Analysis of Charging Kinetics of Oxide Ceramics under Short Electron Beam Irradiation: Numerical Simulation of Secondary Electron Emission

摘要

This analysis is connected with the evolution of trapped charges, during electron injection, using a defocused electron beam of a Scanning Electron Microscope especially equipped with a secondary electron low-noise detector. Hence, during pulses of about ten ms, giving injection doses of a few pC, the measurements of the influence induced currents, Iind(t), due to the image charges Qind (t) in the metallic holder (corresponding to the trapped charges Qp (t) in the sample) and the total secondary electron currents, I??(t), can be carried out. Considering the experimental conditions defined by small primary current density (#104 pA/cm2) and low surface charge density (#10 pC/cm2), the relation, I0 = Iind(t) + I?? (t) can be verified [1] leading to (after integration over the injection time) a charge balance: Qinj = Qind+Q?? = Qp+Q?? The secondary electron emission yield, see(t) = 1 -^s{ Iind (t) / [Iind (t)+I?? (t)] }, is experimentally studied as a function of Qp(t). A simulation, which corresponds to a new mathematical model describing the spatial and temporal charge trapping, computes the temporal evolution of the secondary electron emission, see(t), as a function of net trapped charge, Qp(t), for various values of the kinetic energy of the primary electrons. The comparison between experimental results and numerical simulations would permit to evaluate absorption and transfer cross sections as well as mobility of the secondary electrons.