Field emission from carbon nanotubes:: perspectives for applications and clues to the emission mechanism

We report on the extensive characterization of carbon nanotube electron field emitters. We studied the emission behavior of sin le-wall, closed and opened are-discharge multi-wall, and catalytically grown multi-wall nanotubes, as single emitters and in film form. The nanotube field emitters show excellent field emission properties, but significant differences were observed between the different types of nanotubes. To obtain good performances as well as long emitter lifetimes, the nanotubes should be multi-walled and have closed, well-ordered tips. Complementary results such as energy distribution and luminescence induced by the field emission give further precious indications on the field emission mechanism. The large field amplification factor, arising from the small radius of curvature of the nanotube tips, is partly responsible for the good emission characteristics. Additional evidence however shows that the density of states at the tip is non-metallic, appearing in the form of localized states with well-defined energy levels.