Dynamics of growing carbon nanotube interfaces probed by machine learning-enabled molecular simulations.

Carbon nanotubes (CNTs), hollow cylinders of carbon, hold great promise for advanced technologies, provided their structure remains uniform throughout their length. Their growth takes place at high temperatures across a tube-catalyst interface. Structural defects formed during growth alter CNT properties. These defects are believed to form and heal at the tube-catalyst interface but an understanding of these mechanisms at the atomic-level is lacking. Here we present DeepCNT-22, a machine learning force field (MLFF) to drive molecular dynamics simulations through which we unveil the mechanisms of CNT formation, from nucleation to growth including defect formation and healing. We find the tube-catalyst interface to be highly dynamic, with large fluctuations in the chiral structure of the CNT-edge. This does not support continuous spiral growth as a general mechanism, instead, at these growth conditions, the growing tube edge exhibits significant configurational entropy. We demonstrate that defects form stochastically at the tube-catalyst interface, but under low growth rates and high temperatures, these heal before becoming incorporated in the tube wall, allowing CNTs to grow defect-free to seemingly unlimited lengths. These insights, not readily available through experiments, demonstrate the remarkable power of MLFF-driven simulations and fill long-standing gaps in our understanding of CNT growth mechanisms.

Evaluating the Efficiency of Boron Nitride Coating in Single-Walled Carbon-Nanotube-Based 1D Heterostructure Films by Optical Spectroscopy.

Single-walled carbon nanotube (SWCNT) films exhibit exceptional optical and electrical properties, making them highly promising for scalable integrated devices. Previously, we employed SWCNT films as templates for the chemical vapor deposition (CVD) synthesis of one-dimensional heterostructure films where boron nitride nanotubes (BNNTs) and molybdenum disulfide nanotubes (MoS2NTs) were coaxially nested over the SWCNT networks. In this work, we have further refined the synthesis method to achieve precise control over the BNNT coating in SWCNT@BNNT heterostructure films. The resulting structure of the SWCNT@BNNT films was thoroughly characterized using a combination of electron microscopy, UV-vis-NIR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and Raman spectroscopy. Specifically, we investigated the pressure effect induced by BNNT wrapping on the SWCNTs in the SWCNT@BNNT heterostructure film and demonstrated that the shifts of the SWCNT's G and 2D (G') modes in Raman spectra can be used as a probe of the efficiency of BNNT coating. In addition, we studied the impact of vacuum annealing on the removal of the initial doping in SWCNTs, arising from exposure to ambient atmosphere, and examined the effect of MoO3 doping in SWCNT films by using UV-vis-NIR spectroscopy and Raman spectroscopy. We show that through correlation analysis of the G and 2D (G') modes in Raman spectra, it is possible to discern distinct types of doping effects as well as the influence of applied pressure on the SWCNTs within SWCNT@BNNT heterostructure films. This work contributes to a deeper understanding of the strain and doping effect in both SWCNTs and SWCNT@BNNTs, thereby providing valuable insights for future applications of carbon-nanotube-based one-dimensional heterostructures.

Coexistence of Quantum-Spin-Hall and Quantum-Hall-Topological-Insulating States in Graphene/hBN on SrTiO3 Substrate.

SrTiO3 (STO) substrate, a perovskite oxide material known for its high dielectric constant (ɛ), facilitates the observation of various (high-temperature) quantum phenomena. A quantum Hall topological insulating (QHTI) state, comprising two copies of QH states with antiparallel two ferromagnetic edge-spin overlap protected by the U(1) axial rotation symmetry of spin polarization, has recently been achieved in low magnetic field (B) even as high as ≈100 K in a monolayer graphene/thin hexagonal boron nitride (hBN) spacer placed on an STO substrate, thanks to the high ɛ of STO. Despite the use of the heavy STO substrate, however, proximity-induced quantum spin Hall (QSH) states in 2D TI phases, featuring a topologically protected helical edge spin phase within time-reversal-symmetry, is not confirmed. Here, with the use of a monolayer hBN spacer, it is revealed the coexistence of QSH (at B = 0T) and QHTI (at B ≠ 0) states in the same single graphene sample placed on an STO, with a crossover regime between the two at low B. It is also classified that the different symmetries of the two nontrivial helical edge spin phases in the two states lead to different interaction with electron-puddle quantum dots, caused by a local surface pocket of the STO, in the crossover regime, resulting in a spin dephasing only for the QHTI state. The results obtained using STO substrates open the doors to investigations of novel QH spin states with different symmetries and their correlations with quantum phenomena. This exploration holds value for potential applications in spintronic devices.

