Brightness measurements of a ZrO W Schottky electron emitter in a transmission electron microscope

We determined the reduced brightness of a ZrO/W Schottky electron emitter, with an apex radius of curvature of 0.9 mu m, for extraction voltages ranging from 2.75 kV to 4 kV. The reduced brightness was found by measuring the diameter of a small focused probe in the specimen plane of a Transmission Electron Microscope, together with the current in the probe and the half opening angle. We find that the experimental brightness values, once corrected for lens aberrations and electron diffraction effects, approach the theoretical maximum axial brightness well. No effects of electron-electron interactions (trajectory displacement) were observed for the range of extraction voltages we studied. The highest corrected reduced brightness value we determined was 1.2 x 10(8) A/m(2) sr V, at an extraction voltage of 4 kV. (C) 1999 Elsevier Science B.V. All rights reserved.