Coaxial Nanotubes Research Articles

Electron-scale origin of structural superlubricity

First-principles computations are performed to study the phenomenon of structural superlubricity (SSL) relative to self-mismatched heterojunctions, rotating-mismatched homojunctions and curvature-mismatched coaxial double-walled nanotubes. It follows from the computations that the interfacial electron density fluctuation is responsible for all characteristics of SSL and can serve as predicting and describing them efficiently. This result further reveals that SSL comes from the fact that the incommensurable contact of two inert surfaces weakens their electronic interactions considerably. The model of SSL based on the electron redistribution a fortiori overcomes the limitations presented by the models of SSL based on the registry index (RI) or on the local pinning (LP).

Hierarchical Reduced Graphene Oxide-MnO2@ Polypyrrole Coaxial Nanotube Composite Hydrogel as a Potential Adsorbent for Cr(VI) Removal

Hierarchical Reduced Graphene Oxide-MnO2@ Polypyrrole Coaxial Nanotube Composite Hydrogel as a Potential Adsorbent for Cr(VI) Removal

Arrays of ZnO/MoS2 nanorods and MoS2 nanotubes for spectral enhancement and self-cleaning

Structure and heterojunction of substrates are widely regarded as critical factors to improve Raman detection and recyclibility, but the exact roles are rarely explored for the mixed contributions. Herein, the arrays of ZnO/MoS2 coaxial nanorods (NRs) and MoS2 nanotubes (NTs) were successfully constructed for the surface-enhanced Raman scattering (SERS). The influences of NR and NT length on the morphology, light absorption and emission, as well as SERS performance were systematically investigated. Both the arrays grown for 40 min displayed optimal SERS performance, in which MoS2 NT array owned stronger enhancement with a detection limit of 5 × 10−7 M than that of 1 × 10−6 M for ZnO/MoS2 NR array. The NTs also effectively enhanced photocatalysis, in which rhodamine 6G pollutant was completely degraded within 140 min under ultraviolet light, surpassing that by the NRs. The analysis revealed that band alignment and structure characteristic of the specimens played critical roles in the spectral enhancement and self-cleaning, while the nanostructure surpassed heterojunction as it supplied void interior for extending light propagation and more contact area for adsorbing pollutants. These results would contribute to a better understanding of the Raman enhancement and could be extended to the design of SERS substrates to harness their potential application.

Highly Sensitive and Fast Responding Flexible Force Sensors Using ZnO/ZnMgO Coaxial Nanotubes on Graphene Layers for Breath Sensing.

The authors report the fabrication of highly sensitive, rapidly responding flexible force sensors using ZnO/ZnMgO coaxial nanotubes grown on graphene layers and their applications in sleep apnea monitoring. Flexible force sensors are fabricated by forming Schottky contacts to the nanotube array, followed by the mechanical release of the entire structure from the host substrate. The electrical characteristics of ZnO and ZnO/ZnMgO nanotube-based sensors are thoroughly investigated and compared. Importantly, in force sensor applications, the ZnO/ZnMgO coaxial structure results in significantly higher sensitivity and a faster response time when compared to the bare ZnO nanotube. The origin of the improved performance is thoroughly discussed. Furthermore, wireless breath sensing is demonstrated using the ZnO/ZnMgO pressure sensors with custom electronics, demonstrating the feasibility of the sensor technology for health monitoring and the potential diagnosis of sleep apnea.

Confined tandem catalytic quasi-solid sulfur reversible conversion for all-solid-state Na–S batteries

The designed york–shell structured MnHCF/PPy@MnO2 coaxial nanotubes cooperatively catalyze the conversion of interchannel encapsulated active species within the confined environment, regulating the reversible quasi-solid sulfur conversion.

