Ballistic conduction

As for the coherent length in CNTs, a very interesting paper has been published from the group at the Georgia Institute of Technology about the conductance of individual MWCNTs [34], They have observed the quantisation of conductance by changing the distance between the two electrodes. This result indicates ballistic conduction in a CNT, which suggests the formation of stationary waves of electrons inside CNTs. 

Berger C, Poncharal P, Yi Y, de Heer W (2003) Ballistic conduction in multiwalled carbon nanotubes. Journal of Nanoscience and Nanotechnology 3 171-177. 

Poncharal P, Berger C, Yi Y, Wang ZL, de Heer WA (2002) Room temperature ballistic conduction in carbon nanotubes. Journal of Physical Chemistry B 106 12104-12118. 

Nanofillers have superb thermal and electrical properties. All nanotubes are expected to be very good thermal conductors along the tube axis, exhibiting a property known as ballistic conduction, but good insulators laterally to the tube axis. It has been reported that single-wall carbon nanotubes exhibit thermal conductivity (TC) values as high as 2000-6000 W mK [4] under ideal circumstances. The temperature stability of carbon nanotubes is estimated to be up to 2800 °C in a vacuum, and about 750 °C in air. By comparison, metals have TC values of several hundred W mK , and water and oil have TC values of only 0.6 W mK and 0.2 W mK respectively. Table 19.1 lists the thermal conductivities of various materials, including nanofillers (nanotubes), metals, and oils. 

This paper focuses mainly on the mechanical properties of carbon nanotubes and di.scusses their elastic properties and strain-induced transformations. Only. single-walled nanotubes are di.scussed, since they can be grown with many fewer defects and are thus much stronger. It is shown that under suitable conditions some nanotubes can deform plasiically, while others must break in a brittle fashion. A map of brittle vs. ductile behavior of carbon nanotubes with indices up to (100,100) is presented. The electrical properties of nanotubes are also affected by strain. We will focus here on quantum (ballistic) conductance, which is very sensitive to the atomic and electronic structure. It turns out that some nanotubes can tolerate fairly large deformations without much change to their ballistic conductance, while others are quite sensitive. Both properties can be used in applications, provided that nanotubes of the appropriate symmetry can be reliably prepared or selected. 

Another alternative approach in the direction of introducing nanoscale structures into a polymer matrix is the addition of nanostructures like C60 and CNTs, which hold promise as exciton-dissociating centers and ballistically conductive agents with high carrier mobilities, in addition to being optically transparent, flexible, and environmentally resistant [258]. 

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