The combination of a scanning probe microscope with a photon detector and a Raman spectrometer, referred to as a tunneling-electron-induced light emission (STM-LE) and a tip-enhanced Raman scattering spectroscopy (STM-TERS), is attractive for exploring the optical properties and chemical analysis of nanomaterials beyond the optical diffraction limit. In this study, we performed the STM observation to evaluate structural configuration of chiral organic molecules adsorbed on the metal substrates accompanying the detect of their optical and vibrational properties by use of our laboratory-built STM-LE and STM-TERS systems^1-4. As for the chiral molecules, we used racemic-mixture and enantiopure molecules of the chiral PTCDI (N,N'-Di-n-octyl-3,4,9,10-perylenetetracarboxylic Diimide) and thiaheterohelicene and their derivatives. We clearly observed the high resolution STM images for the chiral molecular assemblies, leading to the important perspective of stereochemical chiral recognition based on the formation of ordered molecular structures combined with their optical and vibrational characterizations. Theoretical calculation based on a density functional theory and a molecular dynamics simulation successfully identified the formation mechanism of the molecular self-assemblies in the chiral recognition schemes.⁵ Moreover, we investigated the optical dissymmetry of the light emission from chiral PTCDI molecules using STM-LE, and that from helicene derivatives using STM-TERS for evaluating the optical activity and identifying the enantiomers of the chiral molecules at a molecular scale. References[1] P. Krukowski, Y. Kuwahara, et al., J. Phys. Chem. C 120, 3964–3977 (2016). [2] S. Chaunchaiyakul, Y. Kuwahara et al., J. Phys. Chem. C 121, 18162–18168 (2017).[3] P. Krukowski, Y. Kuwahara, et al., Appl. Surf. Sci., 589, 152860 (2022).[4] S. Kimura, Y. Kuwahara, et al., Phys. Chem. Chem. Phys. 26(43), 7658-7663 (2024).[5] Changqing Ye, Y. Kuwahara et al., J Phys.Chem. C127(43), 21305-21312(2023)

I appreciate JVSS for giving me such a wonderful award. I have started my research work on surface science in the laboratory of Late Prof. Masaru Onchi of Kyoto University, and engaged in photoemission spectroscopy under the supervision of Prof. Yasuo Sakisaka. We had a chance to start the angle-resolved photoemission experiment in the newly built photon factory of KEK. The angle resolution was achieved by manually changing the angle of the electron analyzer. It was a nice memory that I rotated the analyzer every ten minutes for all night long. Continued photoemission study at the Prof. Weaver lab of University of Minnesota as a post-doc, and had a chance to observe the sharp valence spectrum of C₆₀. At the same time, commercial STM was getting popular, and the Weaver lab started STM research. After that, I have mostly engaged in STM studies to this day. When I worked with Prof. Kawai in Riken, we had a chance to start a 4 K low-temperature machine at a relatively early stage of the cryostat STM development. It has been exciting to develop new spectroscopy of the tunneling current; the vibration spectroscopy, spin excitation, the Kondo resonance detection, and STM-ESR. I would like to thank all collaborators for letting me experience such a wonderful evolution of atomic-scale spectroscopy.

The surfaces and interfaces of transition-metal oxides play crucial roles in devices such as semiconductors and batteries. However, atomic-scale control and investigations of oxide surfaces and interfaces are still limited. Here, I discuss the atomic-level control of oxide surfaces and interfaces by integrating interdisciplinary research. This talk covers research on scanning tunneling microscopy of oxide surfaces, solid-state battery interfaces, and the status and prospects of data- and robot-driven materials research using self-driving experiments. I highlight the importance of integrating different research fields to open up new avenues of research.

Hexagonal boron nitride (hBN) is an atomically thin material with an ultrawide bandgap (> 6 eV), emerging as a key dielectric material for next generation two-dimensional (2D) heterostructure devices and quantum technologies. Unlike conventional 3D dielectrics, single-crystal hBN provides an atomically flat surface, absence of dangling bonds, and ultraclean van der Waals interface, thereby enabling near-ideal electrostatic environment for high-performance 2D optoelectronic architectures. In addition to its exceptional insulating properties, hBN exhibits highly promising characteristics for efficient deep ultraviolet (DUV) light emission, including single photon emission and spin qubits from color centers in hBN.

In this talk, I will present the ultrahigh breakdown electric field (> 50 MV/cm) with suppressed leakage current from carbon-doped hBN heterostructures, which enable the robust power electronics devices and ultra-low power consumption semiconductor devices. I also present the highly efficient deep UV electroluminescence from carbon color center in hBN. These results pave the way for the developments of next-generation semiconductor and deep UV optoelectronics.

When semiconductor devices scaling down to the nanoscale, lithography reaches its physical limit. There are several techniques for building small structures by self-assembly because they allow to build structures that are beyond the limits of lithography and we can therefore miniaturize conventional devices. Self-assembly allows us to make new kinds of structures, not possible by conventional techniques, that enable new devices. It is critical to identify the unique features of nanostructures to examine the confusing nanoscale properties such as resistive switching processes and understand the scalability of reducing the size of the devices to attain a higher density and better device performance. To investigate interesting physical properties underlying the fundamental materials science, a nitride-based material system is introduced in this talk owing to its promising features such as a high response speed and high-power density. Gallium nitride, a third-generation semiconductor, is a nitride- based material with a wide direct bandgap of 3.4 eV and advantageous features such as a high thermal conductivity, high saturated electron velocity, and resistance to acids and alkalis. In the talk, a nanowire memristor from the integration of complementary metal-oxide semiconductor circuits using compatible nitride-based electrodes is presented. We regulate the morphology and surface states with the memristive switching behavior. Thus, our study demonstrates the realization of self-assembled GaN nanowire devices, which is promising for application in the 1D-1D system downsizing required for the brain-inspired neuromorphic computing.

We demonstrate wafer-scale fabrication of highly ordered nanostructure arrays via semiconductor lithography and sputter deposition, achieving diverse architectures—arrays of nanotube, disk, and pillars as well as meshes. This work, honored with an ACS award at Japan Nano Tech 2018 and featured on the 2025 cover of Nanoscale (RSC), enables tunable nanostructures for applications in sensing, energy, and advanced materials. The fabrication methodology employs sputter deposition of metallic layers onto pre-patterned contact-hole array templates fabricated in photoresist. Through the strategic incorporation of both metallic and non-metallic material systems, we demonstrate precise tunability of nanostructure dimensions spanning from sub-micron to 20 micrometers in both height and diameter, while achieving diverse morphological configurations including high-aspect-ratio cylindrical structures, dish-shaped formations, and rhombic geometries.Furthermore, the functional integration of advanced nanomaterials - including ZnO nanowires (NWs), graphene oxide, Au nanoparticles (NPs), and Fe₂O₃ NPs - facilitates the development of hybrid nanostructured architectures. These nanohybrids can be seen in the SEM images of attached figure. These engineered nanohybrid arrays significantly broaden the scope of potential technological applications, particularly in the domains of thermal emission, triboelectric energy harvesting, surface-enhanced Raman spectroscopy (SERS) biosensing platforms, and advanced anti-icing surface technologies.

Understanding the interaction of oxygen with transition metal surfaces is important in many areas including corrosion and catalysis. Of interest to us is the formation and chemistry of subsurface oxygen (O_sub); oxygen atoms dissolved in the near-surface region of catalytically active metals. We seek to understand how incorporation of O_sub into the selvedge alters the surface structure and chemistry and use ultra-high vacuum (UHV) based surface science techniques to characterize Ag and Rh surfaces after exposure to atomic oxygen (AO) to obtain O coverages in excess of 1 ML. We have found that the surface temperature during deposition is an important factor for the formation of O_sub and the consequent surface structures. Rh surfaces are significantly more reactive towards CO oxidation when O_sub is present. This enhanced reactivity is located at the interface between the less reactive RhO₂ oxide and O-covered metallic Rh. This leads to question – what are the microscopic steps the reagents take in a surface-catalyzed oxidation reaction? The ability to obtain velocity distributions of molecules desorbing from surfaces with both high temporal precision and angular resolution provides newfound insight into both the kinetics and the dynamics of recombinative desorption and subsurface emergence.We have recently studied subsurface oxygen emerging from beneath Rh(111) and how the velocity distribution shifts in comparison to the thermally-dominated desorption pathways found for surface-adsorbed oxygen. In addition, it was recently discovered that decomposition of oxygenaceous surface phases on Ag(111) also exhibit pronounced shifts in the energetics of the desorbing oxygen molecules. I will discuss these observations and their potential impacts in oxidation reactions in heterogeneously catalyzed reactions over transition metal surfaces.

Vacuum-based plasma deposition techniques such as pulsed laser deposition and RF Magnetron sputtering are well-known to have excellent process control, good repeatability, a wide range of materials and can accommodate large area substrates. As miniaturization gradually shift from bulk materials to thin films to low dimensional materials, these plasma deposition techniques have to progress accordingly, reaching the point of whether (example) 2D materials can be fabricated as well as other nanostructured materials.

In this talk, we shall like to demonstrate that first, these vacuum-based deposition techniques can be used to fabricate high quality 2D films, with examples such as WS₂, MoS₂ and graphene will be shown. Using vacuum-based depositoin techniques has also other advantages such as at lower temperature growth rate and able to make vertically aligned free-standing 2D structures. The quality of these low dimensional nanomaterials are comparable to the common approach of chemical vapour deposition techniques widely reported to deposit these 2D materials.

We will also show that the growth processes in vacuum plasma deposition techniques can be further modified to give novel nanostructures. An example is nanostructured CuS where it can be used as a non-volatile memory device yet the material can be further modified as a photothermal evaporator.

In a recent study at Central Mindanao University, Tabafa (2023) developed a low-cost PVD system capable of depositing thin films. However, the system faced challenges during reactive oxygen sputtering because its glass chamber could not withstand thermal stress due to the presence of oxygen in the plasma. The previous low-cost, glass chamber low-vacuum magnetron sputter system was upgraded useful for depositing SnO_x thin films under different Oxygen Partial Pressure (OPP) conditions. A post-treatment annealing process was also done at a fixed temperature and time.

Tin Oxide (SnO_x) is a wide bandgap semiconductor suitable for various applications due to its efficient charge transport properties. This study focuses on modifying a low-cost plasma vacuum system for depositing SnOx thin films on Si(100) substrates using DC Magnetron Sputtering. The deposition parameters varied in deposition period and Oxygen Partial Pressure (OPP). The modified chamber used stainless steel and aluminum components. The base pressure was 200 Pa. The deposition operated at -750 V target voltage for 10 minutes. SnO_x thin films were characterized by SEM for surface morphology, EDX for elemental composition, UV-Vis spectroscopy for optical properties, and two-point probe for electrical characteristics. SEM analysis showed Sn metallic phases at 10%, 15%, and 20% OPP, with 15% OPP exhibiting widespread Sn coverage. EDX revealed dominant Si, O, and Sn. UV-Vis absorbance showed Si dominance in the visible range (500–700 nm) and peak shifts in 200–400 nm, indicating SnO_x absorption. Transmittance results confirmed reduced transparency, supporting absorbance findings. The two-point probe showed increasing current in the blank Si(100), while annealed films exhibited enhanced conductance with increasing voltage. The optical bandgap ranged from 3.11 eV to 3.42 eV. Overall, 15% OPP samples yielded optimal and consistent results across characterization methods.

SEM results show the presence of bumps across the film. The particles’ sizes vary depending on the OPP. A trend towards smaller average particle sizes is observed as the concentration of OPP increases. The average size decreases from 6.62 μm at 10% OPP to 3.7 μm at 15% OPP, and further to 3.63 μm at 20% OPP. The distribution plots reflect a transition from a more heterogeneous particle size distribution at lower OPP concentrations to a denser distribution as the concentration increases to 15%. Based also on the two-point probe analysis, the particles at varying OPP affect the electrical properties as it shows that the 20% OPP also accumulate the highest conductance. At 15% OPP, it has denser deposit but not necessarily interconnected, which could limit effective charge transport. At 20% which shows higher conductance suggests a better phase composition for conduction. It may also have oxygen vacancies which act as n-type carriers, enhancing conductivity even if the surface appears less densely packed.

The discovery of free-standing 2D materials has inspired research for exploring new low-dimensional materials. These new 2D materials exhibit abundant unusual physical phenomena undiscovered in bulk forms due to their unique electronic structure. The confinement of charge and heat transport at such ultrathin planes offers possibilities to overcome the bottleneck of current devices in thickness limitation and push the technologies into the next generation. Searching for 2D semiconductors with excellent electronic performance and stability in the ambient environment is urgent. Bi2O2Se, an air-stable layered oxide, has emerged as a promising new semiconductor with excellent electronic properties. Studies demonstrate that its layered nature makes it ideal for fabricating electronic devices down to a few atomic layers. The Bi2O2Se-based top-gated field-effect transistor device shows excellent semiconductor device properties, including high carrier mobility and a superior current on/off ratio of 10^6 with almost ideal subthreshold swing (65 mV/dec). In addition, the moderate bandgap (0.8 eV) of Bi2O2Se makes its device suitable for room temperature operation while requiring only a relatively low operation voltage. These fascinating properties, chemical stability in the ambient environment, and easy accessibility make Bi2O2Se a promising semiconductor candidate for future ultra-small, high-performance, and low-power electronic devices. Moreover, as the Bi-O layer in Bi2O2Se is structurally compatible with many perovskite oxides with rich interesting physical phenomena, it is feasible to fabricate heteroepitaxy/superlattices between Bi2O2Se and perovskite oxides to pursue novel emergent physical phenomena. I will explore Bi2O2Se, Bi2O2S, and Bi2O2Te systems and their related heteroepitaxy with strongly correlated electronic systems based on perovskite oxides.

Titanium hydrides (TiH₂) are reported as hydrogen storage materials because of their high affinity to hydrogen [1]. Titanium can absorb hydrogen atoms and store them in the lattice gaps to form interstitial solid solutions, although it also has a high affinity to oxygen and nitrogen. Also, it has been widely applied as catalysts to lower the temperature of other solid-state hydrogen storage materials [2]. However, there are still many challenges for TiH₂ as a hydrogen storage material and catalyst.

Ball milling is one of effective and direct mechanical approaches to reduce the size of metal hydride and synthesize various mixture or composite, but there are a great deal of parameters affecting the morphology and property of final products such as ball milling atmosphere, time and rotation speed and so on. Here, we pay more attention to two different ball milling atmosphere (nitrogen and Argon) and systematically work on the effect of different ball milling time on the performance of TiH₂. Further, based on our previously reported paper [3], we discussed the effect of oxide layer on the property of ball milled TiH₂.

We conducted two methods to prepare TiH₂ then measured the composition and the hydrogen release temperature of samples. One is commercial TiH₂ was subjected to mechanical ball milling using a planetary ball milling at 400 rpm for 20 min under N₂-filled atmosphere called ball-milled TiH₂ 20 min (N₂). The balls to powder ratio was set to 74:1. The other is commercial TiH₂ ball milled for 1 h, 4 h, 12 h under argon-filled atmosphere to called ball-milled TiH₂ 1 h, 4 h, 12 h (Ar). Then we selected one sample oxidized by air for 24 hours for each condition. Then all of samples were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Thermogravimetry (TG) and thermal desorption spectroscopy (TDS) measurement, Transmission electron microscope (TEM) and so on.

