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.

In this article, we provide an overview of our recent study on light-induced electron emission from single fullerene molecules and subnanometric optical control of their electron emission sites. After depositing molecules on a sharp metallic needle and applying strong electric fields at the apex of the needle, single-molecule protrusions appear on the apex. The electric fields are further enhanced at the protrusions and the enhanced fields drive electron emissions from the single molecules. Single-molecule electron sources can thereby be created. By irradiating such electron sources with light, we observed large modulations in the electron emission patterns. Our simulations revealed that the emission patterns represent molecular orbitals in a single molecule, a mystery scientists have been trying to get to the bottom of for the past 70 years. Our simulations also explain that light-induced modulation is driven by changes in the molecular orbitals that the emitted electrons pass through. In effect, we realize that there are subnanometric modulations in electron emission sites.

Single-molecule junctions (SMJs) have attracted wide attention due to their unique electronic property originating from their structure, i.e. single molecule connected to the electrodes at both ends. Although the junction structure has significant effects on the electronic property of the SMJs, the experimental method to define the geometry of the bridged molecule is limited. Recently, we have succeeded in the observation of surface-enhanced Raman scattering (SERS) spectroscopy in combination with the current-voltage (I–V) response measurement, revealing the junction structure of SMJs. The I–V response obtained by the combination measurement provides the electronic structure of the molecule fluctuated by the connection to the metal electrodes, allowing the analysis of the effect of the charge transfer on the SERS spectra. The strong electronic coupling between metal and molecule enhances the charge transfer resonance and it triggered the excitation of the “Raman silent mode” in the bulk state. Therefore, we have detected the unique SERS spectra in SMJs and revealed the contribution of the charge transfer effects on the SERS spectra at the single-molecule level.

The studies about surface chemistry of formic acid on Cu-based model catalysts including our recent investigation are reviewed from the surface-science point of view. The Cu-based model catalysts including steps and Zn-deposition have been prepared using the well-defined single crystalline Cu surfaces. Formate species are formed by the decomposition from formic acid on the model catalysts surfaces. Various surface spectroscopies have been applied for the assignments of intermediate species, the quantitative estimation of their coverages and the kinetics of adsorbed species. The active sites and reaction mechanisms of the decomposition of formic acid and the hydrogenation of formate species are discussed.

Tribology is an interdisciplinary field related to the science and technology of friction, wear, and lubrication, and is expected to contribute to the realization of a carbon-neutral society. Recent advances in tribology are largely due to dramatic advances in nanotechnology and surface science. Recent topics are introduced along with the history of tribology.

Faceted macrostep formed at equilibrium is demonstrated based on numerical calculations using the tensor network method and the Monte Carlo method. The adopted model is a lattice model where the surface roughness excitations and the step-step attractive energy (ε_int) are taken into consideration. We calculated ε_int–T and p–T faceting diagrams for faceted macrosteps where T is the temperature, and p is the surface slope for an inclined surface. Applying the faceting diagrams to Si(113)＋(114) surfaces, the step-step attractive energy is approximately 123 meV. We also discuss elementary step attachment/detachment processes to/from the faceted macrostep near equilibrium.

In this article, we discuss applications of topology to materials science. We explain how topology is used to express the structure and shape of materials. The structure of a multicyclic polymer is described by applying graph theory and the 3-dimensional shape is described by applying knot theory. Polycontinuous patterns of microphase separation of a block copolymer melt can be analyzed by applying the 3-dimensional topology. We also discuss the topological structures of interlocking molecules composed of metal-peptide rings using the concept of polyhedral links.

Organometal halide perovskites have captured wide interest as a promising material for light-weight and high-efficiency solar cells. Through recent studies of the organometal halide perovskite solar cells (PSCs), the composition of organometal halide perovskites is recognized as one of the key factors in the improvement of the PCE. In this study, we investigated mixed cation perovskite absorber. Additionally, we successfully constructed monolithic PSC mini-module without I-V hysteresis. In the case of MA-free PSCs, the 24.9% PCE (0.187 cm²) and 21.6% PCE (2.76 cm² monolithic PSC mini-module) were obtained, respectively. We also developed semitransparent perovskite top cells with higher durability and transmittance for tandem solar cells. The PCEs of 19.5% (certified 19.3%) and 26.2% were achieved for a 1 cm² semi-transparent perovskite top cell and four-terminal PSC/CIGS tandem solar cells, respectively.

