SPACE-CHARGE EFFECTS IN SPINDT-TYPE FIELD-EMISSION CATHODES

The field emission characteristic of a Spindt-type cathode, cleaned ex tensively in a hydrogen atmosphere while emitting is considered. The m aximum emission reached is about 800 muA. 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 consi dered to simulate the experimental results. The fit to the data is goo d except at the highest emission levels. In this region the difference between the measured currents and the simulation results is due to th e neglect of the variation of the field on top of the tip in the prese nce of space charge.