In the case of N₂, the grain size, crystallite size, and surface oxide layer all decreased sharply as the ball milling time increased. Similarly, the hydrogen desorption temperature also significantly decreased. Especially for ball-milled TiH₂ for 20 min, which had relatively smaller grains, the onset temperature of hydrogen release was reduced from 350 ℃ to around 200 ℃ compared to commercial TiH₂. And the primary first-stage hydrogen injection temperature also decreased from around 470 ℃ to around 300 ℃. Furthermore, the ball-milled TiH₂ samples before and after oxidation were compared. The onset hydrogen release temperature and the first-stage hydrogen release temperature both showed a slight increase, but both remained lower than those of the commercialized TiH₂. In addition, we also compared the ball milling of TiH₂ under different ball milling atmospheres (nitrogen and argon), and found that under the argon atmosphere, TiH₂ could be ball milled for a longer time without changing TiH₂ phase, and the initial and first-stage hydrogen release temperatures were lower. Therefore, our conclusion is the size of TiH₂ is a more important factor than oxide layer for the property of TiH₂ thermaldymic. For TiH₂, ball milling under an Ar atmosphere is generally the better approach. Interestingly, however, under prolonged high-speed ball milling in a N₂ atmosphere, TiN can be formed directly and rapidly from TiH₂.

View PDF for the rest of the abstract.

With the excessive consumption of traditional fossil fuels and the increasing demand for energy, developing alternative sustainable clean energy sources is one of the most promising solutions. There are many applications centered around carbon monoxide (CO) in the industrial chemical synthesis, such as Fischer-Tropsch synthesis, carbonylation, and reduction of metal oxides. Traditional preparation methods such as coke method, water gas method, etc. often require high temperatures and catalysts, separations and purification steps of their products are also very complex. Therefore, production of highly purified CO under mild conditions can offer advantages in terms of energy efficiency, environment impact, economic viability, and broader industrial applicability. Formic acid (FA), a multifunctional molecule, can be considered as an ideal source of CO owing to its well-known decomposition pathways: (i) dehydration reaction: HCOOH → CO + H₂O, and (ii) dehydrogenation reaction: HCOOH → H₂ + CO₂. The current mainstream strategy is to use heterogeneous catalysts to catalyze the dehydration reaction selectively obtain highly purified CO. However, the catalytic decompositions of FA, dehydration and dehydrogenation, are always in a competitive state, so it is crucial to develop highly selective catalysts for dehydration of FA.

Two dimensional (2D) materials such as graphene have shown great potential in catalytic systems due to their large surface area and unique electronic state. Previously, our team has developed a new 2D layered material, hydrogen boride (HB), through an ion exchange method.¹ From the studies, it has been proved that HB plays a role as a solid acid catalyst and chemically stable against water with long time stability.^2-4 This indicates that HB is expected to be used as a novel non-metallic catalyst for dehydration of FA. In this work, we found that HB can catalyze the dehydration of FA from 120 ℃, achieving a FA conversion rate of about 97% and CO production rate of about 15 mmol g^-1 h^-1 at 300 ℃, with 100% CO selectivity across all tested temperature. Moreover, we investigated the catalytic activity at different FA flow rates and found no change in the catalytic performance, which remains comparable to that of state-of-the-art materials. The apparent activation energy (E_a) is 67.9 ± 5 kJ/mol, which is lower than most reported results.

The development of catalysts capable of converting CO₂ into energy is a critical issue for the realization of carbon neutrality. Hydrogen boride (HB) is a two-dimensional material consisting of positively charged hydrogen and negatively charged boron network [1]. HB acts as a solid acid catalyst [2] and can convert CO₂ to hydrocarbons when heated with CO₂ [3]. It is also known that the addition of water to HB lowers its pH [4], and salts formed by neutralization with basic solutions are expected to become HB containing heterogeneous elements, which are expected to improve catalytic performance in terms of the addition of active species or tuning of electronic states. However, the synthesis of HB doped with different elements by such a method has not been reported yet.

In this study, potassium-doped HB was synthesized using a potassium hydroxide solution as shown in Fig. 1. Various measurements have shown that HB with precisely controlled amounts of H⁺ and substitutional K⁺ can be synthesized by adjusting the amount of potassium hydroxide solution added while measuring the pH. The infrared spectroscopy showed that the B-H bond strength in the entire sample weakened with increasing potassium doping. These results suggest the establishment of a versatile method for the synthesis of hetero-element-doped HB with improved catalytic and other functions. The materials prepared by this method are expected to contribute significantly to the future functional enhancement of HB.

References

[1] H. Nishino, et al. J. Am. Chem. Soc. 139, 13761 (2017).

[2] A. Fujino, et al. ACS Omega 4, 14100 (2019).

[3] T. Goto, et al. Commun. Chem. 5, 118 (2022).

[4] K.I.M. Rojas, et al. Commun. Mater. 2, 81 (2021).

1. Introduction

Titanium dioxide (TiO₂) is a widely studied photocatalyst due to its chemical stability and UV responsive activity; however, its practical efficiency is limited by its wide bandgap and rapid recombination of photogenerated charge carriers. Defect engineering has emerged as a promising approach to overcome these intrinsic limitations. In this study, anatase phase TiO₂ thin films were fabricated via magnetron sputtering under controlled plasma conditions to systematically introduce and manipulate oxygen vacancy states. The correlation between these defect states and photocatalytic activity was thoroughly investigated.

2. Experiments

Dense TiO₂ thin films were deposited on quartz substrates using RF magnetron sputtering. After evacuating the chamber to 1.6 × 10^-3 Pa, argon and oxygen gases were introduced to achieve a total pressure of 1 Pa. Pre-sputtering was performed at 200 W for 15 minutes, followed by deposition under the same conditions for 4 hours. Oxygen vacancy states were controlled by adjusting sputtering conditions such as magnetic flux density, oxygen partial pressure, and substrate pretreatment. Post-deposition annealing in a hydrogen atmosphere was also employed. Structural and defect characterizations were carried out using photoluminescence (PL) spectroscopy and X-ray diffraction (XRD). Photocatalytic activity was evaluated based on the degradation rate of methylene blue and acetaldehyde gas, and the relationship between oxygen vacancy types and photocatalytic performance was investigated.

3. Results and Discussion

PL spectroscopy revealed emission peaks associated with oxygen vacancies (V_O), as well as surface defect states. (see Fig. 1) The emissions at 500 nm, 530 nm, and 570 nm are attributed to F centers, F⁺ centers, and Ti³⁺/V_O defect. A positive correlation was observed between the relative intensity of F⁺ centers and photocatalytic activity, whereas films dominated by F centers exhibited lower performance. This difference is attributed to the higher electron occupancy of F centers, which promotes recombination between photogenerated electrons and holes, thereby reducing photocatalytic efficiency.

Interestingly, the presence of surface defects was found to markedly enhance photocatalytic activity, achieving a 13 fold increase compared to conventional anatase TiO₂. Comprehensive analysis using PL spectroscopy, transmission electron microscopy–electron energy loss spectroscopy (TEM-EELS), and first principles calculations confirmed the presence of four-coordinated Ti species and oxygen vacancies within the amorphous surface layer. These defect states likely facilitate charge trapping and molecular adsorption, contributing significantly to the observed enhancement. These findings provide new insights into the role of surface amorphization and defect engineering in photocatalysis, offering a rational pathway for designing high performance and durable photocatalytic materials.

Hydrogen gas (H₂) sensing technologies are gaining increasing importance across various applications, including early disease detection via breath and skin gases, monitoring hydrogen leaks in fuel cell vehicles, and quality control in industrial products. Recently, sensor materials capable of detecting H₂ gas in ambient air and human breath with high sensitivity (1 ppm) have been developed using nanometer-thick platinum (Pt) thin films. This Pt thin-film sensor quantifies the presence of H₂ gas by measuring changes in electrical resistance upon voltage application. It is assumed that variations in the surrounding gas atmosphere induce changes in the chemical state (oxidation/reduction) and crystal structure near the sensor surface, leading to resistance changes; however, the detailed sensing mechanism remains unclear. To investigate changes in chemical states at the sensor's surface, we have recently conducted operando measurements under near-ambient pressure using atmosphere-controlled X-ray photoelectron spectroscopy (AP-XPS). In this study, we performed simultaneous resistance and X-ray absorption fine structure (XAFS) measurements under a hydrogen gas atmosphere to elucidate the sensing mechanism under ambient conditions.

The sample was a platinum (Pt) thin film, approximately 5 nm thick, deposited onto a SiO₂/Si substrate. The intensity of the incident X-rays (I₀) was measured using an ion chamber filled with a mixed gas of N₂ (85%) and Ar (15%). To detect fluorescence X-rays (I₁) emitted from the sample surface, a Lytle-type X-ray detector equipped with a Zn filter was used to suppress elastically scattered X-ray beams. The X-ray energy was calibrated based on spectra obtained from a Pt foil reference. The sensor sample was enclosed within a sealed glass cell allowing control of temperature and gas atmosphere during measurement. The temperature ranged from 298 K (room temperature) to 373 K. The flow rate of hydrogen gas (1% H₂ balanced with N₂) was set at 1 sccm.

Figure 1 illustrates the relationship among XANES spectra, resistance changes, and chemical states when the sample is exposed to H₂ gas under varying temperatures. Linear combination fitting was performed on the XANES spectra to quantify the proportions of metallic and oxide components. Based on the AP-XPS results, the oxidized state of Pt is considered to be PtO or chemisorbed oxygen species, rather than PtO₂. At 298 K, a minor contribution from the oxidized species is observed. Upon exposure to H₂ gas, Pt undergoes reduction, resulting in a predominantly metallic state. Upon heating to 373 K, only trace amounts of oxides remain, indicating complete reduction of Pt. Comparing this with the sensor response, an increase in the metallic Pt fraction leads to a decrease in resistance, suggesting a direct correlation between the chemical state and sensor behavior. These findings are consistent with the operando analysis conducted via AP-XPS. In the XPS measurements performed under ultra-high vacuum and H₂ gas atmospheres, the Pt 4f spectra under H₂ shifted toward lower binding energy, confirming surface reduction. On the other hand, the EXAFS analysis conducted in parallel (within the k-range of 3 < k < 11.0) showed no significant changes in parameters such as coordination number. This suggests that bulk hydrogen diffusion and its influence on the crystal structure are minimal. In conclusion, the sensor response is directly linked to the oxidation and reduction states of Pt. These results indicate that changes in resistivity are associated with electron scattering near the surface.

Soft X-ray absorption spectroscopy (XAS) is widely used to analyze chemical properties and electronic states near surfaces. However, conventional soft X-ray XAS measurements are time-consuming and not well-suited for tracking reaction dynamics in real time, as they require stepwise acquisition of absorption intensity at each energy point. This limitation makes it difficult to observe reactions without interrupting them. To overcome this challenge, we developed a method that illuminates the sample with wavelength-dispersed soft X-rays and collects the emitted fluorescent X-rays spatially resolved across the sample surface [1]. This approach enables the acquisition of a full spectrum in a single shot, allowing real-time observation of chemical reactions. Furthermore, the method is compatible with near-ambient pressure conditions and external fields (e.g., magnetic and electric fields), thanks to recent advances in soft X-ray fluorescence detection. In addition, it allows simultaneous depth profiling during real-time measurements [2, 3]. This method has also been applied to chemical reactions at the solid–liquid interface during electrode potential sweep [4, 5], demonstrating its versatility. Additionally, a dedicated cell was designed to enable real-time observation of chemical reactions at the solid–liquid interface of (photo-)electrodes used for the oxygen evolution reaction (OER) in water electrolysis, a key research area in the pursuit of carbon neutrality. In particular, the electrode for the OER is a performance bottleneck compared to the hydrogen evolution reaction electrode. Therefore, it is essential to develop electrocatalysts based on a deep understanding of reaction mechanisms, achieved through real-time tracking of the entire reaction process at the electrode and identification of reaction intermediates. To this end, operando evaluation focusing on the solid–liquid interface is crucial for elucidating the chemical states of catalytic surfaces and identifying intermediate species. In this study, representative model catalysts, CoO_x and TiO₂, were observed in real time using fluorescence-yield soft X-ray XAS as OER catalysts. Oxygen K-edge XAS spectra were recorded during linear sweep voltammetry for OER, with and without UV illumination (in the case of TiO₂). The spectra during the reaction were obtained every 3 s. Alternation of the spectra appeared during the potential sweep, and the peak intensity differed between the cases with UV light on and off for TiO₂. This spectral change can be attributed to the intermediates formed during the (photo)catalytic reaction at the solid–liquid interface.

This technique is applicable to a wide range of analyses involving (photo-)electrocatalysis and electrochemical reactions at solid–liquid interfaces, enabling the observation of reaction products and intermediates in real time. In addition, we recently conducted real-time operando observations of the oxygen evolution reaction (OER) using hard X-ray XAS with the same CoO_x catalyst, successfully capturing potential-dependent changes in the cobalt species. In parallel, we are preparing for integrated analysis using simultaneous hard and soft X-ray XAS measurements at a new beamline, scheduled for completion in the summer of 2025, enabling simultaneous hard and soft X-ray irradiation for integrated reaction analysis.

References

[1] K. Amemiya, K. Sakata, M. Suzuki-Sakamaki, Rev. Sci. Instrum., 91 093104 (2020).

[2] K. Sakata, M. Suzuki-Sakamaki, K. Amemiya, Nano Lett., 21, 7152–7158 (2021).

[3] K. Sakata, K. Amemiya, J. Phys. Chem. Lett., 13, 9573-9580 (2022).

[4] K. Sakata, K. Amemiya, Electrochem. Commun., 157, 107627 (2023).

[5] K. Sakata, K. Amemiya, Electrochem. Commun., 165, 107771 (2024).

Introduction

Plasma catalysis has recently attracted considerable attention due to its ability to significantly enhance catalytic performance. ^{1, 2)} This enhancement can be attributed to the activation of reactant gases and the modifications in the electronic structure and morphology of the catalyst, which results in opening a new reaction pathway. To unveil the effect of the plasma on the catalyst surfaces at the atomic level, it is essential to develop in situ surface science techniques which are capable of probing electronic state and structure of the catalyst surfaces under the plasma. We have recently constructed in situ/operando PTRF-XAFS apparatus which can measure valence state (XANES) and 3D structure (EXAFS) of active metal species deposited on single-crystal oxide surfaces during catalytic reactions.³⁾ In this study, we further modified this technique and applied it to the Cu/α-Al₂O₃(0001) model catalyst surface to investigate the effect of H₂ plasma irradiation on the Cu morphology.

