A SEM technique for investigating the insulating properties of dielectric surfaces

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Abstract
A technique of investigating the insulating properties of solid dielectric surfaces employing the scanning electron microscope (SEM) was proposed to obtain information regarding the nature of charge creation and electrostatic energy dissipation mechanisms in dielectrics. The experiment provides a qualitative method of obtaining a comparison of the static dielectric constant of different dielectrics at the dielectric-vacuum interface. Two different types of surfaces of 99.9% pure alumina, i.e., as-fired and 0.8- mu m surface finish, were studied. Pulsed flashover experiments were performed on 1-cm-long insulator bridged vacuum gaps. The predictions of the SEM experiment were confirmed by the observed holdoff strength of the different insulator surface finishes.