Electron beam induced charging and secondary electron emission of surface materials

Abstract

Many kinds of insulating materials are used outside a spacecraft. Those are FEP films, polyimide films and so on as thermal control materials. These materials are exposed to charged particles environment around a spacecraft. So these materials charge up due to the charged particles, especially electrons. It is pointed out that charge-up on these materials is likely to cause discharges on the surfaces. Therefore we have investigated the charging potential characteristics by irradiating electrons with various energies below 20 keV. In the dependence of the charging potential on the electron energy, we found that the electron energy at which no charge-up occurs exists below 5 keV. It is thought to be the energy at which secondary electron emission yield becomes one. Each material has the different value of the energy. For example, in the case of Teflon FEP, the energy is about 2.7 keV. This indicates that electron irradiation to the FEP film with the energy lower than 2.7 keV induces positive charging.