Experimental characterisation of charge distribution and transport in electron irradiated PMMA

For studying the space charge distribution and transport in poly-methyl-methacrylate (PMMA) polymer material, the specimens were submitted to electron irradiation using a scanning electron microscope (SEM). An arrangement adapted to the SEM for measuring the leakage and displacement currents have been used. Measurements help in estimating the charge quantity and studying trapping processes during and after the electron irradiation. The properties of the dynamic trapping of PMMA and the time constants of charge processes were evaluated. Many physical processes are involved in the charging and discharging mechanisms; among them surface conduction is outlined. The effective resistivity of the sample is measured and compared with that of classic and standardized methods. The strength of the electric field initiating surface discharge is also estimated.