Space-charge effects in Spindt-type field emission cathodes

The field emission characteristic of a Spindt-type cathode, cleaned extensively in a hydrogen atmosphere while emitting, is considered. The maximum emission reached is about 800 μA. At high current levels the I-V curve clearly deviates from a Fowler-Nordheim behavior. This can be explained by the occurrence of space charge. Several models are considered to simulate the experimental results. The fit to the data is good except at the highest emission levels. In this region the difference between the measured currents and the simulation results is due to the neglect of the variation of the field on top of the tip in the presence of space charge. 15 refs., 14 figs