Positive charging of fluorinated ethylene propylene copolymer (Teflon FEP) by irradiation with low energy electrons

Surfaces of materials irradiated by an electron beam emit low-energy secondary electrons and backscattered primary electrons. The total emission yield. defined as the ratio of the number of emitted electrons to the number of incident electrons. increases with decreasing primary energy. At the second crossover point this ratio equals unity and with further decreasing energy the emission yield reaches a maximum and then decreases until it again becomes equal to unity at the first crossover point. The net current in the investigated material changes its polarity at the first and second crossover point (1).