Carbon Nanotube Junctions Research Articles

Negative Differential Resistance in Carbon Atomic Wire-Carbon Nanotube Junctions

Negative differential resistance (NDR) was recently observed in carbon nanotube junctions just before breaking and hypothesized to arise from the formation of monatomic carbon wires in the junction. Motivated by these results, a first-principles scattering-state approach, based on density functional theory, is used to study the transport properties of carbon chains covalently connecting metallic carbon nanotube leads at finite bias. The I- V characteristics of short carbon chains are predicted to exhibit even-odd behavior, and NDR is found for both even and odd chain junctions in our calculations.

The Intramolecular Junctions of Carbon Nanotubes

AbstractFor the miniaturization of microelectronics, carbon nanotubes (CNTs) are regarded as ideal candidates for the next generation of nanoelectronics because of their excellent properties. To realize CNT‐based electronics, intramolecular junctions are required components, which can not only connect different CNTs for integration, but can also act as functional building blocks in the circuit, such as rectifiers, field‐effect transistors, switches, amplifiers, photoelectrical devices, etc. Therefore, intense attention has been focused on this topic and many advances have been achieved, especially in recent years. On the other hand, some challenges also exist. To provide researchers with a comprehensive overview of this field, this review discusses the synthesis, properties, and applications of intramolecular junctions of CNTs in detail. Among them, the applications of CNT integration are discussed specially. Furthermore, a brief summary and an outlook of future work are provided.magnified image

Double toroids as model systems for carbon nanotube junctions: through-bond currents

We show that the through-bond currents in a closed molecular network originate from their topologically invariant edge-homologies. When applied to double toroidal structures they give rise to topologically induced currents whose 3D manifestations are highly sensitive to the way both loops are merged together i.e. on the nature of their junction.

Photon-Assisted Electron Transport for a Λ-shaped Carbon Nanotube Junction

We theoretically study the electron transport properties for two coupled single-walled carbon nanotube quantum dots connected to metallic electrodes under the irradiation of an external electromagnetic field at low temperatures. Using the standard nonequilibrium Green's function techniques, we examine the time-averaged transmission coefficient and linear conductance. It is shown that by some numerical examples, the photon-assisted inter-dot coupling causes Fano resonance and the conductance of the system is sensitive to the external field parameters. The transport dependence on the external field parameters may be used to detect the high-frequency microwave irradiation.

Ab initio study on the structural, energetic and electronic features of the asymmetric armchair SWCNT junctions

The structural, energetic and electronic features of asymmetric armchair single-walled carbon nanotube (SWCNT) junctions have been studied by ab initio calculations at the B3LYP/6-31G ∗//HF/3-21G ∗ levels. The junctions are composed of two SWCNTs with different radius, which are connected by a set of 5-membered and 7-membered carbon rings. The results show that the metallic–metallic junction is more energetically favorable if the junction is formed with a hexagon inserted between the pentagon–heptagon (5/7) pair defects in the armchair nanotube. The shift of the spatial distribution of HOMO and LUMO shows that the asymmetric electronic structure of the junction could be used as a molecular rectifier.

Structures and stabilities of multi-terminal carbon nanotube junctions

A variety of multi-terminal junctions, including Y-, T- and X-type carbon nanotubes, were generated by connecting individual single-walled carbon nanotubes with different size and helicity. By optimizing these hetero-structures with different geometric features, the energetically favored structures were proposed. The corresponding energy features of the junctions indicate that the tube diameter, the helicity, and the distribution of defects, play an important role on the stability of junctions. The most stable Y-, T- and X-junctions contain six, six, and twelve heptagons, respectively. These defect rings tend to distributed at the corners of the junctions. The zigzag-type junctions are more stable than the armchair ones. Moreover, the average energy of individual atom for Y-, T-, and X-junction is found to be a function of the tube diameter.

Direct growth of carbon nanotube junctions by switching source gases in a continuous chemical vapor deposition

A new method is used to directly grow carbon nanotube (CNT) junctions with two different structures through a continuous chemical vapor deposition (CVD) process. CH 4/B 2H 6/H 2 and CH 4/H 2 source gases were used as the feeding gas, respectively. By switching between different source gases in the CVD process, the junctions composed of boron-doped and pure CNTs were prepared. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the structure and composition of such junctions. The results show that each junction is having a bamboo boron-doped CNT at one side and a hollow CNT at another side, and the two different structures are connected with each other successfully.

