Y-junction Carbon Nanotubes Research Articles

Synthesis of single-walled, bamboo-shaped and Y-junction carbon nanotubes using microwave plasma CVD on low-temperature and chemically processed catalysts

The low temperature nucleation and high yield growth of CNTs with their diverse range of layered structures and shapes is of significant interest to the research community in view of obtaining distinctive properties necessary for specific applications. In this regard, several strategies have been employed to control the growth characteristics of CNTs. In the present investigation, the low temperature growth of CNTs has been enabled using CO 2 as a suitable oxidizing gas. CNTs have been grown via an optimum etching process conducted under diffuse plasma generated using a specially designed shadow mask assembly that shields the growth surface from direct plasma bombardment, and subsequent abrasive etching by the reactive plasma species. Furthermore, CO 2 as a component in the plasma facilitates the elimination of amorphous carbonaceous components from the surface of the CNTs. The growth of narrow CNTs has been achieved via the formation of a low diameter (~20 nm) catalyst comprised of Fe nano-particles grown in a low temperature (10 °C) chemical process under an inert atmosphere via simultaneous aerial oxidation and neutralization in a single step. Further plasma optimization by controlling the MW power has facilitated the growth of CNTs with controlled diameters, wall numbers and different morphologies (e.g., Y-junction and bamboo-shaped MWCNTs, and very low diameter (~1.5 nm) SWCNTs). The tip growth mechanism for CNT nucleation has been established using HR-TEM, in which the Fe catalyst nanoparticles are detected within the top shell of the growing CNTs. • Several strategies have been applied together to control the growth characteristics of CNTs by plasma optimization via controlling the MW power. • Low temperature growth of CNTs was achieved using diffuse plasma under a shadow mask and CO 2 as an oxidizing gas. • Reduction of the CNT diameters was achieved via the formation of tiny Fe catalysts using a chemical process at 10 °C under an inert atmosphere. • CNTs have been grown with precise diameters, wall numbers and different morphologies (e.g., Y-junction, bamboo-shaped MWCNTs and ~1.5 nm diameter SWCNTs).

Thermal rectification in Y-junction carbon nanotube bundle

Abstract Active control of heat flow is one of the important concepts in phononic devices, among which thermal diode is a fundamental building block. The long-standing bottleneck is the relevant experiments lagging far behind theoretical results. In this paper, we experimentally demonstrated considerable thermal rectification in the Y-junction carbon nanotube (CNT) bundle with suspended thermal bridge method. The thermal rectification ratio is up to ∼8.3% ± 0.5% with a relatively low temperature difference (ΔT = 4K). Molecular dynamics simulation results show that asymmetric phonon transmission in different (forward and backward) directions is responsible for the thermal rectification observed in the asymmetric CNT structure.

Structural optimization and shear performances of the nanopins based on Y-junction carbon nanotubes

Abstract Utilizing the classical molecular dynamic, we have briefly conducted geometry optimization on several typical nanopins based on Y-junction carbon nanotubes (CNTs), and further investigated their shear performance. The service performance of the nanopin is not sensitive to the length of the inserting end, while as the height of the branch tube increases, the maximum unloading force increases firstly and then keeps relatively stable. The overlong inserting end and high branch tube can lead to the severe oscillation in unloading force due to the continuous morphology change. Moreover, results show that a small angle included in Y-junction CNTs can contribute to both of the fixity of the nanopin and instability of the uninstallation process. Further investigation indicates that the orientation of the branch tubes of the nanopin determines the maximum shear performance, while the radial stability of the CNTs plays an important role in the shear performance of the nanopin. And the microstructure of the Y-junction CNT occurred during the using process can also influence its service performance.

A novel nanopin model based on a Y-junction carbon nanotube

A prototype of nanopin based on a Y-junction carbon nanotube (CNT) is first proposed. The loading and unloading processes are investigated by using classical molecular dynamics, considering the influences of the fit dimension, positioning error, thermal effect, and the loading/unloading velocity on the performance of the proposed nanopin. The optimum size of the gap between the nanopin and the through hole in a silicon component is obtained, which is responsible for a desired fixity with the acceptable install resistance. It is found that a proper positioning error in a certain direction associated with the branched structure of the nanopin will facilitate the installation process. The performance of the proposed nanopin is not sensitive to thermal and normal axial velocity of the nanopin, while the unloading direction affects appreciably on the service performance of the nanopin attributed to the orientation of the branched CNT. Particularly, the service performance of the proposed nanopin considerably depends on several special deforming configurations in the loading and unloading processes.

Molecular dynamics simulation on the failure mechanism of Y-junction single-walled carbon nanotubes

Abstract Molecular dynamics simulation based on the second generation Brenner potential has been employed to investigate the mechanical properties and failure mechanism of Y-junction carbon nanotubes (Y-CNTs) under tensile loading. It was found that due to the existence of junction heptagonal defects, shear bands induced by the external load may expand outward in the form of spiral and promote the formation of Stone–Wales transformation, which therefore constitutes an effective way to dissipate the energy. We also study the temperature effect on the mechanical properties of Y-CNTs. Our simulation results provide useful insights to the design and fabrication of Y-CNTs based nanostructures and devices.

