About the secondary electron yield and the sign of charging of electron irradiated insulators

Abstract

Following the total yield approach (used to predict the sign of charging of electron irradiated insulators) a positive charging is expected when the primary beam energy E p is situated in the energy range where the number of outgoing electrons, , is larger than the number of incoming electrons, I 0. But a negative charging is often experimentally observed when a positive charging is predicted. The present paper is an attempt to elucidate this experimental fact. The arguments being developed are based on the use of a dynamic double layer model (+ for the secondary electron mission, SEE; − for the incident electron implantation) which explains a negative charging via the influence of an evolving S-shape potential function, V(z), which induces a partial freezing of the nominal (uncharged) SEE, δ°, combined to a progressive compression of the negative space charge below the surface. The observed large difference in the measurements of the yield by using pulse excitation methods, or by permanent irradiation methods, δ° or δ is then explained. Furthermore, the influence of an oblique incidence is also deduced.