14 research outputs found
Statistical Verification of Anomaly in Chiral Angle Distribution of Air-Suspended Carbon Nanotubes
Single-walled carbon nanotubes (SWCNT) have long attracted attention due to their distinct physical properties, depending on their chiral structures (chiralities). Clarifying their growth mechanism is important toward perfect chirality-controlled bulk synthesis. Although a correlation between the chirality distribution and the carbon atom configuration at an open tube edge has been predicted theoretically, lack of sufficient statistical data on metallic and semiconducting SWCNTs prohibited its verification. Here, we report statistical verification of the chirality distribution of 413 as-grown individual air-suspended SWCNTs with a length of over 20 μm using broadband Rayleigh spectroscopy. After excluding the impact of the difference in the number of possible SWCNT structures per chiral angle interval, the abundance profile with chiral angle exhibits an increasing trend with a distinct anomaly at a chiral angle of approximately 20°. These results are well explained considering the growth rate depending on armchair-shaped site configurations at the catalyst–nanotube interface
Ultra-narrow-band near-infrared thermal exciton radiation in intrinsic one-dimensional semiconductors
Thermal radiation is the most primitive light emission phenomenon of materials. Broadband radiation from red-hot materials is well known as the kick-starter phenomenon of modern quantum physics in the early twentieth century; even nowadays, its artificial control plays a central role in modern science and technology. Herein, we report the fundamental thermal radiation properties of intrinsic one-dimensional semiconductors and metals, which have not been elucidated because of significant technical challenges. We observed narrow-band near-infrared radiation from semiconducting single-walled carbon nanotubes at 1000–2000 K in contrast to its broadband metallic counterpart. We confirm that the ultra-narrow-band radiation is enabled by the thermal generation of excitons that are hydrogen-like neutral exotic atoms comprising mutually bound electrons and holes. Our findings uncover the robust quantum correlations in intrinsic one-dimensional semiconductors even at 2000 K; additionally, the findings provide an opportunity for excitonic optothermal engineering toward the realization of efficient thermophotovoltaic energy harvesting
Unidirectional molecular assembly alignment on graphene enabled by nanomechanical symmetry breaking
Precise fabrication of molecular assemblies on a solid surface has long been of central interest in surface science. Their perfectly oriented growth only along a desired in-plane direction, however, remains a challenge, because of the thermodynamical equivalence of multiple axis directions on a solid-surface lattice. Here we demonstrate the successful fabrication of an in-plane, unidirectional molecular assembly on graphene. Our methodology relies on nanomechanical symmetry breaking effects under atomic force microscopy tip scanning, which has never been used in molecular alignment. Individual one-dimensional (1D) molecular assemblies were aligned along a selected symmetry axis of the graphene lattice under finely-tuned scanning conditions after removing initially-adsorbed molecules. Experimental statistics and computational simulations suggest that the anisotropic tip scanning locally breaks the directional equivalence of the graphene surface, which enables nucleation of the unidirectional 1D assemblies. Our findings will open new opportunities in the molecular alignment control on various atomically flat surfaces
Strength of carbon nanotubes depends on their chemical structures
引っ張りに強いカーボンナノチューブの構造を特定 --軽量で高強度な究極の構造材料の実現に一歩近づく--. 京都大学プレスリリース. 2019-07-11.Single-walled carbon nanotubes theoretically possess ultimate intrinsic tensile strengths in the 100–200 GPa range, among the highest in existing materials. However, all of the experimentally reported values are considerably lower and exhibit a considerable degree of scatter, with the lack of structural information inhibiting constraints on their associated mechanisms. Here, we report the first experimental measurements of the ultimate tensile strengths of individual structure-defined, single-walled carbon nanotubes. The strength depends on the chiral structure of the nanotube, with small-diameter, near-armchair nanotubes exhibiting the highest tensile strengths. This observed structural dependence is comprehensively understood via the intrinsic structure-dependent inter-atomic stress, with its concentration at structural defects inevitably existing in real nanotubes. These findings highlight the target nanotube structures that should be synthesized when attempting to fabricate the strongest materials
Synthesis and Size-Dependent Properties of [12], [16], and [24]Carbon Nanobelts
The
synthesis and X-ray crystal structure of the first member of
the carbon nanobelt family is reported. [12]Carbon nanobelt ([12]CNB)
was originally obtained from a nickel-mediated reductive coupling
reaction of a dodecabrominated macrocyclic precursor, albeit only
in 1% yield. The present article reports on the development of this
synthetic strategy and its extension to the preparation of the [16]
and [24]CNB analogues. In particular, our extensive investigations
on the final belt-forming, nickel-mediated reaction led to the development
of a new ligand system that provides [12]CNB in up to 7% yield, contributing
to the commercialization of [12]CNB. The belt structures of [12],
[16], and [24]CNB were characterized by NMR, UV–vis, and Raman
spectroscopy as well as mass spectrometry and X-ray crystallography.
The fluorescence of the CNBs in solution displayed a remarkable dependence
on the ring size, ranging from a broad red emission ([12]CNB) to a
narrow-band blue emission ([24]CNB), while both features are observed
for [16]CNB
Cell Surface Colony-Stimulating Factor 1 Can Be Cleaved by TNF-α Converting Enzyme or Endocytosed in a Clathrin-Dependent Manner
Construction of Covalent Organic Nanotubes by Light-Induced Cross-Linking of Diacetylene-Based Helical Polymers
Organic nanotubes (ONTs) are tubular
nanostructures composed of
small molecules or macromolecules that have found various applications
including ion sensor/channels, gas absorption, and photovoltaics.
While most ONTs are constructed by self-assembly processes based on
weak noncovalent interactions, this unique property gives rise to
the inherent instability of their tubular structures. Herein, we report
a simple “helix-to-tube” strategy to construct robust,
covalent ONTs from easily accessible poly(<i>m</i>-phenylene
diethynylene)s (poly-PDEs) possessing chiral amide side chains that
can adopt a helical conformation through hydrogen-bonding interactions.
The helically folded poly-PDEs subsequently undergo light-induced
cross-linking at longitudinally aligned 1,3-butadiyne moieties across
the whole helix to form covalent tubes (ONTs) both in solution and
solid phases. The structures of poly-PDEs and covalent ONTs were characterized
by spectroscopic analyses, diffraction analysis, and microscopic analyses.
We envisage that this simple yet powerful “helix-to-tube”
strategy will generate a range of ONT-based materials by introducing
functional moieties into a monomer