||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.