Study of the Space Charge Induced by an Electron Beam in an Insulating Target

The building up of the space charge induced by electron bombardment in an insulating target is studied by using a self-consistent Monte Carlo simulation model. The charge is due to the stabilization in polaronic traps of self-trapped electrons and holes. We study the influence of several parameters on the charge distribution. The time evolution of this distribution is analyzed. The spatial extension of the diffusion zone is also discussed, for different primary energies and for different densities of traps. As the target charge builds up, the potential at the surface and the secondary yield vary. The amplitude of the electrostatic field depends on the density of traps. For the energies considered, the target charges positively and the secondary electrons emitted at low energies can be driven back to the surface. Preliminary results about these effects are also presented.