Layered MAX phases (M: transition metal, A: III-A, IV-A group elements, X: C or N) are the parent materials of MXenes, which have recently received attention as a new atomic layer system and are known as industrial materials for applications owing to their excellent properties, which combine the characteristics of both metals and ceramics. Meanwhile, the bulk electronic structure of MAX phases has primarily been investigated using computational methods, primarily because well-characterized single crystals are few. This review presents anomalous electronic states such as Dirac points and line nodes, which have been observed in recent electronic structure studies pertaining to MAX phase single-crystals using angle-resolved photoemission spectroscopy. These states are expected to result in unique topological quantum transport in MAX phases.

The phase-field method is a continuum model used to calculate internal microstructure developments in various materials. Over the past four decades, it has become one of the primary approaches for analyzing microstructures in materials. During this time, both computational thermodynamics (e.g., the CALPHAD method) and material property calculations based on microstructure data have also advanced significantly. Together, these methods are evolving into a robust system that supports multiple aspects of material design. Additionally, data-driven engineering methods can be broadly viewed as a collection of tools for handling forward and inverse models in computational engineering. This tutorial review explores perspectives on the next generation of material design by integrating these approaches.

Nuclear medicine is a powerful clinical diagnostic tool for early cancer detection and characterization. In this review, we explore the potential of future nuclear medical imaging technology using MeV photons compared to advanced optical imaging technology employing eV photons. Specifically, we discuss three main topics within the framework of the MeV energy regime: (1) Multi-color and multi-wavelength imaging, (2) molecular interaction imaging with a quantum sensor, and (3) imaging enhancement utilizing quantum entanglement features.

In 1981, Feynman proposed a computer that operates probabilistically at the hardware level, along with the concept of quantum computers. Boltzmann machine learning, proposed by Hinton et al., the 2024 Nobel laureates in Physics, also models a magnetic system consisting of probabilistically fluctuating spins. As the increasing power consumption associated with the widespread use of artificial intelligence becomes a pressing challenge, this paper discusses spintronics probabilistic computers that naturally realize the proposals of Feynman and Hinton, enabling energy-efficient artificial intelligence computation. Proof-of-concept demonstrations, including combinatorial optimization, machine learning, and quantum simulation, as well as the development of superparamagnetic tunnel junction devices for enhancing computing performance, are described.

Diamond exhibits unique properties enabling the fabrication of high-performance p-channel field-effect transistors, an achievement that remains challenging for other wide-bandgap semiconductors. This distinct potential positions diamond as an exceptional semiconductor material for realizing complementary power inverter circuits and other advancements in power electronics. This paper provides a comprehensive review of the progress on diamond field-effect transistors, with particular emphasis on the diamond/gate insulator interface and its critical influence on device performance.

Injecting high-energy heavy ions into solids can create cylindrical damage zones called ion tracks. The most accepted mechanism for ion track formation is the inelastic thermal spike (i-TS) model in which molten regions induced by large energy deposition along the ion trajectories transform to tracks after quenching. However, diamond, which is in a meta-stable state, does not melt with heating but transforms to a stable state (i.e., graphite). While no tracks have ever been observed in diamond, we successfully formed tracks under MeV C₆₀ ion irradiation. Track formation via a non-melting route is presented herein.

This article introduces experimental studies on plasma–material interactions using an impedance spectroscopy method. Impedance spectroscopy, which has been primarily developed in the field of electrochemistry as a method for monitoring the electrical properties of devices under test, is applied to the analysis of a material surface modified using plasma exposure. Utilizing the electrical conductivity of plasmas, the “in-situ” impedance spectroscopy of material properties is possible and is expected to be a tool for monitoring thin-film deposition and etching processes using plasmas.

Magnetic refrigeration is a reliable cooling method capable of achieving temperatures below 1 K by employing magnetic materials and magnets. Recently, various cryogenic magnetic refrigerants, including rare-earth ions, have been discovered. The effectiveness of these refrigerants, assessed through specialized measurements below 2 K, relies on the properties of the 4f electrons in the rare-earth ions. In this review, the approach for studying cryogenic magnetic refrigerants is outlined, based on the thermodynamic measurements and the condensed-matter physics of the 4f electronic system aimed at identifying high-performance magnetic refrigerants.