It has been reported that the introduction of ferromagnetism by various ways into topological insulators (TIs) can induce concerted effects, resulting in various novel magnetic phenomena such as quantum anomalous Hall effect and skyrmions. In addition, recently, efforts to increase the observation temperature of quantum phenomena by enhancing the crystal quality and improving electronic coherence have been pursued with great enthusiasm. Self-assembled regular alloy crystals such as Mn(Bi,Sb)₂Se(Te)₄ are called “intrinsic” ferromagnetic TIs that have recently attracted much attention, and we have observed skyrmions in sandwich structures based on these crystals. Furthermore, we have newly observed the ferromagnetic proximity effect even at room temperature at the heterojunction interface between Fe and topological crystalline insulator SnTe by polarized neutron reflectometry. As an extension of these efforts, it is hoped that the unique properties of TIs will be utilized to develop next-generation robust devices for such as spintronics and quantum computing.

A new 3 GeV light source named “NanoTerasu” is under construction at Aobayama new campus of Tohoku university. NanoTerasu will form a photon science platform together with SPring-8, which covers a wide spectral range from UV to hard X-rays, by delivering brighter and more coherent soft to tender X-rays with superior stability and reliability. Installation of the accelerator system is in progress for the first light in 2023. NanoTerasu employs a four-bend achromat lattice using combined-function bending magnets to achieve a low emittance of about 1 nmrad with a small circumference of 349 m and a beam current of 400 mA. The storage ring consists of 16 cells to provide 28 user beamlines. This paper presents an overview of NanoTerasu and describe details of the storage ring vacuum system.

We introduce the results of in situ observation of the surface and the solid-liquid interface of calcium carbonate in atomic-level by frequency modulation atomic force microscopy (FM-AFM) in the presence of additives. We have found that the calcite surface transformed into the aragonite structure by the cooperative effect of magnesium and a hydrophilic polypeptide. Furthermore, high-resolution imaging of solid-liquid interface revealed that these additives did not adsorb on the calcite surface but significantly changed the hydration structure in the vicinity of the surface. Especially magnesium ions contribute to change the hydration structure due to their hydrophilicity.

Room-temperature wafer bonding can realize new electronic devices, power devices, optical devices, and microelectromechanical systems. Atomic diffusion bonding (ADB) of wafers is a promising process to achieve room-temperature wafer bonding : thin metal films are fabricated on two flat wafer surfaces using sputter deposition, followed by bonding of the two films on the wafers in vacuum. Any mirror-polished wafer including glass can be bonded using ADB. Recently we demonstrated ADB of wafers at room temperature using oxide films and nitride films. Incident light can pass through transparent wafers bonded with oxide films without reduction in intensity. Moreover, the electrical conductivity of the bonded oxide films and nitride films is negligible. These properties are useful to produce new optical or electrical devices. This paper assesses the technical potential and current status of ADB.

Under the competition of ferromagnetic interaction and Dzyaloshinskii-Moriya interaction, magnetic vortices in real-space, skyrmions, can be induced on a topological insulator (TI), which reflects the chiral spin structure on the gapped Dirac cone in the momentum space. Here, we observe skyrmions emerge on surfaces of two self-assembled ferromagnetic TI layers, Mn(Bi_1－xSb_x)₂Te₄, separated by a spacer of non-magnetic TI layer, (Bi_1－xSb_x)₂Te₃, through topological Hall effect (THE) by tuning the Fermi level with optimizing the Bi/Sb ratio. By the spacer-thickness-dependence of the magnitude of THE, we find that the moderate coupling of surface states between the top and bottom Mn(Bi_1－xSb_x)₂Te₄ layers is essentially important for inducing and stabilizing skyrmions. Moreover, the highly-ordered Mn atoms in the Mn(Bi_1－xSb_x)₂Te₄ lead to a strong exchange interaction therein, making skyrmions “soft magnetic”. This would open an avenue toward a topologically robust easy-rewritable novel magnetic memory for spintronics.

