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.