Semi-conducting CNTs

The tunable electronic properties of CNTs are being explored for next-generation IC architectures. As you may recall from Chapter 4, traditional Si-based microelectronic devices will likely reach a fundamental limit within the next decade or so, necessitating the active search for replacement materials. Accordingly, an area of intense investigation is molecular electronics - in which the electronic device is built from the placement of individual molecules.Not surprisingly, the interconnects of these devices will likely be comprised of CNTs and other (semi)conductive ID nanostructures such as nanowires. 

Nano-confinement of metal and semi-conductor materials can lead to marked changes in their electronic behaviour. Their unique properties resulted in an increased interest in using these nanoparticles (NPs) in materials science. Furthermore, with the discovery of the symbiotic nature of metal/semi-conductor heterostructures, the use of NPs in applications such as photocatalysis and opto-electric devices, like photovoltaic cells, has increased. The exceptional properties of carbon nanotubes (CNTs), as well as their unique structure, have led to increased investigation into their behavior in such hetero-structured complexes. Large surface-to-volume ratios, chemical inertness, and lack of porosity make CNTs prime candidates as catalyst supports. In more complex systems, the electrical properties of the CNTs increase the yield of catalyzed reactions due to the electronic interactions of certain NPs and CNTs. Based on the fact that charge transfer between quantum dots and CNTs has been reported, certain semi-conducting NPs have been covalently linked to CNTs to make hetero-junction electronic devices. ... 

In many of the above mentioned studies, CNTs have been used to improve the properties of the NPs in their various applications. The reverse strategy, where NPs are used to improve the properties of CNT networks, has also been investigated. These strategies rely on the feasibility of electron transfer between NPs and CNTs. The bandgap structure of semi-conducting and metallic single-walled... 

Another effect involves charge transport resistivity at the semiconductor-semi-conductor interface. The charge transport of the Ti02 photoelectrode, limited by its poor conductivity (about 0.1 cm2 V-1 s-1) [94], is the rate-determining step for the power-conversion efficiency in DSSCs [95]. As mention above, an usual strategy to improve charge transport is to add CNTs to the DSSC photoelectrode. It could be expected that the effect is proportional to the conductivity of the CNT, but Guai et al. 

Figure 2.8 Semi-logarithmic plot of the conductivity of the SWCNT /PmPV composite for various mass fractions of CNT powder. The sharp increase of the conductivity is partly due to the intrinsic conductivity of the polymer matrix and not only to the formation of a connective CNT network in the nanocomposite polymer matrix. (From Ref. 79. Reprinted with permission of the American Physical Society]...

When the nanocomposite matrix is semi-ciystalline, incorporation of [nano)particles such as CNTs frequently aims at modifying the crystallization behavior of the polymer in order to improve its properties like, for example, its mechanical performance, and/or to shorten processing cycle times. This way, high levels of mechanical reinforcement can be achieved at low CNT loadings due to the formation of a highly crystalline layer in the immediate vicinity of the CNT walls, ensuring effective interfacial stress transfer. In addition, dispersion of electrically conductive particles into a semi-crystalline [as well as amorphous) polymer matrix also leads to the production of conductive materials. 

The results on MWCNT-polymer nanocomposites reported in this chapter demonstrate the versatility of the latex concept to prepare nanocomposites with a broad range of "home-made" or industrially manufactured polymers, namely, amorphous, semi-crystalline, and blended polymer matrixes. Note that blending can further be done in very different fashions, i.e., in situ, while the emulsion polymerization proceeds, by mixing of two different polymer latexes synthesized independently from each other, or by a "masterbatch approach." This study confirms that the CNT-polymer interactions are of major importance to influence the percolation behavior of the nanocomposites, as well as the viscosity, morphology, and the intrinsic conductivity of the polymer matrix. 

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