We report on a novel instrument that has been designed and built in our laboratory: a scanning projection field emission microscope (SPFEM) designed to study flat broad-area field emission cathodes. The instrument merges capabilities of measuring the electron field emission current from an individual emitting site and genuine projection of electrons onto a luminescent screen.
This is achieved by an optimized shape of the anode probe that is a major improvement compared to previous concepts. Anode probe is realized as a hollow cone with a small hemispherical cap with a smooth-edged pinhole of 0.04 mm diameter. Such configuration generates an uniform macroscopic electric field across the investigated area of the cathode. This fact also enables presentation of the relation between the current density and the applied electric field.
The instrument is designed for investigation of 25.5 mm diameter flat samples, mounted on a XYZ manipulator driven by stepper motors with 1 µm resolution. The true magnification of the electron-optical system alone was calculated by numerical modeling and is around M = 40.
The unique SPFEM performance is demonstrated on several types of nano-structured cathodes such as smooth sulfur doped nanodiamond films synthesized on molybdenum substrates and various carbon based nano-structured cathodes.
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