Review of Metallic Microprotrusion Model and Microdielectrics Model in Vacuum

The formulas related to electron emission are reviewed in this article. The mechanisms of different electron emission models are analyzed systematically. The metallic microprotrusion model and the microdielectrics model are compared. The field enhancement factor $\beta $ in different models is derived and compared, and the reason why the theoretical $\beta $ is greater than the measured value is explained. The reason lies in that the traditional theoretical calculation only takes into account the contribution of the metallic microprotrusion in the pre-emission stage but neglects the electron emission of the microdielectrics, which makes it necessary for the same current density to have a larger metallic microprotrusion.