Several surface adsorptions related field emission behaviors were investigated for W, Pt/Ir metal tips and multi-wall carbon nanotubes (MWNT). With the help of Fowler-Nordheim theory, we show clearly that there exists a stabilization process of the surface effective work function for W, Pt/Ir and MWNT emitters during emitting. Joule heating from electron emission may desorb the adsorbates on the emission sites of the metal emitter. We observed large emission current variation for MWNT emitters when they were tested after exposure to atmosphere. We suggest that there exist two different surface reaction modes in initial emission period, which are H₂O and H₂ dominated processes respectively. An emission-adsorption equilibrium state may form stronger surface-adsorbate bonds. Nitrogen gas is a good protecting environment to maintain emission stability during the vacuum-atmosphere cycle. Operation of MWNT emitters under hydrogen atmosphere may improve the emission, which could be related to the modification of the surface work function. We suggest that surface adsorbate participated reaction is the dominated factor for the emission loss. This work was carried out under a Cooperative Research and Development Agreement between the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility (DOE contract DE-AC05-84ER40150), Varian Vacuum Technologies and Old Dominion University.

Author(s): Changkun Dong, Mool C. Gupta, G. Rao Myneni

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