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ABSTRACT: The charging effect due to electron irradiation in an electron microscope has been studied so far with incident electrons. Here we report on a new specimen holder to control the charging effect by using electrons emitted from an irradiation port in the holder while maintaining a constant intensity of the incident electron beam. Details of the charging effect, such as electric field variation, are expected to be investigated by electron holography. The new specimen holder was developed by modifying a double-probe piezodriving specimen holder to introduce an electron irradiation port in one of its two arms. As a result, the new modified specimen holder consists of a piezodriving probe and an electron irradiation port, both of which can be controlled in three dimensions, using piezoelectric elements and micrometers. We demonstrate that variations in the charging effect for epoxy resin and surface contamination can be observed by electron holography.
Journal of electron microscopy 04/2013; · 1.31 Impact Factor
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ABSTRACT: We investigate the effectiveness of utilizing a conductive probe for a transmission electron microscope (TEM) to suppress charging caused by electron irradiation. To do this, the electric field around a charged collagen fibril was visualized by electron holography and then quantitatively analyzed by computer simulations. The electric field changed noticeably when the conductive probe was moved near the specimen and charging was drastically suppressed when the conductive probe directly touched the charged specimen. The causes of the change in the electric field and suppression of charging are briefly discussed.
Journal of electron microscopy 03/2013; · 1.31 Impact Factor
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ABSTRACT: The magnetic field generated by a magnetic recording head is evaluated using electron holography. A magnetic recording head, which is connected to an electric current source, is set on the specimen holder of a transmission electron microscope. Reconstructed phase images of the region around the magnetic pole show the change in the magnetic field distribution corresponding to the electric current applied to the coil of the head. A simulation of the magnetic field, which is conducted using the finite element method, reveals good agreement with the experimental observations.
Journal of electron microscopy 01/2013; · 1.31 Impact Factor
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ABSTRACT: Nanostructured magnetic materials play an important role in increasing miniaturized devices. For the studies of their magnetic properties and behaviors, nanoscale imaging of magnetic field is indispensible. Here, using electron holography, the magnetization distribution of a TMR spin valve head of commercial design is investigated without and with a magnetic field applied. Characterized is the magnetic flux distribution in complex hetero-nanostructures by averaging the phase images and separating their component magnetic vectors and electric potentials. The magnetic flux densities of the NiFe (shield and 5 nm-free layers) and the CoPt (20 nm-bias layer) are estimated to be 1.0 T and 0.9 T, respectively. The changes in the magnetization distribution of the shield, bias, and free layers are visualized in situ for an applied field of 14 kOe. This study demonstrates the promise of electron holography for characterizing the magnetic properties of hetero-interfaces, nanostructures, and catalysts.
Small 08/2012; · 8.35 Impact Factor
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ABSTRACT: The magnetic domain structure of the writer poles of perpendicular magnetic recording heads was studied using electron holography. Although the domain structure of a 100-nm-thick writer pole could be observed with a 300 kV transmission electron microscope, that of the 250-nm-thick writer pole could not be analyzed due to the limited transmission capability of the instrument. On the other hand, the detailed domain structure of the 250-nm-thick writer pole was successfully analyzed by a 1 MV electron microscope using its high transmission capability. The thickness and material dependency of the domain structure of a writer pole were discussed.
Journal of electron microscopy 06/2012; 61(5):305-8. · 1.31 Impact Factor
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ABSTRACT: Simulations were carried out for the orbit of electron-induced secondary electrons around a charged microfibril of a sciatic nerve tissue. In order to set the parameters for the simulation, the shape of the microfibril was determined from a transmission electron microscopy image, while the electric potential on the surface of the charged microfibril was evaluated from a reconstructed phase image obtained with electron holography. On the other hand, the passing point and the angle of secondary electrons at the microfibril surface were determined from a reconstructed amplitude image. Eventually, simulation of orbits of secondary electrons was carried out by changing the kinetic energy of the secondary electrons. Under the given conditions, the orbit of secondary electrons with a kinetic energy of 29.6 eV fits the observations. If there are thin layers of electrons, the secondary electrons do not reach the surface but they go over it due to the repulsive Coulomb force resulting in successive revolving motion around the charged microfibril. Furthermore, the electric field variation due to the movement of the electric charges resulting from the specimen drift is also discussed briefly comparing it with electron holography data.
