This paper presents a comparative study of electrical charging and discharging behavior of different glasses submitted to electron beam irradiation in scanning electron microscope. Charge storage and charge spreading in these glasses have been examined with help of a time resolved current method. Our interest concerns more particularly the dynamic behavior and the amount of the space charge build-up during and after electron irradiation under different experimental conditions of primary beam energy and current density. The precise contributions of different possible self regulation processes (leakage current and secondary electron emission) for charge accumulation are analyzed. Moreover, to characterize the ability of glasses to store charges in a stable way we introduce a relevant parameter that expresses quantitatively the variation in the released charge. The primary beam energy and the current density effects on the evolution of secondary electron emission yield during irradiation are also examined. As expected, the charge storage and spreading processes appear to be extremely dependent on the incident beam energy, current density and on the chemical composition of the studied glasses.

Recent developments in X-ray projection microscopy and X-ray microtomography applied to materials science

This paper deals with charge trapping and charge transport of polyethylene terephthalate (PET) polymer subjected to electron irradiation in a scanning electron microscope (SEM). Measurement of displacement current and leakage current using an arrangement adapted to the SEM allows the amount of trapped charge during and after electron irradiation to be determined and the charge mechanisms regulation to be studied. These mechanisms involve several parameters related to the electronic injection, the characteristics of insulator and the effects of the trapped charge itself. The dynamic trapping properties of PET samples are investigated and the time constants of charging are evaluated for various conditions of irradiation. The determination of the trapping cross section for electrons is possible by using the trapping rate at the onset of irradiation.Many physical processes are involved in the charging and discharging mechanisms; among them surface conduction is outlined. Through the control of irradiation conditions, various types of surface discharging (flashover phenomenon) behaviour are also observed. The strength of the electric field initiating surface discharge is estimated.

Summary: Using primary beam energies E 0 ranging from 0.2 to 15 keV and an in-lens detector, a series of images of the same region of an artificial microstructured diamond sample have been acquired in scanning electron microscopy. Next, the images were analysed by using a scatter diagram technique to underline the topographic contrast change and contrast reversal. The results obtained from 0.5 to 15 keV are discussed with the help of an expression derived from the constant loss model for the secondary electron yield δ of diamond, but including the respective roles of the angle of incidence, i, and of the angle of detection, α. More surprising is the quality of images obtained at a beam energy as low as 0.2 keV, and more difficult to explain is the significant contrast change between 0.2 keV and 0.5 keV. For the first time, scatter diagrams are used as a diagnostic tool in scanning electron microscopy, and after some improvements it is hoped that the experimental approach followed here may lead to quantitative estimates of the local tilts of a specimen surface.

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