1. Introduction

In recent years, laser-assisted surface modification technologies with high precision and efficiency are widely used in the production of alloy parts. This is because the heat input is small and only the vicinity of the laser irradiated area can be modified locally with minimal damage or deformation [1]. Especially in the case of steel materials widely used for sliding components such as bearings, high-precision heat treatment without any removal is required. To improving the hardness of steel materials, control of carbon content and appropriate temperature control are effective.

In this presentation, a novel method of surface modification for SCM440 by carbonization using short pulse laser irradiation in the atmosphere of PAO4 lubricating oil is proposed. When the pulse laser beam is focused on target high-temperature, high-pressure condition will be generated in the irradiated area and the lubricating oil will be ablated into particles such as atoms, molecules, ions, or radicals [2]. Then ablated particles are reacted with heated and form carbide on surface.

2. Experiment and result

The 900 ps laser pulses at 1064 nm wavelength were delivered by a microchip laser with the repetition rate of 20 Hz. Laser pulses were focused to SCM440 surface by a plano-convex lens with a focal length of 60 mm. To ensure the laser fluence is below the ablation threshold, laser pulses with the pulse energy of 0.5 mJ was irradiated onto the SCM440 plate with a certain defocus distance at normal incidence. The beam diameter on the SCM440 plate was set as 100 μm. The SCM440 plates were fixed to a 2-axis stage and scanned in a reciprocating motion to modify 10mm square area. The effect irradiated pulse number N was set as 1, 2, 4, 8, 16 and 32 by controlling the scanning speed of laser. The hardness of SCM440 surface after the laser irradiation, was evaluated by nano-indentation.

Figure 1(a) shows the hardness of each SCM440 surface before and after the laser irradiation under conditions of different effective irradiated pulse number. The hardness of modified surface increased by approximately 7~8 Gpa compared to before irradiation.

The tribological properties of the irradiated surfaces are investigated with ball-on-disk reciprocating friction tests in PAO4 oil. Figure 1(b) shows transition of friction coefficient. In case of N=1, stable low friction could keep longer than unirradiated surface. However, surface of N=16, 32 have shorter lifetime. It is known that long heating times and high temperatures in the heating cause embrittlement. In this case, the input heat propagates over wider and reheat the previously irradiated area. The reheat causes the embrittlement of the modified layer.

The modified layer was observed by TEM. A thin flake sample for TEM was prepared using FIB. Before using FIB, SCM440 surface is coated by Au layer by vacuum deposition method. Figure 1(c) is a cross-sectional image of a TEM sample irradiated with N=32. This shows the formation of a modified layer with a thickness of about 200 nm on the surface. Figure 1(d) is the diffraction pattern of region (1) of Fig. 1(c). This shows the existence of amorphous Fe5C2 and Fe3C. The localized superheated area on the sample surface, combined with the rapid cooling facilitated by the oil atmosphere, led to the formation of an amorphous state after irradiation.

3. Conclusion

Based on these results, the effectiveness of this method as a localized surface hardening treatment for steel materials using carbonization phenomena has been demonstrated. Furthermore, by using this method, it will become possible to irradiate the material in the environment of machine tools, even with lubricating oil adhered after machining processes.

View PDF for the rest of the abstract.

The electron cloud effect (ECE) has posed serious challenges in recent high-intensity proton and positron rings [1]. One of the applicable solutions is preparing a surface with a low secondary electron yield (SEY) on the inner wall of beam pipes. In this study, we used a commercial method called “thermal spray”, where copper powder was melted and sprayed onto an aluminum substrate to create a rough surface, and was investigated for the first time as a method for producing a low SEY surface [2]. Figure 1(a) is a schematic of the thermal spraying used in this study. After an electron exposure of ≈ 1 ×10^-1 C/mm² at an energy of 350 eV, the lowest δ_max (the maximum SEY within scanning) of the copper thermal spray (T.S.) coating reached ≈ 0.7.

The E_max (the incident electron energy corresponding to δ_max) of T.S. coating was found to be inversely related to the surface temperature during spraying. The roughness parameters and surface composition were measured to clarify the key factors affecting SEY. In addition, to check the applicability of T.S. coating in accelerators, its outgassing rate, adhesive strength, impedance and dust generation rate were measured as a reference.

Finally, an aluminum beam pipe with a T.S. coating was produced and installed in the positron ring of SuperKEKB to measure the electron density around the beam. The measured electron densities were compared with those obtained from other beam pipes with different inner surfaces, and also investigated using a simulation code.

The results show that the outgassing rate and adhesive strength of T.S. coating were acceptable. However, the amount of dust and impedance were not inconsiderable. The measured electron densities of the T.S.-coated beam pipe was comparable with that of the TiN-coated beam pipe even under the influence of the uncoated aluminum screen, as shown in Fig. 1(b-c). Therefore, the T.S. coating can be considered as a candidate technology for reducing ECE, while there are still room for improvement. This study can provide a new and useful information for researchers in this field in developing a low-SEY coating on beam pipes [3].

References:

[1] G. Rumolo and G. Iadarola, Proc. CAS-CERN Accelerator School: Intensity Limitations in Particle Beams, 411 (2015).

[2] M. Yao et al, Vacuum, 207, 111619 (2023).

[3] M. Yao, PhD thesis, Accel. Sci. Dept., SOKENDAI (2023).

Many of the vacuum components in accelerator-based synchrotron light sources are exposed to synchrotron radiation (SR) during operation. Hence, reducing photon-stimulated desorption (PSD) from these components could effectively shorten the commissioning time and contribute to the stable operation of the light source. One approach to limiting the desorption of gases is to cover the surfaces of these components with low-PSD materials. TiZrV alloy is a well-known non-evaporable getter (NEG) coating material and also exhibit lower PSD yields compared with Cu, Al. In a previous study, we newly found that Pd/TiZrV (Pd covered TiZrV) films further reduce the PSD yields compared to the TiZrV films. This finding indicated the possibility of applying Pd as low PSD materials. Another advantage of Pd is low resistivity of 10.9 μW・cm which is much lower than that of Ti, Zr and V metal. In the present study, dense Pd films were prepared on the inner wall of the Cu duct using magnetron sputtering. The PSD analysis and resistivity measurement were carried out. The effects of the photon dose on the desorption yields obtained from the Pd and TiZrV films are summarized in Figs. 5 (a) and (b). Compared with the TiZrV film, the Pd film showed significantly lower initial yields: factor 1/10 for H₂, 1/3 for CH₄ and CO, 1/5 for CO₂. In all cases, the PSD yields gradually decreased over time. After a photon dose of 5 x 10²² photons/m, the yields of CH₄, CO and CO₂ generated by the Pd were still lower than those of the TiZrV. Following irradiation with a photon dose of 5 x 10²² photons/m, the Pd-coated tube was exposed to air then evacuated and heated, after which the PSD yield was measured. The initial H₂, CO and CO₂ yields from this trial were similar to the final PSD yields shown in Fig. 1. It was indicated that the air exposure had little effect on the PSD values. Resistivity data were acquired at ambient temperature using the standard four-probe technique with the applied current parallel to the film surface. The resistivities of the Pd films fabricated under Kr pressures of 0.9 and 0.4 Pa were determined to be 30 and 18 μW・cm, respectively. The latter value was approximately one order of magnitude lower than that of a TiZrV film (175 μW・cm).

INTRODUCTION

Recent years, a portable type sniffer leak detector (LD) has been used for searching leaks of refrigerant gases from air-coordinators to prevent the global warming or hydrogen from fuel cell vehicles. In case of the sniffer leak test, there are some factors to perturb the reliable leak measurement. One factor is a scan speed of the probe of the LD. The scan speed is standardized for the performance test of the leak detector in EN 14624 [1]. According to the previous work, the signal obtained by the LD was decreased with both the increase of the scan speed of the LD and the increase of the distance between the sniffer probe and the standard leak (a small gas flow generator) as a leak [2]. Although a wind seems to be a factor to perturb the leak measurement, its effect has not been well studied due to the difficulty in making a steady flow wind. In this study, the wind effect for the sniffing leak test has been investigated using a wind tunnel.

EXPERIMENTAL

A wind tunnel was an acrylic resin tube, whose inner diameter was 115 mm (Fig. a). The air was introduced through a rectifier (about 300 tubes, inner diameter: 6 mm, length: about 20 mm) at the entrance, a test space, a second rectifier (same as the entrance one), and then sucked by an axial fan (diameter: 120 mm, DC 24 V). The wind speed was changed from 0.4 m/s to 4.0 m/s by changing the DC voltage supplied to the fan. The inner distribution of the wind speed was measured by using a hot wire anemometer (accuracy: 0.1 m/s) with 5 mm step. The wind speed distribution at the DC voltage od 23.9 V is shown in Fig. b. Around the center plus minus 15 mm, the wind speed was almost constant for all tested wind speed. Thus, the test was done at that area. Since an evaluated Reynolds number was 2400 at the wind speed of 0.3 m/s, the gas flow inside the tunnel could be the turbulence.

A commercially available sniffer LD with a built-in pump for HFC-134a was used for the test. A standard leak was used instead of a real leak. Prior to the tests, its leak rate was calibrated to be 5.8 g/year by the pressure rise method flow meter [3]. The inner diameter of the sniffing probe and the standard leak was 8 mm and 6 mm, respectively. The distance, L, between the sniffing probe and the leak was changed manually from 0 mm to 5 mm. During the test, the LD was used in the gas concentration mode. Thus, the detector measures the HFC-134a concentration in the sniffed air. The detector output was recorded by a computer via a digital multi meter.

RESULTS

The LD output was plotted as a function of the wind speed in Fig. c. The distance L was 0 mm, 1 mm, and 2 mm. When the L is 0 mm, both ends of the sniffer probe and the standard leak were faced each other but not connected. For all tested L, the LD output was once increased from 0 m/s to 0.5 m/s, then gradually decreased up to the wind speed of 4.0 m/s. Although the source of the initial increase with an increase of the wind speed is unknow at this stage (may be the turbulence inside the pipe), the LD output was strongly perturbed by the wind at the leak measuring place even if the wind power was in “Light air” (<1.5 m/s) of the Beaufort scale (wind power). For L = 0 case, the LD output was gradually decreased to almost zero at the wind speed of 4.0 m/s.

Reference:

[1] EN 14624:2012 “Performance of portable locating leak detectors and of fixed gas detectors for all refrigerants”

[2] K. Arai et al., Annual meeting of JVSS 2017, 3Ca11

[3] K. Arai et al., Metrologia 51 (2014) 522.

Introduction

In recent years, analysis of light elements contained in materials such as batteries and catalysts has attracted attention. Soft X-ray absorption spectroscopy (XAS) is useful technique to analyze the light elements. In many cases of multi-element materials, however, it may not be possible to carry out XAS experiments for all the absorption edge in a beamline, since the coverage range of X-ray energy is limited in the beamline. It was difficult to keep samples across the beamline without atmospheric exposure. This is because the specifications of sample holders are different depending on the beamline. On the other hand, many materials such as batteries and catalysts are contaminated with oxygen, carbon dioxide and water when exposed to the atmosphere. Therefore, we developed a sample transfer vessel that can transport the sample from the glove box to the analyzer without exposing it to the atmosphere [1, 2]. Furthermore, in order to perform more precise analysis, we developed a sample transfer vessel with a small ion pump [3]. In this study, we have developed a transfer vessel that can measure the soft XAS across the beamline without exposing the sample to the atmosphere, based on the apparatus that we have developed.

Experimental

After heat treatment, the sample was attached to the transfer vessel in a glove box under an argon atmosphere and transported to the analyzer. Near edge X-ray absorption fine structure (NEXAFS) spectra of the sample using both total electron yield (TEY) and partial fluorescence yield (PFY) modes were measured at the beamline 2A of the UVSOR in the Institute of Molecular Science and at the beamline 12 of the SAGA-LS. For TEY, the drain current of the sample was measured. For PFY, fluorescence X-rays were collected using an energy dispersible silicon drift detector (SDD). All experiments were performed at room temperature.

Results and Discussion

Fig. 1 shows a photograph of the developed transfer vessel. This vessel consists of coaxial type linear motion feedthrough, vacuum vessel and sample holder. The sample is fixed to the holder using carbon tape. The sample current is measured using the Bayonet Neill-Concelman (BNC) connector on the upper part of the vessel. Since this vessel can be installed in a conflat flange with an outer diameter of 70 mm (ICF70), it can be connected if there is a free ICF70 port in the beamline or analyzer. We measured the Na K-edge NEXAFS spectra of NaCl powder obtained from TEY at SAGA-LS, and the Cl K-edge NEXAFS spectra at UVSOR. The Na K-edge NEXAFS spectrum is in good agreement with the theoretical calculation results reported by McIntrosh et al. [4], and the Cl K-edge NEXAFS spectrum is in good agreement with those of Orlando et al. [5]. From the above, we were able to measure two absorption edge energy spectra at the same point on the same sample without exposure to the atmosphere, using beamlines in different facilities. We also measured MgO using the same system, and obtained a spectrum without surface contamination. By using the new developed transfer vessel, the sample can be analyzed accurately with high precision.

References

[1] E. Kobayashi, J. Meikaku, T. Okajima, and H. Setoyama, Japanese Patent No. 5234994.

[2] E. Kobayashi, J. Meikaku, H. Setoyama, T. Okajima, J. Surf. Anal., 19, 2 (2012).

[3] E. Kobayashi, S. Tanaka, T. Okajima. J. Vac. Soc. Jpn. 59, 192 (2016).

[4] G. J. Mclntosh and A. Chan, Phys. Chem. Chem. Phys., 20, 24033 (2018).

[5] F. Orlando et al., Top. Catal., 59, 591 (2016).

A dry screw pump operates with clearances between the rotor and its follower, as well as the housing during its operation. To develop an analytical model for dry pumps, it is essential to derive an equation for the conductance of these clearances, incorporating the dimensions of the duct, entrance pressure, and exit pressure, which can be adaptable for different flow regimes. We assume that if the clearances are much less than the diameter of the rotor, the conductance between the rotor and the housing could be approximated by that of a rectangular channel. Studies on flow through rectangular channels have been extensively conducted due to the necessity of fluid applications, but most of these studies have employed numerical methods. There are only a few reports that have measured the conductance of a rectangular channel through flow rate experiments. O'Hanlon reviewed this data and proposed a modified equation in which the conductance of the duct region includes the dimensions of the channel's cross-section. However, the data evaluated in the study is limited. Therefore, we conducted flow rate measurements through rectangular channels and calculated their conductance to evaluate the given model. An overview and external view of the experimental setup is shown in Figure 1. The channel dimensions were a combination of the following: the short side (a) of 0.15, 0.25, and 0.35 mm, the long side (b) of 30 mm, and channel length (L) of 10 and 20 mm. The channels were evacuated to 1500 to 0.5 Pa using a dry vacuum pump. Pressure measurements were made at the inlet and outlet of the channels using diaphragm gauges. First, we investigated the effects of factors a and L on the experimental values of conductance. The conductance was proportional to the square of a and inversely proportional to L in the molecular flow regime. However, in Kn < 0.03 (Knudsen number based on a) regime, these relationships deviated. Next, we compared the conductance of short rectangular channels proposed by Sasaki et al. ⁽¹⁾, Kieser et al. ⁽²⁾ and O'Hanlon ⁽³⁾ with our experimental results. O'Hanlon's model showed excellent agreement within 12% for all channels in Kn < 0.01. However, discrepancies between O'Hanlon's model and our experimental data were noticeable in Kn > 0.01. Therefore, we investigated theoretical approximations to better fit our experimental data in the low-pressure regime and dependence on channel dimensions. Further details of these investigations will be presented at the conference.

