In this article, omnidirectional photoluminescence (ODPL) spectroscopy, which can determine the internal quantum efficiency (IQE) of freestanding semiconductor crystals with a direct bandgap without the need for model calculations, is reviewed. ODPL can determine IQE from the external quantum efficiency (EQE) based on the fact that light with self-absorption energy in the vicinity of the band-edge of a freestanding semiconductor crystal is emitted only in the normal direction of the crystal surface. The procedure and applications for an IQE determination are discussed using gallium nitride, zinc oxide, and metal halide perovskite as example cases. In particular, the ability to measure a large crystal sample outside an integrating sphere is one of the main features of ODPL spectroscopy, and it is expected to be combined with mapping measurements of the entire surface of semiconductor wafers and various types of nonlinear and microscopic spectroscopy.

Room temperature bonding between Al alloys and steel, which can be applied for multi-materialization for car bodies, etc., is investigated. Multi-materialization is a technology that achieves higher strength and lighter weight by using different materials together, such as Al alloys and steel. However, it can be difficult to bond a combination of Al alloys and steel by welding. In this study, the surface-activated bonding (SAB) technique was applied for bonding between Al alloys and steel. As a result, it was found that by activating only the surface of the Al, which is the active metal, the oxygen ions are deprived from the remaining oxide film on the Fe surface, and the oxide formation enables bonding.

SiC power devices have advantages such as low loss high-speed switching, high voltage handling, and high-temperature operation compared to existing devices when MOSFETs are manufactured by taking advantage of their physical characteristics. The only device that can switch at high speed under high voltage is the SiC MOSFET. By developing applications that make the best use of this advantage, it can be expected to be applied to applications that have not been possible with semiconductors, or that have had major problems even if they have been realized.

We have proposed and demonstrated a method that enables unprecedented high-speed operation of ultra-high voltage equipment by utilizing the excellent characteristics of SiC power devices.

We demonstrate that THz wave irradiation enhances the formation of actin filaments. A significant increase in the number of actin filaments was observed in the cytoplasm of living cells when irradiated with a THz continuous wave (0.4 THz). On the other hand, we also found that shockwaves were generated by irradiation of intense THz pulses (4 THz). The intense THz pulses are absorbed at the water surface and the energy concentration results in shockwave generation. Interestingly, the shockwaves disrupt actin filaments in living cells. Our finding of the diametrically opposite effects of THz wave irradiation on actin filament suggests a novel possibility of artificial manipulation of biomolecules and living cells using THz waves.

Antiferromagnets are promising materials for realizing ultrafast spintronic devices because their spin precession motions can be driven at terahertz frequencies. But the readout of the antiferromagnetic spin order is difficult due to the vanishingly-small net magnetization. A noncollinear Weyl antiferromagnetic metal Mn₃Sn shows a large anomalous Hall effect comparable to ferromagnets owing to broken time-reversal symmetry by the cluster spin multipole on the Kagome bilayer at room temperature. We report on observations of the terahertz anomalous Hall effect in high-quality Mn₃Sn thin films by polarization-resolved terahertz spectroscopy and found that the nondissipative large anomalous Hall currents appear up to approximately 1 THz. Our observation of the large response paves the way for ultrafast terahertz readout of antiferromagnetism.

Global production and ownership of automobiles continues to increase mainly due to economic development in emerging countries. In the automobile industry, we are accelerating the development of environmental friendly vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, fuel cell electric vehicles, and battery electric vehicles, and are working to reduce CO₂ emissions from automobiles. Since the electric vehicles are equipped with batteries that are suitable to store the power that is generated from renewable energy, it is desirable to install power generation technologies that use renewable energy as a power source. For example, installing photovoltaic modules in automobiles and supplying running energy with sunlight has attracted attention in recent years. In this paper, we explain the advantages of the installation of photovoltaic modules in passenger cars, using simulations that are based on actual driving data and the measured results of public road driving tests. An example of a new mobility society that can be expected to be realized by utilizing automobiles equipped with photovoltaic modules as part of social infrastructure is also introduced.