Enhanced Thermal Conductivity of Single-Walled Carbon Nanotube with Axial Tensile Strain Enabled by Boron Nitride Nanotube Anchoring.

Thermal conductivity measurements are conducted by optothermal Raman technique before and after the introduction of an axial tensile strain in a suspended single-walled carbon nanotube (SWCNT) through end-anchoring by boron nitride nanotubes (BNNTs). Surprisingly, the axial tensile strain (<0.4 %) in SWCNT results in a considerable enhancement of its thermal conductivity, and the larger the strain, the higher the enhancement. Furthermore, the thermal conductivity reduction with temperature is much alleviated for the strained nanotube compared to previously reported unstrained cases. The thermal conductivity of SWCNT increases with its length is also observed.

Ion and Hydrodynamic Translucency in 1D van der Waals Heterostructured Boron-Nitride Single-Walled Carbon Nanotubes.

An unresolved challenge in nanofluidics is tuning ion selectivity and hydrodynamic transport in pores, particularly for those with diameters larger than a nanometer. In contrast to conventional strategies that focus on changing surface functionalization or confinement degree by varying the radial dimension of the pores, we explore a unique approach for manipulating ion selectivity and hydrodynamic flow enhancement by externally coating single-walled carbon nanotubes (SWCNTs) with a few layers of hexagonal boron nitride (h-BN). For van der Waals heterostructured BN-SWCNTs, we observed a 9-fold increase in cation selectivity for K+ versus Cl- compared to pristine SWCNTs of the same 2.2 nm diameter, while hydrodynamic slip lengths decreased by more than an order of magnitude. These results suggest that the single-layer graphene inner surface may be translucent to charge-regulation and hydrodynamic-slip effects arising from h-BN on the outside of the SWCNT. Such 1D heterostructures could serve as synthetic platforms with tunable properties for exploring distinct nanofluidic phenomena and their potential applications.

Interacting Phonons between Layers in Raman Spectra of Carbon Nanotubes inside Boron Nitride Nanotubes.

We present the resonant Raman spectra of a single-wall carbon nanotube inside a multiwall boron nitride nanotube (SWNT@BNNT). At EL = 1.58 eV, SWNT@BNNT exhibited resonant Raman spectra at 807 (ωBN) and 804 cm-1 (ωGr). Their intensities almost disappeared at EL = 2.33 eV. We assigned ωBN to the out-of-plane BN phonon mode that coupled with ωGr. At EL = 4.66 eV, the G+ and G- bands of the SWNT@BNNT red-shifted 3.8 cm-1 compared with the SWNT, suggesting the interwall interactions between the in-plane modes of SWNT and BNNT. Moreover, the E2g mode of the BNNT in SWNT@BNNT appeared at 1370.3 ± 0.1 cm-1, which is undistinguishable for EL < 3 eV because of the overlap with the D band frequency. The assignment of the present Raman spectra was confirmed through the first-principles calculations.

The Natural History and Management of Hepatic Hemangioma.