References

(1) S. Sasaki and S. Yasunaga, J. Vac. Soc. Jpn. 25, 157 (1982).

(2) J. Kieser and M. Grundner, Vide 201,376 (1980).

(3) O’Hanlon, Journal of Vacuum Science & Technology A 5, 98 (1987).

Introduction

Thermoelectric (TE) film on Si substrate has drawn much attention as a power source for internet of things (IoT) sensor. The TE conversion efficiency monotonically increases with a dimensionless figure of merit; ZT = S²σT/κ, where S is Seebeck coefficient, σ is electrical conductivity, T is absolute temperature, and κ is thermal conductivity [1-3]. The trade-off relationship among three TE parameters has made it difficult to increase ZT. In 2000s, nanostructuring approach drastically decreased κ, boosting ZT. On the other hand, there are no promising methodologies to enhance S²σ. In recent years, we found CaSi₂ films composed of silicene and Ca layer, one of the layered materials [4]. Therein, modulating the buckling structure of silicene highly increased S²σ, which was the highest value (~40 μWcm^-1K^-2) at room temperature (RT) among silicide materials compatible to Si process. Although amazingly-high S²σ was obtained, the film thickness of CaSi₂ does not meet the requirement for power generation. The difficulty in obtaining thick film is Ca desorption during the growth. Therefore, the growth method preventing Ca desorption should be developed.

In this study, we develop the growth method enabling us to increase the thickness of CaSi₂ film. In this growth method, Ca and Si are simultaneously deposited on Si substrates at RT, followed by crystallization at high temperature unlike the previous method of solid phase epitaxy in Ca films/Si substrates. The low temperature deposition prevents Ca desorption, leadind to thick films. Furthermore, we reveal the TE properties of CaSi₂ thick films.

Experimental

CaSi₂ films were grown using molecular beam epitaxy (MBE). Si(111) substrates were introduced into MBE chamber at a base pressure of ~2×10^-8 Pa after the substrates were chemically cleaned. Subsequently, Ca and Si were simultaneously deposited on Si(111) substrates at various deposition ratios at RT. Ca and Si were crystalized by annealing at 450-650°C for 1h. Structural analyses were performed by reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD) and Raman spectroscopy. The carrier concentration, σ and S were measured using Hall effect measurement, van der Pauw method, and ZEM-3 (ADVANCE RIKO), respectively.

Results and discussions

We investigated the relationship between film thickness and deposition ratio. RHHED and XRD results revealed that CaSi₂ films were epitaxially grown on Si substrates regardless of deposition ratio in the Ca/Si range of 1.4-2.8. Epitaxial CaSi₂ film with a thickness of 168 nm was obtained when the deposition ratio of Ca:Si is 972 ML:700 ML. This value is >5 times as thick as CaSi₂ thin film grown by our previous method [4]. The S²σ of CaSi₂ thick film was 2-4 times as high as that of CaSi₂ bulk [5]. However, the S²σ of CaSi₂ thick films was smaller than those of CaSi₂ thin films. This is likely attributed to non-stoichiometry of CaSi₂. In this talk, we will discuss TE properties of CaSi₂ thick films and their physics.

References

[1] D. Narducci, J. Phys. Energy 1, 024001 (2019).

[2] Y. Nakamura, et al., Nano Energy 12, 845 (2015).

[3] T. Ishibe, et al., ACS Appl. Mater. Interfaces 10, 37709 (2018).

[4] T. Terada, et al., Adv. Mater. Interfaces 9, 2101752 (2022).

[5] T. Terada, et al., Appl. Phys. Express 14, 115505 (2021).

Hydrogen boride (HB) sheets are two-dimensional materials consist of negatively charged hexagonal boron networks and positively charged hydrogen atoms with a stoichiometric ratio of 1:1.¹ In a previous study, it was reported that HB sheets reduce metal ions with redox potentials higher than Ni to form metal nanocomposites.² We reported the spontaneous formation of highly dispersed Ni nanoclusters on HB sheets.³ The product is called Ni/HB composites. The spontaneous reduction of Ni ions by the HB sheet was monitored by in situ UV-visible spectrometer. Considering the increase in absorbance over time, the results suggest that Ni metal atoms form nanoclusters on the HB sheets. Based on the results of transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and selected area electron diffraction, Ni nanoclusters were spontaneously formed on the HB sheet, small (1-3 nm in diameter) and randomly distributed (Fig. 1,2) ³.

Mg-based alloys, including MgH₂, are attracting attention^{4, 5} as hydrogen storage materials. MgH₂ has many advantages as a hydrogen storage material; Mg is abundant in the earth, it has a high hydrogen density by weight (up to 7.6 wt%), is thermodynamically stable and can be safely transported (ΔH = -74.5 kJ/mol). However, there are several challenges that must be overcome. One is slow hydrogen release and absorption speed due to the strong bonding between Mg and hydrogen, and another is the amount of hydrogen absorbed decreases with repeated absorption and desorption. In addition, MgH₂ is thermodynamically stable and thus safe, but requires high temperatures for hydrogen release. Therefore, a reduction in temperature and an increase in the rate of hydrogen absorption and release are required for practical use. To solve these problems, supporting finely processed MgH₂ on two-dimensional materials with catalysts has been widely used^4,6. In particular, the use of Ni as a metal catalyst has been reported to increase hydrogen absorption and lower hydrogen release and absorption temperatures^{7, 8}. Herein, we will report that MgH₂ supported on Ni/HB composite (MgH₂-Ni/HB) shows lower H₂ release temperature(Fig. 3). We hypothesized that by loading MgH₂ onto Ni/HB, the aggregation of MgH₂ would be prevented and the catalytic effect of Ni would lower the H₂ release temperature. Practically, the H₂ release temperature of MgH₂-Ni/HB (Ni 2wt%) was 567 K, about 130 K lower than that of commercial MgH₂ (700 K) (Fig. 2). It is also interesting to note that the shape of the hydrogen intensity peak remained unchanged as a single peak. If only the MgH₂ in the Ni contact area were affected, there would be MgH₂ with different compositions and the peak would be split into two or more. Thus, this result suggests that 2wt% Ni affects the entire MgH₂, not just the Ni-MgH₂ contact area. These results suggest two possibilities; one is Ni may act as a catalyst to lower the activation energy, and the other is the formation of a new compound (including Ni, HB, and MgH₂) to raise the energy of the reactants and lower their apparent activation energies. The details of the results and discussion including thermodynamic parameters measurements will be presented.

References : 1) Nishino, H. et al. J. Am. Chem. Soc. 139, 13761 (2017).2) Ito, S. I. et al. Chem. Lett. 49, 789 (2020). 3) Noguchi, N. et al. Molecules 27, 8261 (2022).4) Ren, L. et al. Nano-Micro Lett. 14, 144 (2022).5) Abe, J.O. et al. Int. J. Hydrog. Energy 44, 15072 (2019). 6) Duan, C. et al. Renewable Energy. 187, 417 (2022).7) Dan, L. et al. ACS Appl. Energy Mater. 5, 4976 (2022).8) Xu, N. et al. Int J Miner Metall Mater 30, 54 (2023).

TiH₂ are reported as the hydrogen storage materials because of high affinity to hydrogen¹. Also, it has been widely applied as catalysts to lower the temperature². However, the H₂ release property from TiH₂ has not been well understood especially for the effect of its crystal size on the H₂ release. In our works, we conducted two methods to prepare different size TiH₂ which are ball milling and organic solvent.

Firstly, we have systematically analyzed the hydrogen release temperature of different ball-milled TiH₂ (ball milled for 10, 20, 30 min and 1, 2, 4 h) and commercial TiH₂ as shown in the Figure 1. In every case, hydrogen release was observed to consist of two-stages. The hydrogen release temperature in the first stage is largely reduced from 450 ℃ to 280 ℃ with increasing ball-milling time. On the other hand, the temperature for the second-step hydrogen release continuously decreased from 510 ℃ to 400 ℃ with increasing ball-milling time. The details mechanism of the change in H₂ release temperature will be discussed in the presentation. TPD results show a remarkable improvement in the hydrogen release performance of synthesized TiH₂@HB (hydrogen boride³), with the main peak of the hydrogen release temperature significantly reduced to 270 ℃, compared to commercial TiH₂, as much as decreased 230 ℃.

References:

1. Bhosle, V., Baburaj, E., Miranova, M. & Salama, K. Mater. Sci. Eng. A 356, 190–199 (2003).

2. Ren, Z. et al. Chem. Eng. J. 427, 131546 (2022).

3. Nishino, H. et al. J. Am. Chem. Soc. 139, 13761 (2017).

Mechanical stimuli, such as a compression, tensile, or shear stress, applied on solid sometimes induces chemical reaction and changes the physical or chemical properties. Such mechanically induced reaction is known as the mechanochemistry and attract large interest. Recent decade, thanks to the high spatial resolution of the scanning tunneling microscope (STM) and atomic force microscope (AFM), many chemical reactions have been studied in the single molecule/atom scale. On the other hand, in general, the mechanochemistry has been performed in macroscopic scale. So far, only a few experiments reported the chemical reactions of single molecule induced by the mechanical stimuli from tip of scanning probe microscope[1, 2].

In this study, we demonstrate the structural change of single molecule induced by the mechanical stimuli from AFM tip. We used sumanene molecule. As shown in fig. (a), sumanene is a molecule with bowl-shape. Inversion of a bowl is expected by simply applying the force by AFM tip. Experiments were carried out by qPlus type AFM/STM system operated in ultra high vacuum at 77 or 5 K. Sumanene molecule was thermally deposited on clean Au(111) substrate. Figure (b) shows high resolution AFM image of sumanene layer on Au(111) substrate. According to AFM image, this layer consist of bowl-up and -down sumanene and form 6 x 6 periodicity. This structure is different from the previously reported sumanene layer on Au(111)[3] but rather similar to that on Ag(111)[4]. This is because we successfully prepared sumanene layer with a monolayer thickness. We applied repulsive force on one of the sumanene molecule in the bowl-down state by bringing AFM tip close to the molecule. As a result, structural inversion from down to up was successfully observed. Almost no tunneling current flowed during this switching process, therefore, this is purely force induced reaction.

References

[1] J. N. Ladentjin et al., Nat. Chem., 8, 935 (2016).

[2] A. Ishi et al., Chem. Sci., 12, 13301 (2021).

[3] S. Fujii et al., J. Am. Chem. Soc., 138, 12142 (2016).

[4] R. Jaafar et al., J. Am. Chem. Soc., 136, 13666 (2014).

Hydrogen boride (HB) sheets are two-dimensional materials firstly synthesized in 2017¹, which consist of negatively charged boron and positively charged hydrogen at a molar ratio of 1:1. In this study, we focused on the positively charged hydrogen in HB sheets and aimed to clarify whether the adsorption of NH₃ molecules occurs or not, and its mechanism. HB sheets were synthesized as reported previously¹. We then exposed the HB sheets to ammonia vapor. Specifically, the small bottle with HB (20 mg) was put in the large bottle with 10 mL ammonia water and the large bottle was closed. After specific time had passed, we picked out the small bottle and heated it under vacuum for 30 min under 343 K to dry and got the dried sample. The obtained sample was examined by weight measurement, Fourier transform infrared absorption spectroscopy (FT-IR), temperature programmed desorption mass spectrometry (TPD-MS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS).

The mass of the dried sample was found to increase with increasing exposure time of ammonia water as shown in Fig. 1(a). The maximum mass change of the sample was about 180%. This is larger amount compared to the case of pure water exposure (137%), indicating that NH₃ is adsorbed on HB sheets even after 343 K heating. In FT-IR spectra, the distinct peak was observed near 2500 cm^-1 for original HB sheets as shown in Fig. 1(b), which can be attributing to the terminal B-H stretching vibrational mode.² The absorption peak position was found to shift about 40 cm^-1 to lower wavenumber for the sample after the exposure of ammonia water vapor followed by drying, indicating that B-H bond gets weakened when NH₃ is absorbed on the HB sheets. In TPD-MS, NH₃ (m/z=17) desorption peaks were observed at 450 K and 640 K. Based on the analysis of other samples, the former peak (450 K) could be ascribed to the decomposition of ammonium borate while the latter peak (640 K) could be ascribed to the NH₃ adsorbed on the HB sheets. The adsorption energy of NH₃ was then roughly estimated as 38 kcal/mol, indicating that NH₃ chemisorbed on HB sheets. Detail of NH₃ adsorption will be presented.

References

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

2. Tominaka, S. et al. Chem 6, 406 (2020).

Two-dimensional (2D) materials are used in various fields such as electrode catalysts, photocatalysts, electronics, optoelectronics, inserts and lubricants because of its superior properties. In 2017, experimental realization of the hydrogen boride sheets (HB sheets) have been reported as a new 2D materials¹⁾. HB sheets are composed of boron and hydrogen with stoichiometric 1:1. HB sheets theoretically take the structure of a six-membered ring of boron bridged by hydrogen, but it is only a local structure. In fact, it is reported that HB sheets have two types of bonds: one is three-center, two-electron (3c-2e) bond (B-H-B bond) and the other is two-center, two-electron (2c-2e) bond (B-H bond)²⁾. HB sheets are expected to be used as a hydrogen storage material. It is estimated to exhibit a hydrogen storage of 8.5 wt% and releases hydrogen by heating. Not only itself but also complexes with HB sheets are expected to exhibit a high level of hydrogen storage. For example, Li doped HB sheets theoretically indicate up to hydrogen storage of 11.57 wt%³⁾. However, hydrogen dissociation temperature of HB sheets is very wide because of its structural inhomogeneity, so it is important to control its structure and evaluate hydrogen dissociation characteristics. This attempt may also contribute to other functionalities of HB sheets such as a catalyst or reductant. In this study, HB sheets were heated under extreme conditions such as high-hydrogen partial pressure or ultrahigh pressure to induce structural changes while preventing the decomposition and desorption of hydrogen from the HB sheets.

The purpose of this study is to examine the effects of heating the HB sheets and to clarify how the pressure and temperature conditions affects the physical properties, especially hydrogen dissociation characteristics of the HB sheets.

We have conducted heating of HB sheets under 573~1073 K temperature condition and 5~11 MPa hydrogen partial pressure. We have also conducted heating under ultrahigh pressure (3500 and 5000 MPa) without hydrogen.

