Koji Kuramochi
Tokyo University of Science
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Koji Kuramochi.
Ultramicroscopy | 2009
Koji Kuramochi; Takashi Yamazaki; Yasutoshi Kotaka; Masahiro Ohtsuka; Iwao Hashimoto; Kazuto Watanabe
The effect of the chromatic aberration (C(c)) coefficient in a spherical aberration (C(s))- corrected electromagnetic lens on high-resolution high-angle annular dark field (HAADF) scanning transmission electron microscope (STEM) images is explored in detail. A new method for precise determination of the C(c) coefficient is demonstrated, requiring measurement of an atomic-resolution one-frame through-focal HAADF STEM image. This method is robust with respect to instrumental drift, sample thickness, all lens parameters except C(c), and experimental noise. It is also demonstrated that semi-quantitative structural analysis on the nanometer scale can be achieved by comparing experimental C(s)- corrected HAADF STEM images with their corresponding simulated images when the effects of the C(c) coefficient and spatial incoherence are included.
Acta Crystallographica Section A | 2006
Takashi Yamazaki; Kazuto Watanabe; Koji Kuramochi; Iwao Hashimoto
An extended method is proposed for the precise simulation of high-angle annular dark-field (HAADF) scanning transmission electron-microscope (STEM) images for materials containing elements with large atomic numbers and for thick specimens. The approach combines a previously reported method utilizing two kinds of optical potential [Watanabe, Yamazaki, Hashimoto & Shiojiri (2001). Phys. Rev. B, 64, 115432] with a representation of a crystal sliced into multiple layers. The validity of the method is demonstrated by simulated images for elements with the diamond structure (Si, Ge and alpha-Sn) and for the perovskite BaTiO3.
Acta Crystallographica Section A | 2010
Koji Kuramochi; Yasutoshi Kotaka; Takashi Yamazaki; Masahiro Ohtsuka; Iwao Hashimoto; Kazuto Watanabe
In this study, we experimentally and theoretically show that the intensities of bright spots in a spherical aberration (C(s))-uncorrected high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) image of [011]-oriented Co(3)O(4), which has two different numbers of Co atoms in the projected atomic columns, are reversed with increasing sample thickness. However, C(s)-corrected HAADF STEM images produce intensities that correctly depend on the average number of atoms in the projected atomic columns. From an analysis based on the Bloch-wave theorem, it is found that an insufficient semiangle of the incident convergent beam yields intensities that do not depend on the average atomic number in the atomic columns.
Ultramicroscopy | 2008
Koji Kuramochi; Kentaro Suzuki; Takashi Yamazaki; Kazutaka Mitsuishi; Kazuo Furuya; Iwao Hashimoto; Kazuto Watanabe
The structure and composition of the 1/4{110} twin boundary in alpha-Zn7Sb2O12 have been determined by using quantitative high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) analysis. The noise in the experimental HAADF STEM images is reduced by using the maximum entropy method and average processing, and the parameters used in dynamical simulations are experimentally determined. From the analysis, it has been found that octahedral sites in the twin boundary slightly shift parallel to the [110] direction, and a reduction of the Sb concentration at the octahedral sites on the plane adjacent to the twin boundary was detected. The reduction was measured from three regions in the same twin boundary, and the Sb concentrations were 4 +/- 3, 8 +/- 3 and 19 +/-2 at% from 33 at%.
Acta Crystallographica Section A | 2006
Takashi Yamazaki; Tomoko Isaka; Koji Kuramochi; Iwao Hashimoto; Kazuto Watanabe
A simple and robust method to precisely determine local strain fields using energy-unfiltered convergent-beam electron diffraction is presented. This method involves the subtraction of background intensity, the extraction of higher-order Laue-zone lines by tracing using a Radon transformation and a system of analytical strain determination without the need for an optimization routine such as chi2-based minimization. As an example, the measurement of residual strain in a silicon-on-insulator wafer is demonstrated. It is found from micro-Raman spectroscopy analysis that, at the nanometre scale, this measurement succeeds with an accuracy of 0.06%.
