Electrical characterization of diamond and graphite coated Mo field emitters

Current-voltage characteristics of tip-shaped molybdenum field emitters were investigated before and after coating with diamond or graphite powders. Stable emission was observed only after annealing and formation of a conductive Mo carbide layer at the metal-coating interface. Both coated emitters displayed enhanced emission and "turn-on" voltages reduced by a factor of 2 as compared to the uncoated emitters. For the graphite coated emitter, the enhancement was attributed to an increase in the field enhancement factor due to the coating morphology. Roughening of the Mo-diamond interface via carbide formation during the annealing step was presumed to have been the cause for the enhanced emission for the diamond coated emitter. The transmission probabilities for the Mo-diamond and diamond-vacuum interfaces were calculated, using the WKB method, based on an emission mechanism from the intrinsic diamond's conduction band minimum. With a field locally enhanced to 10(8) V/cm, the transmission probability for the diamond-vacuum interface was 10(8) times larger than that of the Mo-diamond interface. This evaluation confirmed that the electron affinity of the diamond surface is not a governing factor in the emission from intrinsic diamond. (C) 1997 American Vacuum Society.