平原 佳織

Abstract Although CI chondrites are susceptible to terrestrial weathering on Earth, the specific processes are unknown. To elucidate the weathering mechanism, we conduct a laboratory experiment using pristine particles from asteroid Ryugu. Air‐exposed particles predominantly develop small‐sized euhedral Ca‐S‐rich grains (0.5–1 μm) on the particle surface and along open cracks. Both transmission electron microscopy and synchrotron‐based computed tomography combined with XRD reveal that the grains are hydrous Ca‐sulfate. Notably, this phase does not form in vacuum‐ or nitrogen‐stored particles, suggesting this result is due to laboratory weathering. We also compare the Orgueil CI chondrite with the altered Ryugu particles. Due to the weathering of pyrrhotite and dolomite, Orgueil contains a significant amount of gypsum and ferrihydrite. We suggest that mineralogical changes due to terrestrial weathering of particles returned directly from asteroid occur even after a short‐time air exposure. Consequently, conducting prompt analyses and ensuring proper storage conditions are crucial, especially to preserve the primordial features of organics and volatiles.

Abstract Micrometeorites, a possible major source of Earth’s water, are thought to form from explosive dispersal of hydrated chondritic materials during impact events on their parental asteroids. However, this provenance and formation mechanism have yet to be directly confirmed using asteroid returned samples. Here, we report evidence of mild shock metamorphism in the surface particles of asteroid Ryugu based on electron microscopy. All particles are dominated by phyllosilicates but lack dehydration textures, which are indicative of shock-heating temperatures below ~500 °C. Microfault-like textures associated with extensively shock-deformed framboidal magnetites and a high-pressure polymorph of Fe–Cr–sulfide have been identified. These findings indicate that the average peak pressure was ~2 GPa. The vast majority of ejecta formed during impact on Ryugu-like asteroids would be hydrated materials, larger than a millimetre, originating far from the impact point. These characteristics are inconsistent with current micrometeorite production models, and consequently, a new formation mechanism is required.

The returned samples from Hayabusa2 show that C-type asteroid Ryugu experienced various steps of mineralogical alteration within only 1-2 million years after accretion.C-type asteroids are the source of the carbonaceous chondrite meteorites and represent remnants of primitive planetesimals that formed at the outer margins of the early Solar System and may have delivered volatiles to the inner Solar System, in particular the early Earth. However, the nature of carbonaceous chondrites is not well understood owing to terrestrial alteration. Here, we present the petrology and mineral chemistry of surface materials collected by the Japan Aerospace Exploration Agency (JAXA) Hayabusa2 spacecraft from the C-type asteroid Ryugu. The Ryugu particles we studied are similar to CI (Ivuna-type) chondrites but with some important differences, such as the presence of Na-Mg phosphates and Na-rich phases and the lack of ferrihydrite and gypsum. Ryugu particles experienced several steps of aqueous alteration, metasomatism and brecciation under variable conditions. These materials represent mixed lithologies and formed at different locations within their parent asteroid. The evidence presented here demonstrates that the C-type asteroid Ryugu experienced a complex geologic evolution shortly after its formation.

Samples from asteroid Ryugu returned by the Hayabusa2 mission contain evidence of extensive alteration by aqueous fluids and appear related to the CI chondrites. To understand the sources of the fluid and the timing of chemical reactions occurring during the alteration processes, we investigated the oxygen, carbon and Mn-53-Cr-53 systematics of carbonate and magnetite in two Ryugu particles. We find that the fluid was initially between 0 and 20 degrees C and enriched in C-13,O-17 and O-18, and subsequently evolved towards lighter carbon and oxygen isotopic compositions as alteration proceeded. Carbonate ages show that this fluid-rock interaction took place within approximately the first 1.8 million years of Solar System history, requiring early accretion either in a planetesimal less than similar to 20 km in diameter or within a larger body that was disrupted and reassembled.

