ELECTRON-EMISSION ENHANCEMENT BY OVERCOATING MOLYBDENUM FIELD-EMITTER ARRAYS WITH TITANIUM, ZIRCONIUM, AND HAFNIUM

Overcoating Spindt-type field-emitter-array cathodes with several monolayer of Ti, Zr, or Hf leads to a decrease in the voltage for the same emission current by 30 to 40%. This change is entirely ascribable to a 1 eV decrease in surface work function and an increase by a factor of 10 to 100 in the pre-exponential term of the Fowler-Nordheim relation. The postdeposition current voltage characteristics have been observed to remain essentially unchanged for periods of greater than 100 hours at current levels of 10 μA/tip. Field-emission micrographs indicate that the increase in pre-exponential term cannot be attributed to an increase in the emitting area. A plausible explanation is that the electron supply function for these overcoatings is larger than that of the as-fabricated emitter.