Figure 1 shows M/z=2 thermal desorption spectroscopy (TDS) of normal HB sheets and heated HB sheets. Intensity values are normalized with the maximum value as 1. An interesting point is that the peak of hydrogen dissociation shifts toward higher temperatures as the heating temperature increases. Fourier-transformed infrared absorption (FTIR) spectroscopy measurements were also conducted to examine changes in structure, and there were not significant spectral differences between the samples under different heating conditions in terms of peak positions of B-H-B and B-H vibrational modes. The only observed difference is peak positions changes of B-H-B caused B-B distance change²⁾. In addition, X-ray diffraction patterns of B₂O₃ Ⅰ and B₂O₃ Ⅱ were detected in sample heated at ultrahigh pressure.

References:

1) H. Nishino, et al., J. Am. Chem. Soc. 139 (2017) 13761-13769.

2) S. Tominaka, et al., Chem. 6 (2020) 406-418.

3) L. Chen, et al., Phys. Chem. Chem. Phys. 20 (2018) 30304-30311.

Hot spring water is a crucial resource in Japan, as it is one of the world's leading hot spring countries. The hot spring water contains a wide variety of elements such as B, As, Mn, Fe, Si and so on. However, despite the health benefits, the water pollution control act in 2001 restricts the amount of B discharged into the ocean [1]. Similarly, As, Mn, Fe and other elements are restricted their amounts in foods by the food sanitation law [2]. In addition, Si and other components in hot springs cause clogging of a pipe in hot spring facilities. Thus, chemical elements in hot springs are required to be removed.

In our previous experimental and theoretical studies, we have shown that various metallic elements absorb selectively on defects of carbon nanotubes (CNTs) [3, 4]. As such, we expect that CNTs are potential candidates for filtering materials that can remove chemical elements from hot spring water. The purpose of this study is to demonstrate the filtering experiments of CNTs for hot spring water.

In the present experiment, we have been using CNTs (SG-CNTs) fabricated by a super growth method [5]. We soaked SG-CNTs in hot spring samples and measured the concentrations of B, Si, and Fe using inductively coupled plasma mass spectrometry (ICP-MS). We then measured the concentrations before and after the soaking of SG-CNTs in hot spring samples. As a result, the concentration of any element was reduced by immersing SG-CNTs. Additionally, we optimize the amount of adsorbed atoms/molecules by applying several surface treatments to SG-CNTs and demonstrate their potential to solve the problems of hot springs. Details will be discussed in the presentation.

References

[1] Water Pollution Control Law related materials, Ministry of the Environment, Japan.

[2] Specifications and Standards for Foods, Additives, etc., Ministry of Health, Labour and Welfare, Japan.

[3] K.Oshima et al., Mater. Adv, 1, 2926 (2020).

[4] M. Miyabe et al., Meeting abstract of IVC (2022).

[5] SG-CNT samples used in the present study were provided by Zeon corporation.

Oxide quasicrystal (OQC) with dodecagonal clusters was reported to be prepared from ultrathin Ba-Ti-O and Sr-Ti-O films on Pt(111) by Förster et al. and Sebastian Schenk et al., confirmed by scanning tunneling microscope (STM) and low-energy electron diffraction (LEED) [1,2]. In addition, an 8°-rotated sigma phase oxide crystalline approximant (OCA) of ultrathin Ba-Ti-O film has been prepared [3]. Recently, the structural models of OQC and OCA ultrathin Ba-Ti-O films have been proposed [3-5]. Since not all Ti atoms in OQCs and OCAs are Ti⁴⁺ and rare earth metals have 4f electrons, rare earth metal OQCs and OCAs are expected to become superconductors and ferromagnetic materials [6-8]. Here, the rare earth element Ce is used to replace the metallic elements of Ba/Sr, to prepare the OQC ultrathin film on Pt(111). The ultrathin Ce-Ti-O film was prepared by depositing 0.5 ML Ce and 1 ML Ti on Pt(111), following with annealing in oxygen atmosphere and vacuum [9]. An arrangement of dodecagonal clusters, which consists of triangles and squares marked in white, were locally observed in STM image (Fig. 1(a)). In addition, the triangles with two orientations in the center of the dodecagons, which have an unequal distance to the clusters marked in white, leading to the appearance of trapezoids. Thus, it is recognized as OQC-related structure of ultrathin Ce-Ti-O film. In LEED pattern (Fig. 1(b)), two layers of 12 equidistant spot circles were formed around the substrate spots. From the X-ray photoelectron spectroscopy (XPS), and resonant photoelectron spectroscopy, the Ce in OQC-related structure corresponds to Ce³⁺. Titanium is in the form of Ti²⁺ ions from the Ti 2p core level in XPS spectra. The elemental atomic density is estimated by XPS and Rutherford backscattering spectroscopy. Combined with the symmetry of atomic arrangement, the model is proposed, where the Ce atoms occupy the protrusions in STM images (Fig. 1(c)). The stoichiometry of the OQC-related structure model is Ce₁₈Ti₁₄O₄₁ per unit cell.

References

[1] S. Förster et al., Nature 502, 215 (2013).

[2] S. Schenk et al., J. Phys.: Condens. Matter 29, 134002 (2017).

[3] S. Förster et al., Phys. Rev. Lett. 117, 095501 (2016).

[4] J. Yuhara et al., Phys. Rev. Mater. 4, 103402 (2020).

[5] X. Li et al., Appl. Surf. Sci. 561, 150099 (2021).

[6] T. Ueda et al., J. Phys. Soc. Jpn. 73, 649 (2004).

[7] N. Takeda et al., J. Phys. Soc. Jpn. 69, 868 (2000).

[8] D.C.Johnston et al., Mat. Res. Bull. 8, 777 (1973).

[9] X. Li et al., Phys. Chem. Chem. Phys. (2023) (submitted).

Introduction

A polymer electrolyte fuel cell (PEFC) has attracted attention as a highly efficient energy source with low environmental load, because the PEFC has high power density of 1 kW/L which is equivalent to that of gasoline engines and is operated at low temperature (room temperature to 100°C). Various organometallic complexes have been studied as catalysts for oxygen reduction reaction (ORR) to replace platinum because of cost reduction. An iron phthalocyanine (FePc) shows a four-electron reduction process (electron transfer number of carbon-supported FePc is 3.8 [1]) with less overpotential loss in comparison to a two-electron reduction process. Therefore, the FePc has a high ORR onset potential and does not produce toxic hydrogen peroxide [2][3]. However, the agglomeration of FePc degrade the ORR performance. The graphene, which has the largest relative surface area in the carbon-based nano-materials, is suitable material to support the FePc for suppressing the agglomeration. It has been reported that the reduction of FePc supported on graphene oxide (FePc/GO) to form π-π interaction significantly improves the ORR performance [2]. General reduction methods such as a chemical solution reduction or a thermal reduction using hydrogen gas have highly toxic to the human body and the environment or have a high-temperature process. To overcome these problems, the dry reduction treatment using atmospheric pressure plasma is proposed in this study without using chemicals. The electrons and hydrogen atom radicals with strong reducing power to materials are supplied from the plasma. The composite of FePc/GO was treated with atmospheric pressure plasma to remove the oxygen functional groups and the catalytic activity reduced-FePc/GO was evaluated.

Experimental

A FePc/GO powder with FePc/GO weight ratio of 2 was synthesized from a FePc dispersion solution and GO dispersion solution. The reduction treatment was performed by using the atmospheric pressure plasma jet. A schematic diagram of the atmospheric pressure plasma device is shown in the Fig.1 (a). An Ar/H₂ mixture gas with a total flow rate of 2.5 slm was flowed into the glass tube. An AC voltage of 6.75 kV with a frequency of 60 Hz was applied between the external and internal electrodes to generate the plasma. Catalytic activity was evaluated by using cyclic voltammetry (CV) in 0.1M acidic electrolyte HClO₄ solution.

Result

Fig.1 (b) shows cyclic voltammograms of FePc/GO. The onset voltage of the reduction peak increased from 0.65 V vs. RHE to 0.77 V with increasing the treatment time from 0 to 60 minutes because the electrical conductivity of FePc/GO was improved or Fe2+/Fe3+ ratio increased by the remove of the oxygen functional groups [4]. This result indicates that the reduction treatment using atmospheric pressure plasma jet is effective to enhance the catalytic activity of FePc/GO.

References

[1] B. Mukherjee, J. Electronchem. Soc., 165, J3231-J3235 (2018).

[2] Z.-Y. Mei et al, Chem. Eng. J., 430, 132691 (2022).

[3] M. Ohtsuka, Electrochemistry, 83, 376-380 (2015).

[4] K. Irisa et al, RSC Advances, 11, 15927-15932 (2021).

Graphene is a typical two-dimensional layered material that is attracting attention for its physical stability, mechanical strength, electrical conductivity, and other excellent properties, as well as its impermeability to helium atoms [1]. We have studied graphene growth for corrosion-resistant coatings on steel substrates formed by chemical vapor deposition (CVD). The results showed that graphene films coated on steel substrates exhibit high corrosion protection in hydrochloric acid solutions [2]. However, details of the graphene growth behavior on steel substrates were not well understood. Since the graphene growth is related to the deposition conditions, such as amount of carbon supply and temperatures etc., this study mainly investigated the effect of carbon-supply-time on the coverage in graphene deposition.

Steel Plate Cold Commercial (SPCC), which is one of the typical carbon steels and widely used from industrial products to construction materials, was used for substrates with the size of 10 × 10 × 0.2 mm. An atmospheric-pressure thermal CVD method was used for graphene growth. Figure 1(a) shows a typical temperature profile as applied during the CVD process. The temperature was raised to 1100 ℃ for 30 min with an argon gas flow. During the reduction process, hydrogen gas was additionally supplied for 10 min to remove the residual oxide layer on the substrate surface. During the carbon supply process, methane gas (the carbon source of graphene) was supplied to the SPCC substrate. The carbon supply time spans were 10, 20, 30, 35, 40, 45, 60, and 75 min, respectively. During the cooling process, the sample was slowly cooled from 1100 to 727 ℃ over a period of 1 h, and then quenched from 727 ℃ to near room temperature in 10 min.

Figure 1(b) shows optical images of the deposited films with different carbon supply time spans. A bright gray area (Region I) and a dark gray area (Region II) were observed. Figure 1(c) shows typical Raman spectra after a carbon supply time of 30 min. In Region I, a G peak at 1580 cm^-1 and a 2D peak at 2700 cm^-1 were observed. The presence of graphene-like materials on the Fe surface is confirmed by the observation of both G and 2D peaks. In addition, no D peak (1350 cm⁻¹) was observed. As the D peak is related to the graphene defects, these suggest that defect-free graphene films are formed in region I. In region II, neither the G peak nor the D peak were observed. If graphene or amorphous carbon is present on the surface, even as a monolayer, clear Raman peaks should be observed, suggesting that there is no carbon-based material in region II. It is worth noting that graphene grows from the outside positions of the sample with increasing to the carbon supply time, as shown in Fig. 1(b). Figure 1(d) shows the graphene coverage versus carbon supply time. The optical images of each sample were binarized, and the graphene coverage was calculated from the ratio of Region I to Region II. Graphene begins to grow on the steel substrate at carbon supply time between 10 and 20 min. Graphene coverage increased as the carbon supply time increased, but it became difficult to increase the coverage when the carbon supply time exceeded 45 min. Detailed growth mechanisms and graphene morphology will be discussed at the meeting.

[1] J. S. Bunch et al., Nano Lett. 62, 1 (2013).

[2] K.Hiratochi et al., SAT Technology Showcase 2022, P-24; https://www.science-academy.jp/showcase/21/pdf/P-024_showcase2022.pdf

1. Introduction

We found CNT filament formation phenomenon induced by gas discharge breakdown.[1] In this phenomenon, the gas discharge breakdown generated between electrodes, which was covered with carbon nanotube (CNT) film, created a lot of dust-like CNT bundles and these CNT bundles formed long CNT bundles by effect of an electric field. This phenomenon is promising for a simple and high efficiency CNT spinning method. Using this phenomenon, we have successfully formed CNT yarns by spinning these filaments.[2] However, the CNT yarns formed this method is short (typically <15 mm), and formation of longer CNT yarns is necessary. This requires further enhancement of the CNT filament formation by gas discharge breakdown. To this end, we used a collection electrode that consists of both cone-shaped and wire-shaped electrodes to improve the collection efficiency of CNT filaments, instead of the conventional electrode that consisted of cones electrode or wire electrode only. Furthermore, we increased the amount of the CNTs attached on the cathode to increase the formation efficiency of the dust-like CNTs that was required for the efficient CNT filament formation. We examined the effect of these improvements on the filament formation efficiency by the gas discharge breakdown.

2. Experimental

CNTs grown by thermal chemical vapor deposition were formed into a mat-shaped sheet and it was pressed onto a stainless-steel plate (cathode). At this time, the amount of the CNTs attached to the cathode increased three times as much as that of conventional procedure. A tungsten wire (0.15 mm in diameter) was used as the anode, which was fixed parallel to the cathode [Fig. 1(a)]. A wire-shaped auxiliary electrode was placed at the side of the anode, with the tip of the wire facing the anode. In addition, a collection electrode for CNT filaments was placed above these electrodes. A wire was placed both sides of the cone-shaped electrode so that the axes of the cone and the wires were parallel. The discharge chamber in which the electrodes were placed was evacuated and Ar gas was introduced to 6.2 kPa. Bias voltages of +50 V and +100 V were then applied to the collection and auxiliary electrode, respectively. A discharge breakdown was generated by applying a DC voltage of -800 V between the cathode and anode to produce CNT filaments. The CNT filaments were collected by a collection electrode to form filament bundles.

3. Results and discussion

The formation of the CNT yarn using the experimental setup described above was carried out by the following procedure. First, the gas discharge breakdown was generated to create dust-like CNTs from the CNT mats on the cathode. The dust-like CNTs floating around the electrodes were collected by the collection electrode, forming the CNT filaments as shown in Fig.1(b). During the formation of the filaments, the collection electrode was moved upward to form a CNT filament bundle. Then the CNT filament bundle was twisted by rotating the collection electrode [Fig.1(c)]. This process was repeated again to elongate the CNT yarn. Finally, the long CNT yarn was obtained as shown in Fig. 1(d). The length of the yarn was 35 mm, which was longer than in the previous study.[2] It is considered that formation of further longer CNT yarns is possible by further repetition of the process described above.

Acknowledgment

This study was supported by JSPS KAKENHI Grant Number 22K04872.

References

[1] H. Sato et. al., Vacuum 198, 110877 (2022).

[2] H. Hayama et al., Jpn. J. Appl. Phys., 62, SA1010 (2023).

1. Introduction

Carbon nanotubes (CNTs), which have excellent properties such as high strength, light weight, high electrical and thermal conductivity, are expected to be a constituent of composite materials. Composite materials with CNTs have excellent mechanical properties than conventional materials because of reinforcement by the CNTs. In addition, it is possible to give electrical and thermal conductivity by adding CNTs in the matrix. Among the composite materials, composites of cellulose nanofibers (CNFs) and CNTs have recently been studied from the viewpoint of function of material. CNFs are a renewable nanomaterial made by fibrillation of cellulose[1]. CNFs are lightweight and have high mechanical strength. Therefore, CNFs can be used for high-performance structural material. By combination of CNTs and CNFs, it is expected to create further excellent composite material with high mechanical strength, high electric and thermal conductance, and light weight. In this study, we formed CNT/CNF composite sheets and examined those electrical characteristics for purpose of application to flexible electronics.