Experimental

The Cu/α-Al₂O₃(0001) surface was prepared by vacuum evaporation of Cu onto an α-Al₂O₃(0001) surface at room temperature in an ultra-high vacuum (UHV) chamber. The Cu coverage was estimated to be 1 ML from the XPS peak intensity ratio of Cu2p_3/2 to Al2p, where 1 ML was defined as the surface Al density (5.1×10¹⁴/cm²). The sample was then transferred to the in situ PTRF-XAFS cell. The H₂ plasma was generated under the H₂ gas flow using the compact electron cyclotron resonance (ECR) plasma source that was attached to the cell. The Cu K-edge PTRF-XAFS measurements were performed at BL-9A of the Photon Factory at the Institute of Materials Structure Science (KEK-IMSS-PF, Tsukuba, Japan).

Results

Figure 1a shows the Cu K-edge PTRF-XANES spectra of the Cu/α-Al₂O₃(0001) surface measured under vacuum at 473 K. The spectra for both s- and p-polarizations showed similar features to that of Cu foil (see Figure 1d) and exhibit no polarization dependence, indicating the formation of metallic Cu nanoparticles with high symmetry on the α-Al₂O₃(0001) surface. Figure 1b presents the in situ PTRF-XANES spectra of the Cu/α-Al₂O₃(0001) surface obtained during exposure to pure H₂ gas (1.9 mL/min, 1.0 Pa) at the same temperature. No significant spectral changes were observed, suggesting that H₂ gas alone does not alter the state or symmetry of the Cu nanoparticles. In contrast, upon exposure to H₂ plasma under identical flow conditions, clear differences between the s- and p-polarized spectra can be observed (see Figure 1c), indicating anisotropic changes in the Cu nanoparticles. The 3D structural evolution induced by plasma was further investigated by in situ PTRF-EXAFS measurements. The origin of these morphological changes will be discussed in relation to the altered surface wettability of the α-Al₂O₃(0001) substrate caused by H₂ plasma treatment.

References

1) D.-Y. Kim, Y. Inagaki, T. Yamakawa, S. Liu, B. Lu, Y. Sato, N. Shirai, S. Furukawa, H.-H. Kim, S. Takakusagi, K. Sasaki, T. Nozaki, JACS Au., 5, 169 (2025).2) D.-Y. Kim, H. Ham, X. Chen, S. Liu, H. Xu, B. Lu, S. Furukawa, H.-H. Kim, S. Takakusagi, K. Sasaki, T. Nozaki, J. Am. Chem. Soc., 144, 14140 (2022).3) B. Lu, D. Kido, Y. Sato, H. Xu, WJ. Chun, K. Asakura, S. Takakusagi, J. Phys. Chem. C., 125, 12424 (2021).

Introduction

Understanding surface chemistry under realistic conditions is crucial for bridging the long-standing pressure gap between ultra-high vacuum (UHV) studies and practical catalytic environments.¹ Conventional UHV surface science studies often fails to capture the pressure-dependent dynamics of surface reconstructions and adsorbate interactions. Recent development of high-pressure surface science techniques suggests formation of novel, near-ordered adsorption phases that are absent under UHV conditions.²

In this context, we conducted STM observations following high-pressure methanol exposure on TiO₂(110) surfaces at pressures between 0.1 and 100 Pa. Although methanol is adsorbed only on the oxygen defects of the TiO₂(110) surface after exposure to low pressure (10^-6~10^-8 Pa) methanol vapor,³ we observed the formation of a near-ordered and stable adsorption structure stabilized by elevated pressure, demonstrating the profound impact of gas-phase equilibrium on surface adsorption. These findings underscore the importance of high-pressure studies for accurately characterizing catalytic interfaces.

Experimental

A clean and well-ordered TiO₂(110) surface was prepared by repeated cycles of Ar⁺ sputtering and annealing at 973 K under UHV. The sample was then transferred to the high-pressure reactor chamber and exposed to methanol vapor at pressures between 0.1 and 100 Pa for 10-20 minutes. Following the methanol exposure, the TiO₂(110) sample was returned to the UHV STM chamber. Density functional theory (DFT) calculations were performed using VASP to simulate the electronic structure and STM contrast for both molecular and dissociative adsorption states of methanol on TiO₂(110).

Results and Discussions

Figure 1(a) shows an STM image of the TiO₂(110) surface after exposure to 5 Pa methanol for 15 min. Bright round spots can be observed to align along the [001] direction, with spacings of two or three times the distance between the adjacent Ti⁴⁺ sites (0.3 nm), as illustrated in the line profile in Figure 1(b). These features are attributed to methanol adsorbed at five-fold coordinated Ti⁴⁺ sites, with an estimated coverage of 0.3-0.5 ML. Locally, 2×1 ordered domains are observed. The spots exhibit two distinct apparent heights of approximately 0.1 nm and 0.15nm. DFT simulations indicate that the brighter features correspond to dissociated methoxy species, while the dimmer ones are intact methanol molecules adsorbed molecularly. These adsorbates remained stable under the UHV conditions and began to desorb only above 150 ^oC.

Our results indicate that the thermodynamic and kinetic landscape of methanol adsorption is significantly altered by pressure, revealing a non-negligible pressure gap in the surface chemistry of TiO₂.

References:

[1] Ertl, G., Angew. Chem. Int. Ed. 2008, 47, 3524–3535.

[2] Salmeron, M.; Eren, B., Chem. Rev. 2021, 121, 962–1006.

[3] Liu, C.; Lu, B.; Ariga-Miwa, H.; Ogura, S.; Ozawa, T.; Fukutani, K.; Gao, M.; Hasegawa, J.; Shimizu, K.; Asakura, K.; Takakusagi, S., J. Am. Chem. Soc. 2023, 145, 19953–19960.

The conversion of biomass-derived polyols into basic chemicals such as alkenes via deoxygenation-dehydration (DODH) reactions is a critical process for establishing a sustainable chemical industry. The efficiency of these reactions is enhanced by hydrogen spillover, a phenomenon where atomic hydrogen migrates from a H₂-dissociation-active metal catalyst to an oxide support [1]. The conventional mechanism proposes that this process involves the reduction of the support material itself. While previous studies on polycrystalline oxide supports have shown evidence of support reduction and hydroxyl formation, the inhomogeneity of these substrates has obscured a definitive mechanistic understanding [2,3]. The present study aims to understand the chemical states of hydrogen and Ti in the substrate during hydrogen spillover by employing a well-defined FeO_x-Pt/TiO₂(110) single-crystal model catalyst and in-situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS).

The model catalyst was prepared on a TiO₂(110) single-crystal substrate by depositing approximately 0.3 ML of Pt and Fe via resistive heating. Subsequent annealing in an O₂ atmosphere (1×10^-6 Torr) at 200 °C was then performed to induce oxidation of Fe and formation of nanoparticles. In-situ NAP-XPS measurements were conducted at the BL-13B beamline of the Photon Factory (KEK-PF). The sample thus prepared was analyzed under UHV and exposed to 0.1 Torr H₂ at temperatures of 25 °C, 50 °C, and 75 °C.

Figure 1(a) shows Fe 2p XP spectra for FeO_x-Pt/TiO₂(110) surfaces before and after H₂ exposures, which clearly indicates that the FeO_x is reduced from Fe³⁺ to Fe²⁺ by the H₂ exposure. While in the case of FeO_x/TiO₂(110) surfaces, the hydrogen-induced reduction is rather limited as shown in Fig. 1(b), which evidences for that the presence of Pt nanoparticles enhances the hydrogen-induced reduction of FeO_x, indicating hydrogen spillover taking place on the FeO_x-Pt/TiO₂(110) surface. Interestingly, during the hydrogen spillover in-situ analysis of the Ti 2p and O 1s core levels revealed no significant increase in Ti³⁺ or hydroxyl species at any temperature. This result indicates that the classical spillover mechanism, which is predicated on the reduction of the support, may not represent the dominant pathway in the well-defined system we measured.

The results obtained provide direct spectroscopic evidence for a significantly different spillover pathway than that predicted by the conventional model. It can be concluded that atomic hydrogen can migrate from Pt and directly reduce a supported oxide (FeO_x) without mediating through the electronic states of the underlying TiO₂ support, thereby it is desirable to establish a new mechanistic framework for this fundamental catalytic process.

[1] Shun K. et al., Chemical Science, 13, 8137, (2022).

[2] Karim W. et al., Nature, 541, 68 (2017).

[3] Beck, A. et al., ACS Nano, 17, 1091 (2023).

[Introduction] Conversion of carbon dioxide (CO₂) into valuable chemicals and fuels is an efficient way to deal with challenges such as global warming and climate change. Especially, CO₂ methanation (CO₂ + 4 H₂ → CH₄ + 2 H₂O) and reverse water gas shift reaction (CO₂ + H₂ → CO + H₂O) are important as the CO₂ hydrogenation reaction [1]. Ruthenium (Ru) is known as one of the most active catalyst for these reactions [2].

In general, the first step of CO₂ activation on heterogeneous catalysts proceeds through direct dissociation of CO₂* (* represents adsorbed species) into CO* and atomic oxygen (O*) (CO₂* → CO* + O*) or, the formation of formate (HCOO*) or carboxyl (COOH*) by the reaction of CO₂* with H* (CO₂* + H* → HCOO* or COOH*) [1]. On the Ru surface, it is known that the reaction proceeds via CO* or HCOO* intermediates [3]. If the CO* intermediates desorb into gas-phase followed by the reaction of O* with hydrogen to desorb as H₂O, it is RWGS reaction. On the other hand, if CO* or HCOO* decomposes to form atomic carbon (C*) followed by the reaction with H*, the outcome is CO₂ methanation.

In previous studies with theoretical calculations, it has been suggested that the activation energy of the direct dissociation pathway into CO* is lower than that of HCOO* formation pathway [3,4], while the opposite scenario has also been proposed [5]. Furthermore, in a recent experimental study, it has been suggested that CO₂ methanation proceeds on a Ru(0001) surface via HCOO* intermediate [6]. Ambient-pressure X-ray photoelectron spectroscopy (APXPS) is an efficient analytical method for in-situ observation of catalytic surface states including reaction intermediates under reactant gases. However, this technique has not been applied to this reaction system positively, since Ru 3d_3/2 and C 1s components overlap in the spectrum. Despite this difficulty, the XPS analyses for adsorption species including carbon on Ru surfaces become possible by analyzing the high-resolution photoelectron spectra measured with high-brilliance beam of synchrotron facilities. In this study, we investigated the chemical states and reaction intermediates on a Ru(0001) surface formed by the interaction with CO₂ and H₂ gases.

[Methods] A crystal surface of Ru(0001) (99.99% purity, diameter 10 mm, 1.5 mm thickness) was cleaned by repeated cycles of Ar⁺ sputtering (5x10^-7 mbar Ar, 1.0 keV, 15 min) and post-annealing (1100℃, 5 min). High-purity CO₂ and H₂ were used as the reactant gases.

APXPS measurements were conducted at soft X-ray beamline BL08U at NanoTerasu in Sendai and vacuum ultraviolet soft X-ray (VUV-SX) beamline BL-13B at Photon Factory (PF) of high energy accelerator organization (KEK) in Tsukuba. To obtain photoelectrons with kinetic energy of ca. 200 eV, the photon energy was set to 490 eV for Ru 3d and C 1s core levels and 730 eV to O 1s core level. The Fermi-edge was measured with the same photon energy after the measurement of each core level to calibrate the scale of binding energy. To deconvolute the Ru 3d_3/2 and C 1s components, carve-fitting was conducted by fixing the split width and the peak area ratio.

[Results and Discussion] Figure 1 shows the APXPS spectra measured for Ru 3d and C 1s regions under 0.1 mbar CO₂ and 0.3 mbar H₂ (300 ~ 470 K). At 300 K, CO* was observed with O*, which proves the CO₂ dissociation.

View PDF for the rest of the abstract.

The hydrogen boride (HB) sheet is a recently synthesized two-dimensional material composed of hydrogen and boron in a 1:1 stoichiometric ratio [1]. It has attracted attention as a potential material for hydrogen storage due its intrinsically high hydrogen gravimetric density. Indeed it has been shown that hydrogen molecules can be released by heating to high temperatures [2], ultraviolet irradiation, or electrochemical means such as applying a bias potential [3]. The HB sheet has also predicted to act as a hydrogen-absorbing or -adsorbing material upon introduction of foreign atoms [4] or structural defect [5]. In contrast to many borohydrides, which are also regarded as potential hydrogen storage materials, the HB sheet has been shown to be chemically stable in water [6]. Moreover, it exhibits catalytic activity; for example, it converts carbon dioxide (CO₂) into valuable chemicals, such as methane (CH₄) and ethane [7]. In this talk, I will first give a brief overview of the computational framework, including the first-principles methods we employed, followed by a discussion of the electronic structure of the HB sheet [8]. I will then present our investigations on the adsorption and reaction of a water molecule on the HB sheet and its edges [9]. Finally, I will discuss the microscopic details of CO₂ adsorption and its conversion to CH₄on the HB sheet [10].

The theoretical study have been conducted in collaboration with Yoshitada Morikawa, Kurt Irvin M. Rojas, Luong Thi Ta, and Shunsuke Naka of the University of Osaka.

References

[1] H. Nishino et al., J. Am. Chem. Soc. 139, 13761 (2017).

[2] R. Kawamura, et al, Nat Commun 10, 4880 (2019).

[3] S. Kawamura, et al, Small 20, 2310239 (2024).

[4] L. Chen, et al., Phys. Chem. Chem. Phys. 20, 30304 (2018). [5] S. Naka, K. I. M. Rojas, Y. Morikawa, and I. Hamada (submitted).

[6] K. I. M. Rojas et al., Commun Mater 2, 1 (2021).

[7] T. Goto, et al, Commun Chem 5, 1 (2022).

[8] L. Thi Ta, Y. Morikawa, and I. Hamada, J. Phys.: Condens. Matter 35, 435002 (2023).

[9] K. I. M. Rojas, Y. Morikawa, and I. Hamada, Phys. Rev. Mater. 8, 114004 (2024).

[10] L. Thi Ta, K. I. M. Rojas, Y. Morikawa and I. Hamada (unpublished).

[Introduction] The dissociative adsorption of molecular H₂ on transition metal surfaces is crucial in heterogeneous catalysis, particularly in hydrogenation reactions such as methanol synthesis. Under non-vacuum conditions, hydrogen exposure causes surface reconstruction, which affects the dynamics of hydrogen interaction with the metal surface. A notable example is the H-induced surface reconstruction on the low-index facets of Cu surfaces, which has been thoroughly reviewed in the literature[1-2]. The ability of Cu surfaces to undergo reconstruction and create new active sites under hydrogen exposure poses questions on its effect on the dynamical behaviour of the hydrogen interaction with the surface, making them a subject of extensive investigation in heterogeneous catalysis[3-4].

[Objectives] In this study, we aim to elucidate the effect of such reconstruction to the activity of the catalytic reactions, in particular the CO₂ hydrogenation to formate on the Cu surfaces. This study incorporates the realistic active sites, which only emerge when the practical operating condition such as temperature and pressure are considered, thereby bridging the "pressure gap" between the experiment and the vacuum-only traditional theoretical calculations.

