Semiconducting SWCNTs separation

Common separation methods can be divided into chemical and physical routes. Chemical approaches rely on the interaction of the surface of different CNT types with surfactant molecules. Early work has shown that octadecylamine [94] and agarose gel [95] adsorb preferably on semiconducting SWCNTs, while diazonium reagents [96] and DNA [97, 98] show preference with metallic tubes. The assemblies with adsorbed molecular species are considerably larger and heavier than the indi-... 

The physical approach uses alternating current (ac-) dielectrophoresis to separate metallic and semiconducting SWCNTs in a single step without the need for chemical modifications [101]. The difference in dielectric constant between the two types of SWCNTs results in an opposite movement along an electric field gradient between two electrodes. This leads to the deposition of metallic nanotubes on the microelectrode array, while semiconducting CNTs remain in the solution and are flushed out of the system. Drawbacks of this separation technique are the formation of mixed bundles of CNTs due to insufficient dispersion and difficulties in up-scaling the process [102]. 

Such a combination of semiconducting SWCNTs coated with an ordered P3HT layer is expected to enhance the charge separation and transport in the devices active layer, which is a key towards efficiency enhancement. Electrical characteristics (J and V ) of devices were found to strongly dependent on the SWCNT loading (Figure 5.14c), such that both the... 

As mentioned above, the electronic properties of SWCNTs depend on their chirality and may be semiconducting or metallic. There is still no satisfying way to produce just one sort of SWCNTs, which would require the exact control of catalyst particle size at elevated temperature. Hence, the separation of semiconducting from metallic SWCNTs is of paramount importance for their application in, for example, electric devices, field emission and photovoltaics etc. 

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