2. Experimental Method

Multiwall CNTs (MWCNTs: ca. 150 μm in length and 10 nm in diameter) synthesized by thermal chemical vapor deposition method[2] were sonicated in ethanol. Next, aqueous CNFs dispersion was added in the CNT/ethanol solution and sonicated again. The CNFs used in this study was ELLEX-S (Daio Paper Corp.)[3]. Two different kinds of CNFs were used: CNFs made from mechanical pulp (made by mechanically grinding woodchips) and CNFs made from chemical pulp (made by chemically treating woodchips). Formation of CNT/CNF sheets were carried out by a drop-casting method. The solution of MWCNTs and CNFs was poured on a nylon mesh fixed to square aperture (2×2 cm) on a stainless-steel plate. The mesh was then dried on a heater while being compressed by an aluminum plate. After the procedure, a CNT/CNF sheet was formed on the mesh. The surface morphology of the fabricated CNT/CNF composite sheets were observed by scanning electron microscope (SEM). Sheet resistance was measured with a four-terminal resistance meter.

3. Results and Discussion

Fig. 1(a) is a photograph of CNT/CNF composite sheets formed using the chemical pulp CNF. Black-colored paper-like composite sheet was successfully formed. The SEM images in Fig. 1(b) show that the sheet comprises densely packed CNTs and CNFs. Fig. 2 shows the sheet resistance of CNT/CNF composite sheets plotted as a function of the amount of the CNTs added in the sheets. The measurements were carried out for the sheets formed using the mechanical pulp CNFs and the chemical pulp CNF. The sheet resistance of the composite sheets drastically decreases as the amount of CNTs added in the sheet increases and then approaches a constant value. The dependence of the sheet resistance on the amount of CNTs is different between the mechanical pulp CNFs and the chemical pulp CNFs. The mechanical pulp CNF sheet shows lower sheet resistance than that of chemical pulp CNF sheet at the smaller amount of CNTs (< 0.05 mg/cm²). This relation, however, reverses at the larger amount of CNTs (> 0.05 mg/cm²). The chemical pulp CNF sheet shows lower sheets resistance than that of the mechanical pulp CNF sheets. These results indicate that the morphology of the CNFs influences the electrical characteristics of the CNT/CNF composite sheets.

Acknowledgment

The authors thank Daio Paper Corporation for their offer of cellulose nanofibers. This study was supported by JSPS KAKENHI Grant Number 22K04872.

References

[1] H. Zhang et al., Carbohydr. Polym. 222, 115013 (2019).

[2] H. Sato et al., J. Appl. Phys. 100, 104321 (2006).

[3] https://www.daio-paper.co.jp/en/development/cnf/

The atomic intercalation into graphene changes its electronic band structures and results in various modulations of physical properties. We have demonstrated that graphene shows two-dimensional superconductivity by Ca intercalation with the periodicity of √3×√3 [1,2]. In addition, we have found that Yb-intercalated graphene shows ferromagnetism with the Curie temperature up to ~ 100 K [3]. Furthermore, intriguingly, this Yb-intercalated graphene system has also been expected to show superconductivity. The superconductivity transition temperature (T_C) is predicted to be 1.71 K by first principle calculation [4]. Recently, we successfully observe the superconductivity of Yb-intercalated graphene for the first time by in situ electrical transport measurements in UHV.

The sample was prepared by depositing Yb, which is paramagnetic as a simple substance, on a few-layer epitaxial graphene on SiC(0001) and annealing it. Then, we confirmed that the intercalated Yb went in between the buffer layer (an insulating carbon layer) and the SiC substrate and cut the bonds between them as seen by the change in RHEED patterns: disappearing of the spots of the buffer layer. Moreover, we found that more intercalation enables us to see the √3×√3 superstructure of Yb as shown in Fig. 1(a).

By in situ electrical transport measurements in UHV, we succeeded in observing the superconductivity of Yb-intercalated graphene, as shown in Fig. 1(b). Its T_C^onset and T_C^zero were 1.65 K and 0.85 K, respectively. We found that the temperature and magnetic field dependence of resistivity show characteristics of a 2D superconductor by the BKT theory.

From ARPES measurement results, we confirmed that Yb-intercalation caused electron doping into graphene, and with increasing intercalation of Yb atoms, more electrons were doped. Furthermore, Yb-4f states hybridize to the π band of graphene, and after Yb-intercalation, the gap at the Dirac point seems to open probably due to the strong spin-orbit interaction of Yb. After repeating 10 cycles of depositing Yb atoms on graphene and annealing, the top edge of the lower part of the Dirac cone is shifted ~ 0.5 eV downward compared to the Dirac point of the pristine graphene. If the electrons have the properties of 4f electron systems by hybridization, superconductivity may have novel properties similar to heavy Fermion superconductivity. We will check it in the near future.

References

[1] S. Ichinokura et al., ACS Nano 10, 2761 (2016).

[2] H. Toyama et al., ACS Nano 16, 3582 (2022).

[3] J. Jehong et al., 10pPSB-50, JPS 2019 Autumn Meeting (2019).

[4] C. Hwang et al., Phys. Rev. B 90, 115417 (2014).

[5] T. E. Weller et al., Nat. Phys. 1, 39 (2005).

1. Introduction

Iron-encapsulated carbon nanotubes (Fe@CNTs), multiwall CNTs that encapsulate iron nanowires in those inner hollows, have excellent magnetic properties that originate in the encapsulated iron nanowires. Especially, Fe@CNTs have high coercivity due to magnetic anisotropy of the iron nanowires.¹⁾ Thus, Fe@CNTs are promising for various magnetic applications such as electromagnetic shields, flexible magnets and so on. According to our previous studies, the diameter of Fe@CNTs did not depend on those growth conditions, and their outer and inner diameters were almost constant at about 60 nm and 20 nm, respectively. These diameters are relatively larger than those of conventional multiwall CNTs (typically < 20 nm). For the applications of Fe@CNTs, it is desirable to be able to control their inner and outer diameters arbitrarily. In this study, we examined the effect of addition of water vapor during the growth of Fe@CNTs by chemical vapor deposition (CVD) for the purpose to control the diameter of Fe@CNTs. It has been reported that addition of water vapor during the CNT growth by CVD activates the growth catalyst of CNTs and enhances the CNT growth.^{2, 3)} This effect may change the growth characteristics of Fe@CNTs.

2. Experimental method

A SiO₂/Si(100) wafers (10×10 mm square) on which 1.0 nm thickness of Ni catalyst film was deposited were used as substrates for Fe@CNT growth. The substrate was introduced in a CVD chamber for Fe@CNT growth and the chamber was evacuated to < 5 Pa. Then, Ar was introduced into the chamber to 1 atm and the chamber was heated to 775°C. When the temperature was reached to 775°C, sublimated ferrocene [Fe(C₂H₅)₂] and H₂O/Ar mixture gas were introduced into the chamber, and CVD growth of Fe@CNTs was carried out for 10 min. After that, the chamber was cooled to room temperature and the substrate was removed from the chamber. The total flow rate of Ar and H₂O/Ar was 100 sccm, and the flow rate of the H₂O/Ar mixture gas was changed between 0 and 20 sccm. The morphology of the Fe@CNTs was observed by a transmission electron microscope (TEM), and magnetic property of Fe@CNTs was examined by a vibrating sample magnetometer.

3. Results and discussion

Figure 1 shows typical TEM image of Fe@CNT grown in this study. Dependence of the coercivity of the Fe@CNTs on the H₂O/Ar flow rate is shown in Fig. 2. This graph shows that the variation of the coercivity on each flow rate is considerably large, but on average, the coercivity is around 1.0 kOe. The outer and inner diameters of the Fe@CNTs plotted as a function of the H₂O/Ar flow rate are shown in Fig. 3. It can be seen that the addition of water vapor significantly decreases the outer and inner diameters of the Fe@CNTs. The diameters decrease by 50% of those without the addition of water when 10 sccm of H₂O/Ar was added. From this result, it is confirmed reduction of the diameter of Fe@CNTs is possible with keeping those high coercivity by the addition of water vapor during the CVD growth of the Fe@CNTs.

Acknowledgment

This study was supported by JSPS KAKENHI Grant Number 22K04872.

References

1) H. Sato, A. Nagata, N. Kubonaka, Y. Fujiwara, Jpn. J. Appl. Phys. 52, 11NL03(2013).

2) K. Hata, N. Futaba, K. Mizuno, T. Namai, M. Yumura, and S. Iijima, Science, 306, 5700, 1362-1364(2004).

3) Y. H. Yun, V. Shanov, Y. Tu, S. Subramaniam, and M. J. Schulz, J. Phys Chem B, 110, 47, 23920-23925(2006)

Abstract

Hydrogen-substituted graphdiyne(HsGDY) is a two-dimensional material composed of an sp-sp² carbon skeleton, which has attracted much attention recently because of its structure with larger pores and band gap than other nanocarbon materials such as graphene[1]. HsGDY is expected to be applied as a new battery electrode[2,3] due to its high ion diffusivity resulting from its porous structure, and as a carbon framework catalyst[4] without precious metals such as Pt because of its band gap.

In recent years, research has concentrated on synthesizing HsGDY by a simple drop method using copper as a catalyst/substrate[3]. However, this method requires the use of toxic pyridine, and the deposition process takes several days. A method for synthesizing HsGDY by surface reaction on a substrate[5], i.e., homo-coupling reaction on the Au(111) surface, has been proposed as a solution for these problems. This method is expensive because synthesis is carried out in an ultra-high vacuum(UHV), and the UHV chamber limits the synthesizable specimen size, preventing its practical application.

In this study, we aim to develop a synthesis method for HsGDY by the drop method in air, in order to promote the practical use of HsGDY. To achieve this target, we modified previous studies[5,6] and devised a method in which the precursor is dissolved in an organic solvent and dropped onto a substrate.

1,3,5-tris(bromoethynyl)benzene(tBEP), the precursor of HsGDY, was synthesized at room temperature in the air with 1,3,5-triethynylbenzene(TEB) as a raw material, N-Bromosuccinimide(NBS) as a bromine source, and silver nitrate as a catalyst. As a substrate for HsGDY synthesis, the Au(111) surface was prepared by depositing gold on mica and annealing it with a burner. HsGDY was synthesized by dropping the organic solvent solution of tBEP onto this substrate and annealing at 150°C for 5 minutes.

HsGDY synthesized on the Au(111) surface was observed by scanning tunneling microscopy(STM). Fig. 1 shows an STM image of part of the HsGDY structure in the process of homo-coupling reaction, i.e., there is a gold atom between the precursors. The distances between three and neighbor six-membered rings consisting of 6 precursors are around 6 and 3.5 nm, respectively, which corresponds well to the center distances of the three circular structures observed in Fig. 1.

From the above, we have successfully synthesized a portion of HsGDY on Au(111) using the drop method in air. However, the homo-coupling reaction is not completed, and the synthesis conditions need to be optimized. In the future, we will achieve a large area (on the order of µm) of the two-dimensional structure for applications such as catalysts. In order to improve the synthesis method for a large-area structure, it is necessary to search for optimal synthesis conditions by changing parameters such as synthesis reaction time, the temperature at which the substrate is heated, and organic solvents in which the precursor is dissolved.

Our work provides a new and low-cost way to obtain amazing materials.

References

[1] H. Pan et al., App. Surf. Sci. 513, 145694 (2020).

[2] S. Kong et al., Nanoscale 13, 3817-3826 (2021).

[3] J. He et al., Nat. Comm. 8, 1172 (2017).

[4] Z. Zuo et al., Adv. Mat. 31, 1803762 (2019).

[5] Q. Sun et al., ACS Nano 10, 7023-7030 (2016).

[6] A. Okada et al., Surf. Sci. 702, 121718 (2020).

Recently, few-layer transition metal dichalcogenides (TMDCs) have been found to possess unique electronic states and have been applied to electronic and optical devices. In particular, monolayer TMDCs have been found to have a nonlinear susceptibility in the C exciton region that is three orders of magnitude higher than that of conventional nonlinear optical devices such as BBO, and applications to nonlinear optical devices are expected [1-2]. The optical second harmonic generation (SHG) spectra in the C exciton region of these monolayer TMDCs have resonance peaks at approximately the same photon energy as those of differential reflectance (DR) spectra, but there are multiple peaks that are not observed in the DR spectra [3]. The conventional interpretation of the optical modes in the C exciton region is the optical transitions near the Γ point attributed to band nesting effects, but the origin of the multi-peak structure is not yet well understood. In this study we focused on the fact that van der Waals interactions between the layers of TMDCs can modify their band structure, and observed the SHG spectra of monolayer (ML-) and few-layer (FL-) MoS₂, as well as ML- and FL-WS₂.

ML- and FL-MoS₂, as well as ML- and FL-WS₂, were transferred to SiO2/Si(001) substrates by mechanical exfoliation of single crystals, and the number of layers in each domain is identified with Raman microspectroscopy measurements. SHG microspectroscopy in the two-photon energy range from 2.4 eV to 3.2 eV was performed using an optical microscope. The fundamental light emitted from a Ti:sapphire laser (power 0.3 mW) was incident onto the microscope, and the SHG signal reflected from the sample was passed through a spectrometer and detected with a photomultiplier tube.

The SHG spectra of a monolayer (ML-) MoS₂, a trilayer (3L-) MoS2 with 3R structure, a 3L-MoS₂ with 2H structure, a ML-WS₂, a bilayer (2L-) WS₂ with 3R structure, and a five-layer (5L-) WS₂ with 2H structure are shown in Figures 1(a)-(f), respectively. The blue dots are the measured signals, indicating that there are two resonance peaks in the C exciton region. We performed curve fitting using a linear combination of two Lorentz functions. The blue lines are the fitted curves. The light blue and purple curves are the peaks, labeled as C1 and C2, respectively.

The energy of the C1 peak in FL-MoS₂ (3L-3R and 3L-2H) was shifted 0.04 eV lower from the C1 peak in ML-MoS₂, and the energy of the C1 peak in FL-WS₂ (2L-3R and 5L-2H) was shifted 0.10 eV lower from the C1 peak in ML-WS₂. These behaviors indicate that the C1 peak originated from the interband transition in the ring-shaped region, where band nesting occurred near the Γ point [4], like the C exciton in the linear optical spectrum. In contrast, for the C2 peak energy, the difference between FL and ML was small for both MoS₂ and WS₂. These behaviors indicate that the C2 peak is different from the C exciton in the linear optical spectrum and originates from excitation in a region where the band structure has changed little due to interlayer coupling. This peak can be described as a transition to a hidden state, which is specific to nonlinear optical processes. No significant structural difference was observed between the spectra of the two types of stacking structures, 3R and 2H.

In conclusion, we measured and analyzed the SHG spectra of ML- and FL-MoS₂, and ML- and FL-WS₂, and observed distinct resonance peaks called the C1 and C2 peaks.

