Effect of oxygen on field emission properties of ultrananocrystalline diamond-coated ungated Si tip arrays

The effect of O-2 exposure on field emission properties of ultrananocrystalline diamond (UNCD) coated ungated Si tip arrays is reported. The behavior of current degradation during O-2 exposure and current recovery following evacuation of O-2 Strongly depended on the initial current/electric field applied to the emitters. At a low initial current of 50 muA/electric field of 5.8 V/mum, O-2 exposure ( 1 x 10(-7), 5 x 10(-7), and 1 x 10(-6) Torr) resulted in a rapid decrease in current in the beginning, followed by a slow decrease. The current made a strong recovery toward the original value when O-2 was pumped out. With an increased initial current of 180 muA/electric field of 10.3 V/mum, the currents recovered only to a lesser extent after O-2 was evacuated. At an even higher initial current of 930 muA/electric field of 20.5 V/mum, the current decreased steadily and finally stabilized after an exposure of 720 L with only 34% degradation. To explain these observations, we propose a hypothesis of oxygen interaction with the UNCD surface.