Abstract The delivery of water to the inner Solar System, including Earth, is still a debated topic. A preferential role for hydrated asteroids in this process is supported by isotopic measurements. Carbonaceous chondrite (CC) meteorites represent our main source of information about these volatile-rich asteroids. However, the destruction of weaker materials during atmospheric entry creates a bias in our CC data. The return of surface materials from the C-type asteroid 162173 Ryugu by the Hayabusa2 spacecraft provides a unique opportunity to study high-porosity, low-density, primitive materials, unrepresented in the meteorite record. We measured the bulk oxygen isotope composition from four Ryugu particles and show that they most closely resemble the rare CI (CC Ivuna-type) chondrites, but with some differences that we attribute to the terrestrial contamination of the CI meteorites. We suggest that CI-related material is widespread among carbonaceous asteroids and a more important source of Earth’s water and other volatiles than its limited presence in our meteoritic collection indicates.

Abstract Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition.

In situ measurements of the electrical resistance of a parallel contact between carbon nanotubes were performed. The electrical conductivities of individual nanotubes and the interface were derived by varying the contact length systematically.

Capturing and analyzing cometary coma dust lead to elucidate the origin of water and organics within the Solar System. For future sample return missions of fragile organic microparticles from a cometary nucleus, rendezvous operations will become more favorable than flyby missions because the comet rendezvous can reduce impacting velocity of cometary dust particles slow enough to capture them intact, rather than hypervelocity flyby sampling like the Stardust mission to the Comet Wild 2. At JAXA/ISAS, we are developing a core technology for sample return of microparticles ejected at as a lower velocity as an order of 0.1 m/s to 100 m/s after rendezvous with a cometary nucleus. We have devised “Vertically Aligned Carbon Nanotube (VA-CNT)” carpets as an effective capture medium for such a purpose. The VA-CNT carpets can amplify van der Waals force with impacting particles due to the large contact area and can capture intact the microparticles of sub-mm in size or smaller in the vacuum space environment while preserving its adhesive strength. In this study, we modelled capturing mechanism of microparticles on the VA-CNT carpets by the impact analysis software “LS-DYNA” to further improve its particle capture performance. The stress–strain constitutive laws for the VA-CNT carpets were derived via indentation and inputted to our simulations that were consistent with impact experiment results. The simulations reveal that the mechanical property of the VA-CNT carpets is the key for the improvement of its particle capture performance suitable for sampling the cometary dust.

2021年6月のリュウグウ粒子の配分後、約１年にわたり８つの研究チーム(初期分析６チームとPhase2キュレーション２チーム)により系統的な分析が行われた。岩石・鉱物組織からみると、リュウグウは主として含水鉱物と有機物から構成され、微細な組織として複雑に共存することがわかった。また主要元素濃度、高精度酸素同位体などのバルク的分析の結果は、リュウグウ粒子は、太陽系の元素組成を代表する始原的なCIコンドライトと良い一致を示した。我々は、独自に開発した大気非曝露ナノ領域試料加工・分析システムを用い、有機物と含水鉱物の入り交ざった試料から物質科学的情報を得た。その結果、(１)含水鉱物集合体に特異的に濃集した脂肪属炭化水素に富む有機物の存在(２)太陽系で最も始原的な化学組成を持つ物質である証拠、そして(３)太陽系外縁部での形成が明らかになった。

Tungsten ditelluride (WTe2) is a semi-metallic transition metal dichalcogenide (TMDC). WTe2 has attracted a lot of interest for topological properties and various applications such as batteries. In this study, we developed a method to obtain WTe2 nanowires from solution-grown tungsten oxide nanowires. By optimizing the supply of Te vapor, which strongly influences sample composition and structure, and using small-diameter solution-grown nanowires as precursors, we finally synthesized relatively small-diameter WTe2 nanowires with diameters of 15-50 nm. Interestingly, nanowire structures are mainly obtained via tellurization, but when sulfurization and selenization are applied on the same precursors, nanotube structures are obtained. We assume that the volume increase via chalogenization is a key parameter that determines the formation of nanotubes and nanowires.

