  We report a comparative ab-initio study of different types of adsorbates and
their adsorption mechanism on the field-emission performance of single-walled
carbon nanotubes by analyzing electrical properties and transport
characteristics and considering the thermal stability of the adsorbed
structure. Adsorbates were found to reduce the work function by up to 1.3 eV,
enhance tunneling near the carbon nanotube tip, and increase the field-emission
current by as much as two orders of magnitude. A significant localization of
the electron cloud was also observed near the adsorbates under a high applied
electric field .
