Reliability engineering is not only a single engineering discipline, but, similar to applied physics, it is also highly interdisciplinary. For equipment to be people-friendly and dependable, it must also have solid reliability. Through cycles of technological development and overcoming reliability issues, high reliability can be achieved. Lack of reliability in systems that require continuous operation may evolve into political or economic problems. In this paper, we present an approach for solving reliability issues that are becoming more and more important every year, and provide specific examples.

Recently, neutron detection has been applied in various fields, and the development of neutron detectors that are suitable for widespread neutron detection is expected. BGaN has been proposed and developed as a novel neutron semiconductor detection material. BGaN is a ternary nitride alloy that includes B atoms, and is capable of capturing neutrons and detecting signals in a sensitive layer. This report presents a method for the epitaxial growth of BGaN using a new B metal–organic source, TMB, which suppresses gas-phase reactions. By improving the growth conditions, thick growth was achieved and vertical-type thick BGaN pin-diodes were fabricated. The neutron energy spectrum was measured using the fabricated BGaN diodes. The results indicated that BGaN diodes could be used as effective neutron detectors.

Ferroelectrics have been used in a wide variety of applications such as capacitors, memories, and sensor materials. Many ferroelectric materials are solid solutions with complex compositions, and their structures are averaged. In particular, in order to clarify the polarization mechanism of pseudo-cubic structures such as relaxor ferroelectrics, not only average structural analysis assuming a conventional periodic structure, but also local structural analysis must be performed. The pair distribution function method is a technique of local structural analysis in which the radial distribution function is derived from powder X-ray diffraction, and model fitting is performed in real space without assuming a periodic structure. In this paper, the necessity of local structural analysis in dielectrics is discussed.

The gyromagnetic effect is one of the most significant discoveries in physics. It is associated with a mutual conversion of angular momentum between macroscopic mechanical rotation and microscopic electron spin. However, the gyromagnetic field generated by a feasible mechanical rotor is very small for practical applications. Surface acoustic waves are a promising candidate for improving the gyromagnetic effect because an elliptical oscillation of the lattice with a frequency of the GHz order can be realized. In this paper, experimental demonstrations of a gyromagnetic spin-wave excitation and its reciprocal effect, that is, a phase shift of the acoustic wave, are presented. Furthermore, we show that the gradient of the acoustic gyromagnetic field can produce an alternating spin current whose amplitude increases nonlinearly with the frequency.

Among worldwide developments of various quantum-computing hardware platforms, optical quantum computers currently stand out because of their unique approach. Recent progress in optical quantum computing has been remarkable; not only has “quantum supremacy” been achieved by beating supercomputers in specific calculations, but scalable paths to large-scale quantum computers have been discovered. Behind such progress is a new approach that breaks away from the traditional methodology of optical quantum computers. Here, we explain the background of recent progress in optical quantum computers and introduce the development and applications of our original loop-based optical quantum computer based on the new approach.

Toward efficient electrochemical reactions, we are focusing on the utilization of strong coupling between matter and vacuum electromagnetic fields. We introduce plasmonic control for the confinement of light energy for exotic excitation. In addition, we introduce the use of vibrational strong coupling for the modulation of the properties of water.

In the thrust to achieve carbon neutrality by 2050, tandem solar cells composed of perovskite and hetero-junction crystalline silicon solar cells have attracted much attention as next-generation solar cells, and their conversion efficiencies are approaching 30%. In this article, we show the latest results of the R&D activities for Kaneka’s 2-terminal tandem solar cells, which have a conversion efficiency of nearly 29%, and we discuss the light confinement technologies for tandem solar cells based on optical simulations. In addition, we also introduce 3-terminal tandem solar cells that have the potential to combine the state-of-the-art perovskite solar cells and Kaneka’s world-record holding back-contact-type hetero-junction crystalline silicon solar cells.

A state of the art back-illuminated (BI) single photon avalanche diode array sensor realized through a 90-nm CMOS compatible process on a 300-mm silicon platform is herein reported. The array consists of 10-µm pixels, each using a 7-µm thick silicon active layer, which enables the optical sensitivity of the device to be extended up to the near-infrared spectrum. In addition, buried metal full trench isolation is employed to suppress crosstalk. This is a critical feature in a device sensitive enough to be triggered by a single electro-luminescence photon emitted by a neighboring pixel. Finally, to maximize the fill factor and enable a BI structure, a Cu–Cu bonding process is conducted.

