Study of the charge kinetics of MgO (1Â 1Â 0) subjected to high energy electron irradiation

This article presents a study performed with a dedicated scanning electron microscope (SEM) on the electrical property evolution of magnesium oxide (1 1 0) single crystal during 15 and 30 keV irradiation. First, the charging behavior is studied during the charge injection process at low current density J0, by measuring the logarithm of the secondary electron emission yield (lnσ). Next, we have investigated the dependence on the current density of the charge-trapping phenomena in MgO (1 1 0). The results shown that beyond the crossover energy E2, the observed effects varies depending on whether the energy of the primary electrons is lower or higher than an energy called critical energy Ec = 20 keV (in the case of MgO (1 1 0)). When irradiating the material at E0 < Ec and at low J0, self regulated regime is obtained, if J0 is sufficiently intense an aging regime is reached. This latter regime is characterized by a positive surface charge, when a negative charge was expected. At E0 > Ec, and for low J0, the detailed monitoring of the charge kinetic of MgO (1 1 0) at high primary energy E0 = 30 keV, permit to show that the combined effect of the increased negative surface potential during irradiation and extractor field below the surface of MgO fact that lnσ undergoes a strong slope failure at the beginning of the injection and stabilizes at a value much less than zero leading to the formation of an electrostatic mirror. At high J0, the consequences of the charge accumulation are violent and a breakdown phenomenon is observed.