Monte Carlo Calculation of the X-Ray Depth Distributions in an Aluminum Target

A Monte-Carlo simulation of inelastic scattering process developed by Terrissol has been modified and used to calculate X-Ray depth distributions. The elastic scattering is modelled using the Mott collision cross-section and the Hartree-Fock atomic potential. The validity of this model is discussed in a comparison between the Monte-Carlo results and experimental data describing the energy distribution of backscattered electrons and energy loss data

Time dependence of secondary electron yield and of surface potential during charging of amorphous silica target

International audienceWe study herein the charge evolution of a silica amorphous target submitted to an electronic bombardment. During the bombardment, the injected electronic charge and the primary energy as well as the surface bombardment of the target are controlled. The dynamics of the injected charge are described by combining measurements of the secondary electron and X-ray emission using a scanning electron microscope. Thus, we are able to access the evolution of the surface potential and secondary electron yield. Monte-Carlo calculations are used to simulate situations similar to our experiences and to study the effect of certain parameters (density of traps, energy of activation) inaccessible to the measures with our devices

Dynamic investigation of charging kinetics in sintered yttria stabilized zirconia and alpha-alumina polycrystalline ceramics under electron beam irradiation

International audienceA synthesis of work in various research fields shows that (i) the microscopic damage processes in insulating materials under stress (electrical, mechanical, thermal or radiation) are not yet understood but are indisputably related to energy localization on defects. The nature of these defects is still debated but it is acquired that their annihilation is exothermic, (ii) by trapping of charges one localizes a mechanical energy which is relaxed after detrapping, (iii) the charge injection and the dielectrics characterization by electron beam techniques are particularly suited to the damage process study.In the scanning electron microscope chamber, an adapted sample holder measured separately the influence and conduction currents in order to study the charge dynamic during irradiation and discharge dynamic after irradiation of insulating materials. The studied materials are polycrystalline alpha-alumina and yttria stabilized zirconia, characterized by their grain sizes, respectively of 2.5 mu m and 300 nm, their mechanical fracture stress, respectively of 400 MPa and 96 MPa, their electric conductivity, respectively of 10(-14) S/m and 10(-8) S/m and their electrical breakdown field, respectively of 21.2 MV/m and 18.2 MV/m. Interestingly, it was observed that the charging and discharging dynamics of these two materials are quite different. At room temperature, the electrons are trapped in a very stable manner by alpha-alumina and are labile in yttria stabilized zirconia. This difference in stability can be (i) the result of electronic structure differences of both materials, and (ii) the internal stresses effect in the grain boundaries where the oxygen vacancies concentration greatly increases the Debye-Waller factor. This is consistent with the fact that the electron-phonon interactions are at the heart of the damage process. Studies are ongoing to develop characterization techniques to guide the materials manufacture by optimizing their internal stresses