[Method] We performed molecular dynamics (MD) simulations using a machine learning interatomic potential to provide details on the hydrogen interaction with Cu surfaces. The effect of such reconstruction to the CO₂ hydrogenation were further investigated by first-principles calculations and the kinetic modelling.

[Results]

In our presentation, we will show the atomic view of the surface reconstruction, the mechanism, the energetics, and the kinetic rates related to the reactions on more realistic active sites. We provide the atomic view of the reconstructed surface which shows the emerging of the 3-fold hollow sites on the Cu(100) surface (Fig. 1). We also shows that the hydrogen prefers the emerged active sites (3-fold hollow sites) rather than the "original" 4-fold hollow sites of the pristine surface (Fig. 1b). We also show that considering the surface reconstruction in the model indeed gives better consistency in terms of the apparent barrier and experimental reaction rate [5-6]. In particular, we found that the "facet insensitivity" of the catalysis can only be recovered when considering the emerging active sites due to the surface reconstruction. Our results help elucidate the true active sites and bridge the pressure gap between theory and experiment.

[1] Chorkendorff, I.; Rasmussen, P. B. Reconstruction of Cu(100) by adsorption of atomic hydrogen. Surface Science 1991, 248, 35–44.

[2] Matsushima, H.; Taranovskyy, A.; Haak, C.; Gründer, Y.; Magnussen, O. M. Reconstruction of Cu(100) Electrode Surfaces during Hydrogen Evolution. Journal of the American Chemical Society 2009, 131, 10362–10363.

[3] Hellman, A.; Svensson, K.; Andersson, S. Hydrogen-Induced Reconstruction of Cu(100):Two-Dimensional and One Dimensional Structures of Surface Hydride. The Journal of

Physical Chemistry C 2014, 118, 15773–15778.

[4] Zhang, Z.; Wei, Z.; Sautet, P.; Alexandrova, A. N. Hydrogen-Induced Restructuring of a Cu(100) Electrode in Electroreduction Conditions. Journal of the American Chemical Society 2022, 144, 19284–19293.360.

[5] Nakano, H.; Nakamura, I.; Fujitani, T.; Nakamura, J. Structure-Dependent Kinetics for Synthesis and Decomposition of Formate Species over Cu(111) and Cu(110) Model Catalysts. J. Phys. Chem. B 2001, 105, 1355–1365.

[6] Taylor, P. A.; Rasmussen, P. B.; Ovesen, C. V.; Stoltze, P.; Chorkendorff, I. Formate

synthesis on Cu(100). Surf. Sci. 1992, 261, 191–206.

CO-induced Cu clustering has been reported both experimentally [1] and theoretically [2–4], yet its impact on catalytic performance remains insufficiently explored. In this study, we investigate how Cu clusters supported on Cu(111) influence the water-gas shift reaction (WGSR) by developing machine learning force fields (MLFF) and incorporating lateral interactions in microkinetic modeling to evaluate catalytic activity.

The MLFF was constructed using the Gaussian Approximation Potential (GAP) framework [5], trained on 7276 structures and validated on 1350 additional configurations obtained from molecular dynamics, umbrella sampling, and metadynamics simulations. The resulting root mean square errors (RMSEs) are 2 meV/atom for energy and 29 meV/Å for forces in the training set, and 4 meV/atom and 36 meV/Å, respectively, for the validation set. This MLFF enabled efficient Nudged Elastic Band (NEB) calculations to determine activation energies for various reaction pathways on Cu clusters model which illustrated in Figure 1. Vibrational analysis was also conducted to obtain normal mode frequencies.

To incorporate lateral interactions in the microkinetic model, CO-covered surface structure ranging from low to high coverage were obtained using the minima hopping method. Microkinetic simulations of the WGSR were performed on each Cu cluster and on the Cu(111) surface over a temperature range of 400–600 K and a pressure range of 0.1–10 bar using CatMAP [6]. The turnover frequency (TOF) on Cu clusters was found to be up to three orders of magnitude higher than on flat Cu(111), primarily due to the lower water dissociation barriers on the clusters. While lateral interactions had minimal influence on the Cu(111) surface due to low CO coverage, their impact was pronounced on Cu clusters, particularly Cu₇. With lateral interactions included, the predicted TOF falls within the experimental range (10^-3–10^-1 s^-1) [7,8], whereas models neglecting these interactions significantly overestimate reactivity.

In summary, this work demonstrates that Cu clustering significantly enhances WGSR activity, mainly due to the reduction in water dissociation barriers. Incorporating lateral interactions in the microkinetic modeling is essential for accurately capturing the catalytic behavior under realistic CO coverages, especially on Cu clusters where CO binds strongly. The combined approach of MLFF and microkinetic modeling offers an efficient and accurate framework for understanding complex catalytic systems.

References

[1] B. Eren et al., Science 351, 475 (2016).

[2] H. H. Halim, R. Ueda, and Y. Morikawa, J. Phys.: Condens. Matter 35, 495001 (2023).

[3] P. Hou et al., ACS Catal. 15, 352 (2025)[4] Z. Q. Xue and G. C. Wang, J. Catal. 447, 116115 (2025).

[5] A. P. Bartók et al., Phys. Rev. Lett. 104, 136403 (2010).

[6] A. J. Medford et al., Catal. Lett. 145, 794-807 (2015).

[7] C. T. Campbell and K. A. Daube, J. Catal. 104, 109-119 (1987).

[8] N. A. Koryabkina et al., J. Cata. 217, 233-239 (2003)

Antiaromatic molecules, which have 4n π-electrons, exhibit exotic magnetic and optical properties different from those of aromatic molecules [1]. The exotic properties of antiaromatic molecules originate from electronic states with strong electronic correlation in the molecules, which is called diradical state. However, their unstable electronic structures are too unstable to synthesise, and their applications to materials and devices remains difficult.

Recently, it has been reported that unstable organic radicals can be synthesised only on surfaces [2]. In addition, theoretical calculations have shown that interactions with solid surfaces, even at physisorption state, can vary the resonance structure of the radicals and stabilise the diradical states [3, 4]. Hence, the surface interactions would be a promise way to stabilise unstable electronic structures.

From these previous studies, we conceived the idea that the stability of electronic structures of antiaromatic molecules could be controlled by surface adsorption [5]. We then investigated the effects of surface adsorption on the diradical states of cyclobutadiene, which is a typical antiaromatic molecule, using a modified spin-projected density functional theory method [5]. The calculated model was a cyclobutadiene/Ni(111) system, and four spin states were calculated: specifically, (1) Open-singlet: cyclobutadiene has an open-singlet state; (2) Triplet 1: cyclobutadiene has a triplet state and the unpaired electrons couple in parallel with Ni spins; (3) Triplet 2: cyclobutadiene has a triplet state and the unpaired electrons couple in antiparallel with Ni spins; and (4) Closed-singlet: cyclobutadiene has a closed singlet state. The calculated results showed that the diradical states with D_4h symmetry will become ground state at the physisorption state (Fig. 1). This indicates the possibility of controlling the magnetism and stability of antiaromatic molecules by surface adsorption. In other words, we can induce ferro/anti-ferro magnetism on cyclobutadiene, which is a non-magnetic molecule in gas-phase, by surface adsorption. The magnetic change is due to the orbital correlation between cyclobutadiene and metal surface. The calculation also suggested that there is an optimal surface-molecule distance for this surface adsorption effect. Although the optimisations of substituents and surface structures are issues remained, the “control of electronic states of antiaromatic molecules by surfaces” presented in this study will open up a new field of molecular magnetism research. The detailed mechanism and theory are summarised in our recent study [5] and will be explained briefly in the presentation.

[1] C. Hong et al., Eur. J. Org. Chem., 2022, 2022, e202101343.

[2] J. Hieulle et al., J. Phys. Chem. Lett., 2023, 14, 11506.

[3] K. Tada, T. Kawakami, Y. Hinuma, Phys. Chem. Chem. Phys., 2023, 25, 29424.

[4] K. Tada, K. Masuda, R. Kishi, Y. Kitagawa, Chemistry, 2024, 6, 1572.

[5] K. Tada, R. Sugimori, R. Kishi, Y. Kitagawa, Chem. Commun., in-press.

Single-molecule manipulation using scanning probe microscopy (SPM) has served as a model platform for studying nanoscale friction. While previous studies have primarily focused on the forces driving molecular motion [1], the accompanying dissipation dynamics have remained less explored. In this study, we investigate the manipulation of a carbon monoxide (CO) molecule adsorbed on a Cu(110) surface, combining scanning tunneling microscopy (STM), atomic force microscopy (AFM), lateral force microscopy (LFM), and density functional theory (DFT) calculations under ultra-high vacuum and cryogenic conditions.

DFT simulations reveal the preferred adsorption sites of CO as a function of tip height and lateral position, mapping transitions between top, bridge, and adjacent top sites. These transitions are experimentally corroborated by inelastic electron tunneling spectroscopy (IETS) and dissipation signals measured during vertical tip oscillation (AFM) and lateral scanning (LFM) [2-4]. Notably, energy dissipation is localized only along specific manipulation pathways in AFM [2,3], whereas in LFM, dissipation is also observed along additional trajectories [4], correlating with molecular switching events.

This behavior offers clues to the dissipation mechanisms during manipulation and sheds light on the energy landscape governing molecule–tip interactions. This combined experimental-theoretical framework establishes LFM as a powerful tool for visualizing energy dissipation in atomically-resolved manipulation processes.

References

[1] Ternes et al., Science 319, 1066 (2008).

[2] Okabayashi, T. Frederiksen, A. Liebig, F. J. Giessibl, PRL 131 (2023) 148001

[3] Okabayashi, T. Frederiksen, A. Liebig, F. J. Giessibl, PRB 108 (2023) 165401

[4] Okabayashi, A. J. Weymouth, S. Schweiss, S. Nam, T. Frederiksen, F. J. Giessibl, in preparation.

Mechanical stimuli, such as compression, tensile, or shear stress, applied to solid reactants sometimes induce chemical reaction. Such mechanically induced reactions are known as the “mechanochemistry” and attract great interest. In recent decades, many chemical reactions have been studied at the single-molecule scale using scanning tunneling microscope (STM) and atomic force microscope (AFM). However, in general, studies on mechanochemistry have been performed at the macroscopic scale. So far, there have been only a limited number of studies reporting structural change of single organic molecule induced by the mechanical stimuli from the tip of scanning probe microscope [1-3].

In this study, we demonstrate the structural inversion of a bowl-shaped molecule, sumanene (shown in Fig. (a)), induced by mechanical stimuli from an AFM tip. We investigated Inversion of a bowl is expected to occur by simply applying the force with the AFM tip. Experiments were carried out using a qPlus based AFM/STM system operated in ultra-high vacuum at 5 K. Figure (b) shows a high-resolution AFM image of sumanene layer on an Au(111) substrate. The sumanene layer consists of bowl-up and bowl-down sumanenes and forms a 6 × 6 periodicity. This structure is different from the previously reported sumanene layer on Au(111) [3] but is rather similar to that on Ag(111) [4]. We performed force spectroscopy measurement above sumanene in the bowl-down structure. A sudden jump in force curve was observed in the repulsive regime. Subsequent imaging confirmed a successful structural inversion from bowl-down to bowl-up. With the support of theoretical calculations, the mechanism of inversion will be discussed in detail.

References

[1] R. Pawlack et al., ACS Nano 6, 6318 (2012). [2] J. N. Ladenthin et al., Nat. Chem. 8, 935 (2016). [3] A. Ishii et al., Chem. Sci. 12, 13301 (2021). [4] S. Fujii et al., J. Am. Chem. Soc. 138, 12142 (2016). [5] R. Jaafar et al., J. Am. Chem. Soc. 136, 13666 (2014).

The structure of ice that forms through vapor deposition on low temperature surfaces is of fundamental importance in many fields, including atmospheric chemistry, surface science, and cryogenic engineering. The structure and phase of ice are well known to be highly sensitive to growth conditions, such as temperature, pressure, and substrate properties. The structural evolution of amorphous solid water (ASW) upon annealing has been extensively studied. However, systematic studies on how temperature during deposition affects ice structure are scarce.

In this study, we examined the structural evolution of ice on Au(111) as a function of deposition temperature using low-energy electron diffraction (LEED) and atomic force microscopy (AFM). Previous studies have shown that, despite the hydrophobic nature of Au(111) surfaces, water can form bilayer ice — two-layered, hydrogen-bonded structures — that wet the surface [1]. We confirmed that when water was deposited onto clean Au(111) at 136 K, LEED patterns exhibited a (√3×√3)R30° superstructure, consistent with bilayer ice formation in the monolayer regime. However, bilayer formation was no longer observed above ~144 K when the deposition temperature increased. Under these higher temperature deposition conditions, LEED patterns exhibited 18 symmetrically arranged diffraction spots forming a concentric pattern. We conducted noncontact AFM imaging under identical deposition conditions and revealed that the 18 spots of LEED originated from three distinct hexagonal ice domains, each rotated by 20°. Additionally, we found that annealing ASW never results in a three-domain ice structure, highlighting the importance of the difference between the deposition and annealing temperatures.

These results demonstrate that bilayer ice is a metastable structure on Au(111) and that deposition at elevated temperatures favors the formation of rotationally ordered three-domain ice. In this presentation, we will discuss the origin of the 20° rotational domains within the framework of rotational epitaxy, which influences domain selection during nucleation and growth.

[1] R. Ma et al., Atomic imaging of the edge structure and growth of a two-dimensional hexagonal ice, Nature 577, 60 (2020).

Silicon nanosheets with less than 5 nm thickness have a high potential for many applications such as high-mobility transistors, light sensors, and quantum computing. The common challenge in the fabrication of Si nanosheets, such as silicene, is to obtain a fully hydrogenated structure with air stability and semiconductor band gap. One way to approach this problem is by scaling down Si bulk into thin layers. By proposing a method to fabricate thin Si layers from silicon-on-insulator (SOI) wafer, we want to develop a whole wet process mechanism to obtain atomic thick, fully hydrogen-passivated Si layers. In this method, we offer an idea to use Ag nanowire as a "scissor" to assist the etching of atomically flat staircase structure of Si surface. For straight and continuous etching, Ag nanowire needs to be grown thin and uniform along the step edges of Si(111) surface. However, during the sequence development it is: (1) common to encounter Ag particles deposited on top of the nanowire ^[1], and (2) there is an unknown relation between deposited Ag and the nucleation sites beneath it due to limited resolution by observation of tapping-mode atomic force microscopy ^[2].

This research addresses the two above-mentioned problems. First, we want to modify the sequence of the wet process to obtain a more homogeneous Ag nanowire and remove the particles. Second, we want to observe Ag-deposited Si(111) surface on a sub-nanometer scale by scanning tunneling microscopy/non-contact atomic force microscopy (STM/nc-AFM) combined setup. Our goal is to be able to distinguish the conductive and non-conductive species at the surface of Ag-deposited Si(111) surface.

