Carbon nanotubes electric-current-carrying

Early transport measurements on individual multi-wall nanotubes [187] were carried out on nanotubes with too large an outer diameter to be sensitive to ID quantum effects. Furthermore, contributions from the inner constituent shells which may not make electrical contact with the current source complicate the interpretation of the transport results, and in some cases the measurements were not made at low enough temperatures to be sensitive to 1D effects. Early transport measurements on multiple ropes (arrays) of single-wall armchair carbon nanotubes [188], addressed general issues such as the temperature dependence of the resistivity of nanotube bundles, each containing many single-wall nanotubes with a distribution of diameters d/ and chiral angles 6. Their results confirmed the theoretical prediction that many of the individual nanotubes are metallic. 

Semiconductor A generic term for a device that controls electrical signals. It specifically refers to a material (such as silicon, germanium or gallium arsenide) that can be altered either to conduct electrical current or to block its passage. Carbon nanotubes may eventually be used as semiconductors. Semiconductors are partly responsible for the miniaturization of modem electronic devices, as they are vital components in computer memory and processor chips. The manufacture of semiconductors is carried out by small firms, and by industry giants such as Intel and Advanced Micro Devices. 

Larger, nonspherical assemblies of carbon atoms have also been prepared, some with a tubular shape. These so-called nanotubes can be viewed as a rolled-up graphite sheet, perhaps capped with half of a buckyball in some cases. Nanotubes have many potential applications. They may be useful in constructing faster and smaller electronic devices because they can be doped to become semiconducting or metallic and they can be made to carry electrical current at higher densities than metals. They can also be spun into incredibly strong fibers. However, before they can reach their true potential, methods to produce them inexpensively must be developed. 

Moreover, single-wall carbon nanotubes can act as quantum wires (Tans et al., 1997). As electrical devices and their associated power lines get smaller, the lines must carry higher current densities that are predicted to approach the maximum achievable by metal wires. A possible solution might be carbon nanotube-copper composites that have the potential of offering the same conductivity as copper but with 100 times the current carrying capacity (Subramaniam et al., 2013). 

Other carbon materials such as carbon nanotubes (CNTs), carbon nanofibers, and graphene can also be used as conductive agents. CNTs have been discussed in Chapter 7, and will not be discussed again. The electronic conductivity of CNTs is better than that of acetylene black, UFC, and copper. Theoretically, CNTs can carry an electric current density of 4 x 10 A/cm, which is more than 1000 times greater than that of metals such as copper. There are several companies all over the world that manufacture CNTs. Transmission electron micrographs (TEMs) of some typical commercial products, which are widely used as electronic conductive agents, are shown... 

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