Concept and operation of Schottky emitter without suppressor electrode

The Schottky electron emitter is the most frequently used electron source in electron microscopes. A suppressor electrode around the emitter is usually employed to prevent emission from the shank of the cathode. A concept of operating the Schottky emitter without the suppressor electrode is proposed with the aim of lowering the potential of the extractor electrode. Simulation results show that if the suppressor electrode is removed, then the same field as for the standard configuration can be obtained at the tip apex at an extraction voltage of 2265 V instead of 5000 V. The total emission from the shank region is calculated by estimating the emission area of the shank, taking into the account the different work functions of the crystal facets. The total emission for typical operating parameters is calculated to rise from 500 to 668 A. The total emission from the shank and the filament of the Schottky emitter is measured experimentally in two different configurations, which match with the simulated results. The measured total emission of 450–750 A confirms the idea that a Schottky emitter can be operated without suppressor, all the more so because the power at the extractor aperture is even reduced as a result of the lower acceleration voltage. © 2009 American Vacuum Society. DOI: 10.1116/1.3258657