Coaxial Nanotubes Research Articles

Template-based, near-ambient synthesis of crystalline metal-oxide nanotubes, nanowires and coaxial nanotubes

In response to a growing need for metal-oxide nanotubes and nanowires for nanoelectronic applications and size-effect studies, crystalline nanotubes and nanowires in a range of metal oxides have been synthesized at near-ambient conditions and without the application of heat treatments, pressure or an external electric field. Specifically, the mechanisms of formation of crystalline TiO 2 nanotubes and nanowires from flourine-based liquid precursors inside anodic aluminum oxide templates have been elucidated. This method can be extended to synthesizing nanotubes/nanowires of other crystalline metal oxides, such as ZrO 2, SnO 2 and FeOOH. Using sequential deposition, TiO 2/ZrO 2 coaxial nanotubes have been synthesized. In principle, the methods outlined here could be used to fabricate crystalline nanotubes and nanowires of tailored dimensions in other metal oxides. The ability to synthesize, at near-ambient conditions, crystalline metal-oxide nanotubes and nanowires of tailored geometries represents a clear advantage in terms of minimal equipment requirements, low cost and possible incorporation of biomolecules and temperature-sensitive moieties.

Facilitated Lithium Storage in MoS2 Overlayers Supported on Coaxial Carbon Nanotubes

The discoveries of carbon and inorganic fullerene-like nanotubes with a wide spectra of possible applications have stimulated multi- and interdisciplinary research activities. In this paper, we prepared MoS2 overlayers supported on coaxial carbon nanotubes and investigated lithium storage/release properties in relation to their structural properties. The coaxial nanoarchitecture was successfully synthesized by a designed solution-phase route in the low temperature range, which was characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The reversible lithium-storage behaviors involved in the nanoarchitecture were elucidated by means of various techniques including galvanostatic methods, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). A thorough investigation of the composition−structure−property relationships of the coaxial nanoarchitecture highlighted the importance of the underlying carbon nanotubes in improving the lithium storage/release properties of the MoS2 sheath through a unique synergy at the nanoscale. This work should be notably significant for the design of new multifunctional nanoarchitectures by the wet-chemistry process, applicable for energy conversion and storage of the future.

501 カーボンナノチューブの表面改質による炭化物系複合ナノチューブの合成と微細組織観察(セラミック/セラミック基複合材料1)

Single-phase SiC and TiC nanotubes were succeeded in synthesized by the reaction of carbon nanotubes with Si powder and Ti powder. The X-ray diffraction patterns indicate that much carbon nanotubes reacted with Si and Ti were transformed to SiC and TiC with increasing the reacting temperature. The results of TEM observation reveal that C-SiC coaxial nanotubes, which are carbon nanotubes sheathed with SiC layer, were synthesized as well as single-phase SiC nanotubes. On the other hand, carbon nanotubes equipped with TiC nano-particles were synthesized in the case of reaction with Ti powder.

Photoconductive Coaxial Nanotubes of Molecularly Connected Electron Donor and Acceptor Layers

Controlled self-assembly of a trinitrofluorenone-appended gemini-shaped amphiphilic hexabenzocoronene selectively formed nanotubes or microfibers with different photochemical properties. In these nanotubes, which are 16 nanometers in diameter and several micrometers long, a molecular layer of electron-accepting trinitrofluorenone laminates an electron-donating graphitic layer of pi-stacked hexabenzocoronene. The coaxial nanotubular structure allows photochemical generation of spatially separated charge carriers and a quick photoconductive response with a large on/off ratio greater than 10(4). In sharp contrast, the microfibers consist of a charge-transfer complex between the hexabenzocoronene and trinitrofluorenone parts and exhibit almost no photocurrent generation.

Giant Wave-Drag Enhancement of Friction in Sliding Carbon Nanotubes

Molecular dynamics simulations of coaxial carbon nanotubes in relative sliding motion reveal a striking enhancement of friction when phonons whose group velocity is close to the sliding velocity of the nanotubes are strongly excited. The effect is analogous to the dramatic increase in air drag experienced by aircraft flying close to the speed of sound but differs in that it can occur in multiple velocity ranges with varying magnitude, depending on the atomic level structures of the nanotubes. The phenomenon is a general one that may occur in other nanoscale mechanical systems.

Formation of off-centered double-walled carbon nanotubes exhibiting wide interlayer spacing from bi-cables

Novel off-centered coaxial carbon nanotubes have been fabricated by coalescing adjacent double-walled carbon nanotubes (DWNTs) using high temperature heat treatments. The eccentric nanotubes possess wide interlayer spacing, and arise by the merge of two narrow diameter (inner) tubes contained inside a large diameter tubes (also known as bi-cables). We propose a complete description of the coalescence process including the merge of two DWNTs, followed by the formation of bi-cables and the creation of off-centered DWNTs. We also performed molecular dynamics calculations that are in agreement with the experimental observations.