View PDF for the rest of the abstract.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is widely used in various fields because it is a powerful surface analysis technique that can provide 3D molecular imaging and chemical structural information. In general, ToF-SIMS has several hundred to several thousand mass peaks in a spectrum. The identification of the peaks is often difficult because of peak overlapping and matrix effects. Moreover, there are very few databases that show the attributions of these peaks. Therefore, we developed a system to predict ToF-SIMS spectra of unknown organic materials such as peptides[1-3]. Since peptides are composed of 20 different amino acids, unknown peptides could be expressed by using the presence or absence of amino acids as labels for supervised machine learning [2]. In order to predict ToF-SIMS spectra of general organic materials, the labels for a supervised learning method have been improved by applying automatic segmentation of molecular strings with simplified molecular input line entry system (SMILES) notation [3] as an annotation of molecular structures. In this study, ToF-SIMS spectral of peptides, lipids, and their mixture were analyzed using Random Forest (RF), a supervised learning method based on decision trees. ToF-SIMS spectra were converted to numerical data using the peak list used for a former Versailles Project on Advanced Materials and Standards (VAMAS) project on machine learning application to ToF-SIMS spectra [2] containing 4230 mass peaks in the mass range 14-1200 Da, distinguishable between inorganic and organic materials, and then normalized to the total ion count to provide descriptors. The chemical structures of 32 peptide and lipid molecules in the samples were denoted in SMILES strings and then the strings were divided into smaller strings to create modified labels for supervised learning[3]. The number of the structure indicated by a label in a molecule was entered in the label. RF was used to predict the spectral dataset with the modified labels. In addition, the feature importance of RF for each label was obtained to evaluate the effectiveness of the labels. As a result, the prediction by RF for all spectral data yielded a high percentage of correct predictions, suggesting that the prediction is accurate even when lipids are included. The results of importance in RF with a single label showed that the mass peaks associated with the chemical structure set by a label were shown to be of the highest importance for most of the labels. References1) W. Ishikura, K. Takahashi, T. Yamagishi, D. Aoki, K. Fukushima, M. Shiga, S. Aoyagi, J. Surf. Anal., 25(2) 103-114 (2018).2) S. Aoyagi, Y. Fujiwara, A. Takano et al., Analytical Chemistry, 93, 9, 4191-4197 (2021).3) K. Kamochi, M. Inoue, S. Ogawa, S. Aoyagi J. Surf. Anal., 30(1) 15 - 27 (2023).

Introduction: Recently, membrane proteins and some of cellular proteins can be (re)folded on the model biomembranes such as liposomes (a closed phospholipid bilayer system), although the details for the molecular mechanism are still now unclear. In this study, we then applied a single molecular tracking method to the model globular protein, carbonic anhydrase from bovine (CAB) to investigate its refolding process on lipid planar membranes.

Methods: We used two kinds of phosopholipids such as 1,2-dipalmitoyl phosphatidylcholine (DPPC, gel phase) and 1,2-dioleoyl phosphatidylcholine (DOPC, liquid crystallin phase) to prepare the lipid planar membranes. GuHCl-denatured CAB was injected on the lipid membranes to start the refolding reaction process. For a single molecular tracking experiment, CAB was modified with fluorescence probe DAC.

Results: CAB took conformation of native (N) and unfolded state (U), depending on the GuHCl concentration. A lateral diffusion coefficient (D) of CAB on lipid membranes was then determined. The D value depended on the conformation of CAB. Then, the refolding process was monitoring based on D value. In the beginning of refolding, CAB molecules indicated the low D value due to the denaturede state. Some molecules came to indicate the incremental change of D value. This result implies that some of CAB molecules immediately convert from U->I->N state (I intermediate state). Furthere experiment demonstrated that the lateral diffusivity of I state consisted of (i) slaved-diffusion and (ii) adsorption-desorption steps. These steps strongly depended on the gel / liquid-crystalline phase of DOPC and DPPC membranes. By repeating these steps, the refolding reaction process of CAB was advanced, as shown in Fig.1. These results would be helpful to understand the lipid membrane-assisted refolding of other proteins.

In the area of public health, viral infections seem to be one of major issues. Recently, SARS-CoV-2 caused severe pandemic on the human life, for example. Such viruses could cause pandemic and/or epidemic, and then threaten the safety of our life. To avoid this situation, we would like to detect them with higher sensitivity and protect us effectivity. For this purpose, we are developing virucidal agents with the research of the molecular interaction. Then we can obtain safe and effective virucidal agents. Among them, human norovirus is an unenveloped virus and its surface is composed of the virus-coded protein capsid. The virus is the most common pathogen causing acute gastroenteritis and may lead severe illnesses especially among immunosuppressed people. Its symmetric capsid structure with stability, however, might cause difficulty to destroy the virus surface structure, comparing with the enveloped viruses such as SARS-CoV-2, influenza viruses, and so on. There are no effective therapeutic agents or vaccines for norovirus infections. Berberine is an isoquinoline alkaloid belonging to the structural class of protoberberines and is encountered in many plants. The compound has widely been used as a herbal medicine to treat gastrointestinal disorders. Recently, we have identified berberine as a virucidal agent against norovirus in a plaque assay-based screening. That is, in this study, we used a cultivable strain of norovirus, feline calicivirus (FCV), as a surrogate for human noroviruses because the human noroviruses show only insufficient replication in the cell culture systems. The virucidal activity of berberine was assessed by incubating the compound-virus mixture before calculating residual virus infectivity via a plaque assay. Berberine inactivated FCVs in a dose- and time-dependent manner. In order to elucidate possible mechanisms underlying the virucidal activity of berberine, we also assessed structural changes in virus particles following treatment with berberine via transmission electron microscopy. As a result, aggregated FCV particles and particles with partially destroyed structures of protein capsid were observed. The aggregation of virus particles may significantly inhibit the ability of viruses to enter host cells and may result in a loss of infectivity because viral aggregation correlates with decreased viral titers. And also, structural destruction of the protein capsid that binds to the surface of host cells may result in lowering the efficacy of viral binding to the cells. Thus, berberine offers a novel prophylactic option against norovirus infections.

Alzheimer’s disease (AD) is a neurological disorder characterized by the extracellular accumulation of amyloid-β peptide (Aβ) within patients’ brain tissue. Aβ42 prominently features within Aβ aggregates and is widely implicated in synaptic loss and neurodegeneration associated with AD. Recent studies highlight Aβ42 oligomers (oAβ42s) as contributors to neurotoxicity, heightened Aβ aggregation, and increased tau protein phosphorylation [1]. However, the structural diversity and instability of oAβ42s challenge exploring their interactions with additives. Recently, our team has successfully developed an experimental protocol using homogeneous pentameric oAβ42 assemblies derived from monomers, following atomic force microscopy. This homogeneity facilitates the tracking of compound-induced changes, including pharmacotherapeutic agents, in its structural integrity.

In this study, we demonstrate the ability of curcumin, the powerful candidate of therapeutic agents for AD, to disassemble pentameric oAβ42, as quantitatively evidenced with atomic force microscopic imaging. Considering the property of curcumin with phenolic nature derived from turmeric, accompanied by keto-enol structural isomerism (tautomerism) [2], we investigated the impact of keto-enol tautomerism on its disassembly. Curcumin derivatives exhibiting keto-enol tautomerization were also observed to affect the disassembly of pentameric oAβ42, while a curcumin derivative lacking tautomerization had no impact on the integrity of pentameric oAβ42. These empirical findings underscore the essential role of keto-enol tautomerism in the disassembly process.

Based on our findings, we present a mechanistic model illustrating how curcumin tautomerism influences the disassembly of oAβ42, elucidated through molecular dynamics simulations. Upon curcumin and its derivatives binding to the hydrophobic region of oAβ42, the keto-form undergoes a transition to the enol form. This transformation is accompanied by conformational changes (including torsion, planarization, and increased rigidity) and, in turn, results in shifts in potential energy. These combined alterations furnish curcumin with the requisite force to operate as a torsional molecular spring, ultimately leading to pull apart of the intermolecular space of the pentameric oAβ42. The proposed disassembly mechanism casts novel insights into the importance of keto-enol tautomerism as a pertinent chemical attribute in the strategic design of innovative therapeutics targeting protein aggregation.

Introduction: Parkinson's disease (PD) is a progressive disorder that affects the nervous system and the parts of the body controlled by the nerves. In PD, the formation of Lewy body made of α-synuclein that is the main protein component has been reported. Therefore, the detection of alpha-synuclein is a promising approach. Previously, alpha-synuclein binds to lipid membranes via two α-helices at the N-terminus. Interestingly, disrupted associations between lipid membranes and α-synuclein might trigger the formation of Lewy body. Accordingly, α-synuclein aggregation and lipid-synuclein interactions are important for the pathomechanisms of PD. In this study, we displayed IgG on lipid membranes and aimed the detection of alpha-synuclein by IgG unit .

Methods: IgG molecule was used for the detection of alpha-synuclein. The thiol-group was covalently bound to alkane thiol to yield the complex, namely IgG-L. IgG-L was mixed with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) to form the lipid thin film. Afterwards, liposomes were obtained by using a hydration and extrusion method to adjust their diameter into 100 nm. A gel permeation chromatography was performed to separate the IgG-displayed liposomes from free-IgG-liposomes.

Results and Discussion: First, IgG-displayed DOPC liposomes were observed with a cryo-TEM to confirm the intact membrane structure of lipid memebranes. The IgG could interact with alpha-synuclein to interfere with its amyloid fibril formation. By using this interaction, IgG-displayed liposomes could bind to amyloid fibrils. IgG-free liposomes did not bind to amyloids. Therefore, a dispayment of IgG with a certain orientation (or conformation) might be required for binding to amyloids. Besides, a displayment of IgG would surpass the interaction between alpha-synuclein and lipid membranes.

Fluorescence single molecule observation is a technique to visualize individual movements and reactions of probe molecules such as fluorescent dyes and proteins. It has been developed mainly in the fields of biophysics and cell biology as an observation method under physiological conditions, i.e., in aqueous solutions. We have applied fluorescence single molecule observation to observe molecular behavior at the interface between organic solvents and solid substrates as a new method to investigate the molecular mechanism of lubrication [1]. We found fluorescent probes suitable for single molecule observation in organic solvents and investigated their properties and the effects of additive molecules on a glass substrate, which is commonly used for fluorescence observation in aqueous solutions. In this study, the single molecule fluorescence observation was applied to a metal surface, because lubrication and friction are generally handled on the surfaces of metals, such as machine tools and engine. fluorescence may be quenched on metal surfaces.

Hexadecane (HD) and 0 - 0.150 mass% palmitic acid (PA) were used as a base oil and an additive, respectively. Fluorescence single molecule observation was performed in the HD solution in the presence of 1.4 pM BODIPY-NHS 530/550 (BODIPY, ex/em: 534/551 nm). Glass substrates with a 3 nm or 10 nm thick copper layer were cleaned by UV irradiation in air. The substrate surfaces were observed in the HD solutions containing BODIPY at 25 °C with a total reflection fluorescence microscope.

Bright spots were observed on both substrates with 3 nm or 10 nm thick copper layer. They had uniform intensity and faded in one step. Therefore, bright spots were assigned to the fluorescence from individual BODIPY molecule. Fluorescence quenching by metal did not occur, and, on the contrary, the brightness of each BODIPY molecule was higher than that on the glass substrate. The density of the bright spots in the view field decreased under the irradiation of the excitation light and reached a constant value ~15 s after irradiation started (Fig. 1). The density of the bright spots increased in in the presence of PA. The thickness of the copper layer on the substrate did not affect these phenomena. The rate constants of adsorption, desorption, and photobleaching of the BODIPY molecule at the copper/hexadecane interface were evaluated based on the temporal change of the BODIPY density.

Introduction: In this paper, we present the current status of reservoir computation (RC) device development. In particular, not only are reservoir elements used as AI for image recognition and other applications, but also new "intelligent" sensing methods using them as RC devices are introduced here, such as a soft sponge-like sensor (1) that can detect tomato ripeness (2).

RC is a computational framework derived from RNN (Figure 1a) that maps input signals to a higher dimensional computational space through the dynamics of a fixed nonlinear system called a reservoir. After an input signal is input to the reservoir, which is treated as a black box, a simple readout mechanism reads the state of the reservoir and learns to map it to the desired output. since RC is developed to mimic brain functions, such as signal feedback to the reservoir, and neuromorphic operations (3-5) (Figure 1b). To be practical as in-material computing devices using nanomaterials and nanoparticles and to realize efficient information processing systems, robust nonlinearity and memory properties are required. To learn this requirement, we aimed to utilize not only highly conductive molecular networks (6) but also various materials such as Ag/Ag2S nanoparticle assemblies and CNT/polyoxometalate (POM) nanoparticles (7), which have nonlinear conduction regions at the nanoscale.

Method: Random networks of CNTs and other materials were fabricated on a substrate with 16 electrodes extending to the center and forming a gap of several hundred nm. The output of the change in voltage over time was added for each electrode, and the recognition success rate was calculated from the results of one-hot vector representation by linear regression using Python. For the in-sensor calculation, a sensor with a CNT content of 0.3 g and a thickness of 0.5 cm was prepared, and measurements were made 50 times each for 9 object recognitions. The obtained data were used as training and validation data for 25 pieces each, and the success rate of each classification was compared when object grasping was performed.

Results and discussion: The physical RC device using RNW of SWNT/porphyrin-POM (Por-POM) nanoparticle composite fabricated based on the theoretical model previously reported is presented (Figure 1c). The physical RC platform consisting of the SWNT-Por-POM composite network successfully executes the basic characteristics of reservoirs: nonlinearity, high-order harmonic generation, and phase delay. A supervised object classification task using one-hot vectors with the object grasping tactile signal of a Toyota assisted living robot (HSR) (9) was performed according to the task of the RoboCup World Championship. This is the first reported example of introducing a material physics RC device directly into a robot for object recognition (8,10) and has been introduced in many fields (11). Currently, we are aiming to build an RC system inside a sponge sensor (in-sensor computation) by using the above-mentioned sponge sensor (2), and have recently succeeded in implementing the system in a robot hand (12).

Conclusion: We have introduced random network material reservoir devices toward in-sensor tactile computing devices, based on the results obtained.

References: 1) A. TermehYousefi, H. Tanaka et al., Mater. Sci. Eng. C 77, 1098 (2017). 2) S. Azhari, H. Tanaka et al., IEEE sensors J. 21, 27810, (2021). 3) S. K. Bose et al., Nat. Nanotechnol. (2015). 4) T. Chen et al., Nature 577, 341 (2020). 5) H. Tanaka et al., Nat. Commun. 9, 2693 (2018). Most read 50 published in Nat. Commun. in 2018. 6) Y. Usami, H. Tanaka et al., Adv. Mater. 33, 2102688 (2021). 7) T. Ogawa et al., J. Mater. Chem. C (2020).

View PDF for the rest of the abstract.

