Study of the internal electric field effect on charge phenomena in the case of MgO (110)

Charging phenomena of insulating materials were studied thanks to a scanning electron microscope (SEM) which allows the injection of few electrons doses in a large domain of energies and the measurements of the secondary electron emission. The results shown that the secondary electron emission yield (SEE) is a very sensitive parameter to characterise the charging state of an insulator. It is well known that the presence of space charge in an insulator is correlated with an electric breakdown. In this work we investigate the charging effect of (110) magnesium oxide single crystal irradiated with 5 and 30 KeV. The results show the effect of the electric field generated by the trapping of charges within the material. At 5 keV the material reaches an " aging regime " characterized by a positive surface charge, when a negative charge was expected, that is due to the brutal detrapping of accumulated electrons in depth by Poole-Frenkel effect. At 30 keV, we notice that the consequences of the electric field increase are very violent because of the brutal detrapping of the charges accumulated near the surface. In fact the trapped charges create electric fields close to the rupture dielectric field of the material, therefore the irreversible degradation regime is reached in MgO (110).