BACKGROUND: Knowledge of the natural history and management of hepatic hemangiomas is lacking. The aim of this study was to investigate the natural history of hemangiomas and to elucidate the factors that determine tumor growth and optimal management. METHODS: A total of 211 adult patients were enrolled, with follow-up for more than three years. Follow-up was performed with repeated ultrasonography (US) and laboratory tests for liver function and coagulation factors (platelets, prothrombin time (PT), fibrinogen, thrombin-antithrombin III complex (TAT), D-dimer, and fibrin and fibrinogen degradation products (FDP)). RESULTS: Tumor size decreased in 38.9% of patients, showed no change in 31.3%, and increased in 29.8%. The incidence of a size increase was very high in patients under 40 years of age and decreased gradually with age, whereas the incidence of a size decrease increased with age and increased markedly over 60 years of age. The incidence of an increase in size decreased gradually with size enlargement, whereas the incidence of a decrease in size increased markedly with tumor size and further increased rapidly when hemangiomas became larger than 60 mm. Values of TAT, D-dimer, FDP, and Mac-2 binding protein glycosylation isomer (M2BPGi) were closely related to the change in size of hemangiomas. CONCLUSIONS: Hemangiomas in older patients (>60 years of age) and larger tumors (>60 mm in size) had a tendency to decrease in size, resulting from the reduction in coagulation disorders and the progression of liver fibrosis. Therefore, the majority of patients with hemangiomas can be safely managed by clinical observation.

Horizontal Arrays of One-Dimensional van der Waals Heterostructures as Transistor Channels.

The nanotube/dielectric interface plays an essential role in achieving superb switching characteristics of carbon nanotube-based transistors for energy-efficient computation. Formation of van der Waals heterostructures with hexagonal boron nitride nanotubes could be an effective means to reduce interface state density, but the need for isolating nanotubes during the formation of coaxial outer layers has hindered the fabrication of their horizontal arrays. Here, we develop a strategy to create isolated heterostructure arrays using aligned carbon nanotubes grown on a quartz substrate as starting materials. Air-suspended arrays of carbon nanotubes are prepared by a dry transfer technique and then used as templates for the coaxial wrapping of boron nitride nanotubes. We then fabricate the transistors, where boron nitride serves as interfacial layers between carbon nanotube channels and conventional gate dielectrics, showing hysteresis-free characteristics owing to the improved interfaces. We have also gained a deeper understanding of the strain applied on inner carbon nanotubes, as well as the inhomogeneity of the outer coating, by characterizing individual heterostructures over trenches and on a substrate surface. The device fabrication and characterization presented here essentially do not require elaborate electron microscopy, thus paving the way for the practical use of one-dimensional van der Waals heterostructures for nanoelectronics.

Enhancement of oxygen reduction reactivity on TiN by tuning the work function via metal doping.

Oxide layers on conductive TiN have recently been investigated to catalyse the oxygen reduction reaction (ORR) in acidic media. The ORR reactivity, i.e., activity and selectivity, has been correlated with the surface nitrogen atoms. A new strategy, optimising the work function via the doping of foreign metals, is revealed herein to enhance the reactivity.

van der Waals SWCNT@BN Heterostructures Synthesized from Solution-Processed Chirality-Pure Single-Wall Carbon Nanotubes.

Single-wall carbon nanotubes in boron nitride (SWCNT@BN) are one-dimensional van der Waals heterostructures that exhibit intriguing physical and chemical properties. As with their carbon nanotube counterparts, these heterostructures can form from different combinations of chiralities, providing rich structures but also posing a significant synthetic challenge to controlling their structure. Enabled by advances in nanotube chirality sorting, clean removal of the surfactant used for solution processing, and a simple method to fabricate free-standing submonolayer films of chirality pure SWCNTs as templates for the BN growth, we show it is possible to directly grow BN on chirality enriched SWCNTs from solution processing to form van der Waals heterostructures. We further report factors affecting the heterostructure formation, including an accelerated growth rate in the presence of H2, and significantly improved crystallization of the grown BN, with the BN thickness controlled down to one single BN layer, through the presence of a Cu foil in the reactor. Transmission electron microscopy and electron energy-loss spectroscopic mapping confirm the synthesis of SWCNT@BN from the solution purified nanotubes. The photoluminescence peaks of both (7,5)- and (8,4)-SWCNT@BN heterostructures are found to redshift (by ∼10 nm) relative to the bare SWCNTs. Raman scattering suggests that the grown BN shells pose a confinement effect on the SWCNT core.

Surfactant-Assisted Isolation of Small-Diameter Boron-Nitride Nanotubes for Molding One-Dimensional van der Waals Heterostructures.

