Some considerations on the secondary electron emission, δ, from e- irradiated insulators

The so-called "total yield'' approach often fails to explain the measured sign of the surface potential, V-s, and the shift of the nominal critical energy E degrees(C2) (where delta degrees + eta degrees = 1) of electron irradiated insulators. Here, a simple modification of this approach consists in including some extra interactions of the secondary and backscattered electrons with the electron traps generated previously by the irradiation itself. The trends in the evolution of the total yield, delta+eta, and of V-s as a function of the irradiation time (from their initial values up to their steady values) are then deduced for a wide primary beam energy range (1-50 keV) and for different external collector (or specimen holder) bias. New mechanisms are suggested for the contrasts observed in insulators investigated in scanning electron microscopy (SEM). The present analysis applies for a wide variety of electron beam techniques (SEM, Auger electron spectroscopy, and electron probe microanalysis) operated on a wide variety of insulating specimens and this analysis can be easily extended to any device based on the electron emission from insulators. (C) 1999 American Institute of Physics. [S0021-8979(99)03402-7].