Kerr effect microscope based on the photographic method is a device for observing the magnetic domain of a magnetic material by converting a polarization change caused by the magneto-optical Kerr effect. This method is widely utilized because of its features, such as non-contact and non-invasive observation, extensibility of applying a high magnetic field, capability of analyzing dynamical magnetization process, versatility for a wide range of magnetic domain size. The improvements of the performance of the Kerr effect microscope have been quested, mainly based on how to detect minor change in spatial and temporal polarization with high resolution and contrast. In addition, since high-quality magnetic domain images can be acquired owing to the high performance, specific efforts to detect not only magnetic domains but also three-dimensional detection of the local magnetization direction in the magnetic domains have also been performed. In this report, after outline descriptions of these observations techniques, the observation of the centimeter order magnetic domain by the reduced optical system which is the application of the microscope magnified optical technique will be introduced. Furthermore, the attempt of imaging the spatial magnetic field by using the magneto-optical effect of the magnetic transfer film will be reported.

Magnetic force microscopy (MFM) is a widely used magnetic imaging technique, because MFM has a few ten nm spatial resolution and no need of special pretreatment. In recent years, the improvement of spatial resolution and functionalities is required for the research and development of magnetic materials and magnetic devices. We have developed a novel form of magnetic force microscopy called alternating magnetic force microscopy (A-MFM) for the imaging of DC and AC magnetic fields with the ultra high spatial resolution of less than 5 nm. A-MFM utilizes the frequency modulation of cantilever oscillation induced by applying off-resonant alternating magnetic force to a highly sensitive homemade magnetic tip. A-MFM is the first magnetic force microscopy technique that enables near-surface magnetic imaging. A-MFM has several new functionalities including a) zero detection of magnetic field, b) polarity detection of magnetic field and surface magnetic charge (N pole / S pole), c) stroboscopic AC magnetic field imaging, and d) DC magnetic field imaging with selectable measuring axis even at rough surfaces such as the fractured surface of permanent magnets. In this article, the recent progress of A-MFM is reported.

Spin-Polarized Scanning Electron Microscopy (spin SEM) is one of the imaging tools of magnetic domain structures, which takes advantage of spin polarization of secondary electrons. Polarized orientation of the electron spin within ferromagnetic materials is the origin of the materials’ magnetization, and this spin polarization is maintained while the electrons are emitted as secondary electrons. The spin polarization of the secondary electrons is detected by the spin polarimeter, which is a key component of spin SEM.In this article, we introduce the principle of the spin SEM, followed by the explanation of the structure and the advantages of this method. And we show several example of spin SEM measurements, such as visualization of spin structure of anti-ferro magnet NiO(001), and magnetization detection of grain boundary phase of NdFeB sintered magnet.

In this article we report an electron optical system for both Foucault imaging and small angle electron diffraction (SmAED) constructed using non-dedicated conventional transmission electron microscope (TEM). In this system, an objective mini-lens is utilized in order to make a crossover on the plane where a selected area aperture is located. The aperture works for an angular selecting of the Foucault mode. The illumination and the imaging optics can be controlled independently. The maximum camera length is estimated to be approximately 1300 m. Magnetic domain structures in the ferromagnetic metallic phase of La_0.7Sr_0.3MnO₃ using the present electron optical system were presented. In addition, in-situ observation of changes of magnetic domain structures by applying external magnetic fields revealed the formation processes of magnetic bubbles in the M-type hexaferrite.

Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have been widely used for exploring structural information of solid surfaces with atomic resolution. However, in contrast to STM, AFM had been rarely employed for studies of molecules adsorbed on surfaces due the limited resolution down to sub-nanometer scale as well as the difficulty to scan on such the soft materials. Since the first observation of inner structure of molecule with a carbon monoxide terminated AFM tip in 2009, AFM became a powerful tool in a field of surface chemistry. Here, this article describes basics of the functionalized AFM with CO and noble gas atoms as well as recent related studies.

The 2016 Nobel Prize in Physiology or Medicine has been awarded to Yoshinori Ohsumi for his discoveries of mechanisms for autophagy. Autophagy is the major degradative process of the own cytoplasmic components including superfluous or dysfunctional organelles. By a dynamic membrane system, the cargo is delivered to the vacuole/lysosome for degradation. In this commentary, I introduce how the electron microscopy has become to be involved in the early stage of Autophagy research, and what direction has been derived.

Gap junction channels mediate intercellular communication, enabling electrical and chemical coupling between adjacent cells. Two gene families are known to form these channels: connexin in chordates, including vertebrates, and innexin in invertebrates. The genetic correlation is unclear, however, because these two families do not show significant sequence similarity. Recently, we determined an atomic structure of the Caenorhabditis elegans innexin-6 (INX-6) by single-particle cryo-EM. The INX-6 structure exhibited high structural similarity to connexin-26 in terms of the monomeric arrangement and N-terminal funnel, but had a different subunit number. In this review, the structural properties of the INX-6 atomic model and the cryo-EM sample preparation procedure essential for this study are comprehensively summarized.

Lectures on “electron sources and electron guns” are presented in two consecutive articles. The present article comprises the first part and discusses fundamental physics and optics of the electron source, especially the theoretical brightness and the electron emission mechanisms. Both the transmission and scanning type electron microscopes have dramatically improved the performance by adopting high brightness electron sources. The theoretical brightness of electron sources is determined dominantly by the cathode current density. The improvement in the source brightness is done by developing cathodes that provide high density currents. The cathode current density is a function of the ‘work function,’ ‘cathode temperature,’ and ‘electric field intensity.,’ combination of which determines the electron emission mode. The dependence of the cathode current density on those parameters as well as the expected theoretical brightness of the thermionic, Schottky, and cold field emission cathodes are described. It is shown that the cathode current density can substantially be enhanced by the application of electric field.

We found that electron-radiation-induced crystallization microstructure of sputter-deposited amorphous germanium films varies with aging of the amorphous films at room temperature. The analysis in terms of pair distribution function revealed that amorphous structure changes systematically with aging up to several months. In this review, we discussed the relationship between amorphous structure and crystallization microstructure based on the experimental and computational results.

Novel microscopic observation techniques that applied nanotechnology are developing. We developed novel functional nanoparticles termed as organosilica nanoparticles. The organosilica nanoparticles were applied to biomedical research. We investigated macrophage uptakes using fluorescent organosilica nanoparticles. We could evaluate the macrophage uptakes using fluorescent microscopy and electron microscopy, and found novel characteristics of them functionally and structurally. Further multifunctionalization of nanoparticles provide new progress of microscopic observation techniques.