Chemical compositions of materials used for new sample holders (vertically aligned carbon nanotubes [VACNTs] and polyimide film), which were developed for the analysis of Hayabusa2-return samples, were determined by instrumental neutron activation analysis and/or instrumental photon activation analysis, to estimate contamination effects from the sample holders. The synthetic quartz plate used for the sample holders was also analyzed. Ten elements (Na, Al, Cr, Mn, Fe, Ni, Eu, W, Au, and Th) and 14 elements (Na, Al, K, Sc, Ti, Cr, Zn, Ga, Br, Sb, La, Eu, Ir, and Au) could be detected in the VACNTs and polyimide film, respectively. The VACNT data show that contamination by this material with respect to the Murchison meteorite is negligible in terms of the elemental ratios (e.g., Fe/Mn, Na/Al, and Mn/Cr) used for the classification of meteorites due to the extremely low density of VACNTs. However, for the Au/Cr ratio, even small degrees (1.7 wt%) of contamination by VACNTs will change the Au/Cr ratio. Elemental ratios used for the classification of meteorites are only influenced by large amounts of contamination (>60 wt%) of polyimide film, which is unlikely to occur. In contrast, detectable effects on Ti isotopic compositions are caused by >0.1 and >0.3 wt% contamination by VACNTs and polyimide film, respectively, and Hf isotopic changes are caused by >0.1 wt% contamination by VACNTs. The new sample holders (VACNTs and polyimide film) are suitable for chemical classification of Hayabusa2-return samples, because of their ease of use, applicability to multiple analytical instruments, and low contamination levels for most elements.

A sample holder for a suite of synchrotron radiation measurements on extraterrestrial materials, which are fragile and irregularly shaped, was developed using carbon nanotubes and polyimide. The holder enables investigation of such samples with multiple analytical instruments, which means that we can reduce the number of sample transfers between holders. The holder developed in our study also enables investigation of such samples without exposure to the terrestrial atmosphere, which contains abundant contaminants, such as water vapor and organic substances. The stability of the samples in the holder during the measurements and disturbance of the analysis result by the holder were evaluated, which showed that sample drift motion and image disturbance due to x-ray attenuation and scattering of the holder materials are insignificant.

In this study, the nominal tensile strength, Young's modulus and Weibull scale and shape parameter of the nominal tensile strength distribution of the MWCNTs synthesized by a thermal chemical vapor deposition (CVD) method were investigated by conducting uniaxial tensile tests. In addition, the structural defects which induced the failure of the MWCNTs were observed by a transmission electron microscope (TEM). TEM observations revealed that the MWCNTs exhibited several types of structural defects: discontinuous flaws such as holes, kinks and bends and remnant catalysts even though crystalline graphene layers were aligned with the MWCNT axis. The nanotube tested in this study fractured at the structural defects such as discontinuous flaws and kinks and bends, suggesting that the tensile strength of the CVD-grown MWCNTs used in this study was dominated by the above-mentioned structural defects. The tensile-loading experiments demonstrated that the nominal tensile strength, Young's modulus and Weibull scale and shape parameter of the as-grown MWCNTs were 5.2 +/- 2.1 GPa, 210 +/- 150 GPa, 5.9 GPa and 2.7, respectively. The MWCNTs used in this study showed larger Weibull scale parameter values compared with both the CVD-grown and arc-discharge-grown MWCNTs evaluated an earlier study. This suggested that there was an optimal nanotube structure for increasing nominal tensile strength; not too weak but also not too strong inter-tube coupling to permit an adequate load transfer between the nanotube walls and thus a consequent clean break fracture. We also investigated the effects of the thermal annealing on the mechanical properties of the MWCNTs. The structural changes observed after annealing led to no significant impact on the nominal tensile strength of the MWCNTs, which was mainly due to incomplete removal of the structural defects by thermal annealing.

