Studies of spatial depth and density of charge in breakdown-charged polystyrene foils

A detailed study of the initial charge developed on the nonmetallized surface, coupled with that of short-circuit thermally stimulated currents (TSC), has been undertaken in breakdown-charged one-sided metallized 25 μm polystyrene foils. The observed surface charge densities are of the order of 10 −8 C cm −2 . Short-circuit TSC spectra of freshly prepared electrets show a dominant high-temperature peak and two other peaks of small magnitude at lower temperature. The polymer does not become totally discharged before reaching its softening point at 125°C. Analysis of thermally stimulated currents indicates that the electrons are subject to fast retrapping in this polymer. The largest ratios of the mean charge depth to the sample thickness, obtained for electrets depolarized soon after charging and 24 h after changing, are found to be 0.08 and 0.17, respectively. This increase is considered to be due to electron retrapping at various energy levels. The observed initial released charge densities correspond to full-trap densities of the order of 10 15 cm −3 .