To suppress aberrations in the signal electron optics of a scanning electron microscope, we propose ExB deflector (deflector with superimposed electric and magnetic fields) optics that cancel the aberrations generated during large-angle deflection. This improves the resolution of the angle or position of the signal electrons on the sample surface, allowing them to be discriminately detected. The proposed optics consist of two ExB deflectors and a transfer system with two 4-f systems, or systems that have four times the focal length, placed between them. This configuration maintains the symmetry of the electron beam trajectory throughout the transfer system such that aberrations generated by the first ExB deflector are negated by the second. The effect of the proposed optics was confirmed using a ray-tracing simulation of the electron beam, and the aberration was reduced to at most one-tenth of that in the case with only one ExB deflector. Furthermore, as an example, we examined the implementation of the proposed ExB deflector optics to resolve the signal electron angle and found that the sample emission angle range of 80° can be resolved with an angular resolution of 1°. Therefore, the proposed ExB deflector optics can be applied to the signal electron optics of a scanning electron microscope to improve the resolution of the signal electrons.

Electron tomography methods using the conventional transmission electron microscope have been widely used to investigate the three-dimensional distribution patterns of various cellular structures including microtubules in neurites. Because the penetrating power of electrons depends on the section thickness and accelerating voltage, conventional TEM, having acceleration voltages up to 200 kV, is limited to sample thicknesses of 0.2 μm or less. In this paper, we show that the ultra-high voltage electron microscope (UHVEM), employing acceleration voltages of higher than 1000 kV (1 MV), allowed distinct reconstruction of the three-dimensional array of microtubules in a 0.7-μm-thick neurite section. The detailed structure of microtubules was more clearly reconstructed from a 0.7-μm-thick section at an accelerating voltage of 1 MV compared with a 1.0 μm section at 2 MV. Furthermore, the entire distribution of each microtubule in a neurite could be reconstructed from serial-section UHVEM tomography. Application of optimized UHVEM tomography will provide new insights, bridging the gap between the structure and function of widely-distributed cellular organelles such as microtubules for neurite outgrowth.

Key words: microtubule, neurite, section thickness, electron tomography, ultra-high voltage electron microscope

This paper summarizes the research findings on improving the performance of imaging lenses and observation systems to make ultra-high voltage electron microscope suitable for in-situ observation. The study is structured into seven chapters, and the following is an outline of each chapter:
Chapter 1 introduces the features of ultra-high voltage electron microscopes, the performance requirements for in-situ observation, and the associated challenges. It also outlines the objectives of this study and the structure of the paper.
Chapter 2 proposes a new magnetic circuit model that separates the causes of the objective lens's response delay into three factors: the coil, cooling plate, and magnetic circuit. Analytical evaluations of the magnetic flux density at the center of the lens gap were conducted. It was shown that cutting off the eddy currents flowing through the cooling plate significantly improves the response speed. This improvement was quantitatively verified through dynamic analysis of the magnetic flux density using the finite element method.
Chapter 3 describes how processing the lens cooling plate to eliminate eddy currents significantly improved the rise characteristics of the lens. The frequency and time response characteristics of the magnetic flux density at the center of the lens were measured and validated. Additionally, a focusing lens with a small magnetic circuit independent of the objective lens magnetic circuit was introduced to compensate for delay components caused by the penetration of magnetic flux into the deeper magnetic circuit.
Chapter 4 presents a new imaging mode that eliminates the mechanical movement of the aperture, enabling rapid switching between enlarged and diffraction images using only lens excitation switching. The electron optical parameters of this imaging mode when applied to an ultra-high voltage electron microscope were calculated, and its feasibility was confirmed.
Chapter 5 investigates the optimal conditions for fluorescent screens with high resolution and high luminous efficiency for ultra-high voltage electron microscopes. Two types of screens—optically transparent single-crystal screens and opaque powder screens—were studied. The emission spread characteristics were quantified for each thickness and depth. Cross-sectional observations of the fluorescent screens were conducted to quantitatively determine the emission spread distribution, and spread functions were derived. Based on these measurements, the emission spread mechanism of fluorescent screens was clarified, and optimal conditions for fluorescent screens for ultra-high voltage electron microscopes were established.
Chapter 6 quantitatively evaluates the resolution of a newly adopted high-sensitivity, high-resolution HARPICON camera. The resolution of the TV observation system, consisting of the fluorescent screen and TV camera, was determined, and key points for improving resolution were identified.
Chapter 7 concludes the paper by summarizing the findings and discussing future challenges.

Electron microscopy is one of the most important and powerful technique for the microstructure analysis in materials. Tele-microscopy including the remote operation and observation using electron microscopes had been proposed at end of 1990’s, however, the initial stage tele-microscopy had not been widespread because of the underdevelopment of information and communication technology at that time. Now we start the construction of network tele-microscopy system as the cutting edge of tele-microscopy. In the present study, the concept and some experimental results of the network tele-microscopy system focusing on the Hyogo Prefecture in Japan are introduced.

This study presents advancements in electron optical systems, focusing on AI-compatible designs to improve performance in SEM, TEM, and analyzers. Key innovations include: (1) the N-SYLC aberration corrector, which eliminates magnetic hysteresis and enhances magnetic field strength using parallel current lines; (2) the V-SYLC beam deflector for high-speed voltage superimposition; and (3) the DAL electron mirror, offering charging-free energy filtering for compact analyzers. The N-SYLC system simplifies traditional spherical aberration correction by replacing magnetic poles with current lines, improving controllability and efficiency. Integration of these technologies with AI enables autonomous electron beam tuning and noise suppression, laying a foundation for new applications.

We developed a method for 3D surface reconstruction of crystalline materials using electron tomography. The study focused on dendritic crystalline particles growing in an amorphous Fe-Si-B alloy matrix. Bright-field TEM images were acquired using an ultra-high voltage electron microscope (2000 kV, Hitachi H-3000) from 121 angles between -60° and +60° at 1° intervals. To address the complex diffraction contrast typical of crystalline materials, the images were binarized, clearly separating the crystalline particles from the amorphous regions. The reconstruction results showed that binarization significantly reduced noise, producing a smooth and accurate representation of the 3D growth front. This method aids in understanding the growth mechanisms of crystalline particles.

Electron microscopy is a crucial technique for microstructure observation and material analysis, but its high cost and the limited availability of skilled electron microscopists restrict its accessibility. In Japan, electron probe micro-analyzers (EPMAs) with field-emission (FE) guns are installed in only a few public technology centers and universities. Network tele-microscopy offers a solution by enabling remote observation of electron microscope images without requiring expensive equipment or specialized expertise. This study reports on a network tele-microscopy system developed for remote observation, installed at the Research Center for Advanced Metallic Materials, University of Hyogo, and the Hyogo Prefectural Institute of Technology.