SURFACE CONDITIONING OF ACTIVE MOLYBDENUM FIELD-EMISSION CATHODE ARRAYS WITH H-2 AND HELIUM

We studied the interaction of active molybdenum field emitter arrays w ith molecular hydrogen and helium. Upon impact with the field emitted electrons, H-2 gas introduced into the system undergoes dissociation a nd ionization. The emitter surface is conditioned through the interact ion of the hydrogen atoms and ions with molybdenum, resulting in the f ormation of volatile molybdenum hydrides. The volatile species are rem oved by the vacuum system. Surface conditioning of the tips is reflect ed in the reduced work function and increased electron emission. Emiss ion enhancement reaches a maximum for total exposures of 1000-1500 L ( 1 L = 1x10(-6) Torr s) of H-2. For small exposures of helium (<1500 L) , emission enhancement is also observed. Larger exposures result in si gnificant emission degradation, We propose that the interaction of H-2 With active molybdenum field emission arrays can be used as an effici ent, ultrahigh vacuum compatible method for in situ cleaning of the fi eld emitter arrays. (C) 1998 American Vacuum Society.