Nanotechnology: '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.     

Superplastic carbon nanotubes

The theoretical maximum tensile strain--that is, elongation--of a single-walled carbon nanotube is almost 20%, but in practice only 6% is achieved. Here we show that, at high temperatures, individual single-walled carbon nanotubes can undergo superplastic deformation, becoming nearly 280% longer and 15 times narrower before breaking. This superplastic deformation is the result of the nucleation and motion of kinks in the structure, and could prove useful in helping to strengthen and toughen ceramics and other nanocomposites at high temperatures.     

Formation of ordered ice nanotubes inside carbon nanotubes

Following their discovery, carbon nanotubes have attracted interest not only for their unusual electrical and mechanical properties, but also because their hollow interior can serve as a nanometre-sized capillary, mould or template in material fabrication. The ability to encapsulate a material in a nanotube also offers new possibilities for investigating dimensionally confined phase transitions. Particularly intriguing is the conjecture that matter within the narrow confines of a carbon nanotube might exhibit a solid-liquid critical point beyond which the distinction between solid and liquid phases disappears. This unusual feature, which cannot occur in bulk material, would allow for the direct and continuous transformation of liquid matter into a solid. Here we report simulations of the behaviour of water encapsulated in carbon nanotubes that suggest the existence of a variety of new ice phases not seen in bulk ice, and of a solid-liquid critical point. Using carbon nanotubes with diameters ranging from 1.1 nm to 1.4 nm and applied axial pressures of 50 MPa to 500 MPa, we find that water can exhibit a first-order freezing transition to hexagonal and heptagonal ice nanotubes, and a continuous phase transformation into solid-like square or pentagonal ice nanotubes.     

Microfabrication technology: organized assembly of carbon nanotubes

Nanoscale structures need to be arranged into well-defined configurations in order to build integrated systems. Here we use a chemical-vapour deposition method with gas-phase catalyst delivery to direct the assembly of carbon nanotubes in a variety of predetermined orientations onto silicon/silica substrates, building them into one-, two- and three-dimensional arrangements. The preference of nanotubes to grow selectively on and normal to silica surfaces forces them to inherit the lithographically machined template topography of their substrates, allowing the sites of nucleation and the direction of growth to be controlled.     

Microwave devices: carbon nanotubes as cold cathodes

To communicate, spacecraft and satellites rely on microwave devices, which at present are based on relatively inefficient thermionic electron sources that require heating and cannot be switched on instantaneously. Here we describe a microwave diode that uses a cold-cathode electron source consisting of carbon nanotubes and that operates at high frequency and at high current densities. Because it weighs little, responds instantaneously and has no need of heating, this miniaturized electron source should prove valuable for microwave devices used in telecommunications.     

Nanotube electronics: large-scale assembly of carbon nanotubes

Nanoscale electronic devices made from carbon nanotubes, such as transistors and sensors, are much smaller and more versatile than those that rely on conventional microelectronic chips, but their development for mass production has been thwarted by difficulties in aligning and integrating the millions of nanotubes required. Inspired by biomolecular self-assembly processes, we have created chemically functionalized patterns on a surface, to which pre-grown nanotubes in solution can align themselves in huge numbers. This method allows wafer-scale fabrication of millions of carbon-nanotube circuits with single-nanotube precision, and may enable nanotube-based devices, such as computer chips and high-density sensor arrays, to be produced industrially.     

Nanoscale hydrodynamics: enhanced flow in carbon nanotubes

Nanoscale structures that could mimic the selective transport and extraordinarily fast flow possible in biological cellular channels would have a wide range of potential applications. Here we show that liquid flow through a membrane composed of an array of aligned carbon nanotubes is four to five orders of magnitude faster than would be predicted from conventional fluid-flow theory. This high fluid velocity results from an almost frictionless interface at the carbon-nanotube wall.     

填充氩后单壁碳纳米管的导热系数

采用平衡态分子动力学(EMD)模拟方法,计算了填充氩后的(10,10)型和(15,15)型的单壁碳纳米管分别在不同温度下的导热系数.研究了它们随温度的变化情况,并将其与相应的空的碳纳米管的导热系数进行比较,分析在相同温度下,充氩对碳纳米管导热系数的影响.模拟结果发现:在500~1 200 K的温度范围内,(10,10)型碳纳米管和(15,15)型碳纳米管在填充了氩后其导热系数值均随着温度的升高呈下降趋势,这与空的碳纳米管的导热系数随温度的变化关系相似;在相同温度下,这2种类型的碳纳米管在填充了氩后的导热系数值均比相应的空的碳纳米管的导热系数值明显高很多.     