Seebeck effects, the generation of voltages from temperature gradients via thermal electron motion, have been applied to temperature sensors and power generators that convert thermal energy into electricity. Recently, the electron-spin counterpart of the effect — the spin Seebeck effect — was discovered in spintronics, which generates a thermoelectric voltage from electron-spin fluctuation through a spin current. However, these effects have been limited to electrons, and they inevitably disappear at low temperatures due to electronic entropy quenching. In this article, we report thermoelectric generation driven by nuclear spins in a solid, that is, the nuclear-spin Seebeck effect. The sample is a magnetically ordered material, MnCO₃, having a large nuclear spin (I = 5/2) of ⁵⁵Mn nuclei with a Pt contact. In the system, we observed low-temperature thermoelectric signals reduced to 100 mK owing to nuclear-spin excitation. Theoretical calculation show that the interfacial Korringa process plays an important role. The nuclear thermoelectric effect described here provides an approach for exploring thermoelectric science and technologies at ultralow temperatures.

Anisotropic self-assembled nanomaterials in transition metal compounds have attracted much attention because of their rich physical properties and structural controllability. Although peculiar sample preparation conditions and high-temperature processing are generally necessary for fabricating anisotropic nanostructures in oxides, nanometer-scale spinodal decomposition in spinel-type manganese oxides results in highly ordered nanostructures through simple heat treatment at relatively low temperatures. In this paper, we introduce recent studies on the formation of checkerboard and lamellar nanostructures comprising Mn-rich tetragonal and Mn-poor cubic nanodomains in manganite spinel (Co,Mn,Fe)₃O₄ annealed at 375 °C.

Ferroelectrics can function as non-volatile memory thanks to their switchable electric polarization by an electric field. However, realizing ferroelectricity at ultrathin thicknesses remains a challenge in materials science. To tackle this challenge, we artificially created a two-dimensional ferroelectric material using the van der Waals assembly. By manipulating its stacking order, we successfully transformed boron nitride, a non-ferroelectric van der Waals compound, into a ferroelectric material. The resulting ferroelectrics are stable up to room temperature despite their sub-nanometer thickness, enabling non-volatile memory applications. We further demonstrated the versatility of the design principle by converting semiconducting transition metal dichalcogenides into ferroelectrics in a similar manner.

When device scaling reaches the limit imposed by atoms, technology based on atomically precise structures is expected to emerge. In this technology, the assembly of building blocks with identified atomic arrangements without contamination plays a key role. We propose a transfer technique for deterministic fabrication of carbon-nanotube-based optical devices. By using single-crystalline anthracene as a medium, which can form large-area thin films, clean nanotubes are placed on a wide range of substrates. Under in-situ optical monitoring, nanotubes of desired chirality can be placed onto the desired location with sub-micron accuracy. This paper introduces the details of the transfer technique, followed by a few examples of the deterministic construction of heterostructures consisting of nanotubes with defined atomic arrangements and other nanomaterials/nanostructures.

Moiré lattice systems of two-dimensional (2D) materials, which are superlattices based on the moiré interference of crystal lattices, have garnered attention as a new platform for examining the many-body physics of electrons and excitons. Transition metal dichalcogenides (TMDs), which are 2D semiconductor materials, are considered as potential candidates for hosting correlated electrons in moiré lattices because of their relatively heavy mass. Although excitonic properties of TMDs have been extensively studied through optical measurements, the electronic properties of moiré lattice systems remain unexplored owing to the challenges of transport measurements. This study was focused on the recent discovery of strongly correlated electronic states in semiconductor TMD moiré lattice systems using exciton resonance in optical spectroscopy.

Active removal of the generated heat is necessary in many situations, such as in power semiconductors, CPUs in data centers, batteries, and heat engines. Existing thermoelectric conversion methods mostly use heat that has been ejected from the system and hence is utilizable without particular obligations. However, the integration of active cooling with thermoelectric power generation had not been explored previously. Since 2015, we have been creating and studying a new technology that integrates liquid-based thermoelectric conversion with forced convection cooling. In this report, we describe the concept of this technology and summarize our recent results.

Intensive research is being conducted to further improve the performance of lithium-ion secondary batteries. Conventional cathode materials exhibit excellent charge-discharge cycle characteristics because only Li ions are extracted and inserted while maintaining the crystalline structure of the material. In contrast, lithium-rich layered oxide (LLO) materials with a low-crystalline structure have achieved high energy density and extraction/insertion of a large amount of Li ions. Herein, the existence of a low-crystalline phase in the LLO structure, formed by a crystal structure change accompanying the migration of pillar metal ions that support the Li deficient layer during extraction of Li-ions, is revealed by pair distribution function (PDF) analysis.

