Simulation of Low-energy Electron Beam Irradiated PTFE Based on Bipolar Charge Transport Model

Studies on charge transport properties of space grade insulating materials become popular recently because it is closely related to the safe operation of spacecraft. Taking charge carriers retrapping and hole injection into consideration, we simulated the surface charging and the space charge accumulation properties of PTFE under low-energy electron-beam irradiation using bipolar charge transport model in this paper. Parameters for simulation were based on experiments and previous studies. The secondary electron yields of PTFE irradiated by electron-beam of different primary electron energies were measured, and experimental data were fitted with an empirical equation. Thermally stimulated current was measured, and the trap parameters of PTFE were analyzed from the current-temperature curve by initial-rise method. In order to investigate the space charge distribution and the surface potential of steady state, factors like primary electron energy, sample thickness, temperature and trap density were selected as variables separately. It is found that the steady surface potential is nearly linear with the primary electron energy, which also fits the experimental results. The simulation results show the sample thickness affects the charging rate of surface potential mostly, and the charging rate is slower in thinner samples. The steady surface potential fluctuates slightly in the case that temperature is not high, but it increases significantly when temperature is higher than 400 K. With the increase in trap density, the space charge accumulation tends to focus on the surface and the dielectric/electrode interface, and the steady surface potential decreases.