Coaxial boron nitride nanotubes as interfacial dielectric layers to lower interface trap density in carbon nanotube transistors

A semiconductor/dielectric interface is one of the dominant factors in device characteristics, and a variety of oxides with high dielectric constants and low interface trap densities have been used in carbon nanotube transistors. Given the crystal structure of nanotubes with no dangling bonds, there remains room to investigate unconventional dielectric materials. Here, we fabricate carbon nanotube transistors with boron nitride nanotubes as interfacial layers between channels and gate dielectrics, where a single semiconducting nanotube is used to focus on switching behaviors at the subthreshold regime. The subthreshold swing of 68 mV·dec−1 is obtained despite a 100-nm-thick SiO2 dielectric, corresponding to the effective interface trap density of 5.2 × 1011 cm−2·eV−1, one order of magnitude lower than those of carbon nanotube devices without boron nitride passivation. The interfacial layers also result in the mild suppression of threshold voltage variation and hysteresis. We achieve Ohmic contacts through the selective etching of boron nitride nanotubes with XeF2 gas, overcoming the trade-off imposed by wrapping the inner nanotubes. Negligible impacts of fluorinating carbon nanotubes on device performances are also confirmed as long as the etching is applied exclusively at source/drain regions. Our results represent an important step toward nanoelectronics that exploit the advantage of one-dimensional van der Waals heterostructures.

Characterization and Investigating the Effect of Gate-Insulator Thickness on Co-Axial Cylindrical Carbon Nanotube Field Effect Transistor

Characterization and Investigating the Effect of Gate-Insulator Thickness on Co-Axial Cylindrical Carbon Nanotube Field Effect Transistor

Unidirectional Chiral Magnonics in Cylindrical Synthetic Antiferromagnets

Progress in spintronics continues briskly, with many different approaches and physical phenomena underlying candidate technologies. This study uses modern spin-wave theory to predict the magnonic spectrum of a cylindrical synthetic antiferromagnet consisting of two coaxial nanotubes. The proposed device incorporates two coupled ferromagnetic nanotubes hosting oppositely magnetized vortices. Nonreciprocal features of the proposed architecture are provided by both intra- and interlayer dipolar coupling. Unidirectional spin-wave behavior is found, which may impact the realization of low-power magnonic devices operating at nano- to micrometer scales.

ELECTRODE: An electrochemistry package for atomistic simulations.

Constant potential methods (CPMs) enable computationally efficient simulations of the solid-liquid interface at conducting electrodes in molecular dynamics. They have been successfully used, for example, to realistically model the behavior of ionic liquids or water-in-salt electrolytes in supercapacitors and batteries. CPMs model conductive electrodes by updating charges of individual electrode atoms according to the applied electric potential and the (time-dependent) local electrolyte structure. Here, we present a feature-rich CPM implementation, called ELECTRODE, for the Large-scale Atomic/Molecular Massively Parallel Simulator, which includes a constrained charge method and a thermo-potentiostat. The ELECTRODE package also contains a finite-field approach, multiple corrections for nonperiodic boundary conditions of the particle-particle particle-mesh solver, and a Thomas-Fermi model for using nonideal metals as electrodes. We demonstrate the capabilities of this implementation for a parallel-plate electrical double-layer capacitor, for which we have investigated the charging times with the different implemented methods and found an interesting relationship between water and ionic dipole relaxations. To prove the validity of the one-dimensional correction for the long-range electrostatics, we estimated the vacuum capacitance of two coaxial carbon nanotubes and compared it to structureless cylinders, for which an analytical expression exists. In summary, the ELECTRODE package enables efficient electrochemical simulations using state-of-the-art methods, allowing one to simulate even heterogeneous electrodes. Moreover, it allows unveiling more rigorously how electrode curvature affects the capacitance with the one-dimensional correction.

Connecting effect on the charge transport and nonlinear optical properties of heteronanotubes

Carbon/boron nitride heteronanotubes are now at the centre of experimental and theoretical studies because of their tunable properties and diverse applications. Herein, we investigate the charge transport and optical properties of carbon/boron nitride hybrid single- and double-walled nanotubes on the basis of first-principles calculations. Our results reveal that the C/BN heterojunctions with radial junctions parallel (horizontal) to the tube axis have more effects than the perpendicular (vertical) junctions on the charge transport properties of heteronanotubes. Furthermore, we find that the nonlinear optical response can be meaningfully controlled by altering the C/BN content and junction arrangement. In double-walled coaxial heteronanotubes, the interwall interaction is also found to increase the electron and hole transport rates noticeably and to have a major effect on the first hyperpolarizabilities of C/BN heteronanotubes. In contrast with coaxial carbon nanotubes, where the inner constituent is totally shielded by the outer tube, in our studied C/BN coaxial heteronanotubes, the inner shell is only partially shielded by the outer constituent. This study suggests a strategy to high-efficient design heteronanotubes with high charge transport properties and tunable nonlinear optical responses. Moreover, the designed C/BN heteronanotubes can discrete electrons and holes, suggesting their application in solar cell materials.