Journal of electron microscopy 05/2012; 61(4):217-22. · 1.31 Impact Factor
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ABSTRACT: The three-dimensional spin structure of the magnetic vortex of FeSiB, an amorphous soft magnetic material, was investigated by holography observation and computer simulation. Magnetization distribution in the neighborhood of the vortex center was estimated from the phase distribution obtained by holography observation. To confirm this magnetization distribution, sample-tilting experiments were performed: when the sample was tilted with respect to the electron beam direction, the phase-image center was found to shift along the tilting axis. Finite-element computer simulation was carried out to estimate the amount of shifts of the phase-image center in the sample tilting from the experimental magnetization distributions in the no sample-tilting conditions. We found that the simulated shifts of the phase-image center were in good agreement with those in the sample-tilting experiment, thus confirming the magnetization distribution near the vortex center obtained by holography observation.
Journal of electron microscopy 12/2011; 61(2):71-6. · 1.31 Impact Factor
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ABSTRACT: A nanoscale thermocouple consisting of merged Cu and Cu-Ni tips is developed for local temperature measurements on advanced nanomaterials by using a probing technique in a high-resolution transmission electron microscope (TEM) equipped with a double probe scanning tunneling microcopy (STM) unit. The fabricated nanothermocouple works as the so-called T-type thermocouple and displays a quick response and high spatial and thermal resolutions. A generated thermoelectromotive force which reflects rapid temperature changes controlled by electron beam intensity alternations on a metal nanoelectrode proves the technique's usefulness for high-precision local temperature measurements. The developed method demonstrates the effectiveness while also measuring temperature changes in Joule heated multi-walled carbon nanotubes (CNTs) and in a modeled electrical conductive composite nanosystem.
Nanotechnology 12/2011; 22(48):485707. · 3.98 Impact Factor
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ABSTRACT: The distribution of tribocharges in toner samples is studied by electron holography, a powerful tool for direct observations of the electric field. We carry out both in situ and ex situ observations on triboelectricity using model toner specimens, which are laminated with thin films, and a transmission electron microscopy specimen holder with two piezo-driving microprobes. We investigate specimens with stacking layer-patterns of “minus and weak minus” and “plus and minus.” The observed equipotential lines show a simple semi-ellipsoidal shape, regardless of the combination of toner films having different charging characteristics. Computer simulations for quantitative analyses of the electron hologram results with a modulated reference wave by a long-range electric field from the tribocharges are performed. Both the experimental results and the simulations indicate that the tribocharges are not localized at the positions where they are formed; rather they migrate to achieve a gradient charge density in the specimen. The charge quantity of the model toner is also evaluated by the simulation.
Journal of Applied Physics 06/2011; 109(12):124903-124903-8. · 2.17 Impact Factor
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ABSTRACT: We investigated magnetic remanence states of epitaxially grown, exchange-biased MnPd/Fe bilayers by electron holography emphasizing the crystallographic orientations of the layers. Thin-foil transmission electron microscopy (TEM) specimens were carefully prepared along both hard and easy axes of the Fe layer. The ex situ magnetization-reversal process was carried out using the TEM specimens, and magnetic flux densities of the ultra-thin Fe layers were evaluated at different remanence states. We show that a spin configuration in the TEM specimens is determined by the competition between an exchange coupling at the MnPd/Fe bilayer interface, shape anisotropy of TEM specimens and intrinsic magnetocrystalline anisotropy of Fe.