A recent theoretical study by our group suggests that Ag nanowire can be uniformly formed when Si step edges are fully terminated by hydrogen. By approaching this direction, we adjust the pH of wet process solution into a more acidic environment. As a result, we discover that significantly less particles are formed by decreasing the solution pH from 8 to 5. To confirm the existence of the nanowire, we introduced this modified result into our STM/nc-AFM setup. By scanning 50×50 nm² area with nc-AFM mode, we confirm the presence of nanowire at 0.2-0.3 nm heights along the step edges as well as unknown adsorbates at the terraces (Figure 1a). We also conduct observation both by STM and nc-AFM mode to the same area of 500×500 nm². By careful observation of nc-AFM image, thin nanowires appear uniformly along the edges along with many adsorbates at the terraces (Figure 1b). However, both the nanowires and the adsorbates are not visible through STM observation (Figure 1c). Instead, some locations at the edges are decorated with dark pits, as one example is indicated by the circle. These pits are also scattered on the terraces. The image contrasts give an indication about the nature of the nanowires and adsorbates. As nc-AFM scans the real topography of the surface, any surface protrusion will appear at the surface especially in a high-resolution image. However, when the nanowire is very thin, tunneling current does not flow through even though Ag itself is a conductive species, especially when there is an oxidized layer beneath the nanowire.

To summarize, we have observed thin nanowire by nc-AFM at 50×50 nm² scale. However, this nanowire is too thin to be observed by STM observation. In the future, we want to obtain a thicker nanowire by modifying the sequence of the wet process. We hope that this research gain insights into the development of the new fabrication method of silicon nanosheets.

View PDF for the rest of the abstract.

Surface-synthesized coordination polymers offer a promising platform for exploring molecular dynamics at molecular resolution using scanning tunneling microscopy (STM). However, the strong surface adsorption of conventional π-conjugated ligands, such as porphyrins and phthalocyanines, typically necessitates high-temperature treatment above 100 ℃ to initiate polymerization, which often breaks metal–ligand coordination and prevents the study of intrinsic structural flexibility. In this study, we employed a newly designed ligand, 2,7-dicyano-9,9-dimethyl-9H-fluorene (DCF) [Fig. 1(a)], specifically engineered to reduce surface interactions while maintaining coordination capability. Using Cu adatoms on a Cu(111) surface, we achieved the formation of DCF–Cu coordination polymers [Fig.1(b)], thereby preserving coordination bonds and enabling direct visualization of structural dynamics with STM.

STM imaging revealed that the DCF–Cu polymer predominantly adopts a linear, di-coordinated configuration, interspersed with occasional tri-coordinated branched nodes, forming cross-linked polymer-like structures [Fig. 1(c)]. Structural analysis indicates that the CN–Cu–CN bond angle is generally near-linear (∼180°) but exhibits a flexibility of ±20º, imparting significant local curvature to the polymer chain and enabling dynamic reconfiguration. Temperature-dependent STM observations revealed three distinct regimes: below 40 K, the polymer remains static; at 48 K, structural mobility emerges primarily in linear segments with free ends, whereas branched regions remain largely immobile; at 71 K, increased polymer motion includes segmental diffusion, chain scission, insertion, and recombination [Fig. 1(d)]. These findings highlight the role of polymer architecture in governing dynamic behavior, with linear chains exhibiting greater flexibility and mobility compared to branched structures. Notably, local strain accumulation at curved junctions was often followed by bond cleavage, providing insight into the mechanical limits and failure points of supramolecular assemblies.

References

[1] W. Nakanishi, M. Takeuchi, K. Sagisaka, Chem. Sci. 16, 9156–9162 (2025).

Fullerene (C₆₀) is one of the typical n-type organic molecules and has been extensively applied in organic photovoltaics^[1]. Since exciton dynamics in molecular films and at interfaces govern the properties of devices, it is important to investigate them on their intrinsic length scale. Previous reports^[2][3] have reported several types of luminescence spectra with different main peaks for C₆₀ molecular films, where chemical impurities or crystal defects of samples were suggested to influence the luminescence process. Due to the diffraction limit, conventional optical spectroscopy cannot access the detailed luminescence properties at the single-molecule level. Electroluminescence spectroscopy based on scanning tunneling microscope (STM) enables investigating optical properties of material surfaces with sub-nanometer spatial resolution^[4]. In this study, we prepared C₆₀ molecular films on NaCl ultrathin insulating films grown on Au(111) and conducted electroluminescence measurements using STM.

We used ultra-high vacuum STM at 4.2 K. The photons emitted from the STM junction were collected by a lens in the STM chamber. Then they were guided out of the chamber, and refocused onto a grating spectrometer equipped with a charge-coupled device (CCD) photon detector.

Figures 1(a) and (b) show an STM image and a height profile of a C₆₀ nanocrystal obtained at 2.5 V. In the STM image, the C₆₀ nanocrystal was grown on a 2 monolayer (2 ML) NaCl ultrathin film. The film thickness of the C₆₀ nanocrystal was 2.79 nm corresponding to a 3 ML thickness^[5]. In addition, a 1 ML of C₆₀ film (0.64 nm) was also observed at the right-hand region of the STM image.

Figure 1(c) shows a scanning tunneling luminescence (STL) spectrum obtained by placing a tip at the red point on the C₆₀ nanocrystal in Fig.1 (a). The spectrum exhibits a main peak at around 732 nm and smaller peaks at around 746 nm and 820 nm. These emission peaks originate from the excited states of the C₆₀ molecules^[3]. We also investigate the thickness dependence of STL spectra. In this presentation, we will discuss the relationship between the thickness of C₆₀ molecular films and their luminescence properties.

References

[1] K. Ozawa et al., J. Phys. Chem. C, 125, 13963 (2021).

[2] A. Martin-Jimenez et al., Nano Lett., 22, 9283 (2022).

[3] W. Guss et al., Phys. Rev. Lett., 72, 2644 (1994).

[4] K. Miwa et al., Nano Lett., 19, 2803 (2019).

[5] Rossel et al., Phys. Rev. B, 84, 075426 (2011).

Toward a carbon-neutral society, the development of catalysts that convert water and carbon dioxide into useful chemicals like hydrogen and methanol is underway. Among various evaluation techniques, electrochemical measurement is highly effective due to its ability to directly evaluate redox activity. However, conventional methods typically provide only averaged information, making it difficult to resolve local activity differences originating from structural heterogeneity such as edges, grain boundaries, or strains. Thus, an understanding of the relationship between local surface structure and catalytic activity is essential for designing more efficient catalysts.

Scanning probe microscopy (SPM) provides high-resolution insights into surface properties and has been applied in various fields, including catalysis. However, conventional SPM techniques, for instance STM and AFM, are not well suited for directly measuring local electrochemical activity. To overcome this challenge, scanning electrochemical cell microscopy (SECCM) has been developed as a powerful tool for spatially resolved electrochemical imaging. SECCM uses a glass nanopipette to form a local electrochemical cell on the sample surface, allowing direct measurement of redox currents at nanoscale resolution (Fig. a).

There are two main SECCM setups: double-barrel (theta-type, Fig. b), which monitors ionic current between barrels and allows measurements on insulating surfaces, and single-barrel (Fig. c), developed by our group, which uses transient capacitive current as feedback. The latter is now widely adopted for high-resolution studies since it enables finer pipette tips. The SECCM technique has been increasingly applied to study local reactivity on electrocatalytic surfaces. For instance, it has visualized differences between terrace and edge sites on graphite and the structure–activity relationship of Pt-based catalysts. Our group has also developed the application of the SECCM to battery and catalyst materials. In this presentation, we explain the SECCM principles and their operational mode, and introduce our applications to two-dimensional materials and photocatalysts (Fig. d). We also present our recent SECCM works.

According to Yeh et al. [1], high entropy alloys (HEAs) are defined as alloys with five or more elements with concentrations of more than 5 at.%. However, HEAs generally point out equiatomic multicomponent alloys with more than five principal metallic elements [2]. Characteristic properties of HEAs were reviewed in detail by Tsai and Yeh [3]; they have 1) high entropy effect, 2) sluggish diffusion effect, 3) severe lattice distortion effect, and 4) cocktail effect.

Crystal structures and phase stabilities were described in the above review articles [1-3], and simple structures of fcc and bcc are frequently seen in HEAs, which originate from high entropy effect. Chemical short-range orders (CSROs) in HEAs were recently reviewed by Wu [4], and the preference/avoidance of elemental species were not found in the nearest neighbor atomic shells by theoretical works. Using transmission electron microscope, however, the structural motif of CSROs is constructed, showing both the lattice structure and species ordering occupation.

To investigate the local atomic arrangements on the Cantor HEA, we carried out X-ray fluorescence holography (XFH) experiment [5] to obtain element-selective three-dimensional atomic configurations and lattice distortions around the neighboring atoms. The single crystal of the Cantor alloy was grown in an alumina crucible using a modified Bridgman method [6]. After determining the crystallographic orientation using X-ray diffraction, a rectangular parallelepiped with its orthogonal faces parallel to the crystallographic [001] planes was cut using discharge machining with sample size of about 3 x 3 x 1 mm³. XFH experiments for the five transition metals’ Kα fluorescent X-rays were carried out at room temperature at the beamline BL6C of the Photon Factory located in the High Energy Accelerator Research Organization in Tsukuba, Japan. The sample was placed on a rotatable table for the incident angle θ and the azimuthal angle φ. The incident X-rays were set to 8.5 – 12.0 keV in steps of 0.5 keV, and were focused with a size of 0.3 x 0.3 mm² onto a (001) surface of the sample. The measurements were performed in inverse mode by changing 0° < θ < 75° in steps of 1° and 0° < φ < 360° in steps of ∼ 0.35° of the sample. The obtained holographic patterns were analyzed using the SPEA-L1 program package coded by Matsushita [7], which is based on an inverse problem and a sparse modeling.

Figure shows atomic images around (a) Cr, (b) Mn, (c) Fe, (d) Co, and (e) Ni atoms reconstructed on the (001) plane at z = 0.18 nm, where the first, third, fifth, ... neighboring atoms are located. The central atom is located by 0.18 nm below the center of the figures. The magnitudes of the atomic image intensities are given by color bars beside the figure. As seen in the figures, the atomic images exhibit clear fcc arrangements around all the constituent elements. However, the intensities of neighboring atoms differ from each other, which would be due to positional fluctuations of neighboring atoms. Namely, the atomic images around Ni, which is originally fcc, Co, which is densely packed hcp, and Fe, which easily transforms from bcc to fcc with increasing temperature, are strong, whereas the intensities around Mn and Cr, which are stable bcc, is weak, and it is clear that the positional fluctuations of neighboring atoms around them are large. In the presentation, we will show the results of the magnitudes of positional fluctuations around each of the central elements, and discuss the trends of lattice distortions in detail.

View PDF for the rest of the abstract.

Hydrogen, the smallest element, is known to dissolve in metals and can diffuse through them, enabling certain metals to be used as hydrogen filters. PdCu is one such alloy commonly studied for hydrogen filtraction. This binary alloy forms α phase, β phase, or α+β mixed phase depending on its composition ratio and temperature (Fig. 1) and the α+β mixed phase exhibits the highest hydrogen permeability. While various studies have investigated the reason behind the superior permeability of the mixed phase, the exact mechanism remains unclear.In this study, we examined the relationship between hydrogen permeation and alloy structure using our unique operando hydrogen microscopy technique. By comparing hydrogen maps obtained from this technique with electron backscatter diffraction (EBSD) analysis, we evaluated the correlation between grain structure, phase structure, their boundaries, stress, and hydrogen permeation.No significant difference in local hydrogen permeation was found between α and β domains within the mixed phase, nor was permeation concentrated at domain or phase boundaries. Furthermore, comparison of the EBSD-KAM (Kernel Average Misorientation) map, which reflects surface stress, with the hydrogen images revealed a correlation between high KAM values and hydrogen permeation. Because KAM values are related to the presence of dislocations, it is suggested that in the mixed phase, extensive mutual phase boundary effects result in increased dislocation density, thereby enhancing hydrogen permeability.

Nitrous oxide (N₂O) is a greenhouse gas almost 300 times more potent than CO₂ and an ozone-depleting gas. Electrocatalytic N₂O reduction reaction (eN₂ORR) allows us to convert N₂O to N₂ under ambient conditions at room temperature and atmospheric pressure, making electrocatalysis a promising approach for the removal of N₂O. The eN₂ORR can be catalyzed on alloy nanoparticles (NPs) such as Au@Pd core-shell and PtPdSn NPs[1,2]. Mesoporous carbon supports have been explored for reactions such as oxygen reduction reaction (ORR) [3]. However, synthetic strategies and design principles of mesoporous carbon-supported electrocatalysts for the eN₂ORR are still lacking.

In this work, Pt-Pd-Rh-Sn NPs supported by mesoporous carbon (PtPdRhSn NPs/mesoC) and a carbon black without mesopores (PtPdRhSn NPs/C) were synthesized for eN₂ORR based on a reported synthetic procedure [2,4]. Metal precursors were dispersed in a mixture of methanol and water with mesoporous carbon (mesoC) supports (avg. pore sizes: 4, 10 or 38 nm, respectively) or a carbon black (Vulcan, XC-72R), and then, the solvents were evaporated. The residue was heated rapidly at 923 K for several minutes to obtain PtPdRhSn NPs/C. The catalyst ink containing PtPdRhSn NPs/mesoC or PtPdRhSn NPs/C and Nafion was drop-cast on carbon papers and dried to prepare working electrodes. Cyclic voltammograms (CVs) of the prepared electrodes were recorded in a 0.1 M HClO₄ aqueous solution at a sweep rate of 10 mV s⁻¹ under Ar and N₂O, respectively. The catalysts were characterized by scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS) mapping, X-ray powder diffraction (XRD), and inductively coupled plasma optical emission spectrometry (ICP-OES).

The alloy formation in PtPdRhSn NPs was confirmed by STEM and EDS mapping images. The XRD patterns indicate the representative face-centered cubic structure, showing higher crystallinity of NPs on mesoC with the smaller pore sizes. PtPdRhSn NPs/mesoC (pore size: 10 nm) showed higher eN₂ORR current density than PtPdRhSn NPs/C. The mass activity of PtPdRhSn NPs/mesoC (pore size: 10 nm) at +0.16 V vs. RHE for the eN₂ORR is the highest in the catalysts used in this work and is approximately 1.5 times higher than PtPdSn NPs/C previously reported [2]. These results suggest that the carbon pore size is associated with the eN₂ORR activity difference between PtPdRhSn NPs/mesoC: the mesopores function as a nanoreactor for the eN₂ORR and possibly suppress ionomer adsorption and/or improving the mass transport of N₂O to the active site.

[1] K. Kim, J. Byun, H. Kim, K.S. Lee, H. S. Lee, J. Kim, T. Hyeon, J.J. Kim, J.W. Han, ACS Catal., 11, 15089–15097 (2021).

[2] A.C.Sarker, M. Kato, M. Kawamura, T. Watanabe, I. Yagi, Catal. Sci. Technol.,14, 4137–4141, (2024).

