Since the discovery of carbon nanotubes in 1991 by Iijima, there has been great interest in creating long, continuous nanotubes for applications where their properties coupled with extended lengths will enable new technology developments. For example, ultralong nanotubes can be spun into fibres that are more than an order of magnitude stronger than any current structural material, allowing revolutionary advances in lightweight, high-strength applications. Long metallic nanotubes will enable new types of micro-electromechanical systems such as micro-electric motors, and can also act as a nanoconducting cable for wiring micro-electronic devices. Here we report the synthesis of 4-cm-long individual single-wall carbon nanotubes (SWNTs) at a high growth rate of 11 microm s(-1) by catalytic chemical vapour deposition. Our results suggest the possibility of growing SWNTs continuously without any apparent length limitation.

Improved electron transport along a carbon nanotube (CNT) fiber when it is spun from an array of longer nanotubes is reported. The effect of chemical post‐treatments is also demonstrated. For example, the covalent bonding of gold nanoparticles to the CNT fibers remarkably improves conductivity (see figure), whereas annealing CNT fibers in a hydrogen‐containing atmosphere leads to a dramatic decrease in conductivity.

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The grain-size effect on deformation twinning in nanocrystalline copper is studied. It has been reported that deformation twinning in coarse-grained copper occurs only under high strain rate and/or low-temperature conditions. Furthermore, reducing grain sizes has been shown to suppress deformation twinning. Here, we show that twinning becomes a major deformation mechanism in nanocrystalline copper during high-pressure torsion under a very slow strain rate and at room temperature. High-resolution transmission electron microscopy investigation of the twinning morphology suggests that many twins and stacking faults in nanocrystalline copper were formed through partial dislocation emissions from grain boundaries. This mechanism differs from the pole mechanism operating in coarse-grained copper.Nanocrystalline ͑nc͒ materials have been reported to have superior mechanical properties such as high strength, which can coexist with very good ductility. 1-3 These superior mechanical properties are attributed to their unique deformation mechanisms, which are different from those in their coarse-grained ͑CG͒ counterparts. 4 -8 For example, molecular dynamics simulations, which used extremely high strain rates in the order of 10 6 to 10 8 s Ϫ1 , predict that NC Al deforms via partial dislocation emission from grain boundaries, which consequently produces deformation twins. 7 These predictions have recently been verified experimentally in nc Al powder processed by ball milling at liquid nitrogen temperature 9 and in nc Al film produced by physical vapor deposition. 8 These observations are very surprising because deformation twinning has never been observed in CG Al.High strain rate, low temperature, and nanometer grain size are major contributing factors for deformation twinning in the ball-milled Al powder. 9,10 In fact, both high strain rate and low temperature are known to promote deformation twinning. 11,12 For example, CG copper does not deform by twinning 13,14 except at very high strain rate 15,16 and/or low temperature. 17 However, the grain-size effect is not so clear. It has been suggested that both the critical slip stress and twinning stress follow the Hall-Petch ͑HP͒ relationship, with the HP slope for twinning (k T ) significantly larger than that for slip (k S ) for many CG metals and alloys. 18 For copper, the k T is about 0.7 MN/m 3/2 , while k S is about 0.35 MN/m 3/2 . 19 Consequently, dislocation slip rather than deformation twinning is expected to become the preferred deformation mode when the grain is smaller than a certain size. Indeed, Meyers et al. 20 reported that shock compression at 35 GPa produced abundant deformation twins in copper samples with grain sizes of 117 and 315 m, but virtually no twinning in a copper sample with a grain size of 9 m. On the other hand, it has been well known that the HP relationship fails in nc materials. 4,5 These literature observations raise some fundamental questions on the grain-size effect on deformation twinning. Does the trend that smaller grains are harder to ...

From the stone ages to modern history, new materials have often been the enablers of revolutionary technologies.[1] For a wide variety of envisioned applications in space exploration, energy-efficient aircraft, and armor, materials must be significantly stronger, stiffer, and lighter than what is currently available. Carbon nanotubes (CNTs) have extremely high strength, [2][3][4][5] very high stiffness, [6,7] low density, good chemical stability, and high thermal and electrical conductivities.[8]These superior properties make CNTs very attractive for many structural applications and technologies. Here we report CNT fibers that are many times stronger and stiffer per weight than the best existing engineering fibers and over twenty times better than other reported CNT fibers. Additionally, our CNT fibers are nonbrittle and tough, making them far superior to existing materials for preventing catastrophic failure. These new CNT fibers will not only make tens of thousands of products stronger, lighter, safer, and more energy efficient, but they will also bring to fruition many envisioned technologies that have been to date unavailable because of material restrictions. Strong, stiff, and lightweight are critical property requirements for materials that are used in the construction of space shuttles, airplanes, and space structures. These properties are assessed by a material's specific strength and specific stiffness, which are defined as the strength or stiffness (Young's modulus) of a material divided by its density.[9] The combination of high strength, high stiffness, and low density affords CNTs with extremely high values for specific strength and specific stiffness. The most effective way to utilize these properties is to assemble CNTs into fibers. However, despite extensive worldwide efforts to date, the specific strength and specific stiffness of CNT fibers that have been reported by various research groups are much lower than currently available commercial fibers. [10][11][12][13][14][15][16][17][18][19][20][21][22] In early studies, researchers attempted to reinforce polymer fibers with short CNTs, but the reinforcement was limited by several issues, including poor dispersion, poor alignment, poor load transfer, and a low CNT volume fraction. [10][11][12][13][14][15] Recently, pure CNT fibers (also called yarns)were reported with and without twisting. [16][17][18][19][20][21][22] For example, Zhang et al. [20] demonstrated that spinning from aligned CNT arrays could significantly improve the strength of CNT fibers by twisting them. However, to date no breakthrough has been reported in the specific strength and specific stiffness of CNT fibers.Here we report CNT fibers with values for specific strength and specific stiffness that are much higher than values reported for any current engineering fibers as well as previously reported CNT fibers. As shown in Figure 1, the specific strength COMMUNICATION 4198