Nanotubes are Hot

Nanotubes are hot, and might be made to act like tiny filamentary light bulbs, a nanometric equivalent of the carbon filament light sources of a hundred years ago.

A group of physicists at the University of Claude Bernard in Lyon, France sends currents through carbon nanotubes. The electrons, when they arrive at the end of the tube will, if the voltage is high enough, fly forward toward an anode. Such a "field emission" (FE) effect could someday be a component in flat-panel displays.

In the meantime, the researchers have observed a number of interesting and useful properties. The nanotubes can be thought of as nanometric filaments, emitting, in this case, electrons, light, and heat. From the spectrum of the emitted electrons, they have deduced the temperature at the end of the nanotube, the first time this has been done.

They are also the first to measure simultaneously the electrical resistance of the nanotube (by way of the field emissions process) and find it to obey Ohm's law. The heating of the nanotube as current flows through it is therefore simply Joule heating. Above a temperature of about 1500 K, the nanotube emits light.

Stephen Purcell (purcell@dpm.univ-lyon1.fr) and his colleagues from the FE group of Prof. Vu Thien suggest that the emitted light is an example of incandescence and not fluorescence. Owing to the very tiny size of nanotubes (only nm wide) and because of this newfound control over heating, nanotubes might be ideal spot sources of heat, light, and electrons.(Purcell et al., Physical Review Letters, 11 March 2002.)