Overcoming the Sticking Point: Electrical Conductivity of Carbon Nanotube Networks Containing 3d Metals

Carbon nanotubes have excellent electrical conductivity along the length of the tubes. Yet, the electrical conductivity across the nanotube-nanotube intersections is weak and severely limits device performance. Here, we show that the incorporation of 3d metal (period 4) atoms into networks of semiconducting (8,0) carbon nanotubes significantly enhances the electrical conductivity within the network. Our calculations using quantum mechanical methods and semiclassical Boltzmann transport theory predict the changes to the electronic structure and provide directional information about the flow of electrons within the network. The ligand field splitting of the transition metals exerts strong effects on the conductivity. Interestingly, networks doped with Sc, V, or Fe can become insulating along certain directions or have higher conductivity across the junction than along the tubes. This finding suggests that doping with transition metals removes a bottleneck of charge transport within carbon nanotube films.