Nucleation is the initial process by which atoms and molecules come together to form particles and a fundamental phenomenon that occurs universally. Nevertheless, our understanding is very limited. We believe that the physical properties and specific behaviors of nanoparticles are the key to understanding nucleation. We have been using transmission electron microscopy to visualize the nucleation process from solution, which has been a black box until now. We developed an original method using ionic liquids as solvents instead of water, and optimized an observation method of nucleation from aqueous solutions using liquid cells in the early days. Our work has revealed the precipitation and dissolution of nuclei in unsaturated and equilibrium conditions, competition between crystal polymorphs formed at different frequencies, multiple pathways of nucleation in the same experimental system, and the role of the hydration layer in crystallization. These results are expected to contribute to the development of a unified nucleation model.

Ni catalysts have been generally applied to chemical industries such as for hydrogen production, since they have excellent catalytic activity for hydrogen decomposition and inexpensive cost with compared to noble metals. However, agglomeration of Ni catalysts due to oxidation/reduction at high temperatures and carbon deposition to the surface of the Ni catalyst particles cause the decrease of catalytic activities. In this study, we have conducted in situ observation of Ni/MgO・Al₂O₃ catalysts at elevated temperatures under methane atmosphere using environmental TEM. As a result of this, it is found that the crystal structure of Ni catalysts changes from fcc to hcp around at 300 °C, and the spacing of close-packed planes of the Ni crystals increases. This indicates that solid solution of carbon, which is generated due to thermal decomposition of methane, into Ni catalysts results in the transformation from fcc-Ni to hcp-Ni. Growth of graphite layers on the surface of Ni particles were observed after the crystallographic transformation of Ni catalysts.

Zn-air batteries are expected to be utilized as new generation batteries with low-cost and high energy density. However, dendrite formation and capacity degradation during charge-discharge processes are major problems in zinc-air batteries. Dendrite growth from the zinc electrode is known to cause short-circuiting in zinc-air batteries because of their fast growth from the anode toward the cathode. The details of dendrite formation mechanism have not been revealed yet. In order to realize long-life rechargeable zinc-air batteries, the characteristics of zinc electrodeposition are needed to be clarified. We have performed liquid phase transmission electron microscopy (LP-TEM) observations to visualize the initial state of zinc electrodeposition. The electrochemical sample holder allows us to place a liquid sample into the TEM column because the sample is isolated from the surrounding environment by amorphous silicon nitride membranes equipped with the holder. Furthermore, electrochemical reactions can be executed in the holder using electrodes patterned by microelectromechanical system (MEMS) techniques on the membrane. At this moment, we demonstrate in situ TEM observation of zinc electrodeposition on the platinum working electrode.

In recent years, it was reported that semiconductor materials, which were regarded to be brittle, can exhibit high plasticity even at room temperature. For example, in strontium titanate crystals, room-temperature plasticity can be improved by controlling the ratio of the constituent elements. In addition, zinc sulfide crystals are brittle under light irradiation, but show high plasticity in the dark. These unusual plasticity of semiconductor crystals, which had not even been imagined before, has attracted a great deal of attention. These “brittle” materials were not suitable as structural materials before, and consequently have been used exclusively as functional materials. However, the understanding of the mechanisms that can overcome the brittleness of these materials is very useful for various material systems, and the wider application of materials are expected. Here we discuss the recent studies on the improvement of the plasticity of strontium titanate and zinc sulfide based on the in-situ observation of the samples and TEM observations of the dislocation substructures.

The key of compressed sensing technology is to find out the feature elements (bases) contained in the original signal from few sampled measurements. In this paper, we introduce theories of compressed sensing techniques based on machine learning and their application to scanning transmission electron microscopy, electron energy loss spectroscopy, and electron holography, in which the bases are extracted by suitable statistical signal processing (sparse coding and tensor decomposition).

The ATUM-SEM system, which can analyze serial sections for electron microscopy in three dimensionally, is one of the SEM imaging procedure, and has been attracting attention recently. Among the various serial EM observation procedures, this system has excellent features, such as high-resolution imaging with a wide range of biological specimens and the possibility to image sections repeatedly. Furthermore, by combining ATUM-SEM system and multibeam SEM imaging technology which irradiates 61 beams in parallel to image the serial sections, the entire images of the EM block can be obtained quickly and with high resolution. The whole system enables us to carry out three-dimensional structural analysis of large biological samples from the level of millimeter resolution to that of nanometer resolution. Recently, the localization of a specific molecule can be clearly visualized on a wide range of sections by analyzing with the multibeam SEM and with the CLEM methods, simultaneously. In this review, we would like to summarize the ATUM-SEM system, and the procedure for large area imaging with multibeam SEM, and also describe the cutting-edge imaging technology of the large area CLEM imaging with multi-beam SEM, designated as LA-CLEM (large-area CLEM).

Ultracryotomy is a standard immunoelectron microscopy technique in the cell biology field. It is similar in principle to the frozen section technique, which is often used for histochemistry in light microscopy. The reason why the immnoelectron microscopy using ultrathin cryosections is referred to as the Tokuyasu method is that most of the critical steps, from fixation to collecting and observing sections, were developed by Dr. Kiyoteru Tokuyasu about half a century ago, and that his original protocols are basically still in use even today. In this review, the major steps of the current standard protocol of the Tokuyasu method are explained based on the author’s experience. In addition, various applications of the method, especially the combination of the Tokuyasu method with other methods, taking advantage of the non-emmbedded specimen are introduced.

In the process of preparing TEM samples, many cutting/polishing operations are required as pretreatment. Here, we attempted to replace the typical pretreatment of cutting dices with a cutting wheel and polishing to a thickness of 100 μm with stealth dicing. This processing is particularly suitable for semiconductor wafers, and has many advantages such as time saving, high accuracy, automation, resource saving, dryness, and non-contact.

Using high-energy electron irradiation—in-situ TEM observation, we revealed that quantum diffusion of nanoscale defects can take place even in a heavy metal, tungsten, in contrast to a traditional notion.