Recently, biohybrid systems, which are composed of biological and synthetic components, have been proposed as the integration of microfabrication techniques and biological techniques. Among the biohybrid systems, biohybrid soft robots that use cultured muscle tissue as a driving source have been actively studied, and movements such as grasping, carrying, and moving have been achieved [1]. However, skeletal muscle tissue has been fixed with the robot skeleton in previous biohybrid robots, causing the limitation of designs and driving mechanisms of biohybrid robots. In this presentation, we introduce the method for the formation of cultured tissue with the robot skeleton and the characteristics of biohybrid robots.

To form functional cultured tissues in vitro, we demonstrated that cell-laden hydrogel blocks shaped by microfabrication methods are available as cellular building modules for tissue construction. For example, by stacking myoblast-laden hydrogel blocks and culturing stacked hydrogel blocks on the robotic skeleton, we achieve the formation of a millimeter-sized cultured skeletal muscle tissue [2]. Since the hydrogel blocks have stripe-shaped structures which promote alignments of myoblasts to the longitudinal direction of stripe-shaped structures, aligned myotubes are constructible in the cultured skeletal muscle tissue, resulting in the generation of high contractility of muscle tissue. Due to its high contractility, we achieved the formation of the co-cultured tissue composed of skeletal muscle tissue and motor neurons which contracted with the transmission of neural signals via neuromuscular junctions. These engineered tissues showed properties of drug responses, metabolism, fatigue, and recovery comparable to living tissues, indicating usefulness for drug development.

As the demonstration of biohybrid robots driven by cultured skeletal muscle tissues, we developed a biohybrid robot with an antagonistic pair of skeletal muscle tissues. Each skeletal muscle tissue was connected to a joint of a plastic skeleton, similar to the animal arm consisting of flexor muscle and extensor muscle. The biohybrid robot can rotate its joint by selective contractions of each skeletal muscle tissue, leading to performing pick-and-place of a ring [3]. Furthermore, we succeeded in the construction of bipedal bio-hybrid robots consisting of cultured skeletal muscle tissue and flexible substrate, legs with spring-like structures, and a float to maintain an upright posture. In the bipedal biohybrid robots, when electrical stimulation was applied to each leg alternatively, the robot moved forward in a bipedal gait. Moreover, when electrical stimulation was applied to only one of the legs, the robot also achieved a turning motion with the other leg as the axis of rotation. This bipedal biohybrid robot, which can move in straight and turning motions, has a useful operating principle that combines the restorative force from the deformation of the flexible substrate and the gravitational force of the weight. In summary, we believe that biohybrid robots are promising technologies to enable engineering uses of tissues and are applicable in various fields from soft robotics to exercise models.

References

[1] L. Ricotti, et al., Sci. Robot., 2, eaaq0495 (2017).

[2] Y. Morimoto, H. Onoe, S. Takeuchi, Adv. Robot., 33, 208-218 (2019).

[3] Y. Morimoto, H. Onoe, S. Takeuchi, Sci. Robot., 3, eaat4440 (2018).

Information processing in the brain is performed by not only neurons but also glial cells. Glial cells are classified into astrocytes, microglia, and oligodendrocyte. Especially, a major glial cell type, astrocyte, is in charge of the formation and maturation of synapses in order to establish a sustainable synaptic transmission in the brain. In addition, it is known that the physical attachment of astrocytes with neurons is crucial to maintaining synaptic transmission. In general, a higher animal has a bigger brain. There is a potential possibility that the number of astrocytes determines the intricate brain function in which a higher animal’s brain has a higher density of astrocytes. This possibility may be reminiscent of hints to make an effective artificial brain in the future. In this symposium, we show the primary co-culture system of the autaptic single hippocampal neuron with dot-cultured cortical astrocytes, where experimentally modified the density of astrocytes surrounding a single neuron. We also present that a hippocampal neuron with a high density of astrocytes increases excitatory synaptic transmission compared with a low density of astrocytes, which is accompanied by an increment of the readily releasable pool. In light of the heterogeneity of synaptic transmission underlying the presynaptically active synapse (able to release neurotransmitter) and silent synapse (unable to release neurotransmitter), pre-determining the region of synaptic connection would be an important key factor in creating an efficient neural circuit artificially.

The brain is a well-organized organ consisting of telencephalon, diencephalon, mesencephalon, and metencephalon. Each brain region has specific functions and interacts with other regions by neuronal axons and synaptic connections. Since human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) have an ability to generate all cell types in an organism, region-specific neuronal differentiation from hESCs/hiPSCs would help for better understanding human brain development and the pathogenesis of various neurological diseases, and for use in drug development, disease modeling and regenerative therapies.

Parkinson’s disease (PD) is an age-related neurodegenerative disorder that is characterized by the progressive loss of midbrain dopaminergic (mDA) neurons that project to striatum. The loss of mDA neurons causes the motor symptoms such as resting tremor, rigidity, and bradykinesia, which are possible to treat by symptomatic therapy using medicines in early stage of disease. Pathological features from postmortem studies are accumulation of α-synuclein protein in the Lewy bodies that are appeared in remaining mDA neurons of the patients with PD. Furthermore, α-synuclein aggregates propagate through the brain in a prion-like manner with a pattern corresponding to synucleinopathy staging.

During the last years, we investigated cell type composition and gene expression profiles of the developing human ventral midbrain by single cell RNA-sequencing (scRNA-seq) and reveled the difference between human developing mDA neurons and hESC-derived mDA neurons [1]. We subsequently established an induction protocol for mDA neurons from hESCs/hiPSCs by resembling the crucial factors we found from scRNA-seq data of human ventral midbrain. We obtained LMX1A⁺, FOXA2⁺, OTX2⁺ and EN1⁺ midbrain neural progenitors and subsequently gave rise to TH⁺ mDA neurons. Finally, we detected current response of the mature mDA neurons following long-term culture [2, 3]. Moreover, we also established a protocol for generation of striatal GABAergic neurons from hiPSCs by resembling the crucial factors for striatal development. We obtained GSH2⁺ lateral ganglionic eminence (LGE) progenitors and subsequently gave rise to DARPP32⁺ striatal neurons exhibiting spontaneous and evoked monophasic spiking activity [4].

Next, we developed striatal and midbrain neurospheres from hiPSCs using three-dimensional culture system to recapture the higher structure of the brain for the understanding of pathology of PD. We observed the specific marker genes and neuronal subtypes that are presented in each brain region. These brain region-specific neurospheres enable to investigate simpler and reproducible analytical methods for the elucidation of the pathological features of the patients with PD (Fig. 1).

References

[1] G. La Manno et al., Cell 167, 566-580 (2016).

[2] K. Nishimura et al., Stem Cell Reports 18, 337-353 (2023).

[3] K. Nishimura et al., STAR Protoc. 4, 102355 (2023).

[4] N. Amimoto et al., Stem Cell Res. 55, 102486 (2021).

Three-dimensional (3D) cultured cells, such as spheroids have been recognized as promising cellular models for drug screening and regenerative medicine because they effectively mimic the cellular response and metabolic activity in physiological conditions. To better understand the physiological properties of 3D cell models, techniques to measure dynamic activity of cells beyond conventional morphological and static evaluation is required. Electrochemical sensors offer several advantages for the development of such an evaluation system, including continuous real-time measurement, minimal invasiveness, and compatibility to miniaturization.

We have developed electrochemical sensing systems to evaluate 3D cell models, with a particular focus on their respiratory activity. Respiration is one of the major pathways for energy production in mammalian cells and is therefore an important indicator of cell/tissue status. With a microelectrode set in the vicinity of a spheroid, oxygen distribution around the spheroids can be measured using electrochemical reduction current of oxygen, allowing respiratory activity to be assessed in a non-labelled and minimally invasive manner. The system was adapted to tumor and mesenchymal stem cell (MSC) spheroids, and it was shown that respiratory activity reflects cellular status, such as the formation of a necrotic core in tumor spheroids¹ and the differentiation state of MSC spheroids. In addition to simple mono-cultured spheroids, spheroids co-cultured with endothelial cells provide even more biomimetic models containing vascular-like tissues. We have made co-culture models of endothelial cells with fibroblasts² or with MSC spheroids, and the electrochemical respiration measurements have also provided insights into the evaluation of these advanced biomimetic systems.

In terms of device development, in addition to conventional microelectrodes, bipolar electrochemistry was used to develop a detection system in which the spheroid and the analysis chamber are completely independent. Furthermore, we worked on the construction of a method for imaging the distribution of oxygen concentration using electrochemiluminescence³. The development of such measurement systems contributes to higher-throughput and more practical measurement techniques.

In this talk I would like to present the combination of 3D cultured cells and electrochemical measurements that I have been working on and discuss the prospects of microphysiological systems integrated with electrochemical sensors.

1. Mukomoto et al., Analyst, 145, (2020), 6342-6348.

2. Hiramoto et al., Electrochimica Acta, 340, (2020), 135979.

3. Hiramoto et al., Biosensors and Bioelectronics, 181, (2021), 113123.

There is a growing interest for environmentally friendly metal-oxide materials. Vanadium dioxide (VO₂) is known as a phase transition compound which shows insulator-metal transition (IMT) with its structural phase transition (SPT) from low-temperature monoclinic phase (P2₁/c) to high-temperature tetragonal phase (P4₂/mnm) at 68 °C. The abrupt resistivity change over 4 orders of magnitude is realized even in thin films with thickness of less than 15 nm. The reversible and durable IMT has triggered a lot of studies on VO₂ thin films not only for unravelling the physics of phase transition but also for applications to various engineering field. In this presentation, we introduce applications of VO₂ films to energy-saving smart windows [1] and oscillation phenomenon of voltage-induced IMT.

We have been fabricating stoichiometric VO₂ thin films by using reactive magnetron sputtering method. By introducing radio-frequency substrate biasing, we succeeded low temperature growth of stoichiometric VO₂ films on various substrates. As one of promising application, we are trying to fabricate VO₂-coated glasses for smart windows where infrared-light (IR) incidence is automatically controlled to avoid room temperature rise in hot summer. Large change of transmittance for IR concomitant with the IMT enabled VO₂-coated glass as smart windows with automatic reduction of IR with temperature rise. As shown in Fig. 1, we introduced layered structure of VO₂ on ZnO-buffered glass. As performance index, we realized the solar modulation ability (ΔT_sol) higher than 15% which is approaching top-ranking value, although the luminous transmittance (T_lum) around 30% is still rather low.[2]

Electrically biased VO₂ films shows self-sustained electrical oscillation (SEO) phenomenon when current-voltage characteristics possess a negative resistance region. We fabricated planer VO₂ device where Ti/Au electrodes are metallized on the VO₂ film grown on Al₂O₃ (001) substrate. The width and the gap in the electrodes were 5000 μm and 10 μm, respectively, as shown in Fig. 2. In this device, we achieved SEO with frequency from 15 K to 80 kHz, by selecting parallel capacitance to VO₂ as shown in Fig. 3. Further, it is known that parallel circuit of SEO realizes coupled oscillation phenomenon, in which their phases are automatically synchronized [3]. The coupled oscillations are expected to be applied to various issues in mathematical engineering field, such as graph coloring problem. ⁴⁾ In the present study, coupled oscillation with 10 kHz was realized in the coupling of two oscillators. The anti-phase synchronization appeared at the certain supply voltage. We directly observed changes of coupling modes by using curve tracer. In the presentation, we will show minute results of SEO and coupled oscillations.

References

[1] J. Houska, J. Appl. Phys. 131, 110901 (2022).

[2] K. Okimura et al., Sol. Ener. Mater. and Sol. Cells, 251,112162 (2023).

[3] Tobe et al., J. Appl. Phys., 127, 195103 (2020).

α-phase Al₂O₃has been used as a hard coating film for cutting tools because of its excellent wear and oxidation resistance. Currently, commercially available α-phase Al₂O₃ films are mainly formed by thermal CVD. However, the high deposition temperature of over 1000°C by thermal CVD limits the selectivity of the substrate materials, and thus, PVD processes has been attracted as an alternative deposition process to realize low deposition temperature. In addition, roles of nucleation layers on the growth of α-phase Al₂O₃ films have been studied, e.g., as magnetron sputtered α-phase Al2O3 coatings were achieved at deposition temperatures of approximately 700°C by introducing CrN or TiAlN as interlayer between the substrate^[1].In this study, we focused on α-phase Cr₂O₃ films as it has a same corundum crystal structure as nucleation layers and aimed to clarify the effect of its crystal texture on the Al₂O₃ film growth. To realize the evolutions of the crystal textures of the α- Cr₂O₃, high-power impulse magnetron sputtering (HiPIMS) was used, as deposition process which enables flexible control of the film structure through the formation of high-density plasma. Feasibility on the crystal texture evolutions of α- Cr₂O₃ and its effect on the growth of Al₂O₃ coatings has been thoroughly discussed.

The target materials were 3-inch pure Cr and pure Al. Oxide formation was achieved by introducing O₂ gas into an Ar atmosphere. During the growth of Cr₂O₃ films the substrate potential was set at ground, substrate bias voltage U_s: -50 V and -100 V. All experiments were performed in a high vacuum stainless-steel chamber with a base pressure of ∼10⁻⁴ Pa. A planar circular unbalanced magnetron with a Cr and Al disk with a diameter of 75 mm was used as the sputtering target. Ar gas was introduced into the chamber through a mass-flow controller at a constant flow rate of 100 sccm and was maintained at a constant working pressure of 1.0 Pa. O₂ gas of 2.3 sccm was introduced as reactive gas to grow films in the transition sputtering modes. HiPIMS pulses were supplied by a HiPSTER 1 pulsing unit fed by a 1 kW HiPSTER 1-DCPSU DC power supply (Ionautics AB, Sweden). During the growth of Cr₂O₃ films, the substrate bias voltage (U_s) was set at ground potential, U_s: -50 V and -100 V. The crystal structures of the films were characterized by using X-ray diffraction (XRD) and its microstructures were analyzed by using scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

As results, α- phase crystals could successfully obtained for the Cr₂O₃ films and its crystal texture with α(006) became preferentially oriented as the substrate bias voltage is increased, while the randomly oriented crystal structure was obtained at grounded substrate bias configuration. As the (006) plane is known as a thermodynamically stable crystal plane, the higher kinetic energy of incident ions could contribute to the thermodynamic events, leading to exhibit the more preferential orientation.

Moreover, effects of these crystal textures on the growth of Al₂O₃ coatings are clearly observed, showing the strong η-phase Al₂O₃ growth on the highly textured Cr₂O₃ with biased configuration.

View PDF for the rest of the abstract.

When fine particles of several tenth of µm in diameter are injected into a plasma, they are negatively charged and are subjected to an electric force generated by the electric filed in the sheath, and each particle is levitated at the position where gravity and the electric force are valanced. In the present study, we tried to measure the spatial electric filed distribution in the sheath by using spherical particles of synthetic resin containing a fluorescent substance.

Since the shape of each particle is close to a sphere, the mass of the particle is estimated as m = (4/3)πρR³, where ρ is the density of the synthetic resin and R is a radius of the particle. The capacitance of the spherical conductor is C=4πε₀R, so that the particle charge q can be estimated accurately as q = CV_f = 4πε ₀V_fR, where V_f is the floating potential on the particle. Therefore, the mass-to-charge ratio, m/q, is proportional to R² and the electric field at the position where a particle is levitated, E =(m/q) g, is also proportional to R², where g is the gravitational constant. Large particles are, therefore, expected to be levitated near the lower electrode, while smaller particle float higher away from the electrode.

