Reduced brightness of the ZrO/W Schottky electron emitter

The reduced brightness for a <100> ZrO/W Schottky electron emitter with a tip radius of 0.8 mum has been measured. The maximum reduced brightness measured was 2 X 10(8) A/(m(2) sr V). The measurements of the reduced brightness are compared with the extended Schottky theory and the theory on stochastic Coulomb interactions. At high angular current densities the reduced brightness is limited by statistical Coulomb interactions in the gun lens region. The limits to the maximum reduced brightness in an ideal configuration are explored and found to be 2 X 10(9) A/(m(2) sr V) for a 0.2 mum tip and a current limiting aperture in the extractor electrode. (C) 2001 American Vacuum Society.