乙醇催化燃烧法制备竹节形碳纳米管

乙醇催化燃烧法可以方便的制备出碳纳米管和碳纳米纤维。介绍采用该方法制备出一种独特的竹节形的碳纳米管，利用乙醇作为碳源和燃料，提供材料生长所需的能量；利用Cu薄片作为基底；利用FeCl3或Fe（NO3）3作为催化剂先体。通过扫描电子显微镜（SEM），透射电子显微镜（TEM），对黑色絮状的沉积产物进行表征。实验结果表明，产物中的碳纳米管具有较好的竹节形结构。实验也表明制备的竹节形碳纳米管的形貌和微结构与其独特的制备条件有关，如：火焰的抖动，催化剂先体溶液的浓度，制备时间等。并对竹节形碳纳米管的形貌和生长机制进行了详细的讨论。     

Low-temperature synthesis of large-area CNx nanotube arrays

Well-aligned nitrogen-doped multiwall carbon nanotube arrays have been successfully grown over large areas on quartz and silicon wafers by floating-catalyst chemical vapor deposition at low temperatures (600 degrees C). These nitrogen-including nanotubes, derived from pyridine-ferrocene mixtures, have smaller outer diameters but larger inner diameters compared with carbon nanotubes grown from a xylene-ferrocene mixture under similar conditions. The N-doped nanotubes exhibit bamboo-like structures in the core. Elemental analysis and electron energy loss spectroscopy analysis show that the as-prepared nanotubes contain as much as 2.62 wt.% N, with most of the N concentrated in the inner few shells of the nanotube. Such large-scale arrays of well-aligned N-doped nanotubes on silicon wafers have a current density as high as 23.8 mA/cm2 at an applied electric field of 17 V/micron, which can be further improved by patterning the tubes and coating the silicon substrate with a conductive thin metal film for the fabrication of flat panel displays.     

A structure model and growth mechanism for novel carbon nanotubes

The growth of carbon nanotubes from catalytic thermal decomposition of acetylene on fine iron particles has been studied. Electron microscopic images of the carbon nanotubes as formed and after annealing treatment are presented. Besides the ordinary carbon nanotubes which have been reported (S. Iijima, Nature, 354 (1991) 56), we have found, at first time, two other new kinds of carbon nanotubes: one is straight or curved nanotube with many irregular multi-layered diaphragms in the hollow core, in particular, the fringes of the wall of the tubes are not parallel to the axis of the tube; another one has many regular diaphragms (bamboo-like) which keep almost constant distance with each other. A model that postulates two steps growth of nanotubes from catalyst particles is proposed to explain the microstructure of the novel carbon nanotubes.     

Multiwall and bamboo-like carbon nanotube growth by CVD using a semimetal as a catalyst

Multiwall carbon nanotubes have been synthesized on silicon substrates via atmospheric pressure chemical vapour deposition technique using bismuth as a catalyst. Field emission scanning electron microscopy analysis suggests that the samples grow through a tip growth mechanism. High-resolution transmission electron microscopy analysis shows spaghetti-like multiwall carbon nanotubes and with a bamboo-like structure obtained using the Bi catalyst. The quality, in terms of the graphitic crystallinity of the as grown carbon nanotubes, was analyzed by Raman analysis. The study shows that the catalyst, namely bismuth strongly influences the growth density and graphitic crystallinity of the grown carbon nanotubes.     

The concept of cutting lines in carbon nanotube science

A review is presented of one-dimensional cutting lines that are utilized to obtain the physical properties of carbon nanotubes from the corresponding properties of graphite by the zone-folding scheme. Quantization effects in general low-dimensional systems are briefly discussed, followed by a more detailed consideration of one-dimensional single-wall carbon nanotubes. The geometrical structure of the nanotube is described, from which quantum confined states are constructed. These allowed states in the momentum space of graphite are known as cutting lines. Different representations of the cutting lines in momentum space are introduced. Electronic and phonon dispersion relations for nanotubes are derived by using cutting lines and the zone-folding scheme. The relation between cutting lines and singularities in the electronic density of states is considered. The selection rules for carbon nanotubes are shown to be directly connected with the cutting lines. Different experimental techniques are considered that confirm the validity of cutting lines and the zone-folding approach.     

Growth and characterization of bamboo-like multiwalled carbon nanotubes over Cu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The growth of bamboo-like multiwalled carbon nanotubes (MWCNTs) over Cu/Al₂O₃ catalyst by chemical vapor deposition under atmospheric pressure using ethanol as the carbon source has been demonstrated. The obtained MWCNTs are dominant with bamboo-like morphology. The morphologies, graphitization degree, and microstructures of the products were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. The results show that the combination of Cu/Al₂O₃ catalyst and ethanol was critical for the growth of bamboo-like MWCNTs. The possible factors causing the formation of bamboo-like structures were also discussed.     