Stability and electronic properties of hybrid coaxial carbon nanotubes–boron nitride nanotubes under the influence of electric field

Stability and electronic properties of hybrid coaxial carbon nanotubes–boron nitride nanotubes under the influence of electric field

Single-Walled Carbon Nanotubes and Hetero-Nanotubes for Perovskite Solar Cells

Single-walled carbon nanotubes (SWCNTs), graphene, and fullerene (C60 and derivatives) are very efficiently used in organic-inorganic Perovskite solar cells [1, 2]. A film of carbon nanotubes or graphene can be the practical replacement [3] of ITO for the flexible and/or foldable [4] transparent electrode of inverted perovskite solar cells. Doping of SWCNT is essential for high performance solar cells through increased in-plane film conductivity and energy level adjustment. Since p-doping is easier than n-doping, it is more practical to use SWCNT electrode in the hole-transport side. Hence, we have developed the normal type perovskite solar cells composed of ITO/ETL/MAPbI3/HTL-SWCNT. The use of SWCNT as the top electrode instead of metal enhances the stability of PSCs by removing the metal-ion migration, and considerably reduces the fabrication cost, and is suitable for the development of tandem system. Recently, we have improved the performance with higher concentration of hole-transporting material [5]. For MAPbI3 system, we have obtained the highest PCE of 18.8 % compared with the control device with gold electrode with PCE of 18.1%. Because of transparency of SWCNT film is higher than that of ITO in the NIR region, SWCNT electrode based perovskite–silicon tandem solar cells can have better performance than ITO-based one [6]. In addition to our demonstration of 24.4 % total PCE in our previous work [6], we are now demonstrating the higher preliminary PCE of 27.7 %.Finally, the ultimately inorganic stable doping of SWCNT could be possible by using the one-dimensional van der Waals hetero-nanotubes [7]. We have synthesized the coaxial few-layer hexagonal boron nitride nanotube (BNNT) around a SWCNT; SWCNT@BNNT. Then, the further coating of coaxial MoS2 nanotubes results SWCNT@BNNT@MoS2NT as shown in Fig. 1. The inner SWCNT and outer MoS2NT are electrically coupled through a few layer BNNT. The preliminary PSC device using the heteronanotube film shows the advantage [8].Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan.

Novel dam-like effect based on piezoelectric energy conversion for drug sustained release of drug-loaded TiO2 @ BaTiO3 coaxial nanotube coating

Nanotube coatings on titanium surfaces have favorable biocompatibility and structures and are widely used in local drug delivery. However, when a drug freely diffuses out of a nanotube, it leads to an explosive release, making the duration of action extremely short. In this study, a high concentration of vancomycin hydrochloride region similar to a dam was formed on a nanotube coating surface by exploiting the attraction of the electric charge generated by the energy conversion of the piezoelectric effect to vancomycin hydrochloride. The “dam” not only reduces the diffusion rate of vancomycin hydrochloride inside the nanotube into the dam and the diffusion rate of the dam to the outside but also forms a high concentration of vancomycin hydrochloride action region. The free diffusion rate of vancomycin hydrochloride loaded on the TiO2 @ BaTiO3 coaxial nanotubes was reduced by the piezoelectric effect, and the cumulative release of vancomycin hydrochloride for 7 days is reduced by 54.8%. The polarized vancomycin-containing coaxial nanotube coating has a long-lasting antibacterial effect on Staphylococcus aureus. The TiO2 @ BaTiO3 coaxial nanotubes loaded with vancomycin hydrochloride coating with piezoelectric properties has potential application value in controlled drug delivery.

