Time-dependent measurement of the trapped charge in electron irradiated insulators: Application to Al2O3–sapphire

A method is described which uses a scanning electron microscope for the investigation of charge trapping in insulators under electron bombardment. The technique commonly used to deduce the amount of trapped charge and its spatial extent is based on the mirror effect, while in the present approach the electron-beam deflections are measured during the primary irradiation. We have performed measurements of the trapped charge during time in an Al2O3–sapphire sample under electron irradiation. Furthermore, the effects of the electron-beam energy and current on charging are also examined and the errors concerning the method are discussed in detail.