Effect of a nonpenetrating electron beam on enhancing photoelectron yield

The photoelectron yield from polyethylene, Kapton H, and Teflon samples was measured using a Xenon flash lamp with UV spectrum extending down to 190 nm (6.5 eV). These measurements indicated a dramatic increase in the yield when the samples were irradiated by a nonpenetrating electron beam. The photoelectron yield rose with both dose rate and total dose deposited in the insulator. Observations of the yield revealed persistent enhancement even after turning off the electron beam. This delayed component is reminiscent of the delayed conductivity observed in insulators after the ionizing radiation is turned off. Studies showed that this enhancement was not due to precharging of the dielectric surface. Instead, it was attributed to an increase in the population of carriers, generated by the electron beam, which had been in localized traps within the forbidden band. These trapped electrons, lying just below the conduction band absorbed the xenon radiation and were emitted from the sample materials. Enhanced photoelectron yield has importance in determining the surface potential of insulators on spacecraft exposed to the plasma environment for extended periods of time.