[3] Y. Kato, M. Kato, S. Saito, Y. Zhuang, Y. Iguchi, J. Sato, T. Komanoya, K. Soma, K. Suzuki, I. Yagi, Nanoscale, 16, 20505-20509, (2024)

[4] S. Gao, S. Hao, Z. Huang, Y. Yuan, S. Han, L. Lei, X. Zhang, R. S. Yassar, J. Lu, Nat. Commun., 11, 2016 (2020).

1. Introduction

Clean hydrogen production via water electrolysis is a key technology for realizing a sustainable energy future. However, the efficiency of this process is limited by the sluggish kinetics of the oxygen evolution reaction (OER), highlighting the need for high-performance catalysts. Rhombohedral boron monosulfide (r-BS), composed of earthabundant boron and sulfur, has recently gained attention as a promising OER catalyst due to its high activity and stability[1,2]. This study focuses on improving the OER performance of r-BS by optimizing the interaction with various carbon supports and their surface properties.

2. Method

2.1 Materials

All of the commercial materials were used as received without any purification, including amorphous boron, sulfur, graphene, graphite, Multiwalled carbon nanotube(MWCNT), carbon black, Nafion, Ethanol, KOH.

2.2 Synthesis of r-BS

Based on previous Paper[3], r-BS was synthesized by mixing boron and sulfur in a 1:1 molar ratio, followed by highpressure synthesis at 5.5 GPa and 1600°C.

2.3 Preparation of r-BS+Carbon materials-Ni Foam r-BS (5 mg) and carbon material (10 mg) were dispersed in ethanol (1 mL) with Nafion (50 µL) and ultrasonicated for 1 hour to form a uniform ink. Based on the optimized deposition method, the prepared catalyst ink was deposited onto Ni foam (0.51 cm x 1 cm x 0.15 cm) and dried.

2.4 OER Performance Evaluation

The prepared Ni foam electrode was employed as the working electrode and evaluated in 1 M KOH with an Au counter electrode and an Ag/AgCl reference electrode.

3. Results and Discussion

Catalytic performance was evaluated by LSV and violin plot analysis, as shown in Figure 1(a), while contact angle measurements assessed surface wettability. As a result, as shown in Figures 1(b), the surface hydrophilicity of the carbon support significantly affects OER activity. Catalysts supported on more hydrophilic materials exhibited higher OER performance. These findings suggest that enhancing wettability is an effective approach to improve rBS-based catalyst efficiency.

4. Conclusion

The optimized r-BS ink deposition method enhanced both catalyst loading uniformity and catalytic activity. The selection of carbon support, particularly its surface hydrophilicity, was found to play a critical role in determining OER performance. These findings offer valuable insights into the design of next-generation OER catalysts based on earth-abundant elements, contributing to the advancement of sustainable hydrogen production.

References

[1] L. Li et al., Chem. Eng. J. 471, 144489 (2023).

[2] L. Li et al., Sci. Tech. Adv. Mater. 24, 2277681 (2023).

[3] H. Kusaka et al., J. Mater. Chem. A 9, 24631–24640 (2021).

Purpose:

Polymer electrolyte membrane water electrolyzers (PEMWEs) are one of the most promising pathways for large-scale, high purity hydrogen production. It is the strategic development direction for future energy. ⁽¹⁾ PEMWEs require oxygen evolution reaction (OER) electrocatalysts at the anode in strongly acidic environments. Under these conditions, precious metal oxides such as IrO₂ can operate stably over long terms. ⁽²⁾ Although Ir is the most promising OER precious metal, it has been limited by reserves and high costs. Increasing the catalyst durability and reducing the Ir content at the same time remains challenging. Nanostructuring and alloying Ir electrocatalysts would be a promising approach to improve the catalytic durability ^(3,4) and to reduce Ir contents, respectively. ⁽⁵⁾ In this work, structurally stable PtIr nanowires as OER electrocatalysts (Figure 1) were developed. Controlling the synthesis temperatures provided different Ir contents and OER activities.

Experiment methods:

[Pt(acac)₂] and IrCl₃ were used as metal sources to synthesize PtIr alloy nanowires. They were synthesized at 433, 493, and 553 K. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectroscopy (EDS) and inductively coupled plasma optical emission spectrometry (ICP-OES) were used to characterize their nanomorphology and elemental composition at different synthesis temperatures, respectively. A three-electrode cell was constructed with a Pt wire as the counter, an Ag|AgCl (sat. KCl) as the reference electrodes. The catalyst ink was dropcast on a glassy carbon electrode as the work electrode. The catalytic performance was evaluated in comparison with the commercially available IrOX. In addition, the change in the metal oxidation state was observed at different potentials based on in situ X-ray absorption spectroscopy (XAS) at BL12C of PF–KEK.

Results and discussion:

Synthesis temperatures of PtIr alloy nanowires affect Pt:Ir atomic ratios and morphologies. Stable alloy nanowires were formed as the dominant morphology at 493 and 553 K. At 553 K. the highest iridium content of Pt: Ir =1:1 (at.%) was obtained. Through linear sweep voltammetry (LSV) testing, compared with the commercial catalyst IrOx, PtIr NWs@553 K exhibited the highest mass activity at 1.6 V vs. RHE under Ar atmosphere in the 0.1 M HClO₄. The STEM-EDS mapping images demonstrated that Ir atoms were exposed to the surface of nanowires. Furthermore, in situ XAS revealed the oxidation state changes of Pt and Ir during potential changes, also confirming that Ir was deposited on the surface of the nanowires. Compared with the IrOx, the Ir in the nanowires exhibits slighter changes in white line intensity under different

applied potentials. This result indicates the catalyst's electrochemical stability. The high OER activity and durability of PtIr nanowires 553 K possibly is attributed to the exposure of Ir at the surface. Overall, this provides new insights into the development of tunable and structurally stable nanocatalysts for Ir based systems.

Reference:

1) H. Wang et al., Emerging Graphene Derivatives and Analogues for Efficient Energy Electrocatalysis. Adv. Funct. Mater. 2022, 32, 2204755.

2) J.T. Ren et al., Water electrolysis for hydrogen production: from hybrid systems to self-powered/catalyzed devices, Electrochemical Energy Reviews, Energy Environ. Sci., 2024, 17, 49-113.

View PDF for the rest of the abstract.

In the era of carbon neutrality, the development of highly active yet selective electrocatalysts composed of earth abundant elements is of paramount importance.¹ However, this remains a formidable scientific challenge, as our fundamental understanding of electrochemical phenomena is still incomplete.^2,3,4 Historically, even well-established observations, such as the volcano plot, have taken decades to elucidate, and the intricacies of proton-coupled electron transfer continue to pose significant hurdles. With the urgent global mandate to achieve carbon neutrality by 2050, time has become a critical constraint. In this context, we present a suite of approaches aimed at accelerating the discovery of electrochemical materials and deepening our understanding of microscopic electrode processes at electrified solid–liquid interfaces. We argue that both avenues are indispensable, i.e. a rigorous grasp of electrochemical fundamentals is essential for the rational design of high-performance electrocatalysts using on-demand elements, while the development of such catalysts, in turn, enables further insights into the underlying interfacial processes.To this end, we have employed data-science methodologies to expedite the identification of promising electrocatalysts,^5,6 alongside state-of-the-art computational techniques to unravel the complex microscopic behaviours at electrified interfaces.^7,8 In this presentation, we will highlight several key findings from our research team that exemplify these synergistic approaches.

References from the Speaker's works

(1) W. Hoisang, K. Sakaushi, Current Opinion in Electrochemistry, 36, 101136, 2022.

(2) K. Sakaushi, Physical Chemistry Chemical Physics, 22, 11219-11243, 2020.

(3) K. Sakaushi, T. Kumeda, S. Hammes-Schiffer, M. M. Melander, O. Sugino, Physical Chemistry Chemical Physics, 22, 19401-19442, 2020.

(4) K. Sakaushi, Physical Chemistry Chemical Physics, 22, 11219-11243, 2020.

(5) K. Sakaushi, W. Hoisang, R. Tamura, ACS Central Science, 9, 2216–2224, 2023.

(6) M. Wang, A. Ishii, K. Sakaushi, ACS Energy Letters, 10, 22-29, 2025.

(7) T. Kumeda, L. Laverdure, K. Honkala, M. M. Melander, K. Sakaushi, Angewandte Chemie International Edition, 62, e202312841, 2023.

(8) M. Wang, K. Sakaushi, Angewandte Chemie International Edition, 64, e202419823, 2025.

Atmospheric-pressure helium plasma jets (APPJs), which are generated by the propagation of plasma bullets (or guided ionization waves), have been extensively studied since their first discovery by Professor Engemann in 2005 [1]. Conventionally, plasma bullets are typically launched from the nozzle of a tubular dielectric barrier discharge (DBD) device using helium gas.

Meanwhile, we discovered that when a pulsed high voltage is applied to one side of a glass plate, a plasma resembling an APPJ is generated from the opposite surface of the plate that is in contact with helium gas [2]. Time-resolved imaging using an ICCD camera revealed that this plasma is formed by the propagation of plasma bullets launched from the glass surface like a rocket. We have named this type of plasma bullet a surface-launched plasma bullet (SLPB). At present, we are conducting fundamental research both on the potential applications of SLPBs [2] and on the elucidation of the mechanisms and control methods involved in their generation.

We have identified that a key factor determining whether SLPBs can be generated is the rate of voltage change (dV/dt) of the applied waveform. When the dV/dt of the rectangular waveform generated by Si-IGBTs is reduced by an RC delay circuit, the optical emission intensity of the SLPB significantly decreases as shown in Fig. 1 [3]. This suggests that using a dV/dt that exceeds the performance limit of Si-IGBTs may enable the generation of more intense SLPBs. Therefore, we are advancing experimental studies using SiC-MOSFETs (NexFi Technology Inc.) [4], which can achieve higher dV/dt than Si-IGBTs. In this presentation, we will report the results of both experiments and numerical simulations.

Furthermore, we have also revealed that the spatial distribution of the voltage applied to one side of the dielectric is an important control parameter in the generation of SLPBs. When a large-area disk electrode is attached to the dielectric and a voltage is applied, the electric field tends to concentrate near the edge of the electrode, causing the emission points of the SLPBs to localize around the perimeter. As a result, a doughnut-shaped SLPB is formed rather than a sheet-shaped one. Through computer simulations, we have demonstrated that this doughnut-shaped pattern can be suppressed by designing the voltage distribution on the disk electrode to follow a Gaussian profile [5]. If SLPBs can be emitted in the form of a large-area sheet, it would become possible to efficiently generate large volumes of low-temperature plasma, which has been difficult to achieve under atmospheric pressure. We are currently conducting experimental studies to realize this configuration, and the latest results will also be presented.

Acknowledgments

This work has been supported by the MEXT/JSPS KAKENHI (23K25863 and 24K21542), and the Joint Usage / Research Program of Center for Low-Temperature Plasma Science, Nagoya University.

References

[1] Teschke, M. et al. IEEE Trans. Plasma Sci. 33, 310 (2005).

[2] Shirafuji, T. et al. 42nd Int. Symp. Dry Process, H-1 (2021).

[3] Matsumoto, A. et al. JSAP Autumn Meeting, 22p-A309-7 (2023).

[4] Shirafuji, T. et al. JSAP Spring Meeting, 22a-12G-5 (2024).

[5] Shirafuji, T. and J.-S. Oh, JVSS2023, 3Fa02 (2023).

In leading-edge etching processes, process conditions are managed by controlling and monitoring various parameters, and 'temperature' is one of the most important parameters. In particular, the temperature control of silicon (Si) wafers is affected by the etching rate and etching shape. However, in-situ measurement of Si wafer temperature during the actual process has not yet been achieved. The Si wafer temperature measurement with infrared thermometers has been considered problematic due to the low emissivity of the Si wafer and several measurement error factors. We have achieved Si wafer temperature measurement below 200 °C, which had been considered difficult with infrared thermometers, using the Method of Disturbance Temperature Cancellation by Dual sensing (DTCDs). Fig.1(a) shows the experimental setup for in-situ measurement of Si wafer temperature during plasma exposure using the DTCDs from a viewing port on the sidewall of an Inductively Coupled Plasma (ICP) dry-etching chamber. The infrared radiation from the Si wafer (red arrow), the infrared radiation from the side wall of the chamber reflected on the Si wafer surface (green arrow), and the infrared radiation from the electrostatic chuck (ESC) surface transmitted through the Si wafer (blue arrow) are detected by the infrared thermometer simultaneously. Since the emissivity of a typical Si wafer is less than 0.1, the infrared radiation from the sidewall and ESC temperatures accounts for 90% of the infrared radiation detected by the infrared thermometer and becomes major error factors. However, DTCDs can measure Si wafer temperature without the influence of the sidewall and ESC temperature by detecting three or more signals with different characteristics. Fig.1(b) shows the temperature measurement results when Ar plasma was applied for 3 minutes. An experiment was carried out by setting source power to 800, 1600 and 2400W. Before the plasma was applied, Si wafer temperature is almost stable because wafer was chucked by ESC. After plasma was applied, Si wafer temperature rosed rapidly. As the source power is increasing, wafer temperature change during plasma exposure became large. This suggests the possibility of detecting the wafer temperature change by using DTCDs. Details will be reported at the presentation including other results.

Mie-scattering ellipsometry is one of the useful methods for the measurement and analysis of fine particles growing in space, such as in plasmas. Its system has been developed and used to analyze the growth of carbon fine particles in plasmas [1-3]. In Mie-scattering ellipsometry, analogous to thin-film ellipsometry, the parameter angles Ψ and Δ are defined as the ratio of the complex scattering amplitude function of a parallel polarization component (Sp) in the scattering plane to that of a perpendicular component (Ss), where tanΨexp(jΔ) = Sp/Ss. For polydisperse fine particles, Ψ and Δ are calculated using the four Stokes parameters.

A new system for Mie scattering ellipsometry was developed, as shown in Fig. 1(a). It is a rotating-compensator type and applies a machine learning method for the fitting-calculation analysis of a trajectory in the Ψ-Δ coordinate to the measured data. We carried out Python programming to analyze of variations of Ψ and Δ during fine-particle growth , using a regression analysis method such as the gradient descent method.

Figure 1(b) shows an experimental result of the variation of Ψ and Δ during the growth of carbon fine particles in a methane plasma at 80 Pa. The nuclei of carbon fine particles were homogeneously generated in the plasma with an RF power of 30 W. After confirming the generation through faint laser scattering light, the RF power was decreased to 10 W. The results of simulated calculations assuming a lognormal size distribution of fine particles are shown in Fig. 1(c) for the geometric standard deviations, σ, of 1.15, 1.1, and 1.05. By comparing the trajectory of the experimental result in Fig. 1(b) with the simulated ones in Fig. 1(c), the carbon fine particles grew quasi-monodisperse, meaning σ is close to 1. On the other hand, when ultra-fine particles were injected before the growth of fine particles, that is, the carbon fine particles grew by heterogeneous nucleation, the trajectory changed from polydisperse to monodisperse. Figure 1(d) shows the result of analyzing the variation of Ψ and Δ during particle growth using regression analysis with the gradient descent method. The variation of the root mean square deviation (RMSD) between experimental and calculated Ψ and Δ values is shown with the geometric standard deviation, σ, of lognormal size distribution for the first and second loops of the experimental Ψ- Δ trajectory. The minimum RMSD values were obtained at 1.12 for σ in the first loop and 1.05 in the second loop. The results suggest that fine particles grew by the coating of carbon films on smaller ultra-fine particles.