Dynamical observation of bamboo-like carbon nanotube growth

The growth dynamics of bamboo-like multiwalled carbon nanotubes (BCNTs) via catalytic decomposition of C2H2 on Ni catalyst at 650 degrees C was observed in real time using an in situ ultrahigh vacuum transmission electron microscope. During BCNT growth, the shape of the catalyst particle changes constantly but remains metallic and crystalline. Graphene sheets (bamboo knots) within the nanotube preferentially nucleate on the multistep Ni-graphite edges at the point where the graphene joins the catalyst particle, where it is stabilized by both the graphene walls and the Ni catalyst surface. The growth of a complete inner graphene layer growth prior to contraction of the Ni catalyst particle due to restoring cohesive forces will result in a complete BCNT knot whereas partial growth of the inner wall will lead to an incomplete BCNT knot.     

Carbon Nanotubes in the Biological Interphase: The Relevance of Noncovalence

With the increasing interest in the biological applications of carbon nanotubes, their interactions in the biological interphase and their general cytotoxicity have become major issues. In spite of their salient properties, major hurdles still exist for their use in biological applications, due to their main characteristics, including their hydrophobic surfaces and tendency to aggregate, as well as their unknown interactions in the cellular interphase. In this Research News, these characteristics of carbon nanotubes, a model nanomaterial, are investigated. Thus, the cytotoxicity of carbon nanotubes, the influence of functionalization, as well as their interactions with different mammalian cell lines are studied. Moreover, suggestions for the improvement of their biocompatibility and the design of biocompatible carbon nanotube‐based systems are provided.     

氮掺杂碳纳米管的无金属催化剂合成和表征

采用爆炸辅助化学气相沉积法, 以碳纳米管(CNTs)作催化剂, 三聚氰胺作碳源和氮源, 无金属催化剂合成出氮掺杂碳纳米管(CN_x). 通过TEM、EDS、Mapping、XPS、Raman和TG测试手段对CN_x进行了表征. 结果表明, CNx具有竹节状结构, 其掺氮量高达17at%, 且氮元素分布均匀. 氮元素以石墨型和吡啶型掺杂在石墨层中, 由于大量氮元素掺杂造成纳米管石墨化程度降低, 抗氧化能力减弱.     

CNT Cytotoxicity: Carbon Nanotubes in the Biological Interphase: The Relevance of Noncovalence (Adv. Mater. 36/2010)

With the increasing interest in the biological applications of carbon nanotubes, their interactions in the biological interphase and their general cytotoxicity have become major issues. In spite of their salient properties, major hurdles still exist for their use in biological applications, due to their main characteristics, including their hydrophobic surfaces and tendency to aggregate, as well as their unknown interactions in the cellular interphase. In this Research News, these characteristics of carbon nanotubes, a model nanomaterial, are investigated. Thus, the cytotoxicity of carbon nanotubes, the influence of functionalization, as well as their interactions with different mammalian cell lines are studied. Moreover, suggestions for the improvement of their biocompatibility and the design of biocompatible carbon nanotube‐based systems are provided.     

Synthesis and thermoelectric power of nitrogen-doped carbon nanotubes

We have previously shown that high-purity multiwalled carbon nanotubes (pristine MWNTs) can be prepared from a mixture of xylene-ferrocene (99 at% C:1 at% Fe) inside a quartz tube reactor operating at approximately 700 degrees C. In a similar process, approximately 3 g of melamine (C3H6N6) was introduced during the growth of MWNTs to prepare nitrogen-doped nanotubes. The structural and electronic properties of nitrogen-doped MWNTs were determined by scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and thermopower measurements. The individual nitrogen-doped nanotube exhibits a bamboo-like structure and comprises 6-16 tube walls, as evidenced by HRTEM studies. The EELS measurements yielded an average nitrogen content of approximately 5 at% in the doped tubes. The thermoelectric power data of nitrogen-doped MWNTs remained negative even after exposure to oxygen for an extended period of time, suggesting that nitrogen doping of MWNTs renders them n-type, consistent with scanning tunneling spectroscopic studies on similar nanotubes.     

碳纳米管传感器的研究进展

综述了不同功能碳纳米管传感器(微型碳纳米管气体离子传感器、无线被动碳纳米管气体传感器、碳纳米管化学和力学传感器、碳纳米管阵列生物传感器、碳纳米管温度和风速传感器、碳纳米管神经毒气传感器)的制备、结构特点、性能和发展方向.     

STM investigation of carbon nanotubes connected by functional groups

Chemical functionalization of carbon nanotubes (CNTs) is essential for many applications. Attachment of functional groups to nanotubes can dramatically increase the solubility of the nanotube material. Sidewall functional groups should react with polymers and improve the mechanical properties of nanocomposites. Tubes interconnected by chemical bonds will have a reduced contact resistance and can be used for interconnection purposes in nanoscale circuits. Carbon nanotubes covered with functional groups attached to their exterior wall were analyzed using scanning tunneling microscopy (STM) and TEM. The functionalization was carried out in three steps: acid treatment in H₂SO₄/HNO₃ (3:1) mixture, reaction with SOCl₂ and reaction with diaminopropanol (DAP). The binding force between the nanotubes connected by functional groups and the mechanical stability of the connection was investigated.     