Kondo physics in carbon nanotubes

The connection of electrical leads to wire-like molecules is a logical step in the development of molecular electronics, but also allows studies of fundamental physics. For example, metallic carbon nanotubes are quantum wires that have been found to act as one-dimensional quantum dots, Luttinger liquids, proximity-induced superconductors and ballistic and diffusive one-dimensional metals. Here we report that electrically contacted single-walled carbon nanotubes can serve as powerful probes of Kondo physics, demonstrating the universality of the Kondo effect. Arising in the prototypical case from the interaction between a localized impurity magnetic moment and delocalized electrons in a metallic host, the Kondo effect has been used to explain enhanced low-temperature scattering from magnetic impurities in metals, and also occurs in transport through semiconductor quantum dots. The far greater tunability of dots (in our case, nanotubes) compared with atomic impurities renders new classes of Kondo-like effects accessible. Our nanotube devices differ from previous systems in which Kondo effects have been observed, in that they are one-dimensional quantum dots with three-dimensional metal (gold) reservoirs. This allows us to observe Kondo resonances for very large electron numbers (N) in the dot, and approaching the unitary limit (where the transmission reaches its maximum possible value). Moreover, we detect a previously unobserved Kondo effect, occurring for even values of N in a magnetic field.     

Preparation of double-walled carbon nanotubes

Double-walled carbon nanotubes were prepared using the floating chemical vapor deposition with methane as carbon source and adding small amount of sulfur into the ferrocene catalyst. The optimized technological parameters are: the reaction temperature is 1200℃; the catalyst vapor temperature is 80℃; the flow rate of argon is 2000 SCCM; the flow rate of methane is 5 SCCM. The purified DWNTs under these optimized technological parameters have high purity above 90 wt%.     

Organic modification of carbon nanotubes

The organic modification of carbon nanotubes is a novel research field being developed recently. In this article, the history and newest progress of organic modification of carbon nanotubes are reviewed from two aspects:organic covalent modification and organic noncovalent modification of carbon nanotubes. The preparation and properties of organic modified carbon nanotubes are discussed in detail. In addition, the prospective development of organic modification of carbon nanotubes is suggested.     

Materials: carbon nanotubes in an ancient Damascus sabre

The steel of Damascus blades, which were first encountered by the Crusaders when fighting against Muslims, had features not found in European steels--a characteristic wavy banding pattern known as damask, extraordinary mechanical properties, and an exceptionally sharp cutting edge. Here we use high-resolution transmission electron microscopy to examine a sample of Damascus sabre steel from the seventeenth century and find that it contains carbon nanotubes as well as cementite nanowires. This microstructure may offer insight into the beautiful banding pattern of the ultrahigh-carbon steel created from an ancient recipe that was lost long ago.     

单壁碳纳米管修饰电极对色氨酸的电催化氧化

采用单壁碳纳米管修饰的玻碳电极对色氨酸的电极行为进行了研究,在0.1 mol.L-1邻苯二甲酸氢钾-盐酸缓冲溶液(pH 2.5)中,发现该修饰电极对色氨酸有明显的电催化作用,色氨酸浓度为1.2×10-6~3.0×10-4mol.L-1时峰电流与色氨酸浓度呈线性关系,检测限为2.5×10-7mol.L-1.同时,对色氨酸的氧化机理进行了考察,结果表明此反应过程是一个涉及2个电子转移和2个质子转移的吸附控制过程.     

Effective removal of microcystins using carbon nanotubes embedded with bacteria

Adsorption of microcystins (MCs) by carbon nanotubes (CNTs) and clay materials was studied. Compared with various clays tested, CNTs showed a much stronger ability to adsorb MC-RR and LR that were two typical types of microcystins found in China. At initial 21.0 mg/L of MC-RR and 9.5 mg/L of MC-LR in solution, the adsorptiona mounts of MC-RR and LR by CNTs were 14.8 and 6.7 mg/gthat were about five times higher than those by the clay materials of sepiolite, kaolinite and talc, et~ In the presence of CNTs and the bacterial Ralstonia solanacearum that was firstly isolated and used for the biodegradation of MCs by the authors, a remarkable removal of MCs from water were observed. The mechanism was that CNTs could absorb large amount of both MCs and the embedded R. solanacearum so that, even when diluted by a large amount of water, the concentrations of both organic pollutants and the added bacteria could be largely enhanced on the surface of CNTs where a concerted biodegradation reaction was effectively conducted. This finding could be important for the further development of practical techniques to eliminate MCs from polluted drinking waters.