**3.1 PEA signal recorded after electron irradiation**

At first, it was necessary to demonstrate that it is was possible to combine measurements of the surface potential and the distribution of charges in the volume by the PEA method. Initial PEA measurements were performed ex situ by using a classical system. Then, a specially adapted PEA cell to perform in situ measurements during the irradiation was developed [49, 50]. The analysis of surface potential and PEA data provides additional information.

Thanks to the PEA technique, it is possible to follow the buildup of charge into the bulk during an irradiation and then follow the relaxation. The direct observation of the SC distribution with time is providing quite a lot details on the dynamics of the charges migration with time that cannot be obtained by surface potential measurements alone. Depending on their energy, the electrons are expected to be stored at a specific penetration depth that can be predicted by various online programs such as ESTAR [51] that provides, for instance, the range and stopping power in PI. In **Figure 5**, an example of PEA signal recorder on a Kapton®-H film irradiated under a 100 keV electron beam shows a negative peak of injected charges near the back surface in agreement with the theoretical calculation. Thanks to PEA results, it has been shown that the relaxation of these negative charges is quite

### **Figure 5.**

*Space charge distribution recorded by PEA on a previously electron irradiated Kapton®-H film. Irradiation conditions: 100 keV with a flux of 1 nA/cm2 for 20 min [52].*

slow and takes more than 24 h [52] in air. In this case, there was no spreading nor migration of the charge with time as it could be observed in other materials. As mentioned earlier, this type of information cannot be provided by surface potential data.
