Dynamic Charge Transport Behavior of Double-layer Thin Film Materials Under Electron Beam Irradiation

Spacecraft dielectrics in the complex space environment often suffer charging and discharging, causing on-orbit anomalies and failures. Studying charge transport in the dielectric during a spacecraft's charging process is crucial. It helps take measures like surface coating to regulate the surface potential and reduce electrostatic discharges. A double-layer material electron self-consistent transport model, which can simulate the dynamic charge transport behavior of coated spacecraft dielectrics under electron beam irradiation, is developed and used to numerically simulate coated polyimide. It reveals the spatial-temporal distributions of microscopic quantities (charge density, electric field), and temporal evolutions of macroscopic quantities (surface potential, secondary electron yield). Then, the effects of intrinsic properties including electron affinity, band gap, mass density, relative permittivity, and trap density of coating materials on the charging process of spacecraft dielectrics are analyzed, including above microscopic and macroscopic quantities. It is found that decreases in mass density and increases in electron affinity, band gap, and trap density decrease the absolute value of the steady-state surface potential, while the relative permittivity is shown to exert only limited. Obtained trends guide coating material selection for surface charging mitigation. Four coated polyimides' (PI) steady-state potentials are compared, and the diamond-like carbon (DLC) coating with the lowest absolute value of steady-state surface potential is selected to further analyzed for the effect of coating thickness. It is found that the absolute value of the steady-state potential decreases with the increase of the coating thickness, but the effects gradually saturates as the thickness increases. Finally, DLC with a thickness of 200 nm is chosen as the optimal PI coating material, which significantly prevents the charging level from becoming too high while avoiding the negative effects that may be brought about by over-coating, and achieves the purpose of mitigating the electrostatic discharge (ESD) and improving the stable operation of the spacecraft.