<p>In this study, we report the relationship between the mechanical properties and structural defects of multi-walled carbon nanotubes (MWCNTs) synthesized by a chemical vapor deposition (CVD) method. The tensile strength, Young's modulus and Weibull modulus of the individual MWCNTs were determined by conducting uniaxial tensile tests using a manipulator tool operated inside a scanning electron microscope. In addition, the structural defects which induced the failure of the MWCNTs were observed by a transmission electron microscope (TEM). TEM observations revealed that the MWCNTs exhibited several types of structural defects: discontinuous flaws such as holes; kinks and bends; impurities i.e., catalysts even though highly crystalline layers were almost perfectly aligned with the MWCNT axis. The tensile-loading experiments demonstrated that the average tensile strength, Young's modulus and Weibull modulus of the 23 MWCNTs were 5.2 ± 2.1 GPa, 210 ± 140 GPa and 2.7, respectively. The MWCNTs underwent failure leaving either a clean break or a very short sword and sheath failure, suggesting that a significant interwall load transfer might be facilitated by the irregular wall structures as mentioned above. These mechanical characteristics and fracture modes were reasonably consistent with those of previously reported CVD-grown MWCNTs. In order to identify the structural defects controlling the fracture of the MWCNTs, structural analyses were conducted by comparing TEM images captured before and after their breaking. The TEM images of the individual MWCNTs revealed that the defects described above induced the nanotube failure. These suggest that the tensile strength of the CVD-grown MWCNTs used in this study is dominated by the structural defects in particular discontinuous flaws and kinks and bends. The results reported here indicate that improvement and optimization of synthesis methods are needed to prepare stronger MWCNTs with less structural defects reported here.</p>

Carbon nanotube (CNT) bundles are extracted from vertically aligned CNT array by tungsten probes and attached on the tips of these tungsten probes strongly by van der waals forces, forming flexible microprobes, with tip radii varying from 100 nm to 1 μm. The geometries and electrical properties of these original probes are adjusted by laser beam irradiation, electric current application, and alcohol treatment. The resistance measurement of a carbon nanocoil using bundled CNT probes as sensing probes by four-probe method demonstrates great advantages of bundled CNT probes in measuring the system with continuous deformation varying with time. Verification for the flexibility of bundled CNT probes with ultrathin carbon film shows the great application potential in non-destructive testing. This research demonstrates the potential application of bundled CNT as flexible microprobes.

Metal-filled carbon nanotubes (CNTs) are known to be used as pen-tip injectors for 3D manufacturing on the nanoscale. However, the CNT interior cannot accumulate enough material to fabricate complex metallic nanostructures. Therefore a method for refilling the CNT cartridge needs to be developed. The strategy for refilling of CNT cartridges is suggested in this study. Controlled growth of gold nanowires in the interior of isolated CNTs using a real-time manipulator installed in a transmission electron microscope is reported herein. The encapsulation process of discrete gold nanoparticles in the hollow spaces of open-ended multi-wall CNTs was evaluated in detail. The experimental results reveal that the serial loading of isolated gold nanoparticles allows the control of the length of the loaded nanowires with nanometer accuracy. Thermophoresis and the coalescence of gold nanoparticles are assumed to be the primary mechanisms responsible for gold loading into a CNT cartridge.

The wetting behavior of an ionic liquid (IL) on individual carbon nanotubes (CNTs) was experimentally investigated using in situ electron microscopy. The tip of a single CNT was brought into contact with the surface of the IL using a nanomanipulator. The formation of a meniscus was observed immediately at the contact point. A thin layer of IL also formed simultaneously across the entire CNT surface. The force because of wetting was measured using the Wilhelmy method. After correcting the macroscale classical equations by considering an "apparent" diameter that corresponds well with the thickness of the IL layer on individual CNTs, the experimental data indicated that the wettability of single CNTs with diameters of over 10 nm was subjected to classical laws at the macroscale.

