Thermionic emission's the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the forces restraining it. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as "thermions". After emission, a charge will initially be left behind in the emitting region that's equal in magnitude and opposite in sign to the total charge emitted. But if the emitter's c… (More on Thermionic)