Modelling degradation of PTFE under electron irradiation

The electron slowing-down in polytetrafluoroethylene (PTFE) was investigated on the basis of a proposed physical model considering the elastic and inelastic electron scattering on bound fluorine and carbon atoms, electron-phonon scattering and electron trapping. The resonance dissociative and non-dissociative electron attachment cross sections for с-C4F8 molecule were suggested as a basis set to describe the electron trapping in PTFE. Modification of the basis set was carried out by comparison of the calculated total secondary electron yield (TSEY) from PTFE with its experimental values for electron beam energies of 100 eV-5 keV. The electron trajectories were simulated on the base of Monte Carlo technique up to the electron dissociative or non-dissociative attachment. It was shown the calculated positions of electron traps because of dissociative attachment to give the distribution of the broken C-F bonds which cause the (-CF2-) chain scission and appearance of vinyl groups, and, consequently, the PTFE degradation. The calculated TSEY as a function of the large (>80°) incident electron angles demonstrated a sharp drop for high energy electron beams that has never been published anywhere.