Tunneling-current-induced light emission from individual carbon nanotubes

Tunneling electrons from a scanning tunneling microscope were used to excite light emission from individual multiwalled carbon nanotubes adsorbed on a highly ordered pyrolytic graphite surface. In the integral photon-intensity map, spatially uniform emission in the visible region was observed along the identical multiwalled carbon nanotubes. The emission spectra for the individual nanotubes showed unique profiles which differed with each nanotube, and were classified into two types. Our results indicate that the light emission is due to not the localized electronic states at the tube ends or defects but radiative transitions of electrons between the one-dimensional van Hove singularities, indicating that the two types of spectra are attributed to metallic and semiconducting nanotubes.