OBSERVATIONS OF WORK FUNCTION CHANGES IN FIELD-EMITTER ARRAYS

The current-voltage (I-V) characteristics for arrays of microfabricate d field emitter tips have been measured as a function of cathode tempe rature in a range of 30 to 300-degrees-C in a turbomolecular pumped va cuum system with a base pressure of < 10(-10) Torr. The current at a f ixed voltage was found to increase with increasing temperature. The ch ange was reversible provided the temperature was held constant at its new value for about 40 min. This implies that the current increase wit h temperature is due to a change in work function rather than a change in the emitting area or tip shape. The I-V characteristic at each tem perature followed the Fowler-Nordheim field emission equation over fiv e orders of magnitude in current and indicated the occurrence of work function changes between 0.5 and 2.0 eV. Such changes could be due to adsorption on the tip of electropositive atoms originating at the anod e, which reached temperatures of approximately 670-degrees-C due to th e electron bombardment at high anode voltages. Conversely, the lower w ork function could be due to desorption of electronegative atoms (such as oxygen) under the action of the heat and the increased H-2 and CO pressure associated with the relatively high anode temperature. Revers ible desorption has been previously observed from the field emitting w hiskers associated with high voltage vacuum breakdown between large ar ea metal electrodes.