Insulator size effect on electron-irradiated quartz

A time-resolved current experiment measuring separately the surface and bulk currents flowing through an insulating sample under electron beam irradiation employing a scanning electron microscope is performed to investigate charging and flashover phenomena. A set of metallic apertures of various values of radius are used to vary the area of the insulator. It is observed that the bulk current decreases monotonically with time until reaching a constant value, while the surface current exhibits two different trends: decreasing monotonically with time, and decreasing with time at first and then increasing. Such observations are related to the establishment of a dynamic equilibrium between electron trapping and detrapping, as well as the flashover behavior, and depends on the insulator size and the experimental conditions.