Catalytic action of gold and copper crystals in the growth of carbon nanotubes

Multi-wall carbon nanotubes are grown in a chemical vapor deposition process by using bulk gold and copper substrates as catalysts. Nanotube growth starts from a nanometer-sized roughness on the metal surfaces and occurs in a mechanism where the catalyst particle is either at the tip (Au) or root (Cu) of the growing nanotube. Whereas Au leads to nanotubes with good structural perfection, nanotubes grown from Cu show a higher density of defects. High-resolution transmission electron microscopy shows the bonding between Au and carbon at the metal-nanotube interface whereas no bonds between Cu and carbon occur. Highly mobile Au or Cu atoms adsorb at the growing edge of a carbon nanotube from where diffusion along the nanotube wall can lead to the formation of Au or Cu nanowires inside the central hollow of carbon nanotubes.     

A novel non-catalytic approach for fabrication of bamboo-like carbon nanotubes

Bamboo-like carbon nanotubes (BCNTs) were synthesized via pyrolysis of PMMA@PDVB core-shell spheres in argon atmosphere at 900 °C without any metallic catalyst. TEM and HRTEM observations show the carbon nanotubes with bamboo-like structure. The content of polymerized divinylbenzene (PDVB) in the core-shell nanostructures plays a very important role for the formation of BCNTs. The possible growth mechanism for BCNTs is proposed.     

Chemical vapour deposition of single walled carbon nanotubes freely suspended over nanotube supports

Single walled carbon nanotubes (SWNTs) suspended above the substrate can be fabricated simply and rapidly by chemical vapour deposition growth over pre-grown multi-walled carbon nanotubes (MWNTs). SWNTs are suspended either on a randomly organized carbon nanotube network on an unpatterned substrate, or between organized pillars made from vertically aligned nanotube forests on a patterned substrate. All nanotubes are produced during a single growth run using a two step growth technique. This approach enables the fabrication of laterally suspended SWNT networks which are well suited for optical applications.     

Synthesis and device applications of high-density aligned carbon nanotubes using low-pressure chemical vapor deposition and stacked multiple transfer

For nanotube-based electronics to become a viable alternative to silicon technology, high-density aligned carbon nanotubes are essential. In this paper, we report the combined use of low-pressure chemical vapor deposition and stacked multiple transfer to achieve high-density aligned nanotubes. By using an optimized nanotube synthesis recipe, we have achieved high-density aligned carbon nanotubes with density as high as 30 tubes/μm. In addition, a facile stacked multiple transfer technique has been developed to further increase the nanotube density to 55 tubes/μm. Furthermore, high-performance submicron carbon nanotube field-effect transistors have been fabricated on the high-density aligned nanotubes. Before removing the metallic nanotubes by electrical breakdown, the devices exhibit on-current density of 92.4 μA/μm and normalized transconductance of 13.3 μS/μm. Moreover, benchmarking with the aligned carbon nanotube transistors in the literature indicates that our devices exhibit the best performance so far, which is attributed to both the increased nanotube density and scaling down of channel length. This study shows the great potential of using such high-density aligned nanotubes for high performance nanoelectronics and analog/RF applications.     

基于碳纳米管的三维编织复合材料健康监测技术

分析了三维编织复合材料试件结构健康监测技术现状,结合三维编织复合材料编织工艺,提出了碳纳米管在三维编织复合材料试件健康监测方面的应用方法。结果说明碳纳米管应用于三维编织复合材料整体结构监测是可行的。碳纳米管传感器在三维编织复合材料试件结构健康监测中具有优异的应变传感特性,且嵌入的碳纳米管传感器对复合材料的力学性能影响不大。这为内置碳纳米管传感器应用于复合材料制件的健康检测提供了一种新的综合和分布式技术,为先进智能复合材料的研发与应用提供了依据。     

A study of carbon-nanotube-based nanoelectromechanical resonators tuned by shear strain

This paper has investigated, using a classical molecular dynamics simulation method based on the Tersoff-Brenner potential, the resonance-frequency changes of single-walled carbon-nanotube resonators originating from the purely mechanical response of single-walled carbon nanotubes. The tension decreased with increasing rotation angle, so the resonance frequencies could be changed by controlling the rotation angles of the single-walled carbon nanotubes. The resonance frequencies decreased with increasing angle, and when the rotation angle was greater than 60°, the changes were marked. For nanotubes of similar length, the bandwidth for the (3, 3) single-walled carbon nanotube was higher than for the (5, 0) single-walled carbon nanotube. Because properties arising from the shear-strain-induced tension response can affect the electromechanical behavior of carbon nanotubes, the shear-strain-induced tension response should be given serious consideration in the application of embedded carbon nanotubes in nanoelectromechanical systems.     

Quantum conductance of a helically coiled carbon nanotube

Using a π-orbital tight-binding model, we investigate the transport properties of a coiled carbon nanotube (also called carbon nanotube spring), which we construct by connecting carbon nanotubes periodically in three-dimensional (3D) space. The conductance is quantized due to the translational symmetry in the coiled direction. However, the conductance behaviors differ greatly from those of pristine metallic carbon nanotubes but similar to those of carbon nanotube superlattices. We explain that conductance behaviors of the coiled carbon nanotube.