Polymer-Mediated Tunneling Transport Between Carbon Nanotubes in Nanocomposites

Abstract

Electron transport in nanocomposites has attracted a good deal of attention for some time now; furthermore, the ability to control its characteristics is a necessary step in the design of multifunctional materials. When conductive nanostructures (for example carbon nanotubes) are inserted in a non-conductive matrix, electron transport below the percolation threshold is dominated by tunneling and thus the conductive characteristics of the composite depends heavily on the characteristics of the tunneling currents between nanoinserts. A parameter-free approach to study tunneling transport between carbon nanotubes across a polymer matrix is presented. The calculation is done with a combination of Density Functional Theory and Green functions (an approach heavily used in molecular electronics) which is shown here to be effective in this non-resonant transport condition. The results show that the method can effectively capture the effect of a dielectric layer in tunneling transport. The current is found to exponentially decrease with the size of the gap for both vacuum and polymer, and that the polymer layer lowers the tunneling barrier enhancing tunneling conduction. For a polyacrylonitrile matrix, a four-fold decrease in the tunneling constant, compared to tunneling in vacuum, is observed, a result that is consistent with available information. The method is very versatile as any DFT functional (or any other quantum mechanics method) can be used and thus the most accurate method for each particular system can be chosen. Furthermore as more methods become available, the calculations can be revised and improved. This approach can be used to design functional materials for fine-tunning the tunneling transport, for instance, the effect of modifying the nanoinsert-matrix interface (for example, by adding functional groups to carbon nanotubes) can be captured and the comparative performance of each interface predicted by simulation.

A stochastic approach towards a predictive model on charge transport properties in carbon nanotube composites

“…(4) was chosen to be 0.6 Å -1 , which has been calculated for PAN [76]. First, the effect of two related properties, waviness and aspect ratio, is studied.…”

“…Various experimental studies have shown that functionalization [40,[71][72][73][74], chirality [71,75], aspect ratio [17,62,71], host matrix material [11,76], CNT dispersion in the matrix [17,35,[37][38][39]71,74,77], relative alignment [17,65,75] and other processing variables can all have a significant impact on the electrical properties of the composite.…”

“…Indeed, the host matrix material will have an effect on charge transport via the quantum phenomenon of charge tunneling. Previous work has been done to quantify charge tunneling between graphene sheets through a polymer layer where a 4-fold decrease in the tunneling constant, compared to vacuum, was observed for Poly Acrylonitrile (PAN) [76]. This process can be employed to calculate tunneling parameters for any material, giving the model the capability to study how these various materials affect charge transport without experimental input.…”

“…(4) was chosen to be 0.6 Å -1 , which has been calculated for PAN [76]. Results from the simulations on box sizes of 800x100x100 (nm) 3 and 1000x100x100 (nm) 3 were fit to the power law and compared to experimental results on the conductivity of PAN/CNT composites ( Figure 12) taken from references [92,96].…”

Modeling the effect of uniaxial deformation on electrical conductivity for composite materials with extreme filler segregation

“…For simplification, in order to calculate the conductance of the investigated volume element at a given deformation, we assumed the inner resistance of MWCNTs to be negligible compared to the contact resistance between MWCNTs or between the MWCNT and the electrode. 34,35 The relative conductance (the ratio of conductance for a selected degree of deformation to conductance of non-deformed volume) was obtained using Kirchhoff's circuit laws for the grid of unit contact resistances and unit input and output electrical currents flowing through upper and lower faces of the ''inner'' volume. The principle of contact grid formation is illustrated in Figure 5.…”