Charging kinetics features of different modifications of theAl2O3–dielectrics (sapphire, polycrystalline and ceramics) under electron‐beam irradiation

Abstract

The phenomenon of charging dielectrics via the electron‐beam irradiation has been studied very intensively. However, published in recent years the results of experimental and theoretical studies of dielectrics charged under electron irradiation gives contradictory description of this phenomenon [1–6]. These contradictions arise mainly due to the differences in the approaches and fragmentation of experimental studies and differences in used physical models of charging mechanisms. In this report on the basis of extensive experimental data of simultaneous measurement of key charging parameters we are given a balanced assessment of the multiple factors influencing on the charging process. We present the new features of this process and given its interpretation. Based on comprehensive methodology [7, 8], we measure simultaneously the main charging parameters of different modification Al 2 O 3 , such as surface potential V S , electron‐emission current I σ , displacement current I D , and accumulated charge Q versus time of electron irradiation. The experimental setup that allows simultaneously measure the basic charging parameters published in the [9]. The experimental results of complex research of the key charging parameters for sapphire and ceramics Al 2 O 3 are presented in Fig. 1, Fig. 2, Fig. 3 and Fig 4. The main conclusion of these investigations is that although charging processes of dielectric targets are self‐consistent and mutually dependent, the accumulation of the negative charge and, correspondingly, an increase in the charging potential, is the dominant (leading) effect, while the variation in the secondary electron emission coefficient, which depends on the surface potential, is a driven adjusting process. For this reason, a delay occurs in the time for attaining the equilibrium of two fundamental charging parameters, viz., the emission current (a short‐time process) and charging potential (a long‐time process). In other words, for all modifications Al 2 O 3 coefficient of secondary electron emission σ reaches an equilibrium value for used doses of electron irradiation significantly faster than the surface potential. This work was funded thanks to the support of RFBR (grant 15‐02‐01557).