The electrical property of carbon nanocoils (CNCs) annealed from 300 to 2900 K has been studied by a four-probe technique. It was shown that the resistivity of the CNCs decreased with the increase of the annealing temperature owing to the improvement of crystallinity and the most notable change of resistivity occurred at the initial structure change of the CNCs. Besides the measurement of room-temperature resistivity of the annealed CNCs, temperature-dependent resistance of the annealed CNCs was also measured. According to the nearest neighboring hopping mechanism, the average activation energy for electron hopping in the annealed CNCs was calculated, which indicated that the average activation energy reduced with the structural improvement of CNCs. It was also found that the variation of average activation energy was also sensitive to the initial structural change of CNCs. Finally, through studying the electrical property of the CNCs under expansion, it was found that the resistance of the CNC was not changed with elongation. © 2014 Elsevier Ltd. All rights reserved.

The effect of annealing at 1000-2600. °C on the crystallinity of carbon nanocoils (CNCs) has been evaluated to discuss the mechanism of energy dissipation during CNC oscillation and its structural dependence. The crystallinity of the CNCs was evaluated by transmission electron microscopy and electron diffraction. In situ observations of the resonant oscillations of individual cantilevered-CNCs were carried out by inducing a high-frequency electric field in a scanning electron microscope. Experimental results revealed a non-linear correlation between crystallinity and oscillation properties; crystallinity improved with annealing temperature from 1000. to. 2600 ° C and was comparable to graphite on annealing at 2600. °C, while the quality factor (Q) decreased on annealing above 1400. °C. Q showed a strong correlation with the shear modulus. These results suggest that the oscillation properties of CNCs are dominated by two types of energy dissipation mechanisms, originating in the existence of structural anomalies in less crystalline structures and in interlayer slipping in higher crystallinity structures. © 2013 Elsevier B.V.

Sc N@C fullerenes are inserted inside carbon nanotubes (CNTs). The results show that the thermal stability of Sc N@C fullerenes is around 1200 °C for the fullerenes resting on the wall of CNTs. Internal fullerenes show stability up to 1300 °C, which portrays them as one of most stable types of fullerenes. Electron irradiation of the peapods at 90 kV leads to the formation of capsules inside the CNTs at 5 × 10 e nm electron dosage. This value is an order of magnitude higher than the threshold of electron-induced damage in C molecules. Electron energy loss spectroscopy confirms the presence of Sc atoms in capsules. Encapsulation of fullerenes and capsule formation changes the oxidation state of Sc atoms from +2.5 towards +3. This is an evidence of charge transfer between the fullerene/capsule cage and CNT walls. © 2013 The Royal Society of Chemistry. 3 80 3 80 60 9 -2

In this paper, we show that the efficiency in the growth of carbon nanocoils is significantly improved by introducing a SnO buffer layer. Carbon nanocoils were synthesized by chemical vapor deposition using an Fe-Mg-Co or Fe-Mg-Co-Sn catalyst supported on an Al O substrate coated with a 30 nm SnO buffer layer. The carbon nanocoil growth rate improved by more than 200% compared with the non-coated substrate when using Fe-Mg-Co-Sn or Fe-Mg-Co catalyst layers 600 or 300 nm thick, respectively. The byproduct layer was also reduced significantly, which results in more than 50% gain in the consumption of carbon source gas during the synthetic process. The role for an external Sn supply from the buffer layer is discussed based on the experimental results. © 2013 Elsevier Ltd. All rights reserved. 2 2 3 2

Using a transmission electron microscope (TEM) equipped with a manipulator, we recently demonstrated the transition between the flattened state and the tubular state in rather thick carbon nanotubes (CNTs). This unique transition behavior provides a new concept of a nanosized device: a nanotorsional actuator. To realize and design the actuator, we used TEM observations and molecular dynamics simulations to examine the transition behavior and investigate how the torsion angle is determined and what the driving force is. Results indicate that a specific graphitic stacking order taken for the CNT inside determines the initial twist of a flattened CNT and thereby determines the rotational angle. Results also clarified that the transition results from thermal energy. © 2012 Elsevier B.V. All rights reserved.