Mid-infrared photothermal (MIP) microscopy is an emerging imaging technique that visualizes mid-infrared absorption arising from molecular vibrations with high spatial resolution through visible-light detection. In this review, we focus on mid-infrared photothermal quantitative phase imaging (MIP-QPI), a technology recently developed by our group. We present recent advancements, including high-sensitivity, video-rate chemical imaging, and enhanced spatial resolution. In addition, we discuss novel applications such as the direct visualization of intracellular heat diffusion and thermophoresis, underscoring the promising potential of MIP-QPI for life science research.

Positrons, the antimatter of electrons, can be used to detect vacancies and open spaces in materials with high sensitivity and nondestructive properties. As this technique can be applied without requirements, such as sample temperature and conductivity, it is used to study defects in metals, semiconductors, insulators, etc. The depth distribution of defects in the subsurface region can also be evaluated. This paper explains the principle of positron annihilation, introduces recent applications, and evaluates the annealing properties of vacancy-type defects and open spaces in ion-implanted semiconductors, high-k films, and SiO₂.

Two-dimensional (2D) nanosheets, which possess atomic or molecular thicknesses and infinite lateral dimensions, have received increasing attention owing to their unique physicochemical properties distinct from those of their bulk counterparts. In particular, the discovery of graphene has facilitated investigations into the intriguing properties of other layered and non-layered 2D nanosheets. Among these 2D nanosheets, 2D oxide nanosheets are an important target owing to their diverse chemical compositions, structures, and functionalities beyond graphene. Herein, I review recent advances in the synthesis, assembly, and properties of 2D oxide nanosheets, highlighting emerging functionalities in electronic applications.

This paper describes the plasma gene/molecule transfection method, which led to the device’s launch at the end of 2024. Plasma induces endocytosis, the cells' spontaneous uptake of external molecules through combined electrical and chemical stimuli. Since the combined stimuli induce spontaneous uptake of molecules by the cells, the intensity of each stimulus can be weak, thereby suppressing damage to the cells. Furthermore, the micro-plasma method can introduce large molecules, such as plasmid DNA, without causing random genome integration. This is effective as a practical means of introducing genes and molecules with a view to medical applications and is expected to be a valuable tool for genome editing.

Optical wireless power transmission (OWPT) is a technology that uses highly directional light sources, such as lasers, and solar cells, to transmit power over long distances in a compact and efficient manner without wiring. It is expected to be used in various environments and applications, such as multiple Internet-of-things devices, mobility services, such as electric vehicles, drones and robots, and underwater and space applications, without generating electromagnetic noise. Owing to recent advances in light sources, power receiving elements, and related peripheral technologies, the practical application of this technology is progressing in some areas. This paper explains the basic principles and configurations, application examples, technical challenges, and future prospects of OWPT.

Nitride semiconductors have enabled highly efficient blue and green LEDs. The research is presently being extended to red emission to complete the RGB spectrum within the same material system. InGaN (as the emitting layer) provides a tunable bandgap energy range from ultraviolet to infrared. Realizing red LEDs or laser diodes with InGaN would enable full-color emission from the same material system. This would enable the integration of these devices on the same wafer and displays potential for inexpensive and high-performance highly advanced micro-LED displays. However, increasing the In content in InGaN to achieve efficient longer-wavelength emissions remains a significant challenge in terms of material growth. This paper reviews the recent progress in InGaN crystal growth and the development of red-emitting devices.

As a new type of optical fiber that overcomes the limitations of conventional glass-core fibers, hollow-core fibers—which confine light in air through photonic bandgap and anti-resonant effects—are attracting significant attention. In this paper, we describe the fundamentals of hollow-core fibers, the current state of the technology, and prospects for their social implementation.

Photovoltaics is one of the most promising technologies among renewable energies. There is a strong push for the further spread of photovoltaic technology as a primary source of electricity and the development of new applications. Based on the empirical results, new applications and future vision for photovoltaic technology will be discussed, focusing on solar carport, wall-mounted photovoltaics, and agrivoltaics.

A device that converts thermal energy into extractable forms, such as mechanical energy, is termed as a heat engine. The operating medium that powers the heat engine is usually a physical system that follows classical physics. In recent years, research on heat engines, whose operating media follow quantum physics, has been progressing from theoretical and experimental perspectives. In this study, we focus primarily on the theoretical aspects, particularly on how the performance of this type of quantum heat engine improves with an increase in the size of the operating medium. We discuss the research background, recent trends in this field, and our latest findings. The results presented here suggest a significant potential for enhancing heat engine performance by leveraging quantum mechanics as the operating principle.