Journal of electron microscopy 01/2011; 60(3):235-42. · 1.31 Impact Factor
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ABSTRACT: This paper presents a review of the recent electron holography studies on electric field variation that have been carried out using multifunctional specimen holders. In addition to the standard inner potential analysis, studies on electric field variations around field emission tips have been carried out. The electric field variations caused by ballistic emission in the case of a field emitter made of a TaSi(2) nanowire have been analyzed using electron holography. The charges and electric fields in electrophotographic materials such as toner particles and organic photoconductors have been quantitatively evaluated after equipping the specimen holder with a piezodriving probe to shield the specimens from electron irradiation. The conductivity and electric field variations in the case of Ag-based conductive adhesives have been analyzed by applying an electric current through the holder. Finally, the characteristic charging effect induced by electron irradiation in biological specimens has been studied. It has also been pointed out that under certain experimental conditions, the stationary orbits of electron-induced secondary electrons can be located by electric field visualization.
Journal of electron microscopy 01/2011; 60 Suppl 1:S225-37. · 1.31 Impact Factor
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ABSTRACT: An alternating magnetizing system has been developed for in situ Lorentz microscopy for soft magnetic materials in an alternating magnetic field. The electron trajectory in the system is discussed using a simulation based on a simple model. It is clarified that the frequency and amplitude of the alternating magnetic field and the defocus of the objective mini lens can be selected as desired values. The system is successfully applied to the observation of domain wall motion in a soft magnetic material, Fe(84.9)Al(5.5)Si(9.6) (wt%) (Sendust). The system is very promising for investigating interactions between domain walls and lattice defects in various kinds of soft magnetic materials.
Journal of electron microscopy 01/2010; 59(3):207-13. · 1.31 Impact Factor
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ABSTRACT: The magnetic interaction between the pole tip of a single-pole head and a pseudo soft underlayer in perpendicular magnetic recording was observed by electron holography. The magnetic flux density inside the soft underlayer was quantitatively evaluated. The distribution of magnetic flux density was calculated using the finite element method, and the influences of the modulation of the reference wave and stray fields were investigated by comparison with experimental results. The flux density observed was found to be underestimated due to the modulation of the phase shift in reference wave. The magnetic flux measured experimentally was larger than that inside the specimen because of the relatively large stray fields above and below the specimen in the direction of the electron beam.
Journal of electron microscopy 01/2010; 59(5):331-7. · 1.31 Impact Factor
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ABSTRACT: The double-probe piezodriving specimen holder that was recently developed by some of the present authors is modified to introduce a laser irradiation port in one of its two arms. As a result, the new specimen holder consists of a piezodriving probe and a laser irradiation port, both of which can be three-dimensionally controlled by using piezoelectric elements and micrometers. While the piezodriving probe interacts with the specimen set in the holder in several ways, the laser beam causes photo-induced phenomena to occur. By performing electron holography using the new specimen holder, we demonstrate that it is possible to evaluate the change in the electric field resulting from the discharging effect of laser irradiation on organic photoconductors.
Journal of electron microscopy 05/2009; 58(4):245-9. · 1.31 Impact Factor
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ABSTRACT: The magnetic microstructure in a Co-CoO obliquely evaporated tape that was subjected to a recording bit length of 250 nm was studied using electron holography. The reconstructed phase image demonstrated a periodic pattern of magnetic flux loops that were inclined to the film normal due to a well-developed columnar structure. When a magnetic field was applied to the tape for observing the remanent state by holography, the periodic pattern of the flux loops gradually disappeared. Interestingly, on applying a large magnetic field, the contour lines in the reconstructed phase image became approximately parallel to the longitudinal axis of the sliced tape, i.e. the contour lines were made to virtually deviate from the easy magnetization axis. The observations were supported by a computer simulation in which the effect of the stray magnetic field was considered.
