Two field-emission states of single-walled carbon nanotubes

Two field-emission states of single-walled carbon nanotubes have been identified according to their respective emission current levels. The state yielding increased emission current has been attributed to the presence of adsorbates on the nanotubes. It was realized that, by application of high electric fields inducing large emission currents, a transition between the two states could be induced. For the high current state, field-emitted electrons originated from states located 1 eV below the Fermi level, as was determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface that enhanced the tunneling probability of the electrons. These states are removed when the nanotubes are cleaned by application of a large electric field, thus, decreasing the field-emitted current. (C) 2001 American Institute of Physics.