Materials informatics has significantly advanced the prediction technology for new materials. However, not all predicted materials can be synthesized. We have been developing synthesis techniques to handle metastable states and achieve more new materials. This article presents the methods to change the chemical composition while preserving crystal structures by controlling the diffusion of specific constituent elements.

Time-domain reflectometry is an electrical measurement that utilizes the reflected waves of high-frequency electrical signals from portions where impedances are not matched in the high-frequency transmission paths. In the past, it has been used for large-scale measurements such as geological surveys. However, in recent years, technological advances have made it possible to perform small-scale measurements such as LSI quality diagnosis. We adopted this measurement to observe the carrier dynamics in electronic devices by measuring the transient impedance. This paper presents the results of a time-resolved analysis of organic thin-film transistors and organic solar cells.

As AI technology evolves and the demand for high-performance computing increases, high-capacity, low-power, and high-bandwidth memory is becoming more important. However, we are reaching the technical difficulty of achieving two-dimensional device scaling and computer architectures with off-chip memory. This article introduces a research progress on oxide-based 3D-integrated memory devices to break through this difficulty. In particular, the research on the memory devices using HfO₂-based ferroelectrics as memory element and oxide semiconductor as channel material is discussed.

The role of light is expanding beyond communication and measurement to include computing, as observed in the remarkable progress of artificial intelligence (AI) in the midst of the further digitization of society. This paper reviews the latest developments in photonic research aimed at enhancing reinforcement learning and decision-making tasks, both of which are fundamental functions of AI. We introduce methods for solving the multi-armed bandit problem using chaotic itinerancy of semiconductor laser dynamics and provide an overview of collective decision making that leverages quantum light interference.

Decommissioning preparations, including the research and development of solar cell-based radiation detection devices (SRDs) for reactor-internal radiation monitoring systems, are underway following the accident at the Fukushima Daiichi nuclear power plant. SRDs use the principle of electron–hole pairs generated by the incident radiation energy to output a current to an external circuit by the built-in potential. InGaP, CIGS, CdTe, and HOIP have been selected as candidates for radiation-tolerant solar cells for use in high radiation environments. This report presents the development of a radiation detection system using InGaP solar cells, a dynamic range estimation method using visible light, and work on neutron radiation detection.

High-temperature superconductor REBa₂Cu₃O_y (REBCO) microwave devices offer excellent performance. Microwave receive filters using REBCO film have excellent performance with low loss and sharp skirt characteristics and are already used in the receiving systems of mobile communication systems. However, practical applications of microwave devices using REBCO films are limited to receive filters. One reasons for the lack of progress is the low characteristics of the REBCO thin film. Recently, we reported that the characteristics of the REBCO thin film can be significantly improved via metal organic deposition using the trifluoroacetate (TFA-MOD) method and substrate annealing process. Herein, we introduce the TFA-MOD method and substrate annealing for the fabrication of REBCO thin films for high-frequency applications and demonstrate superconducting high-frequency devices based on these films.

Nanopore measurement is a method for the label-free detection and analysis of single biomolecules passing through nano-sized pores. Nanopores are broadly classified into protein and solid-state nanopores. Protein nanopore-based DNA sequencers have garnered significant attention as next-generation sequencers. Conversely, research advancements in solid-state nanopores, which entered the field more recently, have demonstrated significant progress in recent years. This review article outlines solid-state nanopore fabrication methods and introduces a novel photothermal-etching-assisted nanopore fabrication method.

Thermoelectric generators are solid-state devices capable of directly converting heat to electricity. The performance of these modules is limited by the tendency of the metal–semiconductor contacts at the hot-side to degrade due to chemical reactions and/or elemental diffusion. Transverse thermoelectric modules can be employed to address these issues because the temperature gradient and electricity are orthogonal to one another. Consequently, the exposure of metal–semiconductor contacts to high-temperature environments can be avoided, thereby improving the long-term thermal stability of the device. One approach to designing transverse thermoelectric devices is to use materials having goniopolarity, which simultaneously exhibit p- and n-type conduction along different crystallographic directions. Here, we report the goniopolarity of Mg₃Sb₂ and Mg₃Bi₂ due to their band anisotropy.

The dielectric ceramics used in multilayer ceramic capacitors (MLCCs) require not only a high dielectric permittivity but also a high dielectric breakdown strength, which is achieved by precisely controlling the microstructure. The hydrothermal method, which is one of the liquid-phase synthesis methods, is effective at synthesizing well-dispersed dielectric particles with a small particle size, which can be sintered to obtain dense and fine-grained dielectric ceramics. This paper presents our recent attempts to develop new dielectric ceramics using the hydrothermal method, focusing on bismuth potassium titanate-based materials.

