Field Emission Measurements and Electrical Breakdown in Vacuum

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Abstract
Field emitted current-voltage characteristics were determined experimentally in the range 103–108 A/cm2 in the dc mode. For J>105 A/cm2, deviations from Fowler-Nordheim predictions were found, and Dyke's space charge saturation model was found to be inappropriate. These data were obtained at p≈10−12 Torr, with a demountable, metal bakable uhv system with cryogenic capabilities. The (I,V) form of the data was transformed to the (J,V) form by means of the Charbonnier method, which uses the experimentally determined values of I,V and the slope m of the Fowler-Nordheim plot to determine the current density J. Several of the tips were subjected to a high voltage low impedance vacuum arc, and two tips were viewed in the electron microscope before and after breakdown. Tip end radii were 140 and 340 A, ±10% prior to heat treatment. The breakdown data agree better with Alpert's theory of critical field initiated vacuum breakdown than with Dyke's critical current density theory.

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