The Role of Adsorbates on the Field Emission Properties of Single-Walled Carbon Nanotubes

Abstract

AbstractTwo field-emission states of single-walled carbon nanotubes were identified according to their respective emission current levels. The state yielding increased emission current was attributed to the presence of adsorbates on the nanotubes as confirmed by electron emission measurements at different background pressures. Application of high electric fields induced large emission currents and a transition between the two states. During this transition, a current drop to 10% of the original value was observed. Under a constant applied electric field, the current took around 1000 s to recover its original level at a background pressure of 10-10 Torr, while it took half that time at 10-6 Torr. For the high current state, field-emitted electrons originated from states located up to 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 electrons. The adsorbed states are removed at high applied electric fields, presumably due to ohmic heating caused by large emission currents. This adsorption/desorption process is completely reversible.