The fluorescent particles used in the experiments are made of acrylic and have nominal particle diameters of 10 µm (blue emission) and 40 µm (green emission) . Figure 1 shows the size distributions of the two kinds of particles, where the size of the particles was measured by the scanning electron microscope. Figure 2 shows a snapshot of the levitating particles which clearly display the sheath structure. When these particles were injected into the plasma, smaller blue particles were levitated at relatively higher region, while larger green particles were levitated at the lower region as shown in figure 2. If we assume that the particles whose diameters are at the points A, B and C in figure 2 levitate at the height A, B and C in Fig.1, we can estimate the electric field at each height as A: 79.2 V/m, B: 316.8 V/m and C: 1979.8 V/m, respectively.

Our new method has a lot of capabilities for the measurement of the spatial structure of the sheath plasma. When the number of the fluorescent color species increases and the size distribution of the particles is more reduced, the precision of the measurement can be higher. In addition, this method is a real-time observation, and the temporal variation can also be easily measured.

Lowering energy consumption during thin film growth made by magnetron sputtering techniques becomes of particular importance in view of sustainable development goals. As a large fraction of the process energy is consumed for substrate heating with the purpose of providing sufficient adatom mobility to grow dense films, the most straightforward strategy towards more environment-friendly processing is to find alternatives to the thermally activated surface diffusion. A promising route is offered by high-mass metal ion irradiation of the growing film surface, which we show is very effective in densification of transition metal nitride layers grown with no external heating, such that Zone 2 microstructures of the structure-zone model are obtained in the substrate temperature T_s range otherwise typical for Zone 1 growth. The practical implementation of this technique relies on heavy metal targets operated in high power impulse magnetron sputtering (HiPIMS) mode to provide periodic metal-ion fluxes which are accelerated in the electric field of the substrate to irradiate layers deposited from direct current magnetron sputtering (DCMS) sources. A key feature of this hybrid HiPIMS/DCMS configuration is the substrate bias which is synchronized with the heavy metal ion fluxes for selective control of their energy and momentum. Time-resolved ion mass spectrometry analyses provide information about the time evolution of ion fluxes incident at the growing film surface which is a crucial input for film growth experiments. The major fraction of process energy is used at the sputtering sources and for film densification, rather than for heating of the entire vacuum vessel. For the model materials system of TiAlN the process energy consumption can be reduced by as much as 64% with respect to conventional methods, with no compromise on coating quality. Model materials systems include TiN and metastable NaCl-structure Ti_1-xAl_xN films, which are well-known for challenges in stoichiometry and phase stability control, respectively, and are of high relevance for industrial applications. A strong dependence of Ti_0.50Al_0.50N-based film properties on the mass of the HiPIMS-generated metal ions is found where layers deposited with Cr⁺ irradiation exhibit porous nanostructure, high oxygen content, and poor mechanical properties. In contrast, W⁺ irradiation gives films that are fully-dense even with the W fraction on the metal lattice as low as 0.09. Importantly, the precipitation of softer wurtzite AlN phase is avoided hence layers with high hardness and low residual stress can be obtained at low substrate temperatures. The high effectiveness of heavy ions in substituting for the thermally-activated mobility is explained by the large mass difference between the incident ion and the atoms constituting the film, which results in effective creation of low energy recoils, leading to film densification at low T_s. Due to their high mass, metal ions become incorporated at lattice sites beyond the near-surface region of intense recoil generation leading to further densification, while preventing the buildup of residual stress. The critical parameter that controls the growth is shown to be the average momentum transfer per deposited metal adatom. Studies of high-temperature properties of TiAlWN films grown by hybrid W-HiPIMS/TiAl-DCMS co-sputtering led to the discovery of a new age hardening mechanism, which is based on the formation of Guinier-Preston (GP) zones.

View PDF for the rest of the abstract.

After 20 years of continuous development by several research groups and companies it is now clear that real industrial breakthroughs for the high-power impulse magnetron sputtering (HiPIMS) technology are happening. HiPIMS is a state-of-the-art tool for applying high demanding metal and ceramic coatings with superior properties for applications such as: metal fabrication process (machining, stamping, molding or other tools), functional decorative (shinny gold finish in iPhone 12 Pro), trench filling in semiconductor industry, or tribological (H-free DLC coatings with reduced friction, high hardness and enhanced thermal stability). Despite the great perspective and the positive forecasts for HiPIMS-technology since its’ discovery in 1999, it has taken more than 15 years for the real industrial breakthrough to start. For example, the deposition rate of HiPIMS is still considered to be rather low compared with conventional magnetron sputtering and even more so when compared to cathodic arc-deposition. Another issue is the complexity of use due to the large number of adjustable process parameters. It is not only the HiPIMS power supply, which itself has more controllable parameters than any traditional power supply, what contributes to this great deposition technology. It is also the process regulation (monitoring), the magnetron system (magnetic configurations), the gas flow, the pumping speed, etc. Apart from the traditional use of HiPIMS which is being currently implemented by the industry, it has been recently demonstrated that the application of a positive voltage reversal pulse adjacent to the negative sputtering pulse gives rise to the generation of high fluxes of energetic ions. This solution allows unprecedented benefits for the coating industry, such as the energetic deposition onto insulating or grounded substrates, improved coverage on 3D parts or components, or even substrate etching. The key factor is the ability to tailor both the energy and flux of the high fraction of ionized material present in a HiPIMS discharge by controlling the amplitude and duration of both the positive and negative pulses.

Pulsed laser technologies have been revealing ultrafast phenomena in pico- and femto-second ranges. Combining scanning tunneling microscopy (STM), atomic-scale dynamics has been extensively studied. Two types of time-resolved STM have been performed which utilizes non-linear optical supportively [1-3] and light-field-driven bias modulation [4-6]. The light-field-driven STM has an advantage to measure density of states of electrons in scanning tunneling spectroscopy (STS) [5]. Subcycle (less than monocycle) terahertz (THz) field has been used to modulate bias voltage so that the temporal resolution of around 1 pico-seconds. Here, we developed light-field-driven STM using subcycle mid-infrared (MIR) pulses with the center frequency of 30 THz to reveal photo-induced atomic-scale dynamics in femtosecond range.

A laser source of optical parametric chirped pulse amplifier (OPCPA) with the pulse duration of 8.2 fs was used to generate subcycle MIR pulses using a nonlinear crystal of GaSe. Time-resolved STM was conducted by using near-infrared (NIR) pump pulses as shown in Fig. 1(a) which induces interband transition in a layered compound of MoTe₂. Ultrafast modulation of the tunneling current as shown in Fig. 1(b) was succeeded to be measured with the scale of 29 fs which is considered to be contributed by hot-electrons. This technique will pave a new way for studying non-equilibrium electrons in atomic scale. Combining other pump conditions and detection schemes, unambiguous understanding of surface dynamics can be expected [2, 3, 8].

[1] S. Liu et al., Sci. Adv. 8, 5682 (2022). [2] H. Mogi et al., npj 2D Mat. Appl. 6,72 (2022). [3] H. Mogi, et al., Jpn. J. Appl. Phys. 61, SL1011 (2022). [4] T. L. Cocker, et al., Nat. Photon. 7, 620 (2013). [5] S. Yoshida et al., ACS Photon. 6, 1356 (2019). [6] S. Yoshida et al., ACS Photon. 8, 315 (2021). [7] Y. Arashida et al., ACS Photon. 9, 3156 (2022). [8] Y. Arashida et al., Appl. Phys. Exp. 15, 092006 (2022).

The desire to probe and control individual quantum systems has led to significant scientific and engineering advances in quantum information science. Single atoms and molecules on surfaces, on the other hand, have been extensively studied in search of novel electronic and magnetic functionalities. These two paths came together when it was clearly demonstrated that individual spins on a surface can be coherently controlled and read out in an all-electrical fashion [1]. The enabling technique is scanning tunneling microscopy (STM) combined with electron spin resonance (ESR) [2], which provides unprecedented coherent controllability at the Angstrom length scale. In this talk, I present our approach to control multiple electron spins in an artificially built spin structures on surfaces. We found that remote spins, which are outside the tunnel junction, can be controlled by the local oscillating magnetic fields created by a single-atom magnet placed next to them in oscillating electric fields. The read-out of multiple spins is achieved by a sensor atom weakly coupled to them. The resonances of the sensor spin are separated in the frequency domain so that we can independently and simultaneously control the sensor and remote spins.

[1] S. Baumann et al., Science 350, 417 (2015).

[2] Y. Chen et al., Adv. Mater. 2107534 (2022).

The miniaturization of electronic and optoelectronic devices at the nanoscale presents unprecedented opportunities across various technological domains. In these miniature devices, materials are confined to spaces smaller than a micrometer, which raises a fundamental question: do the properties of these materials remain identical to their bulk counterparts? While the quantum confinement effect typically dominates at scales below 10 nm, certain materials and phenomena are influenced by long-range interactions and global propagations, extending the pronounced confinement effects to lengths greater than 100 nm. Moreover, confined materials are inherently more susceptible to their boundaries due to their substantial surface-to-volume ratio, including interactions with substrates and surrounding structures.

However, understanding the properties of these highly confined nanomaterials, influenced by their local carrier and exciton dynamics, presents a major challenge due to the limited applicability of conventional optical spectroscopy techniques at the nanoscale. In this presentation, we demonstrate the use of infrared scattering scanning near-field optical microscopy (IR s-SNOM) and its time-resolved variant, ultrafast IR s-SNOM, to investigate the impact of spatial confinement on nanomaterials. By integrating an atomic force microscope and infrared pulsed excitation, IR s-SNOM offers versatility and a spatial resolution below 50 nm.

Leveraging the Drude response associated with free carriers in the infrared frequency range, IR s-SNOM can distinguish between metals and insulators. We apply this technique to study vanadium dioxide nanoparticles (VO2 NPs), enabling the resolution of their insulator-to-metal transitions at the individual particle level (see Fig 1a). Our observations reveal that smaller NPs exhibit transitions at higher temperatures, possibly due to the presence of fewer nucleation sites within their confined volumes. Additionally, we identify stochastic behavior, where identical NPs exhibit phase transitions at different temperatures during repeated heating cycles. Both findings underscore the metastable nature of superheated VO2 NPs, and IR s-SNOM provides a unique opportunity to observe the signatures of metastability in individual NPs.

Moreover, the infrared frequency range encompasses the distinctive response of photoinduced excitons, including hydrogen-like 1s-2p transitions. We investigate these exciton transitions in carbon nanotubes on a quartz substrate using interferometric ultrafast IR s-SNOM (Fig 1b). This method, employing a lock-in sideband detection scheme, enhances sensitivity to detect photoinduced near-field scattering changes down to ~0.01%. Simultaneously, interferometric detection ensures the extraction of pure near-field contrasts. With ultrafast IR s-SNOM, we not only demonstrate distinct exciton relaxation dynamics between different nanotubes but also reveal significant heterogeneity within each nanotube. Specifically, our research uncovers substantial heterogeneity within bundles of carbon nanotubes, arising from interactions both among tubes and with the substrate.

Our findings establish tip-based infrared nano-spectroscopy as a valuable tool for investigating the effects of nanoconfinement on materials. This understanding holds significant promise in advancing the fields of nanomaterials and nanodevices.

The real-space observation of chemistry and magnetic structure using scanning tunneling microscopy (STM) or synchrotron-based x-ray microscopy (XM) continues to have a tremendous impact on our understanding of nanoscale materials. However, although STM provides high spatial resolution, it lacks direct chemical contrast. On the other hand, XM can provide chemical as well as magnetic sensitivity, but the spatial resolution is inferior. In order to overcome these limitations, we have developed a technique that combines the spin sensitivity and chemical contrast of synchrotron x-rays with the locality of STM.

Generally, materials characterization by x-rays requires a large number of atoms and reducing the material quantity for measurements is a long-standing goal. To date, attogram amount of sample can be detected by x-rays; however, this is still in the range of 10⁴ atoms or more and gaining access to a much smaller samples is becoming extremely arduous.

In this presentation, we show that x-rays can be used to characterize the elemental and chemical state of just one atom [1]. Using a specialized tip as a detector, x-ray excited currents generated from an iron and a terbium atom coordinated to organic ligands are detected. The fingerprints of a single atom, the L_2,3 and M_4,5 absorption edge signals for iron and terbium respectively, are clearly observed in x-ray absorption spectra. X-ray excited resonance tunnelling is dominant for the iron atom. The x-ray signal can be sensed only when the tip detector is located directly above the atom in extreme proximity, which confirms atomically localized detection in the tunnelling regime. Our work connects synchrotron x-rays with a quantum tunnelling process and opens future x-rays experiments for simultaneous characterizations of elemental, and chemical properties of materials at the ultimate single atom limit.

This work was performed at the Advanced Photon Source and the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility under Contract No. DE-AC02-06CH11357.

[1] Nature 618, 69-73 (2023).

Given its central role in various light energy conversion systems, PET from photoexcited molecules has been widely studied using optical spectroscopy and photocurrent measurement. Detailed insights into this process as an initial process of photocurrent generation have been obtained using microscopic techniques that combine scanning probe microscopes (SPMs) and optical systems. These techniques have allowed photocurrent generation efficiency to be related to local molecular morphology on the nanoscale, far below the diffraction limit. However, their spatial resolution remains insufficient to distinguish individual molecules, and observed PET signals from the photoexcited molecule are often obscured by ensemble-averaging over inhomogeneous local structures. Since electron transfer between two substances depends on the direct overlap of their electron wavefunctions, atomic-scale geometric changes can profoundly affect the efficiency of the process. Consequently, it would be highly desirable to develop a photocurrent measurement technique with atomic spatial resolution that could reveal the fundamental physics governing the PET process.

In this study, we report atomic-scale visualization of photocurrent channels through the molecular orbitals of a single free-base phthalocyanine (FBPc) molecule [1] using a scanning tunnelling microscope (STM) combined with a tuneable laser (Figure) [2-4]. PET from the single FBPc molecule in the first excited state was distinctly detected via the photoinduced tunnelling current through the STM tip. Depending on the applied bias voltage, not only the direction but also the spatial distribution of the photocurrent changes markedly. The atomically resolved photocurrent images allowed us to discover multiple counterflowing photocurrent channels even at a voltage where the averaged photocurrent is almost zero. Moreover, we found direct evidence of competition between PET and photoluminescence (PL), and demonstrated the controllability of their branching ratio during energy relaxation by positioning the STM tip with three-dimensional, atomic precision. Our findings present that specific photocurrent channels can be selectively promoted or suppressed by tuning the coupling between molecular orbitals and metal wavefunctions, which provides a new perspective for improving the energy conversion efficiency by atomic-scale electronic and geometric engineering of molecular interfaces.

[1] M. Imai-Imada et al., Nature 603, 829 (2022).

[2] H. Imada, M. Imai-Imada et al., J. Chem. Phys. 157, 104302 (2022).

