Space charge measurements on electron-beam irradiated LDPE films, with and without metallization of irradiated surface
Résumé
One way to characterize and to model charge transport mechanisms in dielectric materials consists of irradiating them with an electron-beam and observing their electrical response. For that purpose, Low Density Polyethylene (LDPE) films of different thicknesses were irradiated by a 80 keV electron beam in an open-circuit configuration. Space charge measurements were performed using the Pulse Electro-Acoustic (PEA) method 'without contact'. Profiles were acquired every two minutes of irradiation for 8 minutes, followed by 24 hours of relaxation under vacuum. The impact of metallization on the irradiated surface as regards the charges transport and generation phenomena are presented and discussed. Even though the deposited electrode was under floating potential, it is shown that the charge and field distribution during irradiation of the dielectric is not the same as without metallization. One clear feature is the build-up of a positive charge onto the electrode during irradiation, which is presumably due to secondary electron emission from the electrode. As a consequence, the equivalence in sample conditioned with or without floating electrode cannot be claimed.
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