Liposomes are lipid vesicles with a cell-like bilayer membrane structure that are used to construct artificial cell models. To ensure the reproducibility of experiments and enable quantitative analysis, a method for producing liposomes with uniform size and high encapsulation efficiency is required. Recently, we developed a system for generating monodisperse liposomes using a microfluidic device. This system can produce monodisperse liposomes with diameters ranging from 25 to 45 µm, achieving a yield of approximately 100%. To apply this system to the construction of artificial cells, we present the results of encapsulating an in vitro transcription/translation system in liposomes to investigate the conditions under which protein synthesis occurs.

With the recent miniaturization of advanced semiconductor devices, there is a growing demand for high-resolution, high-throughput electron beam devices in the semiconductor manufacturing process. Planar electron sources can be fabricated using semiconductor microfabrication technology, facilitating the fabrication of multi-beam arrays; however, challenges persist involving energy monochromaticity and emission current density. This study develops a planar electron source with high emission current density and energy monochromaticity, superior to that of conventional electron sources, by addressing these challenges using the excellent electron transmission characteristics of atomic layer materials.

Research on nanomaterials often focuses on thin films and nanoparticles with uniform shapes and internal structures. In contrast, our research focuses on “nanogap nanoparticles,” where nanoparticles are irregularly arranged on the substrate with nanoscale intervals. To fabricate nanogap nanoparticles, a method for real-time observation of the nanoparticles’ formation process is essential. We have developed a resistive spectroscopy method utilizing resonant vibrations of piezoelectric material. This paper presents a novel method for monitoring the formation process of nanoparticles and discusses our research findings on developing hydrogen gas sensors and observing the formation process of core–shell nanoparticles.

In 2020, the asteroid explorer Hayabusa2, which successfully returned samples from the asteroid Ryugu, carried out an engineering experiment to deploy a rover and landing markers in orbit around the asteroid just before leaving it, and successfully generated the world’s first multiple and smallest asteroid satellites. This paper describes the orbit design strategy around the asteroid, the results of the experiment, and future prospects for orbits around celestial bodies based on JAXA’s future deep space exploration missions.

Energy consumption associated with the recent artificial intelligence has become more critical. To solve this problem, stochastic computing using room-temperature heat has been proposed and demonstrated in spintronics by tuning a magnetic device and allowing the spins to be susceptible to thermal fluctuations. Magnetic skyrmions, which are spin structures in magnetic thin films, behave as particles and exhibit thermal fluctuations of spins as Brownian motion in solid. This article introduces a “Brownian computer” that requires minimal external energy by the Brownian motion and describes the properties of Brownian motion of magnetic skyrmions and their control.

Although mechanical oscillators play pivotal roles in modern science and technology, their application to quantum technology remains challenging. The advent of cavity optomechanics marks a significant breakthrough. In particular, superconducting circuit optomechanics at cryogenic temperatures serves as a pioneering platform for the quantum control and measurement of mechanical oscillators. By introducing an innovative fabrication technique, we have overcome the long-lasting challenges in this field and realized long-lived and scalable superconducting circuit optomechanics operating at the quantum limit. Our systems not only offer a novel framework for many-body physics research but also provide solutions for quantum memory in quantum computing and communication. Additionally, they hold promise for fundamental physics research, including the observation of macroscopic quantum effects and the search for dark matter.

In this study, ultrathin organic solar cells are attached to the abdomen of insects to generate power on the insect without impairing its mobility. Using this approach, we achieved rechargeable cyborg insects. We successfully described the relationship between the basic motion ability and the film’s thickness and Young’s modulus quantitatively based on a buckling load. Additionally, we demonstrated that a thin-film device with a thickness of a few micrometers can fully maintain the motion ability of insects, thereby demonstrating the effectiveness of ultrathin electronics. This study involves multiple disciplines, i.e., device physics, materials science, mechanical engineering, and biology. A clear example is provided to demonstrate that new applications can be presented by transcending fields.

Near-field optical microscopy is a super-resolution technique that utilizes localized light generated at the tip of a metal probe to enable nanoscale optical imaging and analysis. It supports various optical measurements, including Raman spectroscopy, infrared absorption measurement, and photoluminescence spectroscopy, all at the nanoscale as a versatile tool. Recent progress in this field has not only significantly enhanced spatial resolution but also introduced innovative technologies aimed at improving its overall analytical capabilities. This article provides an overview of the recent advancements in near-field optical microscopy, incorporating our research achievements to highlight emerging trends and applications.

