.1016/S1359-6462(02)00627-9, 48, 7, 915-920, 48, 915-920, 2003.08.
||C. Abromeit, S. Matsumura, Kinetics of antiphase domain boundaries during an L12 order-disorder phase transformation: a Monte Carlo simulation, Philosophical Magazine A, 10.1080/01418610210138950, 82, 11, 2287-2302, 82, 2287-2302, 2002.08.
||S. Matsumura, Y. Tanaka, Y. Koga, K. Oki, Concurrent ordering and phase separation in the vicinity of the metastable critical point of order-disorder transition in Fe-Si alloys, Materials Science and Engineering A, 10.1016/S0921-5093(00)01874-8, 312, 1-2, 284-292, 312, 284-292, 2001.05.