Grooving the carbon nanotube oscillators

Using microcanonical molecular dynamics, we investigate effects of single defects on the performance of a nanoscale oscillator composed of coaxial double-walled carbon nanotubes. It is found that at low temperatures a single defect placed on the outer nanotube can significantly reduces axial oscillation energy leakage by impeding intertube rotational modes, and therefore mitigates the frictional effects between sliding nanotubes.

Atomic Layer Deposition on Suspended Single-Walled Carbon Nanotubes via Gas-Phase Noncovalent Functionalization

Alternating exposures of nitrogen dioxide gas and trimethylaluminum vapor are shown to functionalize the surfaces of single-walled carbon nanotubes with a self-limited monolayer. Functionalized nanotube surfaces are susceptible to atomic layer deposition of continuous, radially isotropic material. This allows for the creation of coaxial nanotube structures of multiple materials with precisely controlled diameters. Functionalization involves only weak physical bonding, avoiding covalent modification, which should preserve the unique optical, electrical, and mechanical properties of the nanotubes.

Energy exchanges in carbon nanotube oscillators

Energy exchanges between orderly intertube axial motion and vibrational modes arestudied for isolated systems of two coaxial carbon nanotubes at temperatures rangingfrom 300 to 500 K. It is found that the excess intertube van der Waals energy,depleted from the intertube axial motion, is primarily stored in low-frequencymechanical modes of the oscillator for an extended period of time. This constitutesthe first computer simulation of a nanomechanical device that exhibits negativefriction.

Coaxial carbon nanotubes as shielded nanowires

We report transverse polarizabilities of coaxial carbon nanotubes using first principles density functional theory. These results demonstrate a shielding of the inner nanotube from electric fields by the outer nanotube. This study has implications for nanoelectronics, specifically for the possibility of using coaxial nanotubes as nanoelectrical wires. Shielding is predicted to be on the order of 95% by high-level polarizability calculations. This shielding occurs regardless of whether the outer nanotube is metallic or semiconducting. In addition, a series of calculations on coaxial nanotubes where the inner nanotube is not centered show that the shielding still occurs with approximately the same magnitude. These calculations therefore indicate that it would be possible to use a coaxial carbon nanotube as a shielded nanowire.

Synthesis and characterization of CdS based sulfide coaxial cable and nanotubes by sacrificial approach

Sulfide coaxial cable nanostructures and nanotubes, such as CuS nanotubes, CdS/CuS coaxial cable nanostructures, Ag2S nanotubes, and CdS/Ag2S coaxial cable nanostructures have been prepared by a versatile and sacrificial approach based on substitution reaction and subsequent H2SO4 treatment. The morphology and structure of the nanomaterials have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) pattern. Moreover, the formation mechanism for the sulfide coaxial cable nanostructures and nanotubes has been phenomenologically discussed.

An improved evaluation of the DC performance of carbon nanotube field-effecttransistors

A self-consistent Schrödinger–Poisson solver is used to improve upon a recent evaluation ofthe attainable DC performance of coaxial carbon nanotube field-effect transistors. Theearlier evaluation, which was based on the predictions of a compact model, is shown to beoptimistic because of the model’s inadequate treatment of quantum mechanical reflection ofthermionically injected carriers. This deficiency of the compact model is remedied, to alarge extent, by incorporating a new, short expression for quantum mechanical reflectionunder phase-incoherent conditions.

Dual Raman Features of Double Coaxial Carbon Nanotubes with N-Doped and B-Doped Multiwalls

Double coaxial carbon nanotubes with nitrogen (N)-doped and boron (B)-doped multiwalls possess composite Raman characteristics, originating not only from the outer N-doped but also from inner B-doped layers. Both N and B dopings result in substantial shifts of the characteristic D band and G band of sp(2) carbon constituting nanotube walls but in different ways. The downshift of the G band is correlated with the decreases of electrical resistivity of carbon nanotubes regardless of N or B doping.

Graphite-Incorporated MoS2 Nanotubes: A New Coaxial Binary System

Graphite-filled MoS2 nanotubes were synthesized by pyrolizing propylene inside MoS2 nanotubes prepared by a template-assisted technique. The large coaxial nanotubes were constituted of graphite sheets inserted between the MoS2 layers, forming the outer part, and coaxial multiwall carbon nanotubes intercalated with MoS2 inside. High-resolution electron microscopy (HREM) and electron energy loss spectroscopy techniques along with molecular dynamics simulation and quantum mechanical calculations were used to characterize the samples. The one-dimensional structures exhibit diverse morphologies such as long straight and twisted nanotubes with several structural irregularities. The interplanar spacing between the MoS2 layers was found to increase from 6.3 to 7.4 A due to intercalation with carbon. Simulated HREM images revealed the presence of mechanical strains in the carbon-intercalated MoS2 layers as the reason for obtaining these twisted nanostructures. The mechanism of formation of carbon-intercalated MoS2 tubular structures and their stability and electronic properties are discussed. Our results open up the possibility of using MoS2 nanotubes as templates for the synthesis of new one-dimensional binary-phase systems.