We present a novel methodology for synthesizing functional nanopowders by integrating tandem pulse-modulated induction thermal plasmas (Tandem-PMITP) with time-controlled feedstock feeding (TCFF). The Tandem-PMITP system employs two radio-frequency (RF) coils within a single plasma torch to generate an axially extended plasma column. The upper coil maintains plasma stability, while the modulated lower coil generates dynamic thermal fields. This configuration facilitates efficient feedstock evaporation and promotes robust nanoparticle nucleation, enabling high production rates of 800–1000 g/h at 20 kW for a range of oxide materials. A comprehensive numerical thermofluid model has been developed to characterize the plasma fields, feedstock behavior, and aerosol dynamics. The model indicates that modulation-induced entrainment significantly enhances vapor cooling and nucleation. The proposed Tandem-PMITP+TCFF system exhibits considerable promise for scalable and efficient nanoparticle production.

Quantum networks are a fundamental technology that enable quantum communication and distributed quantum computing. As a key platform for quantum networks, diamond NV centers have attracted significant attention. This study develops a novel approach for spin qubit control under zero magnetic field, an approach that differs from conventional methods. By integrating this technique with spin-photon interfaces and deterministic Bell-state measurements, we systematically establish the core technologies required for quantum network implementation. This study provides a comprehensive overview of these advancements, incorporating techniques such as quantum entanglement, Bell-state measurement, and quantum teleportation, and discusses prospects for further development.

“Ising machines,” which find low-energy states of the Ising model using physical experiments that emulates this model, are now drawing attention as a way to solve combinatorial optimization problems efficiently. A coherent Ising machine (CIM) is an optical Ising machine that uses the discretized phases of degenerate optical parametric oscillators as the Ising spins and employs the measurement-feedback to couple them. In this paper, we report the recent progress of the CIM research, including the realization and benchmarks of an ultra-large-scale CIM that can simulate a 100,000-spin Ising model with arbitrary spin-spin interactions.

Materials with nanospaces, represented by microporous materials like zeolites, are known to have adjustable pores with size of molecular dimensions and with specific shapes that serve as windows, and large specific surface areas owing to the existence of nanospaces. They exhibit molecular sieving abilities and high adsorption performances owing to such features. Their applications are extremely diverse, including catalysts, sensing, biotechnology, and separation. Particularly in the field of separation, technologies that realize molecular-level separations, such as microporous adsorbents and separation membranes, have been developed. In this paper, we introduce our attempts toward developing separation technologies based on microporous materials, e.g., adsorbents and separation membranes, and improving their usability and sustainability.

In polycrystalline ceramics composed of numerous crystal grains, the development of transparent ceramics, which involves minimizing internal scattering sources, holds significant promise for applications in high-average-power solid-state laser fields. However, in non-cubic materials with birefringence, scattering at grain boundaries occurs, making it difficult to achieve laser-quality transparency. Addressing this issue is expected to propel the development of novel laser materials, sources, and applied technologies. This paper provides an overview of the techniques and current status of non-cubic transparent ceramics and presents the author’s research findings on transparent ceramics composed of nanocrystalline grains.

SiC power devices exhibit high energy-saving performance; however, they are expensive. One of the causes of the high cost is the degradation of device performance through bipolar degradation, which is a phenomenon in which basal plane dislocations in the crystal expand into stacking faults (SFs). As a countermeasure, this study has established a method (SF-KHII™ method) that introduces point defects into SiC through high-energy H⁺ or He⁺ implantation to prevent the expansion of SFs. It is expected that the SF-KHII™ method will completely suppress the expansion of SFs in the future, which will result in the widespread use of energy-saving SiC power devices.

This study presents an approach for plasma flow diagnostics employing optical vortex beams with helical wavefronts. Although flow velocities perpendicular to the optical axis cannot be measured using conventional laser spectroscopy, this limitation is overcome herein by applying the azimuthal Doppler effect inherent in optical vortices. Specifically, we demonstrate quantitative velocity measurements of argon metastable atoms in a radio-frequency plasma using optical vortex laser absorption spectroscopy. Moreover, by introducing asymmetry into the beam intensity distribution, the asymmetric optical vortex laser-induced fluorescence method enables the determination of three-dimensional flow velocity vectors from a single laser path. Overall, these results indicate the promise of this diagnostic approach for complex plasma flows with limited optical access.