Fabrication and transport properties of multiwall carbon nanotube crossroads

A multiwall carbon nanotube crossroads has been fabricated by a manipulation technique using a glass microcapillary, and the low temperature transport properties investigated. The two-terminal conductance of an individual tube shows Tomonaga–Luttinger liquid behavior G∝T^α at high temperature and dI/dV ∝V ^α at low temperature. However, no evidence of such a power-law behavior is obtained in the four-terminal conductance at the junction, where the conductance shows an almost metallic behavior ‘corrected’ by weak localization. Weak localization would essentially appear in electron states at the junctions of MWNTs.     

Successful incorporation of multi-walled carbon nanotubes in nickel electrodeposited coating by electrophoresis

A homogenous and adhesive multi-walled carbon nanotube (MWCNT) coating was electrophoretically deposited on stainless steel from an aqueous solution by applying high strength electric fields. Then, nickel was electrodeposited on MWCNT films. MWCNTs content in the composite coatings was reached to 12.5 wt% which was much higher than the content of MWCNTs in conventional nickel-MWCNT electrodeposited coatings. The hardness value of composite coatings significantly increased up to 870 Vickers which it was measured by both micro and nanohardness tests.     

用散粒噪声测量碳纳米管中Luttinger参数

将碳纳米管的载流子输运用基本电荷为ge的Fermi液态模型描述，利用散射理论计算出纳米管中的零频率散粒噪声，在绝对零度下，存在一个强势垒的碳纳米管的散粒噪声为2geI.提出了一种测试纳米管Luttinger参数的新方法：在纳米管上形成一个强势垒，通过测试其散粒噪声，就可以计算出g因子. 关键词： 碳纳米管 Luttinger参数 散粒噪声 散射理论     

Field emission characteristics of carbon nanotubes post-treated with high-density Ar plasma

The field emission characteristics of carbon nanotubes (CNTs) grown by thermal chemical vapor deposition (CVD) and subsequently surface treated by high-density Ar plasma in an inductively coupled plasma reactive ion etching (ICP-RIE) with the various plasma powers were measured. Results indicate that, after treated by Ar plasma with power between 250 and 500 W, the emission current density of the CNTs is enhanced by nearly two orders of magnitude (increased from 0.65 to 48 mA/cm²) as compared to that of the as-grown ones. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to investigate the structural features relevant to the modified field emission properties of CNTs. The SEM images of CNTs subjected to a 500 W Ar plasma treatment exhibit obvious damages to the CNTs. Nevertheless, the turn-on fields decreased from 3.6 to 2.2 V/μm, indicating a remarkable field emission enhancement. Our results further suggest that the primary effect of Ar plasma treatment might be to modify the geometrical structures of the local emission region in CNTs. In any case, the Ar plasma treatment appears to be an efficient method to enhance the site density for electron emission and, hence markedly improving the electric characteristics of the CNTs.     

氢在多壁碳纳米管中的吸附储存

利用巨正则系综蒙特卡罗(GCMC)的方法模拟了氢在多壁碳纳米管中的吸附,氢气分子之间、氢气分子和碳原子之间的相互作用势能采用Lennard-Jones势能模型。模拟了不同结构参数(管内径、管壁数、管壁间距)的多壁碳纳米管在77K和298K下的吸附等温线,分析了多壁碳纳米管的管内径、管壁数以及管壁间距对吸附性能的影响。模拟结果表明:多壁碳纳米管的管壁数和管壁间距对吸附性能的影响较明显;管壁数越少,管壁间距越大,其吸附性能越好;多壁碳纳米管的管内径对其吸附性能的影响甚微。     

液体水银在碳纳米管中传输的压力控制模型

碳纳米管在纳米技术中有一个很重要的应用,就是它可以作为纳米管道传输液体. 本文用分子动力学模拟方法,结合一个液体压力控制模型,对液体水银由于外部压力作用在碳纳米管中传输的现象进行研究. 研究结果表明,当液体水银的内部压强超过一个临界值时,液体水银能够浸入到碳纳米管内部;不断增大液体内部的压强,碳纳米管可以连续地传输液体;而当对液体水银进行循环加压时,碳纳米管可以间断地传输液体水银. 关键词： 碳纳米管 流体传输 分子动力学     

