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.

Data-driven analytics can provide useful information derived from the images of scanning probe microscopy for biological systems including large variety of species and complicated interactions. Bayesian inference is applied to correlation analysis for height distribution of atomic force microscopy images on SasA-KaiC complex formation involved in information transfer from circadian clock oscillator to the output pathway in cyanobacteria. Principal component analysis is applied to the ion images constituted from mass spectra obtained by tapping-mode scanning probe electrospray ionization.

Chemical-state imaging of materials using X-ray microscopes has been developed and applied to various materials such as composites, batteries, ceramics and so on. In this article, after features of X-ray microscopy are discussed, analytical approaches for chemical-state imaging are reviewed by showing typical application to materials : scanning transmission X-ray microscope (STXM), transmission X-ray microscope (TXM), and X-ray absorption spectroscopy imaging (XAS-imaging). X-ray microscopes can provide indispensable information for investigating “trigger sites” that are specific structures or locations in materials where key reactions progress. For this end, analytical approaches using information science and/or applied mathematics will be required to deal with big data obtained by X-ray microscopes.

Hard X-ray photoelectron spectroscopy (HAXPES) is a powerful technique to observe chemical and electronic states of atoms buried inside materials. Recently, a laboratory-based HAXPES system with high throughput has been developed, combining a high-flux Ga (Kα＝9.25 keV) X-ray source and a high-transmission photoelectron analyser. In this article, research using the HAXPES Lab is reviewed, and the data are compared with those using synchrotron light sources. The HAXPES Lab is an attractive option not only for scientists but also for industrialists needing rapid answers for research and development.

The Division of Microbeam Analysis, the Japan Society of Vacuum and Surface Science, publishes the Database for Auger and Secondary Electron Spectra online (https://www.jvss.jp/division/mba/sedb/). These spectral data were measured with an SI traceable cylindrical mirror analyzer developed by Keisuke Goto (absolute measurement system). The database body stores measurement data and spectra of 56 materials and 47 materials as an appendix. This paper reports the concept and characteristics of the absolute measurement system and introduces the electron spectra database.

For realizing single molecular devices using metal-molecule-metal junction, it is necessary to fabricate a steady conductive bridge-structure. Recently, our group reported a molecular bridging method using migration of gold atoms on static nanogap electrodes. It was proposed that repeated cycles of single-molecular-bridging and breaking between benzene-di-thiolate (BDT) molecules and nanogap electrodes using this method. In this paper, to confirm the bridging condition during the cycles, current-voltage curves in each state were investigated. This result indicates that characteristic orbital energies of BDT were revealed while observed conductance was close with 11.0 mG₀. On the other hand, when the observed conductance was below 11.0 mG₀, the magnitude of estimated orbital energies was the similar as that using nanogap electrodes which were not covered by any molecules, which explained that direct tunneling conduction between Au electrodes was dominant. This clearly indicates that cycles between molecular-bridging and disconnection were realized using static nanogap structures.

Germanene, a graphene-like honeycomb crystal of germanium, has been attracting immense attention owing to its exotic properties such as a tunable bandgap and high carrier mobility. However, the fabrication of germanene-based electronic devices is difficult owing to its chemical instability. To overcome this problem, we proposed and developed a new method of germanene growth at graphene/Ag(111) and hexagonal boron nitride/Ag(111) interfaces. The grown germanene at the interfaces was stable in air and uniform over the entire area covered with a van der Waals (vdW) material. As an important finding, a vdW interface provides a nanoscale platform for growing germanene similarly to that in vacuum, while this cannot be achieved with a typical oxide interface (Al₂O₃). We believe that our work is of significantly importance not only for the growth of germanene but also for the fabrication of future germanene-based electronic devices.

Quasi-Nanbu scheme, a new inter-molecular collision scheme proposed in the previous work, has been extended to diatomic molecules and gas mixtures. Then, the extension has been implemented in a Direct Simulation Monte Carlo (DSMC) model created on a commercial FEM software COMSOL Multiphysics^®. N₂ gas heat conduction between parallel plates and two-dimensional supersonic nozzle flows of gas mixtures are demonstrated as application examples.

Photoelectron angular distribution from the valence state of π-conjugated molecules on the surface has been studied to clarify the molecular orientation quantitatively with multiple scattering theory of photoelectron emission intensity. After developing the photoelectron emission techniques together with molecular thin-film preparations, a novel concept of photoemission tomography enables to investigate the electronic states in depth to understand the molecular functional properties in a sense of orbital. The article reviews the recent progress and development of the photoelectron momentum microscope related techniques for molecular science.

X-ray microscopy and time-resolved observation using synchrotron radiation are reviewed based on recent reports on in situ observation of cracking and degradation of structural materials. X-ray microscopy can provide three-dimensional images of microstructures and chemical states with a high spatial resolution down to 50 nm. In situ observation using X-ray microscopy successfully revealed crack initiation and propagation in carbon fiber reinforced plastic (CFRP) while a stress was applied to the specimen. X-ray microscopy was applied to ceramic coating or CFRP to perform chemical-state mapping, which is essential for understanding the trigger sites of degradation. In situ observation of time-resolved X-ray diffraction and/or X-ray absorption spectroscopy was carried out with a time resolution down to a few nanosecond by synchronizing an X-ray pulse with a laser pulse. This technique was applied to investigate the mechanism of deformation and fracture or structural phase transitions of metal and alloys after the laser shock.

Further improvements and development of new polymer electrolyte materials are required to achieve the target values stated in NEDO (New Energy and Industrial Technology Development Organization) roadmap for the fuel cell and hydrogen technology developments. If the final goal is broken down into the performance of polymer electrolyte materials, minor changes to materials that have already been developed or are on the market will not be able to meet that demand. A major technical breakthrough will be required in the next 10 years, and a new concept will be required to achieve it. After showing the research background of polymer electrolyte membranes, this report overviews the current issues of polymer electrolyte membranes, especially the response to the NEDO roadmap for fuel cell and hydrogen technology developments.

Inelastic electron tunneling spectroscopy (IETS) combined with scanning tunneling microscopy (STM) allows us to acquire vibrational signals at surfaces. In STM-IETS, a tunneling electron from the STM tip excites vibrations whenever the energy of the tunneling electron exceeds the vibrational energies. This opens up an inelastic channel in parallel with the elastic one and gives rise to an increase/decrease of the conductivity. As a consequence, a pair of peak and dip shows up at the bias voltages with respect to the Fermi level corresponding to the energy of vibrational energy. Until recently, the application of STM-IETS was limited to the localized vibration of single atoms and molecules adsorbed on surfaces. In principle, STM-IETS should be capable of detecting collective lattice dynamics, i.e., phonons. In this paper, I will introduce the theory of STM-IETS measurement for a metal surface and the application of this theory for surface phonons on Cu(110).