Synthysis of S Doped Y-Junction Carbon Nanotubes by CVD Method

The sulfur-doped Y-junction carbon nanotubes (S-YCNTs) were prepared by chemical vapor deposition of carbon disulfide using Fe as catalyst. Sulfur can be incorporated into the nanotubes with an identifiable amount, forming sulfur-doped carbon nanotubes. The growth of asymmetrical Y-branches in the nanotubes may be related to the presence of sulfur from precursor. The structure and morphology of S-YCNTs can be controlled by processing parameters. The S-YCNTs were characterized by SEM, TEM, EDX, and XPS, respectively. The growth mechanism of S-YCNTs was discussed in terms of the role of sulfur from carbon feedstock.

Direct synthesis of Y-junction carbon nanotubes by microwave-assisted pyrolysis of methane

Both Y-junction carbon nanotubes and individual carbon nanotubes were synthesized without any additive catalyst by microwave decomposition of methane. Detailed microstructures of as-synthesized products have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The results show that these Y-junction CNTs possess an internal bamboo-shaped structure, and some three dimensional multi-terminal junctions are also observed on CNTs. As gas flow rate decreased to 15 sccm, only individual nanotubes could be obtained. A possible mechanism is proposed for the synthesis of the Y-junction carbon nanotubes on these observations. This technique may also have great potential in making other nano-structured carbon materials on a large scale and at low cost.

Y-junction single-wall carbon nanotube electronics

This article presents the synthesis of a Y-junction single-wall carbon nanotube (SWNT) and its electrical characterization. The formation of Y-junction branches is found to be dependent on the catalyst composition, which can be correlated to the Gibbs free energy of metal carbide formation. Radial breathing mode peaks in Raman spectra show that the sample has both metallic and semiconducting nanotubes, and their portion is varied with type of catalyst and growth temperature. The localized gating effect exhibited by the Y-SWNT suggests the resemblance of its electrical characteristics with ambipolar field effect transistor. The temperature dependence of the I–V characteristics reveals that the conduction mechanism in the Y-SWNT is governed by thermionic emission at temperatures above 100 K and by tunneling at T < 100 K.

Formation of Y-junction carbon nanotubes by catalytic CVD of methane

Y-junction carbon nanotubes were grown by catalytic CVD of methane at 700 ∘ C on NiO–CuO–MoO(7:2:1) (w/w/w)/SiO 2 catalyst. For comparison, NiO–CuO(8:2) (w/w)/SiO 2 and NiO–MoO(8:2) (w/w)/SiO 2 catalysts were tested for carbon nanotube formation. TEM analysis indicates that no Y-junction structures were formed with the latter two catalysts. This finding elucidates why the addition of a small amount of MoO to NiO–CuO/SiO 2 catalyst is crucial for enhancing the formation of Y-junction carbon nanotubes.

Three-way electrical gating characteristics of metallic Y-junction carbon nanotubes

Y-junction based carbon nanotube (CNT) transistors exhibit interesting switching behaviors, and have the structural advantage that the electrical gate for current modulation can be formed by any of the three constituent branches. In this letter, we report on the gating characteristics of metallic Y-CNT morphologies. By measuring the output conductance and transconductance we conclude that the efficiency and gain depend on the branch diameter and is electric field controlled. Based on these principles, we propose a design for a Y-junction based CNT switching device, with tunable electrical properties.

Fabrication of Y-junction carbon nanotubes by reduction of carbon dioxide with sodium borohydride

Y-junction carbon nanotubes with a bamboo-shaped structure have been synthesized by reduction of CO2 with NaBH4 at 700 °C. The X-ray power diffraction pattern indicates that the products are hexagonal graphite, and transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images reveal the morphology and structure of carbon nanotubes. The effects of reaction temperature on the growth of the Y-junction carbon nanotubes were also discussed in the paper. Reduction of supercritical CO2 with sodium borohydride is a promising green chemical method for economically producing Y-junction carbon nanotubes.

Ion separation using a Y-junction carbon nanotube

Using molecular dynamics simulations, we show that a Y-junction carbon nanotube can be used toseparate K+ and Cl− ions from a KCl solution. The Y-junction nanotube is formed by connecting two smallercarbon nanotube branches of sizes (5, 5) and (6, 6) to a larger (8, 8) carbon nanotube. Whileuncharged (5, 5) and (6, 6) carbon nanotubes show close to zero occupancy ofK+ and Cl− ions, we show that a negatively charged (5, 5) carbon nanotubeand a positively charged (6, 6) carbon nanotube can be selective toK+ and Cl− ions, respectively. By performing molecular dynamics simulations on the entire systemcomprising the Y-junction carbon nanotube, the KCl solution chamber, the push plate and thereceiving chamber, we show that as the electrolyte moves through the (8, 8) carbon nanotube theK+ andthe Cl− ions can be selectively transported through the (5, 5) and the (6, 6) carbon nanotube,respectively. The formation of ion pairs can affect the separation efficiency and we discussthe conditions under which perfect separation can be obtained.

