Monte Carlo simulation of low energy electron injection and scattering in insulating layers

Low energy electrons scattered in the conduction band of a dielectric solid should behave like Bloch electrons and will interact with perturbations of the atomic lattice, i.e. with phonons. Optical as well as acoustic phonons are included. Moreover, the inelastic scattering is described by the dielectric energy loss function Im(−1/ϵ) especially reflecting the excitation of valence band electrons, i.e. secondary electrons (SE). With these collective scattering models we have performed the simulation of electron injection and excited electron relaxation and attenuation in the insulator SiO2. After secondary electron excitation to a mean initial energy of several eV their energy relaxation occurs within a short time interval of 200 fs to full thermalization. There is a very rapid cooling by impact ionization connected with cascading of electrons at the beginning during the first 20 fs, followed by much slower attenuation due to phonon losses in wide-gap dielectrics and insulators. These attenuation times are connected with SE escape depths, even with and against the direction of an electric field within the nonconductive isolating sample.