Charge injection and transporting of thin film electrets in vacuum

Electrets formed by electron bombardment are charged in vacuum. When a thin film sample is bombarded by an electron beam, electrons accelerate in the high electric field and collide the surface of the film. These electrons inject into the sample deeply and transport in it. This article deals with the charge trapping, exciting and moving after the charging process. For the thin insulating material like polymer film, quantum tunnel current and breakdown can be neglected after it is bombarded. If the energy of injected electrons is large (more than 10/sup 4/ ev), research shows that injected electrons can affect the conductivity of the film by exciting a large number of electron-hole pairs in it. The induced conductivity changes exponentially with the time.