Method for characterizing charge spreading in sintered alumina by secondary electron emission: Effect of microstructure and temperature

The competition involving charge trapping, diffusion and mobility in insulators may give rise to some charge spreading. This phenomenon is investigated by measuring the recovery of the secondary electron emission. A parameter, which assesses the recovery of the secondary electron emission yield during two successive electron irradiations performed with a Scanning Electron Microscope, is defined. This parameter reflects the evolution of the charging state and the electric field of the material near surface. Alumina samples sintered to different grain diameters and containing only 150 ppm of various impurities (mainly silicon), are studied. The experiments are carried out at temperatures lying in the range 300-663 K. It is deduced that when the temperature increases charge spreading is enhanced. For a given temperature, spreading is promoted in larger grains. The competition between charge spreading and trapping is discussed by calling for the trapping centres induced by silicon dissolution in the bulk and at grain boundaries. It is found that trapping at grain boundaries is more stable than in the bulk. This method constitutes the first step towards setting up standard characterization procedures.