The electron beam of a scanning electron microscope (SEM) is used to charge an unmetallized insulator (Al2O3, Y2O3, SiO2) in vacuum. The charging is found to be stable in time after the e-beam is switched off. The SEM is also used to measure the implanted charge by measuring the resulting electrostatic potential. The distribution of potential around the trapped charges is determined by the classical laws of electrostatics. The electrostatic energy stored in the polarized dielectric can thus be determined. The implanted charge can be removed by the introduction of carriers into the polarized sample by flooding the surface with electron beams of varying energies. Slow or rapid relaxation occurs depending on the operating conditions of the flood gun (energy, intensity, etc.) which introduces the electrons. When the relaxation kinetics are slow, the electrostatic charge decreases slowly as a function of time. On the other hand, a rapid relaxation of the dielectric leads to the appearance of a high-density plasma which spreads over the insulator surface, resulting in treeing on the insulator surface. Along the path of the arc, the transfer of energy to the lattice triggers the sublimation of the ceramic and its mechanical fracture through thermal shock. At particular flood gun setup conditions, we have observed the formation of parallel fracture lines along the ceramic surface, away from the treeing region. These results constitute the basis for a new approach to understanding flashover along ceramics-vacuum interfaces. The important step is the plasma initiation, which we interpret on the basis of dielectric relaxation mechanisms. The parameter of the insulator that determines its breakdown initiation is its complex dielectric constant. It is concluded that the insulator’s band gap, the nature and density of defects localized in the band gap, and the dipolar relaxation induced by a variation of the electric field and connected with the presence of defects determine the holdoff level of insulators.
We are interested in the physical origin of the electric charge that is produced in insulators by electron bombardment, by an electric field, or by mechanical stress. The charge is due to the trapping of carriers on the defects formed in the course of the dissipation of energy by the lattice. The characteristics of the charge (potential, electric field) result from the laws of electrostatics. The stability of the charge under an electron beam is interpreted on the basis of the laws governing the behavior of the discharges in gases and in solids. The stability of the charge after shutting off the beam depends on the position of the traps with respect to the surface and the experimental conditions (gas pressure, temperature, time). The charge decay kinetics are then controlled by adsorption-diffusion. These studies allow us to explain some of the electromigration phenomena that had not been interpreted and to determine the optimal experimental conditions for the observation of local variations in the dielectric constant; they also allow the use of the charge phenomenon as an indicator of the mechanical and dielectric properties of insulators. IntroductionWhen an insulator (crystalline or amorphous) is either bombarded by an ionizing beam (electrons, photons, ions) or submitted to a mechanical stress (stretching, friction) or placed in an electric field it acquires an ~~ ~
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.