Conductivity of CP Nanowires, Nanofibers, and Nanotubes

As we discussed in the previous section, in recent years, there has been significant progress in the preparation of various nanoscale CP materials. Nanowires, nanotubes, and nanofibers of a considerable number of materials have been demonstrated. In many studies, individually addressable nanomaterials have been successfully prepared. These advances have provided tremendous opportunities for transport studies of individual linear nanomaterials. In the following, we will review and discuss some of the recent efforts in conductivity studies of this category of materials. 

Determined by their molecular nature, most CP nanoscale materials are either amorphous or polyerystalline. In the latter case, the size of the ordered crystalline grain/island is typically less than 10 nm [106]. This limits the electron and hole delocalization length to a similar scale. Therefore, based on this argument, unless the cross-seetion of a CP nanowire is comparable to the delocalization length, electron and hole transport in such a nanowire should follow their behavior in a 3-D bulk material. As we have discussed in the previous section, many nanowires and nanotubes prepared so far are indeed larger than the characteristic electronic localization length, and it is, in general, valid to treat these nanowires and nanotubes with the already established electronic-transport theories and models for 3-D CP materials. 

Although consistently preparing sub-lO-nm CPNWs is still very challenging, Samitsu and colleagues measured the conductance of a very narrow ( 3.7 nm wide) section of a 

Aleshin and colleagues have conducted detailed studies of conductivities of PAc and PPY nanofibers [91-94,104]. In these studies, the authors tried to take the quasi-1-D nature of the polymer molecules into consideration to explain the observed conductivity as a function of sample temperature - a(T). Experimental results were 

While the temperature dependence of conductance can reveal fundamental transport mechanisms in CPNWs, current-voltage characteristics provide direct information on the electrical properties of CP materials. Kaiser and Park introduced an expression with which the nonlinear I-V characteristics of highly conductive CP materials can be treated as conduction through small barriers between metallic regions [100]  

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