Two field-emission states of single-walled carbon nanotubes

Two field-emission states of single-walled carbon nanotubes have been ident ified according to their respective emission current levels. The state yiel ding increased emission current has been attributed to the presence of adso rbates on the nanotubes. It was realized that, by application of high elect ric fields inducing large emission currents, a transition between the two s tates could be induced. For the high current state, field-emitted electrons originated from states located 1 eV below the Fermi level, as was determin ed by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface that enhanced the tun neling probability of the electrons. These states are removed when the nano tubes are cleaned by application of a large electric field, thus, decreasin g the field-emitted current. (C) 2001 American Institute of Physics.