Translocation of DNA oligonucleotide through carbon nanotube channels under induced pressure difference

This paper presents molecular dynamics (MD) simulations of DNA oligonucleotide and water molecules translocating through carbon nanotube (CNT) channels. Induced pressure difference is applied to the system by pushing a layer of water molecules towards the flow direction to drive the oligonucleotide and other molecules. This novel MD simulation investigates the flow behaviour of oligonucleotide and water molecules in nanochannel while controlling the temperature and volume of the system in canonical ensemble. The results show that the oligonucleotide is unable to translocate through the (8, 8)–(12, 12) CNT channel under the induced pressures applied. However, the oligonucleotide can transport through the (10, 10)–(14, 14) CNT channel easily under the same induced pressures. It is observed that less water molecules permeate through the center of the (8, 8)–(12, 12) CNT channel as the strength of the induced pressure is increased. In contrast, more water molecules flow through the (10, 10)–(14, 14) CNT channel at a higher induced pressure. The conformational energy of the oligonucleotide in the CNT channels has been shown to be affected by both the strength of the induced pressure and the size of the nanotube. Although the interactive force between oligonucleotide and CNT channel is dependent on their distance apart, the induced pressure within the (8, 8)–(12, 12) nanotube channel acts as an external factor that affects the distance between the oligonucleotide and the CNT junction. The insertion depth of the oligonucleotide in the (8, 8)–(12, 12) CNT channel relies on the magnitude of the induced pressure. Both the velocity of oligonucleotide and the interactive force between oligonucleotide and nanotube wall are shown to increase when the oligonucleotide is travelling through the narrower part of the (10, 10)–(14, 14) CNT channel.

OS0211 カーボンナノチューブ接合部における変形集中に関する原子論的研究(先端材料システムの力学とメゾスケールモデリング(2))

屈曲型接合部を有するカーボンナノチューブ(CNT)を対象として,分子動力学法を用いて変形解析を行うとともに,CNTの局所ひずみ評価法を提案し,接合部におけるひずみ集中を解析する.ひずみ集中は,CNT全体形状という巨視的要因(曲管の引張)によるものと,原子配列(五,六,七員環の配列)という微視的要因によるものに分けることができ,接合部内側と外側に位置する七員環部では,微視的要因により特に大きなひずみ集中が生じる.巨視的要因と微視的要因の両方を含むCNTのひずみ分布と,巨視的要因のみを含むはりのひずみ分布を比較すると,接合部近傍において,微視的要因により,前者は後者の約1.5倍の値を示す.

Growth mechanism of Y-junctions and related carbon nanotube junctions synthesized by Au-catalyzed chemical vapor deposition

Y-junctions and related carbon nanotube (CNT) junctions were synthesized by Au-catalyzed chemical vapor deposition. The catalyst was prepared by evaporating a 10-nm-thick Al 2O 3 film and a 1-nm-thick Au film on a Si substrate. Based on thorough investigations under a high-resolution transmission electron microscope, the CNT junctions were proved to be formed by a unified catalyst-merging mechanism. Different merging processes resulted in different morphologies, such as Y-shaped, T-shaped, multi-leveled, multi-terminal and L-shaped CNT junctions.

Inside Front Cover: A Photosynthetic Reaction Center Covalently Bound to Carbon Nanotubes (Adv. Mater. 22/2007)

AbstractOn p. 3901, Shachar Richter, Alexander Holleitner, and co‐workers report on a novel hybrid system, fabricated by covalent binding of photosynthetic reaction center protein photosystem I (PS I) to carbon nanotubes (CNTs) by using carbodiimide chemistry. The versatile chemical modification schemes allow contacting of single PS I protein to two carbon nanotubes, the formation of CNT–PS I–CNT junctions, and electrical contact of carbon nanotubes to gold electrodes via covalent binding to the photosystem. Such nanostructures can pave the way for the construction of electronic circuits for nano‐optoelectronic applications.

Construction of atomic arrangement for carbon nanotube junctions

AbstractAn algorithm will be presented for constructing Descartes coordinates for carbon atoms in a junction of three nanotubes of any chirality. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

New formations of carbon nanotube junctions

A method is demonstrated for constructing models on which we show that carbon nanotubes with optional type and diameter can be connected to different three-dimensional surfaces. Basic examples (zigzag and armchair-type junctions and holes) are studied in this paper.