Rolling two-dimensional (2D) materials into 1D nanotubes allows for greater functionality. Boron-nitride nanotubes (BNNTs) can serve as insulating 1D templates for the coaxial growth of guest nanotubes, without interfering with property characterization. However, their application as 1D templates has been greatly hindered by their poor dispersibility, inevitably resulting in the formation of thick bundles. Here we present the facile preparation of well-dispersed BNNT templates via surfactant dispersions and synthesis of 1D van der Waals heterostructures based on the BNNTs. Comprehensive microscopic analyses show the isolation of clean, high-quality BNNTs. Statistical analyses revealed that small-diameter double-walled BNNTs are highly enriched by chemical peeling of BN sidewalls through the sonication process. We further demonstrate that the isolated BNNTs can template the coaxial growth of carbon and MoS2 nanotubes by using chemical vapor deposition. The present strategy can be applied to the synthesis of a variety of nanotubes, thereby allowing for their characterization.

Micro- and Macrostructures of Aligned Boron Nitride Nanotube Arrays.

Boron nitride nanotubes (BNNTs) possess a broad range of applications because of several engineering-relevant properties, including high specific strength and stiffness, thermal stability, and transparency to visible light. The morphology of these nanoscale fibers must be controlled to maximize such properties, which can be achieved by synthesizing long aligned arrays of crystalline hexagonal boron nitride (hBN) nanotubes. Herein, we synthesize high-quality millimeter length, vertically aligned (VA-) BNNTs using free-standing carbon nanotube (CNT) arrays as scaffolds. In addition to high optical transparency of the VA-BNNTs, we also demonstrate several micro- and macrostructures of BNNTs via patterning and/or postprocessing of the arrays, including engineering of either disconnected or interconnected tubes in VA-, horizontally aligned (HA-), or coherently buckled BNNTs. The internanotube spacings and interconnections between aligned BNNT can thus be tailored to create BN macrostructures with complex shapes and advantaged morphologies for hierarchical materials and devices.

Synthesis of neutral Li-endohedral PCBM: an n-dopant for fullerene derivatives.

Li@PCBM, the first neutral Li@C60 derivative, was synthesized. The Li@PCBM exists in a monomer-dimer equilibrium in solution but as a monomer in the PCBM matrix. The fully dispersed Li@PCBM n-doped the surrounding empty PCBM, raising the Fermi level by 0.13 eV compared with the undoped PCBM film. The hybrid films were utilized as an ETL for PSCs, promoting the efficiency of the device.

Prevalence and Characteristics of Hepatic Hemangioma Associated with Coagulopathy and Its Predictive Risk Factors.

Background: Knowledge of the relationships between hepatic hemangiomas and coagulopathy and the risk factors for hemangiomas is lacking. The aim of this study was to investigate the prevalence and characteristics of hepatic hemangiomas associated with coagulopathy, elucidate the causes of coagulopathy, and identify the predictive factors for hemangioma-related complications. Methods: In 281 consecutive patients with hepatic hemangiomas, we performed ultrasonography and conducted serum laboratory tests for liver function and six coagulation factors, i.e., platelets, as well as five coagulation fibrinolytic markers (prothrombin time (PT), fibrinogen, thrombin-antithrombin III complex (TAT), d-dimer, and fibrin and fibrinogen degradation products (FDP)) as indicators of coagulation disorder. Results: Among 281 patients, 56 (19.9%) had abnormal coagulation factors. Abnormal values of d-dimer were most frequently found among the six coagulation factors. The number of abnormal coagulation factors was significantly correlated with tumor size, M2BPGi, and HDL cholesterol, among which tumor size was the most significant independent predictor of the number of abnormal coagulation factors. Conclusions: The prevalence of hepatic hemangiomas associated with coagulopathy was relatively high and became more frequent with increases in tumor size. Predictive factors of hemangioma-related complications were found to be a tumor size of >5 cm in diameter and coagulopathy, especially the elevation of d-dimer.

Formation of organic color centers in air-suspended carbon nanotubes using vapor-phase reaction.