Novel design and synthesis of 1D bamboo-like CNTs@Sn4P3@C coaxial nanotubes for long-term sodium ion storage

In this work, a novel bamboo-like carbon nanotubes@Sn4P3@carbon (BLCNTs@Sn4P3@C) coaxial nanotubes are designed and prepared using a newly developed hydrothermal method followed by a phophidation process. The prepared Sn4P3 nanoparticles are uniformly coated and wrapped on the one-dimensional (1D) bamboo-like CNTs, which is covered by a uniform carbon layer to form a sandwich-like structure with Sn4P3 in between. The inner CNT and outer carbon can effectively maintain the structural stability and serve as the good electron conductors. Additionally, the outer carbon coating layer can effectively keep BLCNTs@Sn4P3@C nanotubes separate each other, preventing aggregation of Sn4P3 during charge/discharge when this material is used as anode for sodium ion batteries. The anode of BLCNTs@Sn4P3@C shows excellent reversible capacity and a long cycling of over 2000 cycles. The unique design of coaxial nanotubes is greatly beneficial to the electrochemical performance of Sn4P3 for sodium ion storage.

Curvature-induced bandgap reduction in TiO2 double-walled nanotubes

The geometric and electronic properties of the double-walled nanotubes (DWNTs), constructed by the two coaxial single-walled nanotubes (SWNTs) rolling the hexagonal titanium dioxide (TiO2) nanosheet along with the armchair (ac-) and the zigzag (zz-) directions, have been investigated systematically using the methods based on the density functional theory. For the optimized structures, the bandgap values of the TiO2 DWNTs are significantly reduced from that of the constituent SWNTs, falling in the visible light range. Further detailed analysis reveals that the reduction is caused by the band misalignment due to the different curvatures of the inner and outer TiO2 SWNTs.

Zeolite-supported synthesis, solution dispersion, and optical characterizations of single-walled carbon nanotubes wrapped by boron nitride nanotubes

Zeolite-supported carbon nanotube (CNT) synthesis provides a route for its mass production due to the porous surfaces accommodating a large number of catalytic particles and maintaining the fine particle sizes during high-temperature growth. Coaxial single-walled carbon nanotubes (SWCNTs) and boron nitride nanotube (BNNT) van der Waals heterostructures have been produced recently on the CNT thin-film template. To achieve a high yield of the one-dimensional heterostructure, BNNT-wrapped SWCNTs were synthesized on zeolite support coated with catalytic nanoparticles. They were then dispersed in solution and examined by absorption, photoluminescence, and Raman spectroscopy. A robust thermal stability enhancement was observed, and optical characterizations revealed the composition of dispersed SWCNTs wrapped by BNNTs before air annealing includes individual SWCNTs, BNNT-wrapped SWCNT bundles, and BNNT-wrapped individual SWCNTs. Furthermore, the outside wrapping by BNNTs caused a significant down-shift of the photoluminescence spectrum in semiconducting SWCNTs, suggesting that BNNT-wrapped SWCNTs can be preserved after harsh dispersion treatments.

Fabrication and charge storage capacitance of PPY/TiO2/PPY jacket nanotube array

Abstract A PPY/TiO2/PPY jacket nanotube array was fabricated by coating PPY layer on the external and internal surface of a tube wall-separated TiO2 nanotube array. It shows coaxial triple-walled nanotube structure with two PPY nanotube layers sandwiching one TiO2 nanotube layer. PPY/TiO2/PPY reveals much higher current response than TiO2. The theoretical calculation indicates PPY/TiO2/PPY reveals higher density of states and lower band gap, accordingly presenting higher conductivity and electroactivity, which is consistent with the experimental result of a higher current response. The electroactivity is highly enhanced in H2SO4 rather than Na2SO4 electrolyte due to feasible pronation process of PPY in an acidic solution. PPY/TiO2/PPY could conduct the redox reaction in H2SO4 electrolyte which involves the reversible protonation/deprotonation and HSO4 − doping/dedoping process and accordingly contributes to Faradaic pseudocapacitance. The specific capacitance is highly enhanced from 1.7 mF cm−2 of TiO2 to 123.4 mF cm−2 of PPY/TiO2/PPY at 0.1 mA cm−2 in H2SO4 electrolyte. The capacitance also declines from 123.4 to 31.7 mF cm−2 when the current density increases from 0.1 to 1 mA cm−2, presenting the rate capacitance retention of 26.7% due to the semiconductivity of TiO2. A PPY/TiO2/PPY jacket nanotube with high charge storage capacitance is regarded as a promising supercapacitor electrode material.

