Space-charge distributions in electron-beam charged Mylar and Kapton films

The method of laser-induced pressure pulses (LIPPs) was used to determine space-charge distributions in 22-μm Mylar and Kapton films charged with 10- to 40-keV electron beams. For relatively low deposited-charge densities, corresponding to surface potentials below 300 V, two charge layers develop, one at the surface of the samples and one at a depth corresponding approximately to the electron range. For higher deposited-charge densities, when breakdown in the surrounding air occurs during pressurization, the surface charge layer is positive. For deposited-charge densities in excess of 1 μC/cm², the space-charge layer is broader and, in the case of Kapton, is located deeper in the material than for smaller charge densities. Heating of the samples to 100°C causes a decrease of the charge density without broadening of the charge layers