液体水银在碳纳米管中传输的压力控制模型

碳纳米管在纳米技术中有一个很重要的应用，就是它可以作为纳米管道传输液体. 本文用分子动力学模拟方法，结合一个液体压力控制模型，对液体水银由于外部压力作用在碳纳米管中传输的现象进行研究. 研究结果表明，当液体水银的内部压强超过一个临界值时，液体水银能够浸入到碳纳米管内部；不断增大液体内部的压强，碳纳米管可以连续地传输液体；而当对液体水银进行循环加压时，碳纳米管可以间断地传输液体水银.     

On the low-temperature anomalies of specific heat in disordered carbon nanotubes

The low-temperature behavior of the specific heat in disordered nanotubes strongly depends on structure changes and is not explained by the phonon contribution. Expression for electronic specific heat is carried out taking into account the multiple elastic electron scattering on impurities and structural inhomogeneities of short-range order type. The calculated electronic specific heat depends on diameter of nanotube, concentration of impurities, parameters of short-range order (structural heterogeneity) and describes the peculiarities of low-temperature behavior of specific heat observed in disordered CNT.     

形变碳纳米管中水的输运行为研究

水分子通过碳纳米管的运输行为对认识生命的新陈代谢活动、海水淡化和纳米运输器件有着重要的参考作用.本文通过分子动力学的方法研究了水分子通过形变碳纳米管的运输行为,即椭圆柱状碳纳米管的离心率e对管内水分子输运的影响.结果发现椭圆柱状碳纳米管的离心率对管内水分子的偶极矩概率分布、径向函数分布和流量有重要的影响作用.分析认为碳纳米管的形变使管内水分子的偶极矩态及其运输状态发生变化;同时也发现在一定范围内通过改变碳纳米管的形状能起到分子开关的作用.     

形变碳纳米管中水的输运行为研究

水分子通过碳纳米管的运输行为对认识生命的新陈代谢活动、海水淡化和纳米运输器件有着重要的参考作用. 本文通过分子动力学的方法研究了水分子通过形变碳纳米管的运输行为, 即椭圆柱状碳纳米管的离心率e对管内水分子输运的影响. 结果发现椭圆柱状碳纳米管的离心率对管内水分子的偶极矩概率分布、径向函数分布和流量有重要的影响作用. 分析认为碳纳米管的形变使管内水分子的偶极矩态及其运输状态发生变化; 同时也发现在一定范围内通过改变碳纳米管的形状能起到分子开关的作用.     

Applications of carbon nanotubes in high performance lithium ion batteries

The development of lit;triton ion batteries （LIBs） relies on the improvement in the performance of electrode materials with higher capacity, higher rate capability, and longer cycle lift;. In this review article, the recent advances in carbon nanotube （CNT） anodes, CNT-based composite electrodes, and CNT current collectors for high performance LIBs are concerned. CNT has received considerable attentions as a candidate material for the LIB applications. In addition to a possible choice for anode, CNT has been recognized as a solution in improving the performance of the state-of-the-art electrode materials. The CNT-based composite electrodes can be fabricated by mechanical or chem- ical approaches. Owing to the large aspect ratio and the high electrical conductivity, CNTs at very low loading can lead to an efficient conductive network. The excellent mechanical strength suggests the great potential in forming a structure scaffold to accommodate nano-sized electrode materials. Accordingly, the incorporation of CNTs will enhance the conductivity of the composite electrodes, mitigatc the agglomeration problem, decrease the dependence on inactive binders, and improve the clcctrochenfical properties of both anode and cathode materials remarkably. Freestanding CNT network can be used as lightweight current collectors to increase the overall energy density of LIBs. Finally, research perspectives for exploiting CNTs in high-performance LIBs are discussed.     

