Hydrogen readily permeates various materials and modulates their physical properties. Identification of the hydrogen lattice location in crystals is key to understanding and controlling the hydrogen-induced phenomena. Combining nuclear reaction analysis (NRA) with the ion channeling technique, we experimentally determined the locations of H and D in epitaxial nanofilms of titanium hydrides. We found that 11 at.% of H are located at the octahedral site with the remaining H atoms in the tetrahedral site. Density functional theory calculations revealed that the partial octahedral site occupation is attributed to the Jahn-Teller effect induced by hydrogen. In contrast, D was found to solely occupy the tetrahedral site owing to the mass effect on the zero-point vibrational energy. This study demonstrates the potential to fabricate hydrides with arbitrary site occupancy by tuning the isotope ratio, which potentially allows for control over their electronic properties and leads to the discovery of novel phenomena.

The metal–insulator transition (MIT) in VO₂ is strongly governed by nanoscale morphology and structural defects. To elucidate the microscopic origin of this transition, we investigated the relationship between surface structure and MIT dynamics in VO₂ thin films epitaxially grown on TiO₂(110) via pulsed laser deposition. Operando X-ray diffraction confirmed a structural transformation from the monoclinic (insulating) to rutile (metallic) phase. Infrared scattering-type scanning near-field optical microscopy (s-SNOM) enabled direct visualization of individual anisotropic nanodomains with nanoscale resolution. The contrast in near-field amplitude allowed us to spatially resolve metallic and insulating phases across the surface. We observed that metallic domains nucleate and expand heterogeneously, influenced by local grain geometry and anisotropic strain along the [001] direction. These findings provide insight into the interplay between structural features and phase transition pathways in strongly correlated oxide systems.

Data science has emerged as the fourth scientific method, following experiment, theory, and computation. Since the launch of the Material Genome Initiative in 2011, data-driven approaches such as materials informatics and process informatics have been actively applied in materials. To integrate data science into traditional research, it is essential to understand research activities as a data cycle consisting of three phases : data generation, accumulation, and utilization. This cyclic process enhances the efficiency and scope of scientific research. To illustrate the impact of data science in materials research, this paper introduces Bayesian optimization for autonomous experimental system, machine learning potentials, personal databases using JSON format, and high-throughput automatic spectral analysis. These approaches contribute to the advancement of materials science through data-driven methodologies, accelerating the data cycle.

We review our recent study on the electronic states of Te(0001) using high-spatial-resolution angle-resolved photoemission spectroscopy (ARPES) with micro-focused synchrotron light. The results demonstrate the formation of in-gap states confined to the edges, and support topologically nontrivial character of Te helix chain.

Development of operando soft-X-ray surface spectroscopy techniques using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and ambient-pressure soft-X-ray absorption spectroscopy (AP-sXAS) and their application to operando observations for surface catalytic reactions are reviewed. First, we will explain soft-X-ray surface spectroscopy end-stations that we developed for operando observations at the Photon Factory. As for the application, we introduce studies on CO oxidation on Pt-group metals and their alloys and photoinduced carrier transfer to cocatalysts on a SrTiO₃-based photocatalyst. We will also discuss future advancements of the operando soft-X-ray surface spectroscopy techniques.