Some applications of carbon nanotubes require just a single nanotube, whereas others, such as transparent electrodes, require a network or mat of nanotubes. Network conductivity is a key parameter for these applications, and it is set by the resistance of individual nanotubes, the quality of junctions between neighbouring nanotubes and the overall morphology of the network. Ongoing efforts to improve network conductivity could be aided by an understanding of the relative importance of each of these factors. Now, Mauro Ferreira and colleagues at Trinity College Dublin, Dresden University of Technology and the Fluminense Federal University have shown that the conductivity of the latest nanotube networks may be approaching a limit set by network morphology1.

Ferreira and colleagues considered a model network characterized by nanotube length and diameter. Even when assuming ballistic transport along individual nanotubes and ideal junctions, they calculated a conductivity that was only one order of magnitude higher than experimentally demonstrated values. This suggests that further improvements in nanostructured electrodes may need to come from using better-conducting components, such as metallic nanowires, rather than continuing to improve nanotube junctions.