Improvement of electronic properties of carboxylated zigzag single wall carbon nanotubes by interaction with benzene derivatives

In this article, we reported the structural and conductive properties of benzene derivatives/carboxylated zigzag SWCNTs. It was noticed that the carboxylated carbon nanotubes were appropriate adsorbents for benzene derivatives. We presented novel density of states and band structures for modified SWCNTs by both carboxylic group and benzene derivatives. The result showed that nitrobenzene/COOH-SWCNT comprising superb electronic properties can be effectually applied for electronic devices and solar cells, instead of aniline/SWCNT combined system.     

Effects on the field emission properties by variation in surface morphology of patterned photosensitive carbon nanotube paste using organic solvent

Photosensitive carbon nanotube (CNT) paste was prepared by 3-roll milling of multi-walled carbon nanotubes (MWNTs), UV-sensitive binder solution, and Ag as filler additives. Arrays of MWNT dots with a diode structure were fabricated by a combination of screen printing method and photolithography using these paste, and acetone utilized as the developer. The MWNT dots were well-defined and the organic binder materials in the dots were partially removed. The MWNT film without a heat treatment showed a high current density of 1.35 mA/cm² at 3.25 V/μm and low turn-on field of 2.2 V/μm at 100 μA/cm². Acetone can be used as an efficient developer to form patterns and to remove the organic residues in patterns, simultaneously.     

Charge transport in carbon nanotubes based materials: a Kubo–Greenwood computational approach

In this contribution, we present a numerical study of quantum transport in carbon nanotubes based materials. After a brief presentation of the computational approach used to investigate the transport coefficient (Kubo method), the scaling properties of quantum conductance in ballistic regime as well as in the diffusive regimes are illustrated. The impact of elastic (impurities) and dynamical disorders (phonon vibrations) are analyzed separately, with the extraction of main transport length scales (mean free path and localization length), as well as the temperature dependence of the nanotube resistance. The results are found in very good agreement with both analytical results and experimental data, demonstrating the predictability efficiency of our computational strategy. To cite this article: H. Ishii et al., C. R. Physique 10 (2009).     

Quality improvement of single-walled carbon nanotubes by doping B in Fe/MgO catalyst

We demonstrate that the quality of the as-grown single-walled carbon nanotubes (SWCNTs) can be effectively improved by the addition of the B ingredient in the Fe/MgO catalyst. The as-grown SWCNTs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The SWCNTs prepared by the pure Fe/MgO catalyst have relatively low graphite crystallinity and are coated by much amorphous carbon. The intensity ratio of the D- and G-bands (I_D/I_G) in Raman spectra is relatively high (0.098 for laser 532 nm and 0.075 for laser 785 nm). The SWCNTs grown from the Fe/MgO catalyst doped with 0.1 part of B have more regular graphite structure with little amorphous carbon. The I_D/I_G values reduced remarkably (0.041 for laser 532 nm and 0.040 for laser 785 nm). The effect would be attributed to the inhibitory action of the doped B on the formation of radical hydrocarbon species for the formation of SWCNTs.     

Enhanced etching of silicon didioxide guided by carbon nanotubes in HF solution

This paper describes a new method to create nanoscale SiO₂ pits or channels using single-walled carbon nanotubes (SWNTs) in an HF solution at room temperature within a few seconds. Using aligned SWNT arrays, a pattern of nanoscale SiO₂ channels can be prepared. The nanoscale SiO₂ patterns can also be created on the surface of three-dimensional (3D) SiO₂ substrate and even the nanoscale trenches can be constructed with arbitrary shapes. A possible mechanism for this enhanced etching of SiO₂ has been qualitatively analysed using defects in SWNTs, combined with H₃O⁺ electric double layers around SWNTs in an HF solution.     

Detection of invisible phonon modes in individual defect-free carbon nanotubes by gradient-field Raman scattering

We provide an effective method to investigate the field gradient effect in nanoconfined plasmon-matter interaction.Aligned ultralong SWNTs without defects were grown on marked substrates, followed by assembling gold nanoparticle clusters around individual nanotubes. The Raman scattering behavior of a nanotube placed in an atomic scale nanogap between adjacent nanoparticles was studied. In addition to the expected plasmon-induced Raman enhancement up to 103,the defect-free D-mode of an individual SWNT induced by gradient field is found for the first time. When the light is confined at atomic scale, gradient field Raman scattering becomes significant and dipole-forbidden phonon modes can be activated by quadrupole Raman tensor variation, indicating breakdown of the Raman selection rules.     