We investigate the factors that degrade the conversion efficiency in the crystalline silicon heterojunction (SHJ) solar cell using hard X-ray photoelectron spectroscopy (HAXPES) and the potential of new materials for the carrier selective contact (CSC). Regarding the emerging transparent conductive oxide film (TCO) used in the SHJ solar cell, the hydrogenated indium oxide (IO:H) with high carrier mobility forms an oxide layer at the IO:H/substrate interface revealed by the evaluation of chemical bonding states by HAXPES, resulting in increasing the contact resistance. Moreover, the IO:H is reduced from the catalyst in the silver electrode paste, and silver oxide tends to form at the electrode/IO:H interface. In addition, the role of MoS₂, a two-dimensional layered material, as a CSC layer was investigated, found that and MoS₂ layer works as an electron selective layer for n-type Si substrate using angle-resolved HAPXES band bending evaluation.

We have recently reported a new two-dimensional material of boron monosulfide (BS) nanosheet. It was produced by the mechanical exfoliation of rhombohedral boron monosulfide (r-BS) synthesized by heating the mixture of amorphous boron and sulfur at 1873 K and 5.5 GPa. Experimental characterizations and density functional theory calculations revealed tunable band-gap of BS nanosheets as much as approximately 1.0 eV. These results are introduced in detail.

This report reviews fabrication processes and epitaxial growth technology of InP-based high electron mobility transistors (InP-HEMTs) and Tera-Hertz monolithic ICs (THz-ICs) in order to develop 300-GHz-band frequency, which is one of the candidates for “Beyond 5G/6G” network. We also introduce a successful result of a wireless transmission with 300-GHz 16-QAM format with InP-HEMT-based THz-ICs.

Angle-resolved photoemission spectromicroscopy with submicron resolution (nano-ARPES) is a powerful technique to study electronic structure of microcrystals and microdomains. Transition-metal compounds such as FeTe and IrTe₂ exhibit unique phase transitions due to orbital symmetry breaking (orbital order). In nano-ARPES studies on FeTe and IrTe₂ surface, we observed interesting domain textures which would be related to their microscopic orbital orders. The antiferromagnetic phase of FeTe hosts stripe-type domains driven by its anisotropic electronic state. In case of IrTe₂, each domain harbors quasi one-dimensional surface bands forming fragmented Fermi surfaces (Fermi arcs). The nano-ARPES measurement enabled us to identify the unique domain dependent surface states in the orbital ordered phase of IrTe₂.

We introduce our chemical vapor deposition (CVD) growth of high-quality monolayer and bilayer graphene on epitaxial metal catalysts. An epitaxial Cu(111) film prepared on sapphire substrate allows the synthesis of monolayer graphene whose orientation is registered by the underlying Cu(111) lattice. Pure AB-stacked bilayer graphene was synthesized by long-time CVD, and the bilayer device showed high on-off ratio indicating the band gap opening. Moreover, interlayer 2D nanospace of the bilayer graphene was used to intercalate metal chloride molecules, and the significant reduction of sheet resistance as well as the unique 2D super-structures of metal chloride molecules is observed. We also visualized the graphene CVD process based on radiation-mode optical microscopy (Rad-OM), obtaining important insight into the graphene growth mechanism.

This is a research report about fully automated analysis of X-ray photoelectron spectroscopy (XPS). We developed a fully automated method to perform XPS spectral analysis based on the information criteria. Our method searches a large number of initial fitting models by changing the degree of smoothing, and obtains a series of fitting results. The goodness of those optimized models is ranked using information criteria. We found that, using the Akaike information criterion, a complicated model tended to be selected, with a larger number of peaks than expected from the spectral shape. On the other hand, using the Bayesian information criterion (BIC), a simple model with reasonably good agreement and a moderate number of peaks was selected. The model selected by the BIC was close to the result of peak fitting performed by XPS analysis experts. We also present the difference in modeling between Gaussian noise and Poisson noise.

Electric double layer (EDL) is formed at the electrolyte / electrode interface and provides a field of energy storage or accumulated career conduction in addition to that of electrochemical reaction i.e. electron transfer with chemical bond rearrangement. Electrochemical frequency modulation AFM (EC-FM-AFM) enables acquisition of the liquid side information from the highly sensitive force spectrum vertical to the interface as well as the atomic scale resolution imaging of the solid side at the electrode surface, both are often affected by the electrode potential. In this article, some examples of “operando analyses” of such electrochemical interfaces by using EC-FM-AFM are introduced.