1D Sb2S3@nitrogen-doped carbon coaxial nanotubes uniformly encapsulated within 3D porous graphene aerogel for fast and stable sodium storage

The Sb2S3 anode materials with high theoretical capacity were troubled by their sluggish electrochemical kinetics and huge volume expansion in sodium-ion batteries. Herein, we firstly designed a unique Sb2S3@nitrogen-doped carbon (Sb2S3@N-C) nanotube encapsulated by porous graphene aerogel to solve the above technical barrier. The composite aerogel with ingenious structure was creatively designed by coating polydopamine (PDA) onto the Sb2S3 nanorods. The PDA was not only a precursor of nitrogen-doped carbon (N-C) layer adjusting volume change of Sb2S3 during storage Na+ but also acted as a reducing agent assisting to create graphene aerogel. Moreover, the formation of unique Sb2S3@N-C coaxial nanotubes was facilitated by the N-C layer, which triggered the strong interaction between the Sb2S3 and graphene to maintain structural integrity. Importantly, the composite aerogel synergized the superior electrical conductivity, abundant porous channels, and excellent electrochemical reactivity into one. As a result, the optimized anode exhibited high reversible capacity, superior rate capability, and impressively cycling stability. Furthermore, the full cell was constructed from the optimized composite aerogel anode and Na3V2(PO4)3 cathode, exhibiting a high reversible capacity of 388 mA h g−1 at 0.1 A g−1 with a remarkable energy density of 189 Wh kg−1.

Novel Design of Multiple Nested Coaxial ZnO Nanotube Gas Sensors Synthesized in Porous Templates By Atomic Layer Deposition

Among the various Metal Oxide Semiconductor (MOS) gas sensor types, solid-state gas sensors based on ZnO nanostructures have been widely used due to their properties of large exciton binding energy, wide band gape of 3.37 eV, good electrical conductivity, low cost, and high mechanical stability. In this work, ZnO nanotube nanostructures were employed for gas sensing of ethanol vapor concentrations, which is aided by their high electrochemical stability, nontoxicity, and, especially, high surface-to-volume ratio. Multiple coaxial nested ZnO nanotubes were synthesized inside porous membranes and porous templates to further enhance the sensing response to ethanol vapors with vastly increased reaction surfaces.In this study, ZnO nanotubes were synthesized by Atomic Layer Deposition (ALD) on porous Anodic Aluminum Oxide (AAO) templates with sacrificial Al2O3 layers and on porous Si membranes. The Al2O3 sacrificial layers were synthesized on porous AAO and porous Si by ALD with TMA (Al2(CH3)6) and DI water as ALD precursors. Then ZnO thin films were deposited on the surface of the sacrificial layer with precisely controlled thickness by ALD. The entire ALD procedure is considered as one ALD super cycle. More super cycles were applied to synthesize additional coaxial ZnO nanotubes. For the final removal of the sacrificial layer, Precision Ion Polishing System (PIPS) was used to first remove the top ALD surface cover. In this way, the Al2O3 sacrificial layers were exposed for Sodium Hydroxide (NaOH) etching. The objective of the Al2O3 sacrificial layers was to expose additional reactive sensing surfaces to react with the target gas by subsequent removal of these sacrificial layers. Finally, after the sacrificial layers were completely removed by wet chemical NaOH dissolution, the nested coaxial ZnO nanotube gas sensor design was fabricated with multiple sensing surfaces.To investigate the sensing performance of ZnO nanotube gas sensors to ethanol vapor, a gas sensor testing system was developed with a sealed reaction chamber and control system with stable temperature control and accurate concentration control. The sensing performance of single ZnO nanotubes, two nested coaxial ZnO nanotubes, and three nested coaxial ZnO nanotubes to ethanol vapor were measured and analyzed under various ethanol vapor concentrations and at different operating temperatures. The ZnO nanostructures sensing results on ethanol vapor demonstrated the sensing performance was considerably enhanced due to the increased surface to volume ratio in the ZnO tube structures.

Performance analysis of an enclosed, coaxial carbon nanotube (CNT) speaker in presence of flow using COMSOL Multiphysics

Performance analysis of an enclosed, coaxial carbon nanotube (CNT) speaker in presence of flow using COMSOL Multiphysics