Direct Observation of Uncoated Surface of Insulators with Scanning Electron Microscopy between 150°C and 500°C

Abstract

In scanning electron microscopy (SEM) observation, ceramic insulators are usually coated with conductive elements such as gold, palladium-gold alloy and carbon to avoid charging-up. In the present investigation, it was observed that charging is not serious above a certain temperature, even without coating. Those particular temperatures are 150°C for yttria-doped zirconia, 400°C for alumina and silicon nitride and 500°C for hexagonal boron nitride. The order of these temperatures is consistent with the order of reported electric resistances of them. Disappearance of the charging problem has been explained as due to transport of electrons through enhanced diffusion layers on the surfaces.