Organic color centers in single-walled carbon nanotubes have demonstrated exceptional ability to generate single photons at room temperature in the telecom range. Combining the color centers with pristine air-suspended nanotubes would be desirable for improved performance, but all current synthetic methods occur in solution which makes them incompatible. Here we demonstrate the formation of color centers in air-suspended nanotubes using a vapor-phase reaction. Functionalization is directly verified by photoluminescence spectroscopy, with unambiguous statistics from more than a few thousand individual nanotubes. The color centers show strong diameter-dependent emission, which can be explained with a model for chemical reactivity considering strain along the tube curvature. We also estimate the defect density by comparing the experiments with simulations based on a one-dimensional exciton diffusion equation. Our results highlight the influence of the nanotube structure on vapor-phase reactivity and emission properties, providing guidelines for the development of high-performance near-infrared quantum light sources.

Direct Visualization of Ultrastrong Coupling between Luttinger-Liquid Plasmons and Phonon Polaritons.

Ultrastrong coupling of light and matter creates new opportunities to modify chemical reactions or develop novel nanoscale devices. One-dimensional Luttinger-liquid plasmons in metallic carbon nanotubes are long-lived excitations with extreme electromagnetic field confinement. They are promising candidates to realize strong or even ultrastrong coupling at infrared frequencies. We applied near-field polariton interferometry to examine the interaction between propagating Luttinger-liquid plasmons in individual carbon nanotubes and surface phonon polaritons of silica and hexagonal boron nitride. We extracted the dispersion relation of the hybrid Luttinger-liquid plasmon-phonon polaritons (LPPhPs) and explained the observed phenomena by the coupled harmonic oscillator model. The dispersion shows pronounced mode splitting, and the obtained value for the normalized coupling strength shows we reached the ultrastrong coupling regime with both native silica and hBN phonons. Our findings predict future applications to exploit the extraordinary properties of carbon nanotube plasmons, ranging from nanoscale plasmonic circuits to ultrasensitive molecular sensing.

Universal Map of Gas-Dependent Kinetic Selectivity in Carbon Nanotube Growth.

Single-walled carbon nanotubes have been a candidate for outperforming silicon in ultrascaled transistors, but the realization of nanotube-based integrated circuits requires dense arrays of purely semiconducting species. In order to directly grow such nanotube arrays on wafers, control over kinetics and thermodynamics in tube-catalyst systems plays a key role, and further progress requires a comprehensive understanding of seemingly contradictory reports on the growth kinetics. Here, we propose a universal kinetic model that decomposes the growth rates of nanotubes into the adsorption and removal of carbon atoms on the catalysts, and we provide its quantitative verification by ethanol-based isotope labeling experiments. While the removal of carbon from catalysts dominates the growth kinetics under a low supply of precursors, resulting in chirality-independent growth rates, our kinetic model and experiments demonstrate that chiral angle-dependent growth rates emerge when sufficient amounts of carbon and etching agents are cosupplied. The kinetic maps, as a product of generalizing the model, include five types of kinetic selectivity that emerge depending on the absolute quantities of gases with opposing effects. Our findings not only resolve discrepancies existing in the literature but also offer rational strategies to control the chirality, length, and density of nanotube arrays for practical applications.

Synthesis of Conjugated Donor-Acceptor Antiaromatic Porphyrins and Their Application to Perovskite Solar Cells.

A conjugated donor-acceptor antiaromatic porphyrin, composed of an antiaromatic thieno-fused porphyrin structure and a diketopyrrolopyrrole mioety, was synthesized and applied in a perovskite solar cell for the first time. Enhanced light absorption in the device by the antiaromatic porphyrin resulted in a significantly increased power conversion efficiency of 19.3%.

One-Dimensional van der Waals Heterostructures: A Perspective.

As a new frontier in low-dimensional material research, van der Waals (vdW) heterostructures, represented by 2D heterostructures, have attracted tremendous attention due to their unique properties and potential applications. The emerging 1D heterostructures open new possibilities for the field with expectant unconventional properties and yet more challenging preparation pathways. This Perspective aims to give an overall understanding of the state-of-the-art growth strategies and fantastic properties of the 1D heterostructures and provide an outlook for further development based on the controlled preparation, which will bring up a variety of applications in high-performance electronic, optoelectronic, magnetic, and energy storage devices. A quick rise of the fundamentals and application study of 1D heterostructures is anticipated.