[3] H. Imada, M. Imai-Imada et al., Science 373, 95 (2021).

[4] Rafael B. Jaculbia, et al., Nat. Nanotechnol. 15, 105 (2020).

Aprotic Li-O₂ batteries are one of the emerging next-generation batteries, boasting a much higher theoretical energy density compared to the state-of-the-art Li-ion batteries. However, before Li-O₂ batteries can be practically applied, it is essential to address the high charging overpotentials of these devices, which inevitably lead to irreversible parasitic reactions. Utilizing a redox mediator (RM) is an effective strategy to reduce the charging overpotential and suppress these parasitic reactions. The Br^-/Br₃^- redox couple is particularly interesting as it is less prone to decomposition compared to organic RMs. Nonetheless, the mitigating effect of RMs is currently inadequate, making it imperative to elucidate the Li₂O₂ reductive growth and oxidative decomposition mechanisms. Specifically, identifying the true reactive interfaces is crucial. In this study, Nano-secondary ion mass spectrometry (Nano-SIMS) isotopic three-dimensional imaging and differential electrochemical mass spectrometry (DEMS) analyses of individual Li₂O₂ particles revealed the reactive interface in a system containing the Br^-/Br₃^- redox couple as the RM. By combining the Nano-SIMS analyses and the DEMS data acquired using ¹⁸O₂, both discharging and charging reactions take place at the Li₂O₂/electrolyte interrace. Results of similar examinations in other electrolyte systems (amide-based electrolyte without RM) will also be reported. Briefly, in the amide-based electrolyte systems, it was also revealed that both charging and discharging reactions are proceeding at the Li₂O₂/electrolyte interface despite not using RM. Such characteristics are important for reducing the charging voltage and consequently improving the cycle characteristics.

Supercapacitor is a promising device for the power storage. In the University of Santo Tomas, biomaterials have been extensively investigated for the electrode materials for supercapacitors.

Easily accessible energy is a necessity in the present world. While technology advances, more alternative sources of energy are discovered. With the fast-growing demand for energy and power, the development of energy storage devices, like batteries, capacitors, and super capacitors, is a clear solution.

The University of Santo Tomas Fabric Super capacitor Team utilized local Philippine natural fibers, such as pina, abaca, banana, and water hyacinth blended with polyester or cotton. These woven textiles coated with conducting polymers carbon nanotubes or rice straw biochar performed well as super capacitor electrode materials. The team gained wisdom from the challenges and successes of working with natural fabrics as energy storage devices. We hope that the materials from nature will be used in the near future.

Introduction

AEMFCs have emerged as an important future replacement for proton exchange membrane fuel cells in portable applications such as automobiles because of their potential to operate free of Pt group catalysts. Their durability, however, still needs improvement to be fully competitive. To optimize the power output of a given anion exchange membrane (AEM) and reduce its susceptibility to degradation, it is essential to understand the membrane hydration characteristic during operation. In this paper, we investigated the steady state and transient water distribution in an AEMFC during operation using an in-house build CARS spectroscopy system newly developed in our laboratory. With this system, we recently obtained the in-situ vibrational spectra of OH species in an AEM for the first time.

Procedure

AEM film of QPAF-4 (Fig. 1) of 2.0 meq g^-1 IEC and 30 µm thickness was solution cast as reported [1]. Gas Diffusion elements (GDE) of size 2 cm × 2 cm and a Pt loading of 0.2 mg cm^-2 were swirl-sprayed using Pt/CB catalyst [2]. A cell with Parallel flow channels was assembled as reported [3]. The cell was operated with H₂/O₂ at a flow rate of 100 ml min^-1, cell temperature of 60 °C, and relative humidity of 90%.

An 11 mW 785 nm pump and 16 mW Stokes lasers were irradiated in the cell during CARS measurement. The exposure time was 200 ms. For steady-state measurement, the current density was varied from 0 A/cm² to the maximum achievable value in steps of 0.05 A/cm². For the first 10 s of transient response measurement, the current was maintained at 0.01 A cm^-2. After 10 s, the current density was raised to 0.1 A cm^-2 in a single step. The spectra were recorded from the cathode side to the anode side in steps of 5 µm. Spectral normalization was done using the aromatic peak around 1620 cm^-2.

Results

During power generation, water in the membrane on the anode side increased steadily with increasing current density. At the center of the membrane, water reduced with increasing current density up to 0.05 A cm^-2. Above 0.05 A cm^-2, the water increased. On the cathode side, water decreased with increasing current density up to 0.1A cm^-2 (Fig. 2 shows the spectrum at 0.1 A cm^-2). Above 0.1 A cm^-2, water increased. Fig. 3 shows the change in OH with current density.

The transient hydration response to a sudden change in current density partly mirrored the steady-state response. However, the decrease in water on the cathode side was more severe than the increase on the anode side. The severe drop in water could be because of the slower diffusion of water to the cathode compared to H₂O formation at the anode. The membrane hydration was also observed to recover much sooner than expected. This could be because immediately after the current was changed, water moved to the anode side by electro-osmotic drag (hydroxide-induced water movement); after this initial response, diffusion migration, and sorption quickly established a new water balance approximating the initial level because the change was relatively small. This could have also been made possible by the fact that the cell was being operated at 90%RH, which means there was enough moisture in the cell to defuse the change in hydration. Fig. 4 shows the change in OH at different positions in the membrane with time.

Conclusion

Without power generation, the water distribution is uniform across the membrane; however, during power generation, the local hydration conditions depend on the depth inside the AEM. On the anode side of the AEM, the hydration response to an increase in current density is a steady increase.

View PDF for the rest of the abstract.

Introduction

The lithium-air battery (LAB), which has ten times the energy density of conventional lithium-ion batteries (LIB), is one of the promissing candidates for the next-generation storage batteries, and there are great expectations for its development [1]. However, the reaction mechanism of the cathode reaction (2Li⁺+ 2e^- + O₂ --> Li₂O₂) is still unclear, and the type of Li₂O₂ that is the product of the cathode in discharging is still unknown. The main reason for this is considered to be that it was difficult to directly observe the compounds generated at the cathode during LAB operation. By improving the laboratory XRD and the observation cell, we succeeded in operando XRD measurements of the cathode reaction in the LAB. In addition, under general conditions, the cathode product was Li_1.5O₂ with some Li missing from the crystal lattice of Li₂O₂ [2]. Here, we describe the details and discuss the reaction mechanism.

Experimental

An electrochemical cell covered with a Kapton® dome was constructed to allow constant oxygen flow to the cathode side of the LAB, and was attached to the diffractomator of a Rigaku Ultima IV XRD measurement system. A Cu Ka was used as the incident x-ray, a high-speed one-dimensional detector was used as the detector, a Ketjen black free-standing film was used as the cathode material, and tetraglyme solution with 0.5 M LiTFSI + 0.5 M LiNO₃ + 0.2 M LiBr was used as the electrolyte solution. The LAB was discharged and charged at a constant current density of 0.4 mA/cm² for 10 hours (4.0 mAh/cm²) each, and the XRD profile was recorded every 20 minutes. Each XRD profile was subjected to Tietveld analysis using Rigaku’s SmartLab Studio II software to determine the cathode product and its crystal structure.

Results and discussion

Figure 1 shows the XRD profile measured during discharging. The peaks marked with as an asterisk in the figure are from the cell parts, and the peaks marked with a diamond are from the cathode product. As a result of detailed Rietveld analysis, the cathode product at the discharging capacity of 4.0 mAh/cm² (dark blue line profile at the top of the figure) is Li_1.5O₂. Instead of the normal LiO₂ with a rectangular crystal structure, LiO₂ with a hexagonal crystal structure, which is the same as that of Li₂O₂, was observed immediately after the discharge. As the discharge progressed, Li was added to it, and the lattice constant gradually extended in the c-axis direction, forming Li_1.5O₂ at a discharge of 4.0 mAh/cm². In the presentation, the charging process and the charge-discharge cycle characteristics would also be discussed.

Rererences [1] W. J. Kwak, et al., Chem. Rev. 120, 6626 (2020). [2] M. Aoki and T. Kondo, et al., J. Phys. Chem. C in press (2023).

Room temperature ionic liquids (RTILs) are promising electrolyte materials for various electrochemical applications. One of the electrochemical features that are absent in molecular solvents were found in metal electrodeposition: significant overpotentials of ~1 V were found at RT and decrease at higher temperatures to be disappeared at ~200 °C. A possible origin of such characteristic behaviors is a double layer structure at RTIL/electrode interfaces consisting of multiply-ordered layers of ions. This interfacial structure is so rigid that a certain “overpotential” is required for alternating the order of the ionic layers [1], and thus suspected to inhibit electrochemical reactions. However, the origin of such an characteristic electrodeposition behavior has been unclear due to lack of direct evidences. Thus, we performed in-situ observation of RTIL/electrode interfaces under reaction condition by using surface-enhanced infrared absorption spectroscopy (SEIRAS) that can selectively probe molecular vibrations at the interfaces.

SEIRA spectra were recorded for a polycrystalline Au electrode in a typical RTIL [C3mpy][TFSA] (Fig.1, inset) containing 0.1 M Co(TFSA)2 during potential scans. At all examined temperatures (300 to 370 K), SEIRA spectra indicate anion-to-cation replacement in the first ionic layer on the electrode as represented by steap change in intensities. The onset of this interfacial ion replacement agree with that of Co electrodeposition observed in voltammograms as shown in the Fig. 1. Furthermore, both onsets positively shift at higher temperatures. This onset shift was also observed for neat [C3mpy][TFSA], meaning that this feature is intrinsic for the RTIL. It was also confirmed that reactivity of Co electrodeposition depends on the interfacial structures with anionic or cationic first layer. Thus, the characteristic temperature-dependent overpotential of Co electrodeposition was ascribed to the potential-induced interfacial restructuring [2]. Its microscopic mechanism that can be explained with extended application of Marcus theory will be discussed in the presentation. [1] K. Motobayashi et al., J. Phys. Chem. Lett. 4, 3110 (2013); Electrochem. Commun. 100, 117 (2019). [2] K. Motobayashi et al., J. Phys. Chem. Lett. 11, 8697 (2020).

Since its exceptional qualities in the storage of energy applications, two-dimensional in nature molybdenum sulphide (MoS ₂ ) has been the subject of intense investigation over the past two decades. MoS ₂ contains a large number of active sulphur edges, but conductivity and efficiency are constrained by the existence of inactive surfaces. Thus, in this research, we sought to promote more active sites by doping nickel (Ni) in various weight percentages (2%, 4%, 6%, 8%, and 10%) into the structural framework of silicon dioxide (MoS ₂ ). The impacts of this doping were examined using physio-chemical analyses. X-ray diffraction (XRD) pattern, Raman, and chemical composition (XPS) analyses were used to confirm the Ni incorporation in MoS ₂nanosheets. Microscopic investigations demonstrated that Ni-doped MoS ₂ nanosheets were vertically aligned with enhanced interlayer spacing. Cyclic voltammetry, Galvanostatic charge-discharge, and electrochemical impedance spectroscopy investigations were used to characterize the electrochemical characteristics. The 6% Ni-doped MoS ₂ electrode material showed better C _SP of 528.7 F/g @ 1 A/g and excellent electrochemical stability (85% of capacitance retention after 10000 cycles at 5 A/g) compared to other electrode materials. Furthermore, the solid-state asymmetric supercapacitor was assembled using Ni-doped MoS2 and graphite as anode and cathode materials and analyzed the electrochemical properties in the two-electrode system. First-principles computations were performed to determine the impact of the Ni-atom on the MoS 2 surface. Further, it was examined for electronic band structure, the projected density of states (PDOS), and Bader charge transfer analyses.

In recent years, with the elucidation of the importance of local structure in heterogeneous catalysis and the development of single-molecule electronics, there has been a strong desire to measure electrochemical interfaces at the single-molecule level. Electrochemical scanning tunneling microscopy (EC-STM) enables direct observation of electrochemical interfaces with a nanoscale spatial resolution by bringing a metal tip close to the electrochemical interface and measuring tunneling current. The use of this technique is expected to lead to the development of single-molecule measurements of chemical reactions and tip-enhanced spectroscopy. In this study, we visualized the reaction of a single ferrocene (Fc) molecule using EC-STM by establishing a sample preparation method suitable for single-molecule measurement. Then, we established a new tip fabrication technique to solve a long-standing difficulty in EC-STM.

To fabricate mixed self-assembled monolayer (SAM) of 8,13-trimercaptotriptycene (Trip) and its Fc derivative (Fc-Trip) on an Au(111) electrode, the Au(111) electrode was immersed in acetone solution (0.1 mM) of Trip (0.1 mM) and Fc-Trip (0.1 mM) for 10 min respectively, and then kept at 60 degrees for 2 hours in the Trip solution. A three-electrode electrochemical cell was prepared using the mixed SAM as the working electrode (WE), an Au wire as the counter electrode (CE), and a quasi-reference electrode (RE). EC-STM measurements were performed in 0.1 M HClO₄ solution using MS-10 STM (Bruker) controlled by a NanoScope V (Bruker) with a Pt/Ir wire coated with Apiezon wax as a tip. Next, a three-electrode cell was constructed using glass-insulated carbon microelectrode probes (carbon probe) as WE and Au wires as CE and RE. −0.4 V vs Au wire was applied in AuCl₄⁻solution using a bipotentiostat (Bruker) for about 600 s to deposit Au. Using the Au deposited carbon probe as a tip, EC-STM measurements of 1,1',4',1"-terphenyl-4-thiol (Ph₃SH) SAM on Au(111) were performed in 0.1 M HClO₄ solution by the method described above.

The EC-STM images of a single Fc molecule were successfully obtained by preparing a SAM(Fig. 1a) in which Fc was isolated and dispersed using Trip as a base (Fig. 1b) [1]. The protrusions height of Fc single molecules decreased upon oxidation (Fig. 1c), which was attributed to the change in the electronic state of Fc during redox reactions. Since various functional groups can be bonded to Trip, Trip can be used as a new platform for single molecule reaction measurement with EC-STM [2].

While EC-STM has been shown to be a powerful tool, the difficulty of tip fabrication is one of the issues that reduce its versatility. Conventionally, a metal wire was etched to create an atomically sharp tip, which was then coated by hand using wax or other insulating materials in order to suppress Faradaic current from ions and molecules in solution. However, the success rate was low due to the difficulty of coating the tip except for the very end that detects the tunneling current. In this study, we have established a tip fabrication technique that enables EC-STM measurement with a higher success rate to solve the long-standing problem of tip fabrication [3]. The EC-STM tips were fabricated by electrochemically depositing Au on carbon probes with a diameter of several hundred nm [4] (Fig.1d). EC-STM images of PH₃SH SAM were successfully measured using these tips (Fig.1e), with the success rate up to 80%. The new tip fabrication method is expected to greatly expand the scope of EC-STM measurements. In the presentation, we will also discuss the results of tip-enhanced Raman spectroscopy (TERS) using this tip.

[1] F. Ishiwari et al. J. Am. Chem. Soc., 141, 5995 (2019).

View PDF for the rest of the abstract.