While global warming and fossil fuel drain pose a problem, development of the hydrogen storage material which can store and convey compactly and safely hydrogen is important; hydrogen can mutually alter to electricity. The characteristics such as hydrogen absorption capacity, cycle ability and reaction rate are related to the microstructure in a hydrogen absorption process. In this research, the TEM sample holder with an ex situ cell was produced for the purpose of clarifying microstructure of the hydrogen storage material during hydrogenation. When TEM observation was carried out as it was, without taking out in the atmosphere the palladium powder which was exposed to hydrogen gas, the coarsening of the crystal grain was observed. Next, environmental TEM performed in situ observation on hydrogenation of Mg-Ni films. As a result, it was clarified that MgH2 crystallized after Mg2NiH4 formation.
In-situ transmission electron microscopic (TEM) observations are highly attracted because high resolution images of specimens can be obtained at high temperature with introduction of gases. Especially, for the research on metal nanoparticles, this technique is a promised one as an evaluation method of nanoparticles for some applications. Structural changes in nano-dimension including oxidation and phase transition can be observed in real-time with this technique. In this review, we introduce some special TEM equipments for high temperature in situ observation of metal nanoparticles at high temperature, and also introduce our resent works of high temperature in-situ TEM observation of anisotoropically shaped metal nanoparticles and Cu fine particles used for a conductive paste.
We have developed a closed-type environmental-cell (E-cell) transmission electron microscope (TEM) enabling to observe catalyst specimens reacted at ambient conditions. As a part of the developed system, a coaxial-type gas-flow specimen holder has been invented. A hybrid membrane has been also developed as a window material of the E-cell, which consists of an amorphous carbon film and a silicon nitride thin layer. The membrane showed high performances such as less deterioration of spatial resolution, high toughness for pressure difference, and high stability for electron beam irradiation. As an application of our developed system, nanoparticulate gold catalysts supported on TiO2 anatase substrates were observed dynamically at a condition of a selective oxidation of propylene. In-situ observations by the E-cell TEM revealed that product materials of catalytic reaction were formed from the perimeters of the gold/TiO2 interfaces.
Recently, various power sources, such as fuel cells, rechargeable batteries, capacitors, have been developed and put into practical use. These power sources employ the chemically synthesized nanomaterials. Since the fine structures of these nanomaterials are closely related to their performance，it is essential to analyze the structures in detail. TEM is one of the most powerful and useful tools in the studies of these nanomaterials. However, most of these nanomaterials are extremely sensitive to the electron beam irradiation and easily change their structures as soon as the electron dose exceeds the limit. Therefore the highest attention must be paid in the structural characterization of these nanomaterials using TEM. In this paper, an example of the structure analyses of a chemically synthesized Pt/CB electrocatalyst for the polymer electrolyte fuel cell (PEFC) using TEM and the observation conditions for minimizing the electron beam irradiation damage are reported. In addition, in situ TEM observation of the degradation process of the Pt/CB electrocatalyst in the highly-humidified and not-humidified air atmospheres are reported as an application of ETEM technique. An ETEM based on a conventional analytical TEM and a specimen heating holder employed a gas injector were used in the study.
Coherent X-ray diffraction imaging (CXDI) is a lensless X-ray imaging technique based on coherent diffraction measurement and iterative phasing methods. X-ray ptychography is a CXDI technique which can measure an extended object. We have developed high-resolution and high-sensitivity X-ray ptychography using the focusing optics installed with a spatial filter at SPring-8. Recently, we have first demonstrated hard X-ray ptychography using a multislice approach, which can solve the limited spatial resolution under the projection approximation.
A number of proteins are involved in DNA replication, which is essential for the inheritance of genetic information. These proteins assemble to form a huge complex, called replisome, and accomplish each function through highly regulated manner. Electron microscopic single particle analysis is one of the most powerful methods to study such complex system, which is difficult to study by X-ray crystallography. DNA replication in archaea and eukaryotes is executed by family B DNA polymerases (PolB). PolB interacts with the DNA clamp, PCNA, which forms a trimeric ring structure that encircles the DNA, and increases the processivity of the bound PolB by tethering it to the DNA. It is known now, that PCNA also interacts with various protein factors, to control DNA replication, DNA repair, and cell cycle progression. We have investigated the structures of PolB-PCNA-DNA and DNA ligase-PCNA-DNA, which play very important roles in replisome. The obtained structures, both revealed unexpected configurations of the complexes. Intriguingly, besides the authentic interaction through a PCNA-interacting protein box, a novel contact was found between both polymerase-PCNA and ligase-PCNA. The obtained molecular architecture of the complexes, including the newly found contacts, provides clearer insights into the mechanism of the regulation of the fork complex.