Journal of electron microscopy 02/2009; 58(1):7-13. · 1.31 Impact Factor
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ABSTRACT: It is well known that the deposition of an intermediate Ru layer under high Ar pressure during the fabrication of CoCrPt – SiO <sub>2</sub> perpendicular recording media is effective in improving the magnetic properties of the upper CoCrPt – SiO <sub>2</sub> layer. The change in the switching fields of the CoCrPt – SiO <sub>2</sub> recording layer resulting from the presence of the high-pressure Ru layer is investigated through experiments and computer simulation. The monotonous increase in the magnetic anisotropy K<sub>u</sub> and the decrease in the intergranular exchange coupling of the CoCrPt grains due to the presence of the high-pressure Ru layer result in a slight increase in the nucleation field, a significant increase in the coercivity and the saturation field, and a decrease in the slope of the hysteresis loop.
Journal of Applied Physics 02/2009; · 2.17 Impact Factor
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ABSTRACT: In order to understand the excellent properties of nanoscale hybridized materials, it is very important to investigate the
microstructures and interfaces of these materials at the nanometer scale. In this chapter, we present the basic principles
of transmission electron microscopy and its applications to these materials. In addition to high-resolution transmission electron
microscopy (HREM) and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM), analytical electron
microscopy, including energy dispersive X-ray spectroscopy (EDS) and electron energyloss spectroscopy (EELS) as well as elemental
mapping methods using these spectroscopy techniques will be presented. Also, the electron holographic technique for characterization
of magnetic fields of nanohybridized materials will be explained. In addition to electron microscopic observation techniques,
recently developed specimen preparation techniques, which are indispensable for obtaining homogeneous and thin films of nanohybridized
materials, will be presented. In particular, a focused ion beam (FIB) method will be emphasized. The nanohybridized materials
discussed in this chapter include carbon-based core–shell structure, nanocrystalline soft magnetic materials, nanocomposite
magnets, and high-T
c
superconducting oxides. Application data will be provided in order to explain the usefulness of these analytical techniques
for characterization of nanohybridized materials.
12/2008: pages 219-246;
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ABSTRACT: Electron holography, which visualizes magnetic and/or electric fields in materials on the nanometre scale, is a powerful tool for the study of fundamental issues in physics as well as the characterization of advanced materials. This paper presents an overview of recent electron holography studies on advanced magnetic materials, which include hard magnetic materials (both nucleation-type and pinning-type magnets), soft magnetic materials (both classical alloys and recently developed nanostructured materials), magnetic recording materials (Co–CoO tape and other related topics) and magnetic functional materials (ferromagnetic shape memory alloys and colossal magnetoresistive manganites).
Journal of Physics D Applied Physics 08/2008; 41(18):183002. · 2.54 Impact Factor
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ABSTRACT: The charging effect in a ZrO2 sintered body was investigated by using scanning ion microscope (SIM) images. In this study, we report interesting features caused by the charging effect in the ZrO2 sintered body during the Ga ion beam irradiation: a bright contrast with a distorted net shape appears around the positively charged specimen. From this feature in the SIM image, it is clarified that the Ga ion beam is strongly deflected and the wide area of the internal parts of the focused ion beam machine is irradiated by the Ga ion beam, depending on the extent to which the specimen is charged. We discuss the mechanism of the characteristic charging effect through observing SIM images by varying the intensity of the Ga ion beam.
Journal of electron microscopy 05/2008; 57(2):53-7. · 1.31 Impact Factor
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ABSTRACT: The visualization of two-dimensional dopant profiles and the quantitative analysis of the built-in potential across the p-n junction, DeltaV(p-n), by electron holography were carried out with specimens prepared from the backside ion milling method combined with the focused ion beam technique. It was possible to obtain dopant profiling of the large field of view with low surface damage and gradually changed thickness. From the quantitative analysis using the phase information of electron holography and the thickness information of electron energy-loss spectroscopy, DeltaV(p-n) was estimated to be about 0.78 V assuming that the thickness of the dead layer on both surfaces is 50 nm, which is to show the difference of within 12% from the calculated value. It demonstrates that the backside ion milling method is a very promising specimen preparation technique for the reliable and quantitative analysis of dopant profiling with electron holography.
Journal of electron microscopy 02/2008; 57(1):13-8. · 1.31 Impact Factor