Nickel oxide (NiO) is a wide-bandgap oxide semiconductor and functional material that offers advantages including p-type conductivity, a high absorption coefficient, and a relatively small ionization potential. It is, therefore, a promising material for use in novel applications such as “invisible” solar cells, sensors, transistors, and hole-injection layers. This study examined the fundamental properties of NiO thin films deposited using conventional RF magnetron sputtering. In addition, several devices transparent to visible light using NiO, including solar cells, Internet of Things monolithic gas sensors, and self-powered devices, have been introduced, and the robustness of such devices, including radiation resistance, was investigated.

This study aimed to develop wireless multi-modal and multi-tasking flexible sensor sheets. To realize multimodal flexible sensor, various sensors using low-cost solution-based process were proposed for integration on flexible films. In particular, monitoring of continuous vital signals was demonstrated by attaching a sensor sheet to a human. For multitasking systems to make X-in-1 sensors, reservoir computing, which is one of the machine learning techniques, was applied to a flexible sensor. As a proof-of-concept, weather sensors that detect the rain droplet volume and wind velocity were developed. Although there are remaining issues that must be resolved to realize practical devices, the proposed method can be used to build a multimodal and multitasking low-power sensor system in the future.

Plasma–material interaction (PMI) refers to phenomena that occur at the interface between the plasma and solid surfaces. The plasma, which has high energy and low density, facilitates the formation of nanometer-scale structures on solid surfaces. Nanotechnology is supported by the PMI. In nuclear fusion research, plasma-induced microscopic changes in solid surfaces of the inner wall of the vacuum vessel are important issues. For instance, the reaction product of helium plasma induces a fuzzy nanostructure on a tungsten surface. In PMI, while focusing on spatially microscopic changes, the plasma irradiation time is extremely long, ranging from seconds to hours. Certain elementary processes occur on microscopic time scales; however, to elucidate the entire process, the PMI must be regarded as a special subject in microscopic space and macroscopic time. From this perspective, this study introduces the difficulty and interest in the numerical simulation of PMI for future efforts.

A copper chalcopyrite compound CuGaSe₂ (CGS) thin film is a promising material for application to photoelectrochemical (PEC) water splitting into hydrogen (H₂). In this article, we first review the operating principle and measurement methods of PEC water splitting using semiconductor-based electrodes before reviewing studies on PEC H₂ evolution over CGS-based photocathodes. The requirements of surface modifications of the CGS thin film with a CdS layer and nanoparticulate Pt catalysts for realizing efficient PEC H₂ evolution are then introduced. Moreover, the effects of insertion of a Cu-deficient layer between the CGS film and the CdS layer and doping of Rb components into the CGS film for improving PEC properties are discussed. Finally, a critical problem of current CGS-based PEC devices for their practical applications, i.e., poor disabilities under an operating bias, is discussed.

Giant magnetic responses and magneto-thermoelectric phenomena emerging in topological materials hold promise for applications in the next generation of electronics. Inspired by the remarkable properties in crystals of a topological ferromagnet Fe₃Sn₂, we have been involved with developing Hall devices using amorphous-like thin films of a ferromagnetic alloy of Fe_0.6Sn_0.4 as a more versatile material form. The amorphous-based device is composed of inexpensive and environmentally benign elements, potentially offering new applications that take advantage of the high temperature stability of the device itself and the mechanical flexibility of the metallic film. As the magnetoresistance effect specific to magnetic materials can be measured simultaneously with the anomalous Hall effect, this device can be applied to the detection of three-dimensional (3D) magnetic field vector with a single planar-type structure. In this paper, we overview the operating principles of various thin-film magnetic sensors and introduce the fabrication method and basic properties of Fe–Sn amorphous-like thin films as well as the principles and characteristics of two devices: a cross-shaped Hall device and a planar-type 3D magnetic field sensor.

Effective solar energy utilization is extremely important in realizing a carbon neutral society. Therefore, a power generation technology that can utilize the full spectrum of sunlight is required. Solar energy conversion based on thermophotovoltaics (TPVs), called solar-TPV, potentially enables the use of the full spectrum of sunlight and high-efficiency conversion with single-junction cells. Here, we introduce a technology for controlling the thermal radiation spectrum (which is important for achieving high-efficiency solar-TPV), as well as the results of experiments using a designed solar-TPV system. In addition, we describe the prospects for advanced solar energy utilization by solar-TPV.

In recent years, the number of studies that include the terms “data-driven research” and “informatics” in their titles has increased, and efforts toward DX (Digital Transformation) with high-throughput and autonomous experiments have become active. While the materials and sample morphologies to be studied are wide-ranging, we have focused on multinary oxide powders and engaged in the development of methods leading to informatics research, such as automated preparation of powder samples based on liquid phase processing, fast powder X-ray diffraction, tools for characterization of physical properties and tools for synchrotron powder diffraction.