Charge dynamics in electron-irradiated polymers

Recent studies of charge trapping and charge transport in polymer films irradiated and charged with monoenergetic electrons of range smaller than the sample thickness and thereafter stored or annealed under various conditions are discussed. An analytical model used to describe the phenomena takes the following parameters into consideration: Charge and energy deposition profiles, charge drift due to a shallow-trap-modulated mobility, deep trapping without release, trap filling due to a finite trap density, and ohmic relaxation due to a radiation-induced conductivity during irradiation and its delayed component after irradiation. The model calculations show the effect of various parameters on the shape of the initial charge distribution and on its evolution with annealing time. - Experiments with, the laser-induced pressure-pulse (LIPP) method on 12 and 25 mu m thick fluorocarbon and polyimide films, charged with 10 or 20 keV electron beams, respectively, yield the charge distributions after irradiation and the changes of the distributions due to annealing of the samples at 120 degrees C for various times. A comparison of experimental and analytical results reveals the trapping kinetics and permits to estimate the deep-trap density and the mu tau-product, where mu is the trap-modulated mobility and tau is the trapping time.