Physicists in the US have generated extra-bright beams of infrared light from single-walled carbon nanotubes. The new technique is more efficient than many existing methods for producing light and could have applications in optoelectronics (Science 310 1171).
Phaedon Avouris of IBM Research, Jie Liu of Duke University and co-workers began by laying down nanotubes with diameters of 2-3 nanometres by chemical vapour deposition. The nanotubes spanned trenches in a silica coating on a silicon substrate. Palladium source and drain electrodes were then added to the nanotubes.
The IBM-Duke team found that when certain voltages were applied, the nanotubes emitted infrared light at the junction between the suspended and supported parts of the tubes. The emission was localized in a nano-sized area, which resulted in a very bright source of light: a 3 milliamp current was able to produce about 105 times more photon flux than a large area LED.
The scientists believe the location of the emission is due to bending of the conduction and valence bands at the interface between the suspended and supported regions. This accelerates charge carriers (electrons or holes), which then create bound electron-hole pairs (called excitons) that recombine to emit light. According to the team, this excitation mechanism is about 1000 times more efficient than the conventional recombination of independently injected electrons and holes.
Avouris says that the nanotubes emit light with a wavelength of 1-2 microns, which covers the wavelengths employed in optical communications. Moreover, it is possible to tune the emission wavelength, producing either infrared or visible light, by using nanotubes with different diameters.
