Stacking order reduction in multilayer graphene by inserting nanospacers

Toward macroscopic applications of graphene, it is desirable to preserve the superior properties of single-layer graphene in bulk scale. However, the AB-stacking structure is thermodynamically favored for multilayer graphene and causes strong interlayer interactions, resulting in property degradation. A promising approach to prevent the strong interlayer interaction is the staking order reduction of graphene, where the graphene layers are rotated in-plane to form a randomly stacking structure. In this study, we propose a strategy to effectively decrease the stacking order of multilayer graphene by incorporating nanospacers, cellulose nanofibers, or nano-diamonds (NDs) in the formation process of porous graphene sponges. We conducted an ultrahigh temperature treatment at 1500 °C with ethanol vapor for the reduction and structural repair of graphene oxide sponges with different concentrations of the nanospacers. Raman spectroscopy indicated an obvious increase in the random-stacking fraction of graphene by adding the nanospacers. The x-ray diffraction (XRD) analysis revealed that a small amount of the nanospacers induced a remarkable decrease in ordered graphene crystalline size in the stacking direction. It was also confirmed that a layer-number increase during the thermal treatment was suppressed by the nanospacers. The increase in the random-stacking fraction is attributed to the efficient formation of randomly rotated graphene through the ethanol-mediated structural restoration of relatively thin layers induced by the nanospacers. This stacking-order-reduced graphene with bulk scale is expected to be used in macroscopic applications, such as electrode materials and wearable devices.Zizhao Xu, Taiki Inoue, Yuta Nishina, and Yoshihiro Kobayashi, "Stacking order reduction in multilayer graphene by inserting nanospacers", Journal of Applied Physics 132, 174305 (2022) https://doi.org/10.1063/5.010382

Gas flow-directed growth of aligned carbon nanotubes from nonmetallic seeds

Kite growth is a process that utilizes laminar gas flow in chemical vapor deposition to grow long, well-aligned carbon nanotubes (CNTs) for electronic application. This process uses metal nanoparticles (NPs) as catalytic seeds for CNT growth. However, these NPs remain as impurities in the grown CNT. In this study, nanodiamonds (NDs) with negligible catalytic activity were utilized as nonmetallic seeds instead of metal catalysts because they are stable at high temperatures and facilitate the growth of low-defect CNTs without residual metal impurities. Results demonstrate the successful growth of over 100-$\mu$m-long CNTs by carefully controlling the growth conditions. Importantly, we developed an analysis method that utilizes secondary electron (SE) yield to distinguish whether or not CNTs grown from metal impurities. The absence of metallic NPs at the CNT tips was revealed by the SE yield mapping, whereas the presence of some kind of NPs at the same locations was confirmed by atomic force microscopy (AFM). These results suggest that most of the aligned CNTs were grown from nonmetallic seeds, most likely ND-derived NPs, via the tip-growth mode. Structural characterizations revealed the high crystallinity of CNTs, with relatively small diameters. This study presents the first successful use of nonmetallic seeds for kite growth and provides a convincing alternative for starting materials to prepare long, aligned CNTs without metal impurities. The findings of this study pave the way for more convenient fabrication of aligned CNT-based devices, potentially simplifying the production process by avoiding the need for the removal of metal impurities.Comment: Accepted version. Main manuscript: 26 pages, 6 figures. Supporting information: 8 pages, 9 figure

CityRefer: Geography-aware 3D Visual Grounding Dataset on City-scale Point Cloud Data