References

[1] Y. Hayashi and K. Tachibana, Jpn. J. Appl. Phys. 33, L476 (1994).

[2] Y. Hayashi and K. Tachibana, Jpn. J. Appl. Phys. 33, 4208 (1994).

[3] Y. Hayashi, J. Vac Sci. Jpn 44, 617 (2001).

At national research institutes, as NIMS, it is possible to determine research themes with a long-term perspective in mind. Nevertheless, it is important to consider that the results of any research should eventually be returned to society. Even for competitive funds such as KAKENHI, I believe that the application of research outcomes and the section on future prospects have come to be regarded as important. I have been studying the reactions between solid surfaces and gas molecules from the viewpoint of surface science. Knowledge of vacuum technology was essential for my research.

After the terrorist attacks in the United States on September 11, 2001, research that could contribute to counter-terrorism measures received funding worldwide. We conducted fundamental research on gas sensing for the detection of poisonous gases and explosives at airports and large facilities, with a focus on detecting surface stress caused by adsorbed molecules. We developed gas sensing method with surface stress to detect gas molecules in air, directly[1]. That was the arrangement of DNA sensing in solution or smell sensing by olfactory cells via biological fluids [2]. Using vacuum equipment, we fabricated clean sensing films and performed quantitative detection using well-defined gases. Our research also expanded to fundamental studies, including the characterization of the sensing films’ physical properties and the analysis of gas diffusion rates within the films.[1, 3, 4]. At the point when we began detecting hydrogen gas, we switched our sensing film material from polymers to metal films[5, 6].

In hydrogen sensing using steel, issues arose due to differences in the steel film quality and low reproducibility caused by repeated sensing cycles. Therefore, I began research focusing on visualizing the locations where hydrogen exists within the metal films[7]. Utilizing Electron Stimulated Desorption (ESD), a commonly used technique in the field of surface science, I developed an Operando Hydrogen Microscope (OHM), capable of imaging the spatial distribution of hydrogen that had permeated metal membrane[8].Research on renewable energy was already increasing as a measure against global warming, but after the Great East Japan Earthquake in 2011, there was an urgent push to develop alternatives to fossil fuels and nuclear power. The development of peripheral materials for hydrogen utilization became essential for the advancement of hydrogen energy. Because hydrogen in metals is difficult to detect, our OHM technology garnered considerable attention from steel material manufacturers. In this presentation, I will report on the hydrogen permeation properties of several metal materials and discuss their interpretation[9, 10].

[1] S. Igarashi, A.N. Itakura, M. Toda, M. Kitajima, L. Chu, A.N. Chifen, R. Foerch, R. Berger, Sensors and Actuators B-Chem. 117 (2006) 43-49.

[2] J. Fritz, M.K. Baller, H.P. Lang, H. Rothuizen, P. Vettiger, E. Meyer, H.-J. Guntherodt, C. Gerber, J.K. Gimzewski, Science 288 (2000) 316-318.

[3] S. Igarashi, A.N. Itakura, M. Kitajima, Japanese Journal of Applied Physics 46 (2007) 7812-7815.

[4] M. Kitajima, T. Narushima, T. Kurashina, A.N. Itakura, S. Takami, A. Yamada, K. Teraishi, A. Miyamoto, Journal of Physics: Condensed Matter 25 (2013) 355007-355011.

[5] T. Yakabe, G. Imamura, G. Yoshikawa, M. Kitajima, A.N. Itakura, Journal of Physics Communigations 4 (2020) 025005.

[6] T. Yakabe, G. Imamura, G. Yoshikawa, N. Miyauchi, M. Kitajima, A.N. Itakura, Scientific Reports 11 (2021) 18836.

[7] A.N. Itakura, S. Suzuki, S. Takagi, Y. Murase, M. Tosa, Proceedings of the 11^th Nanomechanical Sensing WorkshopNMC 2014, Madrid, Spain, 2014.

[8] N. Miyauchi, K. Hirata, Y. Murase, H.A. Sakaue, T. Yakabe, A.N. Itakura, T. Gotoh, S. Takagi, Scripta Materialia 144 (2018) 69-73.

View PDF for the rest of the abstract.

0.2wt%Be-Cu (BeCu) exhibits superior properties compared to stainless steel (SUS), including 13 times higher thermal conductivity, less than one-seventh thermal radiation, and less than one-tenth outgassing [1]. However, due to its high material cost, its use has been limited to specific vacuum components. In previous studies, the authors applied BeCu to small vacuum chambers (W140 × D143.8 × H148mm) and demonstrated several advantages : 1) an outgassing rate approximately one-tenth that of SUS, 2) chamber temperature uniformity within ±1°C, and 3) stable reflectance in Al thick-film sputtering - highly sensitive to vacuum quality - without surface hazing observed in SUS chambers [2]. Despite these benefits, BeCu has been constrained by high processing costs due to the difficulty of welding. In this study, the authors investigated the fundamental characteristics of BeCu welding using a Blue+IR hybrid laser system [3]. Experiments included 1) butt welding of BeCu plates, 2) fabrication of a one-side rotating nipple (ICF70) that cannot be manufactured by conventional machining, and 3) welding of dissimilar welding between SUS and BeCu. Figure 1 shows photograph of the SUS piping / BeCu ICF70 flange fabricated by welding. This welding was performed by fixing the laser position and rotating the BeCu flange (IR : 3kW, Blue : 1kW). Figures 1(a) and (b) show the appearance after welding, indicating that good weld quality was achieved under the preliminary test conditions. At this stage, the leak rate was <10^-11 Pa·m³/sec. Afterward, bead machining and Ni plating were performed, followed by heat treatment at 400°C (Fig.1 (c)). The leak rate after all processing steps was confirmed to be <10^-11 Pa·m³/sec. Furthermore, the tensile strength of the SUS/BeCu dissimilar welded joint exceeded that of Cu alone, verifying the feasibility and reliability of the proposed welding technique. We will explain the results of the experiment 1) and 2) in our presentation.

These trials demonstrated that vacuum components previously considered unmanufacturable can be realized through this welding technology. Furthermore, tensile tests of the SUS/BeCu dissimilar welded joints showed strengths exceeding that of Cu itself, confirming the establishment and effectiveness of the welding technique.

References

[1] https://toel.co.jp

[2] T. Nakamura, S. Kishikawa, M. Kuroiwa and R. Kamei, Vacuum and Surface Science, 66, 52(2023)

[3] https://www.furukawa.co.jp/fiberlaser/product/lineup/hybrid_blue.html

Introduction

A Ti-Zr-V type non-evaporable getter (NEG) coating, which was developed at CERN, is a breakthrough vacuum technology because it makes the vacuum chamber wall a getter surface by a low activation temperature around 180-300 ℃ [1, 2]. The chamber itself can function as a vacuum pump by applying a NEG coating to the inner wall of the chamber.A build-up test, which is gas accumulation without evacuation by the vacuum pump was performed on the coated chamber.

Measurements

The build-up test was repeated 22 times, with one set consisting of vacuum evacuation, baking at 200°C for 24 hours (activation),build-up test (up to 96 hours),and exposure to atmospheric air. Figure 1(a) shows the configuration of the measuring equipment.After vacuum evacuation, activation was performed with the valve between chambers P1 (NEG coating) and P2 (exhaust chamber) open, and then the valve was closed and the build-up test was performed. After that, the variable leak valve was opened to allow air to enter and release chamber P1 to the atmosphere.

Fig. 1(a) Schematic diagram of the equipment used for the build-up test. TMP: turbomolecular pump; DSP: dry scroll pump; EXG: extractor gauge, and RGA: residual gas analyzer;

Fig. 1(b) Results of build-up test pressure

Experimental results

The NEG coating on the inner wall of the chamber allows the chamber itself to function as a vacuum pump.The chamber was removed after the 14th activation.After that, atmospheric release and activation were repeated up to 22 times, but the pressure reached 96 hours after the start of the build-up test did not exceed 3.0E-7Pa. In this way, the vacuum performance was evaluated by repeating atmospheric release and reactivation.

References

[1] C. Benvenuti, et al., VACUUM 50, 57 (2001).

[2] O. B. Malyshev, et al., Journal of Vacuum Science & Technology A 27, 321 (2009).

Turbomolecular pumps (TMPs) have long served as the main pump in fields where the precise vacuum conditions are crucial, such as semiconductor manufacturing and analytical instruments. One might think that the principle of its operation is easy from the combination of stator blades and rotor blades that rotate at nearly the speed of sound. However, the conventional explanations of the mechanisms of the internal flow of TMP [1, 2] are difficult to understand. From the viewpoint of the kinetic theory, we have to supply some explanations of the exchange of momentum from the circumferential direction into the axial direction, since the gas molecules mainly obey the diffuse reflection on the blades, where molecules obtain the circumferential momentum.

In the present study, we aim to clarify the internal gas transport mechanism of TMPs by performing numerical simulations based on a highly simplified model of the pump. We also evaluate the relationship between flow rate and pressure ratio. The left half of Fig. 1 is our model of TMP. This model is two-dimensional, consisting of a pair of rotor and stator blades, represented as arrays of inclined flat plates, along with gas reservoirs and baffles that block the circumferential (horizontal in the figure) motion of the gas. Previous studies on rarefied gas flow in such simplified 2D TMP models have mainly employed the direct simulation Monte Carlo (DSMC) method [3–4]. However, the time-average process, which is essential to the DSMC process, increases the computational cost to super-computing levels. As a result, the time evolution of the flow field remains unclear in previous studies. To address this, we employed a new high-speed deterministic simulation method for rarefied gases [5], which enabled us to visualize the time-dependent behavior of the flow field and to evaluate the relationship between pressure ratio and flow rate inside the TMP.

An example of the snapshot of the flow is the right half of Fig. 1. The detailed information enabled us to propose a more straightforward explanation of the operating mechanism of a TMP. Molecules entering the rotor region from the stator region tend to collide with the rotor blades on the left end in the figure, since the rotor moves to the right in Fig. 1. Conversely, molecules entering the stator region tend to collide with the stator blades on the right end in the figure, because the stator moves leftward relative to the rotor. This tendency is also evident in the pressure distribution shown in Fig. 1, where high pressure is observed on the left side of the rotor and the right side of the stator. Due to the inclination of the blade, the molecules in the high-pressure regions tend to reflect downward, and those in the low-pressure regions upward. As a result, a net downward flow is generated.

The above simple mechanism suggests the possibilities of a novel type of TMP, where the rotors do not follow the wing-like shape. Our numerical tests demonstrate that moving plates with holes can serve as the rotor. The simple rotor structure may help to achieve higher rotor speeds and, consequently, greater throughput. Eliminating the tilt of the rotor blades would allow the use of lighter materials, making it possible to achieve higher rotational speeds and, consequently, greater throughput. The effects of blade angle, blade height, rotor speed, and the Knudsen number, etc., on the pump performance will be presented at the meeting.

References

[1]W. Becker, Vacuum, 16, 625–632 (1966).

[2]H. Kumagai and G. Tominaga, Vacuum Science and Engineering (1970) (in Japanese).

[3] G. A. Bird, Molecular Gas Dynamics and the Direct Simulation of Gas Flows, ser. The Oxford Engineering Science Series, 42, (1994).

[4] N. Y. Bykov and V. V. Zakharov, Physics of Fluids, 34, 057106 (2022).

View PDF for the rest of the abstract.

The Crookes radiometer is an experimental apparatus consisting of a glass container enclosing low-pressure gas and a vane wheel with one side of the vanes painted black. When exposed to light, a force called radiometric force arises, causing the vane wheel to rotate. Many scientists have believed that the temperature difference between the black surface, which absorbs light, and the white surface, which reflects light, causes this force. However, recent studies have reported cases where radiometric force occurs even when there is no temperature difference between the front and back surfaces of the vanes. For example, curved vanes are observed to generate radiometric force and cause rotation. Additionally, numerical calculations have shown that radiometric force can arise due to differences in accommodation coefficients even on isothermal bodies. This research experimentally investigates radiometric force caused by differences in accommodation coefficients, which had previously been demonstrated only numerically. We used thin glass as the vane material, with black spray paint applied to only one surface. This asymmetric surface treatment results in a difference in accommodation coefficients between the front and back of the vanes. Due to the extreme thinness of the vanes, no significant temperature difference arises between the two surfaces. Thermocouple measurements confirmed that the temperature difference was below detectable levels. In contrast, conventional mica vanes showed about 10 K temperature difference, consistent with previous studies. We fabricated several uniform-temperature radiometers using these glass vanes, which rotated under illumination. As a control, we also prepared radiometers with vanes painted black on both sides. These showed much weaker rotation. Furthermore, we examined how rotational speed depends on internal gas pressure and proximity to the container wall. The rotation speed peaked at 1–5 Pa, reaching up to 400 rpm. Rotation was stronger when the container was smaller and the vanes were closer to the wall. These results suggest that surface treatment differences alone can induce gas motion and radiometric force, even without a temperature gradient.

References

[1] W. Crookes, On attraction and repulsion resulting from radiation, Phil. Trans. R. Soc. London 164, 501–527 (1874).

[2] O. Reynolds, On the forces caused by the communication of heat between a surface and a gas; and on a new photometer, Phil. Trans. R. Soc. London 166, 725–735 (1876).

[3] J. C. Maxwell, On stresses in rarefied gases arising from inequalities of temperature, Phil. Trans. R. Soc. London 170, 231–256 (1879).

[4] G. H. Chen et al., Optical manipulation of macroscopic curved objects, Front. Phys. 20(1), 012201 (2025).

[5] K. Denpoh, Another possible origin of temperature and pressure gradients across vane in the Crookes radiometer, J. Vac. Soc. Jpn. 60(12), 471–474 (2017).

[6] W. Gerlach and W. Schlitz, Untersuchungen an Radiometern. IV. Experimentelle Beitrage zur Prufung der Theorien des gewohnlichen Einplatten-Radiometers, Z. Phys. 80, 117–133 (1933).

With the development of the semiconductor industry and the transition toward a hydrogen-based energy society, the demand for vacuum measurement has been rapidly increasing. Against this backdrop, the Spinning Rotor Gauge (SRG) has been attracting significant attention. The SRG is widely recognized as one of the most accurate vacuum gauges for the pressure range from 0.1 mPa to 1 Pa. SRG has long been used as a reference standard in the field of metrology.

National Metrology Institutes (NMIs) around the world maintain several vacuum standards based on physical principles-such as static expansion systems, optical pressure standards, and orifice flow methods-for the calibration of vacuum gauges including SRGs, diaphragm gauges, and ionization gauges. For example, Japan's static expansion system is capable of calibrating an SRG using the static expansion system with a relative uncertainty of 0.28% (k=2). Even higher accuracy is expected when combined with an optical pressure standard.

