Zentaro Akase

In situ Lorentz microscopy in an alternating magnetic field

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.

Split-illumination electron holography for improved evaluation of electrostatic potential associated with electrophotography

Precise evaluation of the electrostatic potential distributions of and around samples with multiple charges using electron holography has long been a problem due to unknown perturbation of the reference wave. Here, we report the first practical application of split-illumination electron holography (SIEH) to tackle this problem. This method enables the use of a non-perturbed reference wave distant from the sample. SIEH revealed the electrostatic potential distributions at interfaces of the charged particles used for development in electrophotography and should lead to dramatic improvements in electrophotography.

Imaging of magnetic flux distribution in vicinity of insulating particles in high-Tc superconductor by electron holography

REBaCuO (RE: rare earth) bulk superconductors, whose microstructures can be controlled by quench and melt growth (QMG) processing, have a high critical current density Jc, which makes them well suited for use in practical applications. Through a combination of electron holography and a focused ion-beam technique, we succeeded in visualizing a fluxon pinned by an insulating particle in a QMG bulk Y-Ba-Cu-O superconductor. We also clarified the magnetic flux distribution in the vicinity of the insulating particles at different temperatures in a uniform external magnetic field.

Electron holographic visualization of collective motion of electrons through electric field variation

This study demonstrates the accumulation of electron-induced secondary electrons by utilizing a simple geometrical configuration of two branches of a charged insulating biomaterial. The collective motion of these secondary electrons between the branches has been visualized by analyzing the reconstructed amplitude images obtained using in situ electron holography. In order to understand the collective motion of secondary electrons, the trajectories of these electrons around the branches have also been simulated by taking into account the electric field around the charged branches on the basis of Maxwells equations.

Electron holography study of the charging effect in microfibrils of sciatic nerve tissues.

The charging effects of microfibrils of sciatic nerve tissues due to electron irradiation are investigated using electron holography. The phenomenon that the charging effects are enhanced with an increase of electron intensity is visualized through direct observations of the electric potential distribution around the specimen. The electric potential at the surface of the specimen could be quantitatively evaluated by simulation, which takes into account the reference wave modulation due to the long-range electric field.

Electron holography of magnetic field generated by a magnetic recording head

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.

In situ Lorentz microscopy in an alternating current magnetic field

By utilizing an alternating current (AC) magnetizing system recently developed on our transmission electron microscope (TEM), in-situ Lorentz microscope observations of soft magnetic materials were carried out in an AC magnetic field [1]. The domain walls moved smoothly in a low frequency AC magnetic field. It was demonstrated that in-situ Lorentz microscopy in an AC magnetic field is very useful for the investigation of interactions between the microstructure and the motion of magnetic domain walls in soft magnetic materials.

Secondary electron effect on electron beam induced charging of SiO2 particle analyzed by electron holography

Charging of a SiO2 particle induced by electron illumination was investigated by changing the illuminated area of the particle and its support film through control of the position of the mask plate inserted in a transmission electron microscope illumination system. The electric fields around the charged SiO2 particle were analyzed using electron holography. The amount of charge was evaluated quantitatively by comparing the reconstructed phase images with the simulated phase images. When the support film was not covered against the incident electron beam, secondary electrons emitted from the conductive support film were attracted to the charged particle, resulting in particle discharge. In contrast, when the support film was completely covered, secondary electrons were not emitted from the film, so that the particle remained positively charged.

Strain measurement in ferromagnetic crystals using dark-field electron holography

This study proposes a method to separate the geometric phase shift due to lattice strain from the undesired phase information, resulting from magnetic fields that are superposed in the dark-field electron holography (DFEH) observations. Choosing a distinct wave vector for the Bragg reflection reversed the sense of the geometric phase shift, while the sense of the magnetic information remained unchanged. In the case of an Nd-Fe-B permanent magnet, once the unwanted signal was removed by data processing, the residual phase image revealed a strain map. Even though the applications of DFEH have thus far been limited to non-magnetic systems, the method proposed in this work is also applicable to strain measurements in various ferromagnetic systems.

Electrostatic-Potential Analysis of Charged Particles by Split-Illumination Electron Holography

1. Central Research Laboratory, Hitachi, Ltd., Hatoyama 350-0395, Japan 2. Center for Emergent Matter Science (CEMS), RIKEN, Wako 351-0198, Japan 3. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan 4. Department of Materials Science & Engineering, Dong-A University, Busan 604-714, Republic of Korea 5. System Research & Development Center, Ricoh Institute of Technology, RICOH Co., Ltd., Kanagawa 224-0035, Japan