312 research outputs found
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-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
Improved performance of strain sensors constructed from highly crystalline graphene with nanospacer
This is the version of the article before peer review or editing, as submitted by an author to Japanese Journal of Applied Physics. IOP Publishing Ltd are 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/10.35848/1347-4065/ad0cdb.Xu Zizhao, Himura Yuna, Ishiguro Chikako, et al. Improved performance of strain sensors constructed from highly crystalline graphene with nanospacer. Japanese Journal of Applied Physics 63, 015001 (2023); https://doi.org/10.35848/1347-4065/ad0cdb.Graphene shows promise as an alternative material for strain sensors due to its excellent properties and could overcome the limitations of conventional metal sensors. However, current graphene-based strain sensors are fabricated from chemically reduced graphene oxide (rGO) and suffer from low linearity and large hysteresis in the sensor response as well as high initial resistance. These issues are caused by functional groups and defects remaining on the rGO. Herein, highly crystalline rGO is employed for the fabrication of the strain sensor. Porous rGO sponge with low defect density is prepared in bulk scale via the ethanol-associated thermal process at ultra-high temperature. The obtained rGO sensor exhibits improved linearity, low initial resistance, and very small hysteresis owing to the high crystallinity of the rGO. The composite of rGO with nano-diamond, which has the role of a nanospacer to separate the rGO layers, is found to be highly effective in enhancing the sensitivity
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
Green tea drinking and subsequent risk of breast cancer in a population to based cohort of Japanese women
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