City-scale 3D point cloud is a promising way to express detailed and complicated outdoor structures. It encompasses both the appearance and geometry features of segmented city components, including cars, streets, and buildings, that can be utilized for attractive applications such as user-interactive navigation of autonomous vehicles and drones. However, compared to the extensive text annotations available for images and indoor scenes, the scarcity of text annotations for outdoor scenes poses a significant challenge for achieving these applications. To tackle this problem, we introduce the CityRefer dataset for city-level visual grounding. The dataset consists of 35k natural language descriptions of 3D objects appearing in SensatUrban city scenes and 5k landmarks labels synchronizing with OpenStreetMap. To ensure the quality and accuracy of the dataset, all descriptions and labels in the CityRefer dataset are manually verified. We also have developed a baseline system that can learn encoded language descriptions, 3D object instances, and geographical information about the city's landmarks to perform visual grounding on the CityRefer dataset. To the best of our knowledge, the CityRefer dataset is the largest city-level visual grounding dataset for localizing specific 3D objects.Comment: NeurIPS D&B 2023. The first two authors are equally contribute

水平配向単層カーボンナノチューブの合成制御

学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 丸山 茂夫, 東京大学教授 大久保 達也, 東京大学准教授 塩見 淳一郎, 東京大学准教授 加藤 雄一郎, 東京大学講師 千足 昇平University of Tokyo(東京大学

Trion confinement in monolayer MoSe2 by carbon nanotube local gating

We have successfully confined trions into a one-dimensional restricted space of a MoSe2 device with CNT gate electrodes. The dry transfer process, including deterministic dry transfer of aligned CNTs, has led to an hBN-encapsulated MoSe2 device with CNT back gate electrodes. In contrast to a location without CNT gate electrodes, applying voltage via CNT gate electrodes significantly alters PL spectra at a location with CNT gate electrodes. PL imaging has revealed that image contrast from trions is linear along the CNT electrode underneath, consistent with 1D confinement of trions in response to the CNT local gating. The confinement width obtained from the PL image is 5.5 x 10^2 nm, consistent with nanoscale 1D confined trions with the diffraction limit broadening. This work has demonstrated electrical control of excitonic states at the nanoscale, leading to novel optoelectronic properties and exciton devices in the future

Thermal defect healing of single-walled carbon nanotubes assisted by supplying carbon-containing reactants

We experimentally investigated the effect of carbon-containing reactants (C2H2) on healing the defects in single-walled carbon nanotubes (SWCNTs) by thermal processes at high temperatures (∼1100 °C). Introducing C2H2 notably improved the crystallinity of healed SWCNTs compared with the thermal process in Ar ambient without C2H2. The defect healing rate increased with increasing C2H2 partial pressure, and the healing effect of C2H2 was more remarkable for relatively thinner SWCNTs (<1.1 nm). Combined with the relevant theoretical work reported previously, we propose a healing model in which C2H2 helps to heal the vacancy defects and increases the healing rate at high temperatures.This is the version of the article before peer review or editing, as submitted by an author to Applied Physics Express. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.35848/1882-0786/acaaec

Xanthogranulomatous inflammation of the perimetrium with infiltration into the uterine myometrium in a postmenopausal woman: a case report

BACKGROUND: Xanthogranulomatous inflammation is an uncommon form of chronic inflammation that is destructive to the normal tissue of affected organs. Although xanthogranulomatous endometritis and xanthogranulomatous salpingitis of the female genital tract has been described previously, to the best of our knowledge, this is the first report of xanthogranulomatous inflammation with infiltration into the uterine myometrium from the perimetrium without endometritis. CASE PRESENTATION: A 68-year-old Japanese woman with intermittent lower abdominal pain and low-grade fever who was initially treated with antibiotics underwent hysterectomy due to abscess formation in the posterior wall of the myometrium and perimetrium (the outer serosal layer of the uterus). Histopathological findings revealed that the abscess was caused by xanthogranulomatous inflammation with the granulation tissue and chronic inflammatory cells that consisted of focal and sheets of foam cells. The inflammation destroyed the perimetrial elastic lamina, and the myometrium was deeply infiltrated by the xanthoma cells. Neither endometritis nor salpingitis was coexistent with the xanthogranulomatous inflammation. CONCLUSION: The patient was diagnosed as xanthogranulomatous inflammation, most likely arising from the perimetrium. Our findings suggest that the perimetrium, as well as the endometrium and adnexae, is one of the origins of xanthogranulomatous inflammation in female genital tract