To verify the consistency of vacuum standards in each country, NMIs regularly conduct international comparisons of vacuum standards. Since direct comparison of the standards themselves is difficult, a common approach is to transport a vacuum gauge, such as an SRG, and calibrate it against the standards in each country. In this process, the reproducibility of the SRG becomes a major issue. Although SRGs are highly precise instruments, their readings can change by approximately 1% during transportation, which limits the achievable precision in international comparisons.

Therefore, to improve the accuracy of future international comparisons, it is essential to carefully select SRGs with excellent reproducibility and to develop a deep understanding of calibration conditions. This study experimentally investigated the following two aspects:

[1: different SRGs] SRGs had previously only been commercially available from MKS Instruments in the United States, but in 2023, a new model became available from PHI. While both SRGs operate on the same basic principle-measuring pressure via the deceleration rate (DCR) of a freely rotating sphere in vacuum-they differ significantly in the strength of the magnetic field used. The MKS model uses a magnetic field of 45 mT, whereas the PHI model uses 90 mT. The stronger magnetic field in the PHI model may enable more stable retention of the rotor sphere, potentially resulting in improved long-term reproducibility and zero-point stability. To determine which SRG model is more suitable for metrological applications, two SRGs from MKS and one from PHI were calibrated while varying several conditions, including sphere rotation frequency, rotor units, and flange mounting angle.

[2: calibration methods] In 2022, the ISO document titled “Vacuum technology - Vacuum gauges - Specifications, calibration and measurement uncertainties for spinning rotor gauges” was published. This document outlines two types of calibration methods for SRGs:

A simple and user-friendly procedure in which the NMI calibrates the SRG at a pressure near 20 mPa and provides the calibration parameter to the user. The user then inputs the parameter into the SRG controller, allowing the indicated value to represent the actual pressure directly.

A more advanced procedure requiring additional steps. The NMI calibrates the SRG across a range of 80 mPa to 2 Pa and provides multiple calibration parameters. The user inputs the reported parameter into the controller and then calculates the actual pressure using a prescribed equation.

The key difference between the two methods lies in the approach to correcting the influence of gas viscosity-either by using the internal correction function of the SRG controller (Method A), or by applying the user's own measurement data (Method B).

View PDF for the rest of the abstract.

私たちは、2010年6月に日本で初めて計量法トレーサビリティ制度（JCSS）の真空計校正事業者として登録および国際MRA 認定を受けて校正事業を開始した。2018年6月には、標準リークの校正事業も開始した。JCSSは、計量法関係法規及び校正機関の能力に対する要求事項を規定した国際規格(ISO/IEC 17025)に適合した校正事業者登録制度である。JCSS登録事業者は発行する校正証明書に特別な記章を記載することが許され、その記章がある校正証明書は国家標準にトレーサブルであることを証明される。

　また国際MRAは、複数の国や地域での認証や校正の結果を相互に認め合う枠組みであり、JCSSは国際MRAに加盟している。国際MRA認定を得たJCSS校正事業者は校正証明書に、MRA付きJCSS認定シンボルの入った校正証明書を発行することができる。その校正証明書は、MRA加盟国のどこでも受入れられる。

　真空計・標準リークのユーザはJCSSの記章あるいは認定シンボルの入った校正証明書を用いることで、測定結果の信頼性を容易に確認することできる。

　私たちがJCSSに登録されている校正範囲は、真空計が1×10^-4～1.33×10⁵ Paで、リーク計が1.0×10^-10～1.0×10^-6 Pa m³/s である。

　真空計の校正は1×10^-4～1 Paと1×10⁴～1.33×10⁵ Paが国家計量標準にトレーサブルな真空計との比較校正、1～1×10⁴ Paの間は膨張法をもちいている。

　膨張法は、バルブ等で連結された二つ(あるいは複数)の容器を用意し所定の圧力まで気体を導入し、バルブを閉じ、片側だけ排気した後バルブを開放することで、気体をためていた容器の体積が増えて気体が膨張し、膨張比の分だけ圧力を下げるという手法である。

　最初の圧力を1×10⁴～1.33×10⁵ Paにして、1 Pa以下になるまで膨張を繰り返し、それぞれ圧力を国家計量標準にトレーサブルな真空計で測定する。すると、最初と最後の圧力差と何回膨張させたかで過程の圧力がわかる。以上の手続きを踏むことで、1～1×10⁴ Paの間のトレーサビリティを担保している。

　リーク計の校正は1.0×10^-8～1.0×10^-6 Pa m³/sが真空計、オリフィスおよび標準コンダクタンスエレメント(SCE)を用いた組み立て校正、1.0×10^-10～9.9×10^-9 Pa m³/sが四重極型質量分析計(QMS)とSCEを用いた組み立て比較校正法をもちいている。

　リーク計の組み立て校正は、オリフィスのコンダクタンス、その上流と下流の圧力からリーク量を求める。コンダクタンスは開口径と厚さから求められ、オリフィスの上流と下流の圧力は真空計で測定している。しかしながら、1.0×10^-8～1.0×10^-6 Pa m³/sを導入した時の圧力の変化は小さく1×10^-4 Pa以下の圧力測定が必要になるがトレーサビリティの担保ができない。そこで1×10^-4 Pa付近で、真空計の校正を行ったのち、開放型標準リークの一種であるSCEを使って1×10^-4 Pa以下の圧力でも真空計の感度が変わらないことを確認することで、1.0×10^-8～1.0×10^-6 Pa m³/sのトレーサビリティを担保している。SCEは、10⁴ Pa以下の圧力なら一定のコンダクタンスを持つ機器であり。SCEを介して流れる流量は、SCEのコンダクタンスとその上流の圧力の積で求めることができる。

　組み立て比較校正法は、被校正器である標準リークとSECを介して流れる流量を比較することで流量を求める。組み立て校正の結果をもとにSCEのコンダクタンスを求め、SCE上流の圧力をトレーサブルな真空計で測定することで、既知の流量を作り出せる。その流量と、被校正器の流量を導入した時の装置分圧の変化をそれぞれQMSで測定、比較することで1.0×10^-10～9.9×10^-9 Pa m³/sのトレーサビリティを担保している。

　また、組み立て校正、組み立て比較校正をした標準リークをもとに市販のHe Leak Detectorを用いた比較校正手法を確立することで、組立校正法より安価で納期も短いJCSS校正をユーザに提供している。

　2010年6月の認定から今日まで、校正依頼件数は増加し続けている。特に2021年度に校正件数が増加しており、その多くが自動車業界の依頼である。これは自動車産業に特化した品質マネジメントが、2018年9月にISO/IEC16849からIATF16949に移行し、この移行に伴いISO/IEC17025の認定を受けた事業者の校正証明書の要求が厳しくなったことが要因の一つだと予想される。それ以外には航空宇宙、原子力、医療、そして真空業界等の依頼が来ている。それらも堅調に推移している。

このように依頼元は多岐にわたり、多くの業種でJCSSが認知されつつある。

　私たちの役割は国際規格(ISO/IEC 17025)に適合した校正に基づく校正証明書を普及することである。この役割は日本の真空技術の信頼性、並びに真空ユーザの利便性を高め、真空業界の発展につながるだけでなく、産業全体の根幹を支える大切なものだと考えている。

　そのためにも、日々の業務だけでなく、弊社ホームページでの広報、コンポーネントメンテナンス品返却時の案内配布など地道な活動を続けている。

Two-dimensional (2D) layered semiconductors are promising for next-generation nano-optoelectronic applications, including low-power computation, high-density memory, high-efficiency light emission and detection, and high-efficiency power generation. III–VI layered semiconductors, such as Ga_xS_y and In_xSe_y, offer unique properties: a broad range of bandgaps from the infrared to ultraviolet regions with thickness-dependent bandgap tunability, high carrier mobility, and strong Rashba spin–orbit coupling. They have various crystal phases with distinct properties, including ferroelectric phases that further enhance their potential for multifunctional devices. Controlling the crystal phase in thin-film growth is therefore critical for the functional integration of 2D electronic and photonic devices. In this presentation, we introduce metal organic chemical vapor deposition (MOCVD) growth technologies for III–VI layered semiconductors and demonstrate the phase engineering strategies [1, 2].

We first present MOCVD growth diagrams for Ga_xS_y. Ga₂S₃ phase forms at higher growth temperatures while GaS phase forms at lower temperatures. This trend matches the bulk phase diagram, indicating thermodynamic stability mainly governs the crystal phase formation. In addition, the crystal phase depends on the VI/III gas source ratios: Ga₂S₃ is obtained at higher VI/III ratios, while GaS forms at lower ratios. High VI/III ratios in gas phase results in S-rich surface stoichiometry, favoring S-rich phase Ga₂S₃ formation. Since surface stoichiometry is influenced by precursor decomposition as well as atom adsorption and desorption, surface kinetic also play an important role in determining the crystal phase in MOCVD growth. A similar growth phase diagram was obtained for In_xSe_y compounds.

The crystal morphology of GaS also depends on VI/III ratio. S-rich conditions yield 2D triangular islands, whereas Ga-rich conditions produce one-dimensional (1D) nanobelts. Under Ga-rich conditions, Ga clusters form during the initial growth stage, catalyzing the S precursor decomposition and leading to GaS nanobelt formation via self-catalyzed vapor–liquid–solid (VLS) growth. VLS-grown GaS nanobelts exhibit high optical quality comparable to exfoliated flakes, with similar photoluminescence intensity and linewidth. Photodetectors based on GaS nanobelts show higher photocurrent than exfoliated flakes, with superior responsivity attributed to efficient edge contacts. Furthermore, MOCVD enables precise bandgap engineering through alloying. For example, GaS_xSe_1-x ternary alloy nanobelts have been synthesized, enabling tailoring of optoelectronic properties.

In summary, the MOCVD growth phase diagrams for III–VI layered semiconductors provide practical guidelines for controlling crystal phase and related functionalities. We demonstrated, for the first time, self-catalyzed VLS growth of GaS nanobelts with excellent optoelectronic performance, underscoring their potential for future bottom-up integration in nano-optoelectronic applications.

References

[1] Y. Endo, Y. Sekine, and Y. Taniyasu, Appl. Phys. Lett. 126, 043105 (2025).

[2] Y. Endo, Y. Sekine, and Y. Taniyasu, Journal of Crystal Growth 631, 127612 (2024).

For Ga₂O₃, there are six crystal polymorphs. Among them, β-Ga₂O₃ has received the most attention due to its highest thermal stability. Recently, the orthorhombic κ-Ga₂O₃ has gained attention due to its large spontaneous polarization and its ferroelectricity. For κ-Ga₂O₃, Si is usually used as the dopant to control the electrical properties. There are three inequivalent Ga atomic sites as the dopant sites in κ-Ga₂O₃; octahedral (Octa), pentahedral (Penta), and tetrahedral (Tetra). Therefore, to control the electrical properties, the atomic site occupancy of Si dopant in Si-doped k-Ga₂O₃ should be clarified. In the present study, we investigated the atomic site occupancy of the Si dopants for Si-doped κ-Ga₂O₃ using photoelectron holography (PEH).

The Si-doped κ-Ga₂O₃ epitaxial layers were grown on a c-plane sapphire substrates prepared by the MOVPE method. The PEH measurements were performed at the BL25SU beamline of SPring-8.

Figure 1(a) shows the Ga 3p and Si 2p PES spectrum for the Si-doped κ-Ga₂O₃(001) measured at an incident photon energy of 911 eV. The corresponding PEH for Si 2p are shown in Fig. 1(b). Figure 1(c) shows the experimental and the simulated Si 2p PEHs for the Si-doped κ-Ga₂O₃(001). By comparing the experimental and the simulated PEHs, the ratios for the Tetra, Penta, and Octa Si_Ga sites are estimated to be 51.0%, 35.2%, and 13.8%, respectively.[1]

[1]Y. Tsai et al., Nano Letters 24, 3978 (2024).

Introduction

Multiferroic materials, which exhibit both ferroelectricity and magnetic ordering, are expected to be used in magnetic sensors and memories as ultra energy-saving materials[1]. BiFeO₃, a leading room-temperature multiferroic material, has an R3c structure and exhibits complex ferroelectric switching[2]. To simplify the switching process, Ba-doping and (Ba, F) co-doping have been attempted to create a simpler P4mm structure. Bi_1-xBaxFeO_3-x/2 and Bi_1-xBa_xFeO_3-xF_x (x = 0.2, 0.3) were fabricated in thin film form and small magnetization at 300 K was observed[3]. It was also found that Bi_1-xBa_xFeO_3-xF_x exhibited ferroelectricity at 300 K, whereas Bi_1-xBa_xFeO_3-x/2 did not exhibit that[3]. However, further investigations of the electronic states are needed to determine the effects of fluorine on the magnetic sites in the films. In this study, we performed resonant X-ray photoemission spectroscopy (RPES) and X-ray magnetic circular dichroism (XMCD) measurements on the magnetic Fe ions in Bi_0.8Ba_0.2FeO_2.9 and Bi_0.8Ba_0.2FeO_2.8F_0.2 thin films.

Experimental

A perovskite-type Bi_0.8Ba_0.2FeO_2.9 thin film was prepared by pulsed laser deposition as an epitaxial film on a Nb0.5% doped SrTiO₃ (100) substrate. A perovskite-type Bi_0.8Ba_0.2FeO_2.8F_0.2 thin film was obtained by topochemical fluorination of the Bi_0.8Ba_0.2FeO_2.9 film (heating with polyvinylidene difluoride at 200 °C for 12 h in Ar gas flow). The crystal structure of the films was confirmed by X-ray diffraction (XRD) measurements, and the iron valence was determined by X-ray absorption spectroscopy (XAS). For RPES, valence band XPS spectra were obtained in an incident energy range of 704–714 eV. XMCD was performed in the out-of-plane and in-plane directions.

Results

In RPES, the most enhanced spectra were obtained for both films at an incident energy of 709 eV. At an incident energy of 704 eV, where the iron contribution is small, the spectra show a different valence band shape, similar to the results shown in the valence band spectra observed at photon energy of 1200 eV[3]. Conversely, the spectra nearly overlapped at energies where the Fe 3d contribution was significant, suggesting no difference in magnetic site states between Bi_0.8Ba_0.2FeO_2.9 and Bi_0.8Ba_0.2FeO_2.8F_0.2.

The figure shows the polarization-dependent XAS and XMCD spectra of the Bi_0.8Ba_0.2FeO_2.9 precursor and Bi_0.8Ba_0.2FeO_2.8F_0.2 films (out-of-plane) around the Fe L_2,3-edges obtained at 300 K. Here, μ₊ and μ_- denote the absorption coefficients for photon helicity parallel and antiparallel to the Fe 3d majority-spin direction, respectively. The spectra were normalized by the intensities of the pre- and post-edge regions. A XMCD signal was detected at the Fe L_2,3-edges in each spectrum in the figure, indicating that these films are ferromagnetic at 300 K. A comparison with the XMCD spectra reported in Ref.

View PDF for the rest of the abstract.