Determination of the charge distribution within an e-irradiated dielectric using the pressure wave propagation method

The pressure wave propagation (PWP) method is used to investigate charge storage in Teflon FEP films irradiated with a monoenergetic electron beam in a vacuum. Signals obtained at different time intervals during charging of the material up to -7 kV are presented and analyzed. The PWP method clearly shows the incident electrons trapped near the surface and positive charges injected at the opposite metal-polymer interfaces. These charges remain trapped after a surface discharge. However, the buried electrons disappear. A numerical treatment leads to an improved determination of the charge distribution throughout the sample and gives the value of the mean depth of penetration versus the beam energy