Charge kinetics in spinel and yttria-stabilized zirconia

Spinel and zirconia were studied by measuring the total secondary electron emission (SEE) yield sigma in a dedicated scanning electron microscope ( SEM) especially equipped to study the fundamental aspects of the charge trapping in insulating materials during a 1.1 keV electron irradiation at room temperature. The variation of the total SEE yield with the injected dose for both spinel and zirconia is different. In spinel the coefficient s starts from its intrinsic value sigma(0) = 4 and reaches a plateau at sigma = 1 at the end of irradiation, which corresponds to the self-regulated regime. The continuity of the curves, shot after shot, proves that the trapped charges are stable and does not spread out in the material as injection proceeds. In this case spinel is called "trapper insulator''. In contrast with the spinel, sigma in zirconia, never reaches unity while the injected charge increases: it evolves from its intrinsic yield sigma(0) = 2.3 to a steady value a few percent above 1. The curve shows the relaxation of the positive generated charge. In this case zirconia is called "conductive insulator''. The difference in the charging kinetics of the two materials is attributed to the difference in conductivities. (C) 2008 Elsevier B. V. All rights reserved.