Electronic transport on carbon nanotube networks : a multiscale computational approach/
Summary: Carbon is arguably the most versatile of chemical elements. For the last 25 years research on carbon nanostrutures has been one of the most active areas of science. Carbon-based nanoelectronics is the most promising alternative to replace the ageing silicon-based technologies. In particul...
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| Endereço do item: | https://app.bczm.ufrn.br/home/#/item/222819 |
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Carbon is arguably the most versatile of chemical elements. For the last 25 years research on carbon nanostrutures has been one of the most active areas of science. Carbon-based nanoelectronics is the most promising alternative to replace the ageing silicon-based technologies. In particular, carbon nanotubes present remarkable physical properties such as very low electrical resistance and very high mechanical strength. These characteristics have led to the development of nanotube composites which in turn led to the fabrication of nanotube network films. Films produced by deposition of carbon nanotubes show extraordinary electric conductance and mechanical resistance, making them excellent candidates for the development of flexible electronic devices. A nanotube film contains a complex interconnected network of randomly distributed nanotubes and bundles. The electronic transport characteristics of nanotube networks is defined by a combination of intrinsic nanotube transport properties with the morphology of the random network. Electrons can travel along a single nanotube with very low resistance, but have to tunnel through junctions between individual tubes. The junction resistance is considerably higher than the intrinsic resistance along a typical carbon nanotube. The production of transparent electrodes to be utilised in novel flexible displays requires very high electrical conductivities. Chemical treatments can be applied to lower the junctions resistance but the morphology of the network itself plays a significant role in the resistivity of nanotube films.
This work is focused on modelling the electronic transport properties of carbon nanotube films. We have aimed at developing a computationally efficient framework capable of modelling electronic transport on disordered nanotube networks. The approach developed consists of tackling the problem from two different length scales. On a macroscopic level, carbon nanotubes are modelled as rigid rods of specified length and diameter. Disordered networks are generated by randomly distributing rods inside a containing volume representing the film. Within this approach it has been found that the connectivity of the networks scales universally with the volume fraction of the films, as well as with the aspect ratio of the rods. Meanwhile, in a microscopic level, nanotubes are described within an atomistic semi-empirical Hamiltonian. With the application of Green function methods, networks consisting of thousands of nanotubes have been simulated, and their conductance calculated. The combination of both length scales leads to a multiscale model of electronic transport through carbon nanotube networks. Theoretical predictions were compared and combined with experimental results providing an estimate for the average inter-tube resistance, which is in accordance with independent experimental studies. Furthermore, by considering a purely ballistic transport regime we have been able to estimate an upper bound for the conductivity of carbon nanotube films. The maximum conductivity calculated was found to scale universally with the density of the network, as well as the average length and diameter of the nanotubes and bundles in the film. When compared to the best experimental values reported our results indicate that nanotube films are reaching their conductivity limit. Furthermore, our simulations lead to the conclusion that metallic nanowire films (other than nanotubes) are better suited for applications in flexible displays. As an extension of the developed models we have considered two further applications. First, it was found that, in spite of their good electronic conductance, nanowire networks are not suitable as a medium to facilitate magnetic coupling. Finally, by considering a capacitive network model, we have been able to reproduce the onset of local electric activation observed in experiments with silver nanowire films. |
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