Autophagy is involved in the intracellular bulk degradation system, and is crucial for cellular homeostasis and stress response mechanisms. Upon autophagy signal, isolation membrane (phagophore) emerges and sequestrates the cytoplasm, which is closed to become autophagosome. The constituents are then degraded after fusing with lysosomes. Because this system involves dynamic changes in the membranous structures, analyses at electron microscopic levels are required to understand the detailed processes. However, some precautions are necessary for appropriate evaluation of the autophagy-related structures. Especially, preservation of the double membrane structure of the isolation membrane is greatly influenced by fixation and other sample preparation procedures. In this review, we first describe how we should identify and evaluate several autophagy-related organelles while pointing out some precautions, and second, introduce recent understanding on origins of the isolation membrane, a long-standing issue in autophagy research.
Heat-induced antigen retrieval (HIAR) methods that denature protein structure and expose epitopes in fixed tissues are commonly used for immunohistochemistry in recent years, whereas preservation of protein structure has been thought to be important. In this paper, I discussed the mechanisms of HIAR in the tissues fixed with formaldehyde or with glutaraldehyde and osmium tetroxide and described the application of HIAR to immunoelectron microscopy using specimens embedded in LR-White and epoxy resins. In addition, I demonstrated that the selection of diluents for the primary and secondary antibodies is one of the important factors to obtain a sensitive immunoreaction with low background staining.
Scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) can not only identify atomic columns but also carry out elemental and electronic state mapping with atomic resolution. This paper describes recent results of high spatial resolution electronic state analysis for transition metal oxide using Cs-corrected STEM with some cautions for experiment and interpretation.
Zeolites have a great potential for application in various fields. Now, zeolites are again at a center of public attention in Japan as stable adsorbents and solidification materials of fission products, such as 137Cs coming from damaged nuclear-power plants. Although ion-exchange mechanism within zeolitic nanocavities have been poorly understood. There are still open questions, at the atomic-level regime, on physical and chemical origins of ion-exchange selectivity and detailed atomic structures of counter cations inside the nanocavities. For practical application of zeolite as adsorbent of fission products, atomic-scale structural information of zeolites are indispensable. Here, precise locations of Cs+ captured within NaA-type zeolite were analyzed by high-resolution electron microscopy and theoretical calculation. Stable positions of adsorbed Cs+ in the nanocavities were identified, and the bonding environment with the zeolitic framework are revealed to be a key factor for the adsorbed cation locations.
Split-illumination electron holography has been developed by splitting coherent electron wave into two separate waves and illuminating them on two separated areas at the sample plane. With this method, it became possible to observe areas far from the sample edge and to reduce reference wave modulations due to the field around the sample by locating the reference wave far from the observation area. The advanced double-biprism type split-illumination electron holography without Fresnel fringes enables us to perform high-precision electromagnetic field analyses and opens up a new field of possibilities of holographic observations. In this report the developed methods are discussed in detail with their applications for studying magnetic flux distributions around pinning site of magnetic domain-wall in electrical steel and electrostatic potential distributions in n-type metal-oxide-semiconductor field-effect transistor (nMOSFET) located far from the sample edge.
Electron microscopic diagnosis of renal biopsy is conventionally performed by observation of ultra-thin sections of the renal tissue using a transmission electron microscope (TEM). However, it takes weeks to months to get a definitive diagnosis because of the long processing time. Furthermore, disadvantages of the use of TEM include sample size limitations and difficulty in obtaining three-dimensional information. Therefore, we developed a rapid three-dimensional analysis method using renal biopsy paraffin sections by low vacuum scanning electron microscopy (LVSEM) in the backscattered electron (BSE) mode. Unstained paraffin sections were deparaffinized, stained with platinum blue (Pt-blue) or periodic acid silver-methenamine (PAM), and directly observed with a table-top type LVSEM. Cut side views and surface views of glomeruli were shown under LVSEM. Pathological features could be investigated in some cases of human glomerular disease (minor glomerular abnormalities, IgA nephropathy, and membranous glomerulonephritis) at magnifications between ×50 to ×30,000. On Pt-blue-stained sections, podocyte, endothelium, mesangium and glomerular basement membrane (GBM) were clearly distinguished due to the different yields of BSE signals. PAM-positive GBM distinctly showed morphological alterations through overlying cells. LVSEM is expected to provide a novel approach to the pathological diagnosis of human glomerular diseases using conventional renal biopsy paraffin sections.