Applied Physics Letters | 2004
Kazuto Watanabe; Y. Anzai; N. Nakanishi; Takashi Yamazaki; Koji Kuramochi; Kazutaka Mitsuishi; Kazuo Furuya; Iwao Hashimoto
Our study using systematic transmission electron microscopy observation and simulation shows that microstructures formed in recrystallized Si are characterized as microtwin or lamellar microtwin. Detailed analysis leads to their atomic structures. The discovery of exceptional diffraction spots offers direct evidence of long-periodic-order structures and antiphase boundaries, due to the ordering of projected lamellar microtwins.
Journal of Electron Microscopy | 2008
Takashi Yamazaki; Akihiro Kashiwagi; Koji Kuramochi; Masahiro Ohtsuka; Iwao Hashimoto; Kazuto Watanabe
The quantitative measurement of a crystal bending effect is performed using low-order zone-axis convergent beam electron diffraction (CBED) patterns. Although the accuracy of the present method is inferior to that of the method of using split higher order Laue zone lines, this method enables us to estimate the crystal bending effect at a region very close to the interface and to easily judge whether the crystal bending effect results in a tensile bend or a compressive bend. As an application of the present method, the crystal bending effect at a region close to the SiGe/Si interface was measured. It was found that the crystal bending effect is due to a thin-foil relaxation of almost 0.3 degrees at a region that is approximately 10 nm away from the interface.
Japanese Journal of Applied Physics | 2008
Fumihiko Uesugi; Takashi Yamazaki; Koji Kuramochi; Iwao Hashimoto; Kenji Kojima; Shiro Takeno
A distortion measurement in a region close to the interface between different materials in LSI is performed using a convergent beam electron diffraction (CBED) pattern. Split higher-order Laue zone (HOLZ) lines emerge in the CBED pattern so that a stressing region is observed close to the interface. The calculation method of the split HOLZ lines based on kinematical approximation with the samples deformation model well reflects the experimental results. As a result of split HOLZ line analysis using the present method, it is found that there is distortion depending on the external form of a multi-finger transistor.
Japanese Journal of Applied Physics | 2008
Kazuhide Kusakabe; Takashi Yamazaki; Koji Kuramochi; Tokuma Furuzuki; Iwao Hashimoto; Shizutoshi Ando; Kazuhiro Ohkawa
A polar-dependent phase with spontaneous atomic ordering is found in a nonpolar (1120) plane In0.08Ga0.92N film grown by metalorganic vapor-phase epitaxy. An atomic arrangement is a periodic sequence of group-III sublattices, such as In0.04Ga0.96N/In0.12Ga0.88N, that is only observed in a nitrogen polar region through systematic transmission electron microscopy investigation. Cathodoluminescence (CL) in the nitrogen polar region, i.e., spontaneously ordered atomic structure of InGaN, reveals anomalous emission behavior, specifically an S-shape-like (increase–decrease) temperature dependence of CL peak energy. It is suggested that the spontaneous ordered atomic structure of InGaN plays the role of a localized center owing to band gap shrinkage, which has been reported in other III–V alloy systems.
Ultramicroscopy | 2008
Koji Kuramochi; Kentaro Suzuki; Takashi Yamazaki; Kazutaka Mitsuishi; Kazuo Furuya; Iwao Hashimoto; Kazuto Watanabe
The structure and composition of the 1/4{110} twin boundary in alpha-Zn7Sb2O12 have been determined by using quantitative high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) analysis. The noise in the experimental HAADF STEM images is reduced by using the maximum entropy method and average processing, and the parameters used in dynamical simulations are experimentally determined. From the analysis, it has been found that octahedral sites in the twin boundary slightly shift parallel to the [110] direction, and a reduction of the Sb concentration at the octahedral sites on the plane adjacent to the twin boundary was detected. The reduction was measured from three regions in the same twin boundary, and the Sb concentrations were 4 +/- 3, 8 +/- 3 and 19 +/-2 at% from 33 at%.