ELECTRON-SPECTROSCOPY STUDY ON THE CAUSE OF HIGHER BREAKDOWN STRENGTH IN ETHYLENE-STYRENE COPOLYMER.

It is known that electrons with energies near the ionization potential (referred to here as high-energy electrons) play an important role in triggering the damage process in polymeric insulators. An investigation is reported in which the interfacial photoemission technique was used to test for the existence of a mean free path on the order of 10-n mu m to prove the existence of high-mobility electrons in the breakdown field. This method is similar to the photoemission into vacuum, except that the hot electrons are injected from the metal directly into the conduction band of the insulator. To measure the energy distribution of the photoexcited electrons passing through the dielectric, the retarding-potential method was chosen. The kinetic energy distribution of the photoelectrons is obtained by varying the retarding voltage applied to the emitter and taking the derivative of the generated current-voltage characteristic. The negative derivative(-dI/dV//R) gives the number of photoelectrons per unit energy, i. e. , the energy distribution curve (EDC). The results of the present study help to clarify the cause of the increase in the breakdown strength of the copolymer by giving direct experimental evidence of the energy absorption property of the benzene-ring structure.