High-resolution Rutherford backscattering spectroscopy (HR-RBS) is a powerful tool for non-destructive compositional depth profiling of nano-scale thin film samples. It provides highly quantitative composition with sub-nm depth resolution. In this contribution, the analysis of insulating glass and ionic liquid solutions of alkali metal salts is presented to demonstrate the performance of HR-RBS for various types of samples.

We have been developing a novel hydrogen sensor using sintered ceria (CeO₂-σ) nanoparticles in collaboration with JAXA for spacecraft applications. This sensor is able to rapidly detect hydrogen in either vacuum or oxygen-free condition. This property has originated from the fact that ceria is an oxide ion-electron mixed conductor. In this article, the adsorption state of gases on the ceria surface is discussed based on the relationship between the gas partial pressure and the carrier concentration. In addition, the sensing mechanism is clarified by combining the results of in-situ XAFS analysis of the valence change of ceria before and after hydrogen adsorption.

Thermoelectric (TE) power generation, which is one of the potential clean power technologies, has attracted much attention due to the recent development of high-performance TE materials. We have focused on Mg₂Sn and aimed to improve its TE performance by preparing single crystals (SCs) and introducing lattice defects. In this paper, experimental results on crystal structure analysis, microstructure observation, and TE properties are presented to demonstrate that we can enhance TE performance of Mg₂Sn SCs superior to that of Mg₂Sn polycrystals via lattice-defect engineering.

Lattice thermal conductivity is an important property that determines the heat insulation and dissipation of materials. Recently, to reduce the lattice thermal conductivity, nanocrystalline materials have been extensively fabricated in the field of thermoelectrics by utilizing the thermal resistance of grain boundaries. However, the suppression mechanism of thermal conduction in nanocrystalline materials remains to be elucidated. For example, the correlation between grain boundary structure and thermal conductivity, the decrease in intragrain thermal conductivity in nanocrystals, and the effect of grain shape on thermal conductivity are still unclear. This paper introduces two cases that have clarified these issues from a microscopic point of view, using atomic-level computational methods and machine learning techniques such as structure descriptors.

In this article, we introduce our studies on application of chalcopyrite phosphides to solar cells, such as bulk crystal growth based on phase diagram, and thin film deposition based on chemical potential diagram. As well known, phase diagram is a useful tool for fabrication of multicomponent materials, while chemical potential diagram, which is a kind of phase diagram with chemical potentials as axes, is well adaptable with vapor growth. The difference of deposition mechanism between ZnSnP₂ and CdSnP₂ thin films is well explained. We also introduce a discussion on the stability of hetero-interface through chemical potential diagrams, and bandgap control via order-disorder phenomena. Especially, we demonstrated the bandgap of ZnSnP₂ is controlled from 1.2 to 1.7 eV without composition change.

As a new target for the photovoltaic (PV) power generation, a vehicle-integrated PV is being promoted. Since the bodies of vehicles are composed of smooth curved surfaces from the viewpoint of aerodynamics and design, solar cells must be applied to curved surfaces. However, all the solar cells available today are flat, and the most popular Si solar cell is a brittle material that is easily broken. Since the vehicle body is not a two-dimensional shape with unidirectional bending like a cylindrical surface, but a three-dimensional shape like a spherical surface, a different development approach is required. This article introduces the bending tests of solar cells, mechanical stress analysis, prototyping and outdoor test of 3D curved surface modules.

In biological analysis, innovative measurement techniques are coveted to obtain various physical and chemical parameters quantitatively in a microenvironment, such as inside a cell. Here, I introduce the development of nanoscale quantum sensor techniques using fluorescent nanodiamond containing nitrogen-vacancy centers (NV centers) as novel measurement probes for nanometer-scale quantitative measurements. In addition, we show recent reports by us and others in which nanoscale quantum sensors were used to analyze nanoscale biological phenomena and detect trace biomolecules to describe the prospects of the research field and the development of nanoscale quantum sensors.

MOS structures play an important role in semiconductor devices. This paper describes Terman method and the conductance method, which are typical methods for evaluating interface trap density of the MOS structures. We refrain from using energy band diagrams and formulas as much as possible, and explain the principles of these methods qualitatively. We also describes points to note in the actual evaluation.