Biomedical subjects

D Shindo

Publications and source records attributed to D Shindo.

10 recordsLinked to original sources

PubMed2006

Development of a magnetizing stage for in situ observations with electron holography and Lorentz microscopy.

A magnetizing stage, by which approximately horizontal magnetic fields can be applied to thin-foiled specimens, has been developed so that magnetization process can be observed in situ with electron holography and Lorentz microscopy. It is possible to apply magnetic field up to 200 Oe without serious image distortion by utilizing the magnetizing stage, beam-deflection-back coils and a magnetically shielded objective lens. The devised system can be used to studies of magnetization processes in many soft magnets.

Letter↗

PubMed2005

Three dimensional magnetic resonance imaging by magnetic resonance force microscopy with a sharp magnetic needle.

An electropolished magnetic needle made of Nd(2)Fe(14)B permanent magnet was used for obtaining better spatial resolution than that achieved in our previous work. We observed the magnetic field gradient |G(Z)|=80.0G/microm and the field strength B=1250G at Z approximately 8.8 microm from the top of the needle. The use of this needle for three dimensional magnetic resonance force microscopy at room temperature allowed us to achieve the voxel resolution to be 0.6 microm x 0.6 microm x 0.7 microm in the reconstructed image of DPPH phantom. The acquisition time spent for the whole data collection over 64 x 64 x 16 points, including an iterative signal average by six times per point, was about 10 days.

Journal Article↗

PubMed2004

Interaction of separated ferromagnetic domains in a hole-doped manganite achieved by a magnetic field.

We report the change in the magnetic microstructure with the application of a magnetic field to a hole-doped manganite La0.81Sr0.19MnO3 in the mixed-phase state, in which ferromagnetic and paramagnetic phases coexist. In situ observations by electron holography have revealed that the applied magnetic field generates a "channel" of the magnetic flux in the paramagnetic phase region, thereby connecting the separated ferromagnetic domains. The magnetic flux density of this channel is estimated at 0.33 T, which is comparable with that of the ferromagnetic domains. The connection of the separated ferromagnetic domains appears to promote the conduction in the mixed-phase state as predicted for many manganites exhibiting the magnetoresistance effect.

Journal Article↗

PubMed2003

Magnetization distribution in the mixed-phase state of hole-doped manganites.

The effect of 'colossal magnetoresistance' (CMR) in hole-doped manganites--an abnormal decrease of resistivity when a magnetic field is applied--has attracted significant interest from researchers in the past decade. But the underlying mechanism for the CMR phenomenon is not yet fully understood. It has become clear that a phase-separated state, where magnetic and non-magnetic phases coexist, is important, but the detailed magnetic microstructure of this mixed-phase state is so far unclear. Here we use electron microscopy to study the magnetic microstructure and development of ferromagnetic domains in the mixed-phase state of La(1-x)Sr(x)MnO3 (x = 0.54, 0.56). Our measurements show that, in the absence of a magnetic field, the magnetic flux is closed within ferromagnetic regions, indicating a negligible magnetic interaction between separated ferromagnetic domains. However, we also find that the domains start to combine with only very small changes in temperature. We propose that the delicate nature of the magnetic microstructure in the mixed-phase state of hole-doped manganites is responsible for the CMR effect, in which significant conduction paths form between the ferromagnetic domains upon application of a magnetic field.

Journal Article↗

PubMed2001

New source of stacking faults in heteroepitaxial systems.

A new stacking fault formation mechanism has been observed for the first time in ZnO/LiTaO(3) heteroepitaxial films. High resolution electron microscopy studies combined with electron diffraction and numerical image computation suggest that the observed type I1 intrinsic stacking faults in an epitaxial film can be dominantly formed as a result of tilting of the lattices between films and substrate required to maintain a particular orientation relationship.

Journal Article↗

PubMed2001

Precursor effects of martensitic transformations in Ti-based alloys studied by electron microscopy with energy filtering.

