Measuring Nanotubes' Conductivity

How well nanotubes conduct electricity depends a lot on their environment. Hongjie Dai and his colleagues at Stanford have made the first electrical measurements of currents flowing under high voltage (high bias) through single-walled carbon nanotubes suspended like miniature power lines. They discovered that in suspended form a micron-scale-long nanotube could carry about 5 micro-amps of current, whereas lying in the plane of a substrate the same tube can carry about 25 micro-amps. The reason for the better in-the-plane performance is that the substrate helps to dampen "optical phonons," high-energy vibrations of the nanotube atomic lattice. Dai (650-723-4518, hdai1@stanford.edu) believes that with careful engineering of the interface between a nanotube and a substrate, maximum currents could be raised to higher levels than previously possible, which might make carbon nanotubes useful for applications in high-power transistors and even nanoscale transmission lines. To make the kind of transmission lines you see in the countryside out of nanotubes, you'd have to develop a process for producing km-length carbon tubes, which is not feasible for the foreseeable future. (Pop et al., Physical Review Letters, upcoming article)