Preparation and characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes

Preparation conditions of single-phase SiC nanotubes and C-SiC coaxial nanotubes were investigated. The characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes were carried out. The SiC nanowires, which were made of the catenated SiC grains of 50–200 nm in diameter, were obtained in carbon nanotubes reacted at 1450 °C. The only C-SiC coaxial nanotubes were formed at 1300 °C. A few single-phase SiC nantoubes were synthesized at 1200 °C for 100 h. More than half number of nanotubes reacted at 1200 °C for 100 h were altered to single-phase SiC nantoubes by heat treatment of 600 °C for 1 h in air since the remained carbon was removed. The energy dispersive X-ray spectroscopy analysis revealed that the atomic ratio of Si to C in single-phase SiC nanotubes was almost 1; these single-phase SiC nanotubes consisted of near-stoichiometric SiC grains.

A tribological study of double-walled and triple-walled carbon nanotube oscillators

We reported in a previous study (Zhao et al 2003 Phys. Rev. Lett. 91 175504) that energytransfer from the orderly intertube translational oscillation to intratube vibrational modesfor an isolated system of two coaxial carbon nanotubes at low temperatures takes placeprimarily via two distinct types of collective motion of the carbon nanotubes, i.e., off-axialrocking motion of the inner tube and radial wavy motion of the outer tube, andthat these types of motion may or may not occur for such a system, dependingupon the amount of the initial extrusion of the inner tube out of the outer tube.Our present study, using micro-canonical molecular dynamics (MD), indicatesthe existence of an energy threshold, largely independent of system sizes andconfigurations, for a double-walled nano-oscillator to deviate from the intertubetranslational oscillation and thus to encounter significant intertube friction. Thefrictional forces associated with several distinct dissipative mechanisms are all foundto exhibit no proportional dependence upon the normal force between the twosurfaces in relative sliding, contrary to the conventional understanding resultingfrom tribological studies of macroscopic systems. Furthermore, simulation hasbeen performed at different initial temperatures, revealing a strong temperaturedependence of friction in the early phase of oscillation. Finally, our studies ofthree-walled nano-oscillators show that an initial extrusion of the middle tubecan cause inner-tube off-axial instabilities, leading to strong frictional effects.

The Template Synthesis of Double Coaxial Carbon Nanotubes with Nitrogen-Doped and Boron-Doped Multiwalls

We present the first synthesis of double coaxial carbon nanotubes with nitrogen-doped and boron-doped multiwalls by the template technique with two-step chemical vapor deposition. X-ray photoelectron spectra confirm the coaxial formation of different-doped structures. The electrical conductance and oxygen chemisorption measurement indicate dual electrical properties and chemical activity at their outer and inner layers.

Double Coaxial Structure and Dual Physicochemical Properties of Carbon Nanotubes Composed of Stacked Nitrogen-Doped and Undoped Multiwalls

Carbon nanotubes with a double coaxial structure of nitrogen-doped and undoped multiwalls were successfully prepared by the template technique using porous anodic aluminum oxide film as a template. The inner carbon layer (or the outer carbon layer) of the double coaxial carbon nanotubes is free from N, while the outer carbon layer (or the inner carbon layer) is uniformly doped with N. Transmission electron microscopy cannot differentiate between the outer and inner layers, but all the results by Raman, X-ray diffraction, and X-ray photoelectron spectroscopy provide evidence that the N-doped layer is less crystallized than the undoped one. Furthermore, the N-doped layer has apparently higher chemical reactivity toward oxygen than the undoped one due to more edge-active sites resulting from the introduction of nitrogen species. Electrical conductance measurement indicates that despite poorer crystallinity the N-doped layer has higher conductivity than undoped one. The resulting multiwalled carbon nanotubes thus have not only double-stack coaxial structure but also dual physicochemical properties.

‘Buckypaper’ from coaxial nanotubes

Double-walled carbon nanotubes are needed in a pure, highly crystalline form before features such as their electronic properties, thermal transport and mechanical behaviour can be investigated. Here we fabricate a paper-like material that consists of hexagonally packed bundles of clean, coaxial carbon nanotubes whose double walls vary little in diameter; it is prepared in high yields using chemical-vapour deposition with a conditioning catalyst and two-step purification. Our results will enable investigation of the physical properties of double-walled carbon nanotubes, which are predicted to be superior to those of both their single- and multiwalled relatives.

Synthesis of Silicon Carbide Nanotubes

Single‐phase silicon carbide (SiC) nanotubes were successfully synthesized by the reaction of carbon nanotubes with silicon powder at 1200°C for 100 h. X‐ray diffraction patterns indicated that most of the carbon from the carbon nanotubes that were reacted with silicon at 1200°C for 100 h was transformed to SiC. Transmission electron microscopy observations revealed that both single‐phase SiC nanotubes and C–SiC coaxial nanotubes, which are carbon nanotubes sheathed with a SiC layer, were synthesized after 100 h of reaction. The ratio of single‐phase SiC nanotubes to C–SiC nanotubes increased with heat treatment at 600°C in air for 1 h because the remaining carbon was removed.