Physical characterization of molybdenum microtips field emitter arrays

Abstract

We used a dedicated hemispherical energy analyzer to measure energetic and angular distributions of electrons emitted from molybdenum microtips integrated in a 1 cm2 field emitter array designed by the CEA/LETI laboratory. Such cathodes typically deliver about 25 mA at an extraction voltage of 100 V, and are studied in order to replace heated wires as electron sources for space applications. We find that the energy distribution of the beam strongly depends on the extraction voltage, and is therefore expected to vary across the emission lifetime of the device, at a rate depending both on the alteration of the resistive structure with time and on the fate of adsorbed contaminants at the tip surface. A semi-empirical model of the emitters is proposed and used to determine parameters of energetic and angular distributions. The energy dispersion of the beam is found to increase from 2 eV ± 20% up to 9 eV ± 20% eV, for extraction voltages varying from 40 to 100 V. The mean angular dispersion of the beam is found to be 42° ± 20% when a null electric field is set at the grid extraction surface.