Improved synthesis of carbon nanotubes with junctions and of single-walled carbon nanotubes

Pyrolysis of thiophene over nickel nanoparticles dispersed on silica is shown to yield Y-junction carbon nanotubes with smaller diameters than those obtained by the pyrolysis of organometallic-thiophene mixtures. In the presence of water vapour, the pyrolysis of organometallic-hydrocarbon mixtures yields single-walled nanotubes, as well as relatively narrow-diameter carbon nanotubes with Y-junctions. Pyrolysis of organometallic-hydrocarbon mixtures, in the absence of water vapour, only gives nanotubes with T- and Y-junctions.

New aspects on pulsed laser deposition of aligned carbon nanotubes

We have grown carbon nanotubes (CNT) by pulsed laser deposition (PLD) at 1000 °C in Ar atmosphere. A Nd/YAG laser was used for irradiation of a graphite target containing Ni and Co rods. High-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM) images showed that “closed” carbon nanotubes were grown between clusters of metallic particles, so that the individual nanotubes were arranged in parallel to each other forming a shape of “Rope-Bridge”. The nanotubes structure was analyzed by high-resolution transmission electron microscopy (HRTEM) and their type was found to be of MWNT, containing about five SWNT. Total diameter was 5–20 nm and their length was about 1 μm. High homogeneous distribution carbon nanotubes were grown and different structures were observed such as well-aligned carbon nanotubes, bamboo-like and Y-junction carbon nanotubes.

Differential current amplification in three-terminal Y-junction carbon nanotube devices

We present three-terminal transistor-like operation of Y-junction carbon nanotubes with three independent contacts. Using one of the terminals as a controlling gate, differential current gain of up to 300 is observed at low temperature (4.2K) in the biasing region where the gate current is small. We present evidence that the observed transistor characteristics can be ascribed to a new amplification mechanism: gated hopping via conducting grains.

Influence of pyrolysis temperature on the growth of Y-junction carbon nanotubes

Y-junction carbon nanotubes, grown through thermal pyrolysis of acetylene over nanocrystalline Ni-P deposited SiC whiskers, were investigated by transmission electron microscopy. The pyrolysis temperature, which ranged from 800 °C to 1000 °C, was found to be crucial for the growth of different Y-junction carbon nanotubes. At pyrolysis temperatures below the partial melting point of the Ni-P alloy catalyst, only single-junction nanotubes could be synthesized. Whereas, due to partial melting of the alloy catalyst at higher pyrolysis temperatures, liquid-assisted growth of multiple Y-junction nanotubes could occur.

Novel electrical switching behaviour and logic in carbon nanotube Y-junctions

Carbon-nanotube-based electronics offers significant potential as a nanoscale alternative to silicon-based devices for molecular electronics technologies. Here, we show evidence for a dramatic electrical switching behaviour in a Y-junction carbon-nanotube morphology. We observe an abrupt modulation of the current from an on- to an off-state, presumably mediated by defects and the topology of the junction. The mutual interaction of the electron currents in the three branches of the Y-junction is shown to be the basis for a potentially new logic device. This is the first time that such switching and logic functionalities have been experimentally demonstrated in Y-junction nanotubes without the need for an external gate. A class of nanoelectronic architecture and functionality, which extends well beyond conventional field-effect transistor technologies, is now possible.

Synthesis of Y-junction carbon nanotubes within porous anodic aluminum oxide template

Abstract Y-junction carbon nanotubes with the average diameter about 200 nm were successfully synthesized within porous anodic aluminum oxide template, which was prepared by anodic anodizing aluminum sheet in 1.0 mol/l H3PO4 solution at a constant anodization voltage 90 V.

Rapid Prototyping of Site-Specific Nanocontacts by Electron and Ion Beam Assisted Direct-Write Nanolithography

Rapid prototyping of bottom-up nanostructure circuits is demonstrated, utilizing metal deposition and patterning methodology based on combined focused ion and electron beam induced decomposition of a metal−organic precursor gas. Ohmic contacts were fabricated using electron beam deposition, followed by the faster process of ion beam deposition for interconnect formation. Two applications of this method are demonstrated: three-terminal transport measurements of Y-junction carbon nanotubes and fabrication of nanocircuits for determination of electromechanical degradation of silver nanowires.

Thermal conductivity of Y-junction carbon nanotubes

The thermal conductivity of a Y-junction carbon nanotube with a (14,0) trunk splitting into two (7,0) branches has been investigated using a molecular dynamics approach. It has been found that the thermal conductivity of the Y-junction nanotube is less than that of a corresponding straight (14,0) nanotube, due to lattice defects in the form of nonhexagonal carbon rings at the junction. These lattice defects result in a discontinuity in the temperature profile of the Y-junction nanotube. Defects that were introduced to a straight (14,0) nanotube resulted in a similar discontinuity in the temperature profile.