Photostimulated discharge of corona and electron-beam charged electret polymers

Despite the long-time use of space-charge electrets in various commercial applications, the mechanism of charge storage is still poorly understood. To study the energy distribution of deep traps, photostimulated discharge spectra of electron-beam and corona-charged polytetrafluoroethylene (PTFE), polyethylene terephthalate (PETP) and cellular polypropylene (PP) films were recorded for wavelengths between 200 and 400 nm. In addition, space-charge profiles were measured using the piezoelectrically generated pressure-step (PPS) method in order to monitor the detrapping process. Strong discharge currents of up to 15 pA/cm² were found in PETP around the UV absorption edge near 310 nm. Initial results show a quantitative depopulation of near-surface charges, whereas only partial detrapping could be achieved for bulk charges. Three distinct trapping levels could be identified in PP films.