Papers by Author: Masaki Takeguchi

Abstract: Phase shifting electron holography is a transmission electron microscope technique that a number of holograms with different initial phases are acquired by changing the angle of the incident electron beam, and the intensity variation at a certain point on the holograms is fitted by sinusoidal curve to retrieve the object wave passing through a specimen. In reality, however, Fresnel fringes caused by the electrostatic biprism modulates the electron wave, limits the fitting accuracy and results in phase errors in phase reconstruction. In this study, we suggest a modified phase reconstruction method for phase shifting electron holography. The intensity variations at a certain point on each hologram are fitted not by sinusoidal curve, but by Fresnel diffraction affected curve to retrieve the object wave. This would provide better fitting accuracy, and has a potential to improve the precision of phase shifting electron holography. Simulations demonstrated the improvements of this method comparing with conventional phase shifting holography method.

Abstract: We investigated the relationship between the microstructure and magnetic properties of a Cu–10 at% Ni–5 at% Co alloy by using a transmission electron microscope (TEM), a SQUID magnetometer and a magnetic thermo–balance. TEM observations were performed to examine the microstructures of the Cu–Ni–Co specimens annealed at four temperatures between 873 K and 1073 K below and above the Curie point (983 K).Particles with cubic shapes were linearly arranged along the <100> direction of the copper matrix in specimens prepared by isothermal annealing at temperatures below the Curie point, while octahedral precipitates were sparsely formed by annealing above the Curie point. The TEM observations confirmed that the microstructural evolution in the Cu–Ni–Co specimens isothermally annealed at 1023 K. Although coherent cubic particles appeared at the initial stage of annealing, incoherent precipitates were finally formed with increased annealing time at 1023 K. The present SQUID measurements indicated that the curve of coercive force vs. annealing time had a peak at a short annealing period.

Abstract: A new method is proposed for mapping of phase distribution in electron holography. A stage-scanning system was used for moving the specimen to obtain a series of holograms with different specimen positions in a fixed electron-optics configuration. By applying a digital aperture which selects an area on holograms with different specimen positions, an interferogram of the specimen can be obtained directly without a complex reconstruction method such as the one using Fourier transformation. Experimental results for a Co particle demonstrated the practicability of this method.

Abstract: Scanning confocal electron microscopy (SCEM) is a novel technique for threedimensional observation with a nanometer-scale resolution. Annular dark field (ADF) SCEM imaging has been demonstrated to have better depth resolution than bright field (BF) SCEM imaging. However, the depth resolution of ADF-SCEM images is limited by the vertical probe size determined by spherical aberration and convergence angle. Therefore, we attempted to employ a deconvolution image processing method to improve the depth resolution of SCEM images. The result of the deconvolution process for vertically sliced SCEM images showed the improvement in the depth resolution by 35-40%.

Abstract: The precipitation behavior of nano–scale magnetic particles formed in a Cu–Fe–Ni alloy on isothermal annealing at 873K and 1073K have been investigated by means of transmission electron microscopy (TEM). Nano–scale magnetic particles were formed randomly in the Cu–rich matrix after receiving a short annealing due to phase decomposition in the alloy. With increasing the isothermal annealing time, however, the striking features that two or more nano–scale particles with a cubic shape and precipitates with a needle shape were aligned linearly along <100> directions were observed on isothermal annealing at 873K and 1073K, respectively. To investigate the relationship between microstructures and magnetic properties of precipitates in a Cu–Fe–Ni alloy were also carried out the superconducting quantum interference device (SQUID) magnetometer. The present study revealed that several significant influences to magnetic properties were induced during the precipitation process in this alloy.

Abstract: Electron beam induced-deposition (EBID) is a promising technique for fabricating nanometer-sized structures in a position- and size-controlled manner. The resolution of EBID is now reaching down to subnanometers. However, the deposits obtained by EBID contain a large amount of carbon. Thus, carbon reduction techniques are needed. In this study, nanostructures, such as nanowires, were fabricated by EBID using an iron pentacarbonyl precursor. Several techniques to reduce carbon were applied, including post-deposition heat-treatments and the modification of precursor. It was found that the post-deposition heat-treatment in air resulted in a formation of Fe2O3, and that carbon-free Fe3O4 was formed by mixing a small amount of water vapor in the iron pentacarbonyl precursor.

Abstract: SrTiO3 crystals were implanted with 100 keV xenon (Xe+) ions at 673 or 1073 K up to 2.0 × 1020 ions m−2. Defect clusters formed in the ion-implanted samples were investigated with conventional and high-resolution transmission electron microscopy. Nanometer-sized clusters were formed in the samples. The clusters grew large in size after post-implantation annealing and with increasing the implantation dose. The clusters were faceted with {100}, or {110} of SrTiO3. Though the nano-sized clusters were expected to contain Xe atoms, they were not in crystalline state. The results suggest that even if the clusters contain Xe atoms, they also contain other point defects such as vacancies.

Abstract: Electron beam induced deposition (EBID) was carried out with gas introduction systems attached to field emission scanning electron microscope (FE-SEM). Using iron carbonyl and ferrocene, three dimensional (3-D) antenna structures were fabricated in the range of 30-50 nm in diameter and 500-1000 nm in size. Post-deposition annealing of iron nanostructures resulted in the formation of crystalline alpha-iron and iron carbide phases. The iron concentration was controlled by the partial pressure of iron carbonyl and ferrocene. Electron holography observation with field emission transmission electron microscopy (FE-TEM) revealed that the remanent magnetic flux density Br of the nanostructures also depends on the iron concentration.