A density functional theory study of the electronic structures and magnetic properties of Fe（1-x）Cox alloy nanowires encapsulated in （10,0） carbon nanotubes

Under the generalized gradient approximation, the electronic structures and magnetic properties of Fe_(1-x)Co_x alloy nanowires encapsulated inside zigzag (10,0) carbon nanotubes (CNTs) are investigated systematically using firstprinciple density functional theory calculations. For the fully relaxed Fe_(1-x)Co_x/CNT structures, all the C atoms relax outwards, and thus the diameters of the CNTs are slightly increased. Formation energy analysis shows that the combining processes of all Fe_(1-x)Co_x/CNT systems are exothermic, and therefore the Fe_(1-x)Co_xalloy nanowires can be encapsulated into semiconducting zigzag (10,0) CNTs and form stable hybrid structures. The charges are transferred from the Fe_(1-x)Co_xnanowires to the more electronegative CNTs, and the Fe-C/Co-C bonds formed have polar covalent bond characteristics. Both the spin polarization and total magnetic moment of the Fe_(1-x)Co_x/CNT system are smaller than those of the corresponding freestanding Fe_(1-x)Co_xnanowire, and the magnetic moment of the Fe_(1-x)Co_x/CNT system decreases monotonously with increasing Co concentration, but the Fe_(1-x)Co_x/CNT systems still have a large magnetic moment, implying that they can be utilized in high-density magnetic recording devices.     

Effects of oxygen-containing defect complex on the electronic structures and transport properties of single-walled carbon nanotubes

The electronic structures and transport properties of (10,0)$(10,0)$ single-walled carbon nanotube ((10,0)$(10,0)$ (SWNT)) with oxygen-containing defect complex are investigated using density functional theory in combination with nonequilibrium Green?s function method. The complex delocalizes the local states of (10,0)$(10,0)$ SWNT induced by mono- and di-vacancy but strengthens the localization of the states induced by the Stone–Wales defect. As a result, the complex partially restores the transport properties of (10,0)$(10,0)$ SWNT with vacancies, but reduces the transmission of (10,0)$(10,0)$ SWNT with Stone–Wales defect. However, the oxygen-containing defect complex only slightly influences the transmission gap and threshold voltage of the system.     

Changes in the vibrational modes of carbon nanotubes induced by electron‐beam irradiation: resonance Raman spectroscopy

Influence of electron‐beam (e‐beam) irradiation on multi‐walled (MW) and single‐walled (SW) carbon nanotube films grown by microwave chemical vapor deposition technique is investigated. These films were subjected to an e‐beam energy of 50 keV from a scanning electron microscope for 2.5, 5.5, 8.0, and 15 h, and to 100 and 200 keV from a transmission electron microscope for a few minutes to ∼2 h continuously. Such conditions resemble an increased temperature and pressure regime enabling a degree of structural fluidity. To assess structural modifications, they were analyzed prior to and after irradiation using resonance Raman spectroscopy (RRS) in addition to in situ monitoring by electron microscopy. The experiments showed that with extended exposures, both types of nanotubes displayed various local structural instabilities including pinching, graphitization/amorphization, and formation of an intramolecular junction (IMJ) within the area of electron beam focus possibly through amorphous carbon aggregates. RRS revealed that irradiation generated defects in the lattice as quantified through (1) variation of the intensity of radial breathing mode (RBM), (2) intensity ratio of D to G band (I_D/I_G), and (3) positions of the D and G bands and their harmonics (D* and G*) and combination bands (D + G). The increase in the defect‐induced D band intensity, quenching of RBM intensity, and only a slight increase in G band intensity are some of the implications. The MW nanotubes tend to reach a state of saturation for prolonged exposures, while the SW ones transform from a semiconducting to a quasi‐metallic character. Softening of the q = 0 selection rule is suggested as a possible reason to explain these results. Furthermore, these studies provide a contrasting comparison between MW and SW nanotubes. Copyright © 2006 John Wiley & Sons, Ltd.