TSDC and TSPC due to polarization by space charge migration over macroscopic distances

Most of the space charge in an electret is supposed to stay near its surface. The authors used two methods of investigating the charge near the surface of a polymer electret. One is the removal of a thin layer from the surface. The thermally stimulated depolarization current (TSDC) of such an electret is far smaller than before the removal. The other experiment is an investigation of stacked electrets. A stack of three sheets of polymer film, with or without metal foils between them, is poled to become a thermoelectret. After cooling, it is separated into three sheets. The author found that the TSDCs of the outer two sheets are larger than that of the middle one. This shows that space charge mainly gathers in the outer sheets. To inquire into the type of charge, the thermally stimulated polarization current (TSPC) was also measured. The results suggest that most of the space charge is ions