Bridging the Junction: Electrical Conductivity of Carbon Nanotube Networks

Carbon nanotube (CNT) films have excellent conductivity
and suitable
flexibility for chemical sensing and touch screen devices. Understanding
the pathways of charge transport within the network is crucial to
develop new functional materials and improve existing devices. Here,
we study the electrical conductivity of networks of CNTs containing
Group 11 metals (Au, Ag, and Cu), s–p metals (K, Ca, and Al),
AuCl3, AuCl4, and Cl using quantum mechanical
methods and semiclassical Boltzmann transport theory. The conductivity
is characterized along the nanotubes and across the intersecting junction.
The conductivity is much weaker across the junction than along the
nanotubes and could be strengthened in all directions using dopants.
The largest increase in conductivity is induced by Al along the nanotubes
and by Cu across the intersection [389-fold and 14-fold relative to
the pristine (8,0) network, respectively]. Additionally, Ag dopants
activate charge transport along the semiconducting nanotube in heterogeneous
networks of mixed metal and semiconducting nanotubes. The conductivity
along the semiconducting nanotube increased 781-fold. This activation
removes the bottleneck of charge transport along the semiconducting
nanotubes within the network of mixed chiralities. Small amounts of
dopants within nanotube networks drastically change the directional
conductivity and provide new pathways for charge transport for applications
such as chemical sensing or touch screens.