This study investigates electron transport properties of a Joule heated multi-wall carbon nanotube at temperatures as high as about 2100 K. Results show that the electrical resistance is temperature-dependent. The temperature dependence of the resistance is inferred to originate from the temperature-dependent intrashell resistance and intershell conductance. The resistance variation was analyzed using a resistive transmission line model. Results well reproduced those obtained using a double shell conduction model where the electrons transport in the outermost shell and the second inner shell. © 2012 The Japan Society of Applied Physics.

We measured the recovery forces generated by a shape memory effect of plastically bent carbon nanotubes (CNTs) using a manipulator installed in a transmission electron microscope. The recovery force as estimated with the moment is as high as 120 aNm for a curvature of 0.025 nm of the plastic bend. It is indicated that recovery force depends on bending curvature: a larger curvature generates a larger recovery force. This result is discussed in terms of the gliding rate of topological defects to be repaired. © 2012 The Japan Society of Applied Physics. -1

We experimentally investigated a torsional actuator consisting of a carbon nanotube (CNT). Transmission electron microscopy revealed that the CNT, from its flattened state when energetically stable at room temperature, changes states reversibly to a tubular state depending on the amount of current applied to the CNT. The flattened CNT can be twisted, with its twist angle dependent on its chirality and length. The transition from the flattened state to the tubular state reverses the twist and generates a torsional torque as strong as ca. 5 nNnm, which is 50 times stronger than that of an artificial bionanorotary device. © 2012 American Institute of Physics.

Using a conductive soft Si probe for atomic force microscopy as an electrode of nanomanipulater installed in a transmission electron microscope, we successfully measured forces generated by one-way shape memory effect of a carbon nanotube (CNT). We revealed from the measured forces that the recovery moment is about several tens aNm for a 3.5 nm-diameter CNT consisting of four walls. The measured recovery forces are around thousand times stronger than the output of nano-sized bio-molecular actuators. This finding indicates that a CNT has an advantage as high-power actuators.

We report a feature of carbon nanotubes (CNTs) that arises when the surfaces of two vertically-aligned CNT brushes are pressed together. Adhesion between the CNTs creates a plane fastener-like device. Observations from scanning electron microscopy and measurements of adhesion properties indicate a device-dependence on CNT density and shape near the tip region. Among other applications, such fasteners have the potential to attach small components onto micron-sized electronic devices. © 2011 Copyright 2011 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License.

Recognizing the main factors affecting the spinning of carbon nanotube (CNT) yarns from vertically aligned brush-like CNTs (BCNTs) persists as a difficult challenge. Here, using in-situ drawing of as few as 20 CNTs from as-grown BCNT and measuring the force required for their separation from BCNT, we demonstrate that samples with different spinnability levels exhibit different separation force behaviors. Moreover, the average separation force per CNT differs among samples. Results show that the separation force in spinnable samples depends on the drawing location: it can be as high as 15 nN/CNT at the top of a sample and as low as 3 nN/CNT in the middle of a sample. In contrast, this force is around 10 nN/CNT for un-spinnable samples and is nearly constant throughout such samples. Detailed drawing site observations can pave the way to elucidation of the mechanisms of dry drawing processes of BCNT, which are vital for enhancing the strength of carbon nanotube yarns. © 2011 Elsevier Ltd. All rights reserved.

Molecular dynamics simulations were carried out on the ductile behavior of single-walled carbon nanotubes (SWNTs) under tensile stress by moving both ends at constant velocity at high temperature. The (10,10) armchair-SWNT resulted in plastic elongation through the sequential Stone-Wales (S-W) transformation, and the chirality changed keeping the two indices equal by alternately taking two dislocation directions with Burgers vectors b→=(1,0) and (0,1) instead of choosing only one of them toward zigzag-chirality with one index equal to zero. The comparison in the activation and formation energies for the two directions revealed that the torsional strain induced by the preceding S-W sequence was the main cause of this alternating choice. © 2011 Elsevier B.V. All rights reserved.