Quantitative measurement of surface potential and amount of charging on insulator surface under electron beam irradiation J. Appl. Phys. 92, 6128 (2002); 10.1063/1.1513205Effect of deposition interruption and substrate bias on the structure of sputter-deposited yttria-stabilized zirconia thin films This article presents a study performed with a dedicated scanning electron microscope on the electrical property evolution of surfaces of ͑0001͒-oriented sapphire (Al 2 O 3 ) and ͑100͒-oriented yttria-stabilized zirconia ͑YSZ͒ single crystals, during a 1.1 keV electron irradiation at room temperature. The type of charges trapped on the irradiated areas and the charging kinetics are determined by measuring the total secondary electron emission yield during the injection process, by means of two complementary detectors. At low current density (Ͻ7ϫ10 6 pA cm Ϫ2 ) where positive charging is observed in both materials, charges trapped in Al 2 O 3 are stable, whereas they are unstable in YSZ. This leads to two different charging kinetics. As charging is progressing in Al 2 O 3 , varies from its initial intrinsic value 7.5 down to a steady value ϭ1 which corresponds to the self-regulated regime. Under the same conditions, varies in YSZ from 2.35 down to a steady value above 1 ͑ϭ1.1 in the experiment presented͒. At high current density ͑above 7ϫ10 6 and 6ϫ10 9 pA cm Ϫ2 , respectively, for Al 2 O 3 and YSZ͒, the regulation of the charge regime is controlled by the formation of a negative charge layer due to the reduction of the secondary electron emission by the elastic interaction of incident electrons with secondaries. The difference in the charging kinetics of the two materials is attributed to the difference in conductivities. The higher conductivity of YSZ is responsible for the slower charging kinetics in YSZ, the less pronounced current density effect, and the vanishing of positive charges when irradiation stops.
A scanning electron microscope has been equipped to study the fundamental aspects of charge trapping in insulating materials, by measuring the secondary electron emission (SEE) yield σ with a high precision (a few percent), as a function of energy, electron current density, and dose. The intrinsic secondary electron emission yield σ0 of uncharged MgO single crystals annealed at 1000 °C, 2 h, has been studied at four energies 1.1, 5, 15, and 30 keV on three different crystal orientations (100), (110), and (111). At low energies (1.1 and 5 keV) σ0 depends on the crystalline orientation wheras at high energies (30 keV) no differentiation occurs. It is shown that the value of the second crossover energy E2, for which the intrinsic SEE yield σ0=1, is extremely delicate to measure with precision. It is about 15 keV±500 eV for the (100) orientation, 13.5 keV±500 eV for the (110), and 18.5 keV±500 eV for the (111) one. At low current density J⩽105 pA/cm2, the variation of σ with the injected dose makes possible the observation of a self-regulated regime characterized by a steady value of the SEE yield σst=1. At low energies 1.1 and 5 keV, there is no current density effects in MgO, but at high energies ≈30 keV, apparent current density effects come from a bad collect of secondary electrons, due to very high negative surface potential. At 30 keV energy, an intense erratic electron exoemission was observed on the MgO (110) orientation annealed at 1500 °C. This phenomenon is the result of a disruptive process similar to flashover, which takes place at the surface of the material.
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