Monolayer graphene, representative of atomically thin crystals, has recently shown unexpectedly high proton and deuteron permeability under ambient conditions. It also permeates (filters) hydrogen (deuterium) isotope ion with high selectivity (～10 at room temperature). These results suggest possible ways of developing novel and efficient hydrogen isotope gas enrichment techniques for manufacturing silicon semiconductors, optical fibers, drug development, nuclear fusion, and other related applications. And yet, despite its importance, experimental studies remain scarce and the separation mechanism contentious. Here, we introduce our recent findings on how quantum tunneling of hydrons through graphene could account for the high hydron selectivity of graphene.

In order to control the interfacial structure between the perovskite layer and solid substrate surface at atomic levels, the Au(100) single-crystal, the self-assembled monolayer (SAM), 4-aminothiophenol (4-ATP), and the alternating dipping method were employed as a solid substrate (charge transport layer), a linker between the perovskite layer and substrate, a SAM constructing molecule, and a preparation method, respectively. 4-ATP SAM has high orientation and flexibility and is expected to relax the mismatch between the perovskite and gold surface atomic arrangements. Surface morphology and crystal configuration of the constructed MAPbBr₃ perovskite layers on 4-ATP SAM modified Au(100) were investigated by scanning tunneling microscopy (STM) and grazing incidence surface x-ray diffraction (GISXRD) using synchrotron radiation. As a result, we succeeded to construct the epitaxially grown MAPbBr₃ perovskite ultra-thin layers on the 4-ATP SAM modified Au(100) surface due to the high orientation and high flexibility of the 4-ATP SAM.

As Au(001) surfaces exhibit a quasi-one-dimensional corrugated structure, Hex-Au(001), its periodicity was predicted to change the electronic structure of graphene when graphene was grown on this surface. Furthermore, the hybridization between graphene and Au is known to introduce bandgap and spin polarization into graphene. Here, we report angle-resolved photoemission spectroscopy and density functional theory calculation of graphene on a Hex-Au(001) surface. A bandgap of 0.2 eV in the graphene Dirac cone was observed at the crossing point of the graphene Dirac cone and Au 6sp bands, indicating that the origin of the bandgap formation was the hybridization between the graphene Dirac cone and Au 6sp band. We discussed the hybridization mechanism and anticipated spin injection into the graphene Dirac cone.

Microscopic studies on electrolyte solution/electrode interfaces provide the most fundamental information not only for understanding the electric double layer formed at the interfaces but also for designing sophisticated electrochemical devices. As with various electronic devices, it is critical to understand the electronic structure of the interfaces, but direct assessment has been limited by the presence of solution. This article presents our exploration of the electronic structure of electrochemical interfaces using photoelectron spectroscopy and electrochemical measurements.

The gapless electronic states in the topological insulators (TI) with symmetry protection are the viable platform for Majorana qubits in future fault-tolerant topological quantum computation. Among transition metal dichalcogenides, tungsten ditelluride (WTe₂), which has a large spin-orbit coupling, is considered as a promising material for such TI. In this report, we introduce our recent research on WTe₂ platform. We report on a heterostructure of WTe₂ and superconducting material with high quality, using spontaneous formation of superconducting PdTe. We demonstrate Josephson junction devices with weak links for multi-layer WTe₂. We show the electronic states of monolayer and bilayer Td-WTe₂ using density functional theory. These Td-WTe₂ layers can exhibit quantum spin Hall states depending on the directions of stripes and step edges, which expands the availability of WTe₂. These studies deepen the process technology and material science of WTe₂, which will pave the way for realizing a platform for Majorana particles.

All-solid-state batteries (ASSBs) have been attracting attention as the next generation batteries, but they face challenges, including internal resistance at the solid electrolyte/electrode interface. This study examines a LiPON/LiCoO₂ interface using multi-technique X-ray photoelectron spectroscopy (XPS) to analyze chemical states and energy band diagrams. Results show that interlayer formation and structural changes during manufacturing stimulate Co reduction in the LiCoO₂ layer near the interface, leading to an increase in interfacial impedance. To minimize internal resistance, preventing Co reduction is necessary. The study offers insights into the chemical interactions between LiPON and LiCoO₂ layers, which may help address challenges in ASSBs commercialization.

To investigate electronic states at the interface between surfaces that exhibit unique spin-split band dispersions is an important step in the development of a new materials that can be used to spintronics device. Antimony (Sb) and bismuth (Bi) are interesting targets for studying the nature of peculiar spin properties due to spin-orbit interactions. In this study, we fabricated the Sb ultrathin films on Bi substrate. The surface structure and electronic states of Sb/Bi heterostructure was confirmed by the low-energy electron diffraction measurement and angle-resolved photoemission spectroscopy, respectively. For 2 and 3 BL Sb film on Bi substrate, we observed a “V”-shaped electronic band, which is significantly different from the electronic state of Bi thin film and freestanding Sb ultrathin film. We conclude that this band dispersion is caused by the tensile lattice strain of Sb ultrathin film and the hybridization effect of the wavefunction with the Bi substrate.