Observation of field emission sites and study of heat treatment effects

Field emission is known to play a dominant role in the electrical breakdown of gaps in vacuum. Electrons are emitted from micro-projections on clean cathode surfaces where the field strength is enhanced and the tunnel effect is observed. The location of emission sites was observed in this study by using a microchannel plate with a luminescent screen. The effects of the heat treatment on the behavior of emission sites is also discussed. A number of emission sites were observed on the cathode surface which disappeared after electron emission. Furthermore, heat treatment of electrodes decreased the number of emission sites and the number of electrons emitted from a projection. Field emission, in the region <10/sup -14/ A, which takes place at the atomic scale, was observed on the cathode surface.