Precursor effects of martensitic transformations in two well-known shape memory alloys, Ti50Ni48Fe2 and Ti50Pd34Fe16, were studied extensively by energy-filtered electron microscopy, including in-situ observations, and high-resolution electron microscopy. Energy-filtered dark-field images, where weak diffuse scattering was utilized, clearly showed the microstructure in the premartensitic state of Ti50Ni48Fe2. Tiny domains observable in this state were close to spherical rather than thin and slender, and the temperature dependence of the domain-like structure was clarified by the in-situ observations. It was found that Ti50Pd34Fe16 exhibited a domain-like structure similar to that of Ti50Ni48Fe2, which was attributed to a transverse lattice displacement. High-resolution images of Ti50Pd34Fe16 showed that a domain was coupled with other ones with different orientations of distortion, so as to reduce the total strain due to their formations. Furthermore, effects of including a fundamental reflection, in addition to the diffuse scattering, on dark-field images were discussed based on the observations and the image processing.

Journal Article↗

PubMed2000

HRTEM image contrast of short range order in Ni4Mo

The high resolution transmission electron microscope (HRTEM) imaging of short range order (SRO) in Ni4Mo was investigated by means of multi-slice image simulations. The HRTEM images of Ni4Mo exhibit locally bright dot patterns corresponding to the [001] projections of the N2M2-type (chalcopyrite-like) structure. The multi-slice simulations revealed that the N2M2 patterns are rationalized as the projection patterns of the SRO structure which consists of subunit cell clusters of D1a, D022 and Pt2Mo structures. The N2M2-type image contrast appears when both the fundamental fcc lattice reflections and the 1 1/2 0 diffuse scattering of SRO contribute enough to imaging. This suggests that a good coincidence in intensity distribution between the Fourier power spectra of HRTEM images and the electron diffraction patterns is one of the conditions for the image contrast of SRO to be interpreted in terms of the projection contrast.

Journal Article↗

PubMed1999

Computer Simulations for the Growth Process of Peanut-Type Hematite Particles.

The growth process of a monodispersed peanut-type hematite particle consisting of much smaller elongated subcrystals has been reproduced by computer simulation. On the basis of the microscopic internal structure, the simulation was performed by replacing the sequential events of surface nucleation and the subsequent growth of each subcrystal in the actual process with an arranged deposition of rectangular segments of fixed dimensions under different conditions in their site-dependent deposition rate and in the flexibility of their tilt angles. The most successful simulation model was obtained on the assumptions of a relatively fast deposition of the segments on the outermost side-surface of the ellipsoidal particle and the flexible tilt angle of each segment depending on the position of a neighboring new segment placed afterward. The result of the simulation strongly supported the previous elucidation of the growth mechanism in terms of the outward bending of adjoining subcrystals by nucleation and growth of a new subcrystal in each space between them. Enhancement of the outward bending of subcrystals by a large amount of sulfate ions adsorbed to the growing subcrystals was also suggested. Copyright 1999 Academic Press.

Journal Article↗

PubMed1996

Internal Structure Analysis of Monodispersed Pseudocubic Hematite Particles by Electron Microscopy.

Morphology and internal structure of monodispersed pseudocubic hematite (alpha-Fe(2)O(3)) particles produced by the gel-sol method were investigated in detail through high-resolution electron microscopy on their thin sections prepared with an ultramicrotome. It was confirmed that the c-axis of a particle corresponded to the longest diagonal axis of the particle. High-resolution electron micrographs of thin sections directly revealed the polycrystallinity of the particles and clearly showed the arrangement of the subcrystals and their crystallographic orientations. The subcrystals near the surface of a particle were of a rectangular shape bound by the $ \{01\overline{1}2\} $ planes, and their width was about 12-16 nm with small variation of the length depending on the position in a particle. The subcrystals were radially developed from the center of a particle in all directions, but most preferentially in the longest diagonal axis of a particle. Besides, it was found from EDX analysis that the adsorbed Cl(-) ions as a shape controller were incorporated into the pseudocubic hematite particles during their growth.

Journal Article↗

PubMed1989

High-resolution electron microscopy study on crystal structures of high-Tc superconductors.

Recent studies of high-resolution electron microscopy on the high-Tc superconductors of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O are presented. The observed images of crystals thinner than 3 nm, taken under conditions that approached the Scherzer defocus condition, directly show the arrangements of cations and oxygen-vacant positions. The results reveal structural characteristics of the atomic scale; this offers important insights into the origin of the high-Tc superconductivity. The usefulness of high-resolution electron microscopy for studying complicated crystal structures is demonstrated for the high-Tc oxides.

Bismuth↗