Sensing an electromagnetic field with photon-assisted Fano resonance in a two-branch carbon nanotube junction

A photon-assisted Fano resonance in a two-branch single wall carbon nanotube junction (NJ) is considered. The NJ branches are misaligned by a finite angle $\ensuremath{\vartheta}$ and represent two coupled one-dimensional quantum dots where quantized electron states are formed. The inter-dot tunneling coupling causes a Fano resonance. When an external electromagnetic field (EF) is applied, the interdot tunneling becomes photon assisted. The resulting dc conductivity of each NJ branch shows series of satellite singularities arising in addition to the steady state Fano peaks. Magnitudes and positions of the singularities depend on the frequency, amplitude, and polarization of the EF, which may be used for sensing purposes.

Spin-dependent transport in Fe-doped carbon nanotubes

We report on a first principles calculation of spin-dependent quantum transport in Fe-doped single-wall carbon nanotube (CNT) junctions. For junctions of a pristine $(9,0)$ CNT in contact with Fe-doped $(9,0)$ CNT leads, the total current in parallel configuration of the moment is larger than that of antiparallel configuration under lower bias voltage. For higher bias voltages the opposite happens. A tunnel magnetoresistance ration as large as 40% is found at zero bias, it decays with bias, and eventually goes to negative values at larger bias. Similar results are obtained for junctions with pristine $(10,0)$, $(8,0)$ CNT in contact with Fe-doped $(10,0)$ or $(8,0)$ CNT leads. The spin-dependent transport features can be understood by analyzing microscopic details of the transmission coefficients.

Novel ZnO nanostructures grown on carbon nanotubes by thermal evaporation

We report on the formation of ZnO/carbon nanotubes heterostructures achieved by means of a thermal evaporation method. Scanning electron microscopy revealed that the main building block of the observed morphologies was the nanorod whose self-assembling resulted in various structures such as polypods and nano-hedgehogs, depending on various factors as well as the location of the ZnO–CNT junction. X-ray diffraction and photoluminescence spectroscopy were used to study the structure and optical properties of obtained nanostructures. Semi-empirical molecular orbital calculations gave evidence for the nature of the binding between ZnO and CNTs.

Magnetic-field effects on transport in carbon nanotube junctions

Here we address a theoretical study on the behaviour of electronic states of heterojunctions and quantum dots based on carbon nanotubes under magnetic fields. Emphasis is put on the analysis of the local density of states, the conductance, and on the characteristic curves of current versus voltage. The heterostructures are modeled by joining zigzag tubes through single pentagon-heptagon pair defects, and described within a simple tight binding calculation. The conductance is calculated using the Landauer formula in the Green functions formalism. The used theoretical approach incorporates the atomic details of the topological defects by performing an energy relaxation via Monte Carlo calculation. The effect of a magnetic field on the conductance gap of the system is investigated and compared to those of isolated constituent tubes. It is found that the conductance gap of the studied CNHs exhibits oscillations as a function of the magnetic flux. However, unlike the pristine tubes case, they are not Aharonov-Bohm periodic oscillations.

STM/STS investigation of carbon nanotube junctions

In this paper we present scanning tunneling microscopy/spectroscopy investigations of multiwall carbon nanotube junctions. We concentrated on bent and narrowing junctions, which my be formed by introducing pentagon–heptagon defects into a hexagonal network of a carbon nanotube. It was expected that the defects introduced to the nanotube could cause changes in the local density of states. The scanning tunneling spectroscopy results were used to search for and identify these defects. We also discuss a hypothesis for a combination of a telescope junction and a pentagon–heptagon induced junction.

Filtering out the transmission ofπ electron Fermi states with odd symmetry through a carbon nanotube junction

Filtering out the transmission ofπ electron Fermi states with odd symmetry through a carbon nanotube junction

All-carbon nanotube-based junction with virtual source and drain of carbon nanotubes by in situ one-step process for practical integrated nanoelectronics

The authors propose a suspended in situ lateral grown all-carbon nanotube-based junction and report on the dc carrying behaviors of the carbon nanotube junction, especially with and after UV exposure. Also, the release of carriers of the junctions was studied by capacitance (C) measurements with ac excitation. The designed diluted magnetic impurity doped oxide film was adopted as catalyst in the fabrication of the junction. The suspended nanotube channel showed ambipolar function and almost the same low barrier height for the holes and electrons, which was determined by I-T(K) measurements. Subsequent measurements on the channel treated by low intensity UV resulted in a highly conductive channel with high current carrying behavior. Both their junction structure and analogy between dc I-V and capacitance can be applied to develop a practical and accessible system for forming reproducible integrated nanoelectronic junctions as well as to accelerate the realization of all low dimensional molecular devices.