Evaluation of the effective cross‐sections for recombination and trapping in the case of pure spinel

• Published in: Journal of microscopy (Oxford) 2015-03, Vol.257 (3), p.201-207
• Main Authors: BOUGHARIOU, A., DAMAMME, G., KALLEL, A.
• Format: Article
• Language: English
• Subjects: Cross‐section for electron–hole recombination; logarithm of the SEE yield (lnσ); pure spinel; R&D; Research & development; Scanning electron microscopy; trapping cross section
• ISSN: 0022-2720; 1365-2818
• DOI: 10.1111/jmi.12202

Summary In this paper, we have investigated the evolution of the secondary electron emission in the case of pure spinel during electron irradiation, achieved in a scanning electron microscope at room temperature, which is derived from the measurement of the induced and the secondary electron currents. It was observed from the experimental results, that there are two regimes during the charging process: a plateau followed by a linear variation, which are better identified by plotting the logarithm of the secondary electron emission yield lnσ as function of the total surface density of trapped charges in the material QT. For positive charging, E0 = 1.1 and 5 keV, the slope of the linear part, whose value is of about 10−10 cm2 charge−1, is independent of the primary electron energy. It is interpreted as a microscopic cross section for electron–hole recombination. For negative charging of pure spinel, E0 = 15 and 30 keV, the slope is associated with an electron trapping cross section close to 10−14 cm2 charge−1, which can be assigned to the microscopic cross section for electron trapping. This trapping cross section is four orders of magnitude lower than the recombination one. Lay Description In this paper, we have investigated the evolution of the secondary electron emission from pure spinel irradiated at four primary energies 1.1, 5, 15 and 30 keV, by using a scanning electron microscope (SEM). The dependence of SEE yield on surface density of trapped charges has led to the evaluation of microscopic cross sections for electron‐hole recombination (when the material is positively charged: E0 = 1.1 and 5 keV) and electron trapping (when the material is negatively charged: E0 = 15 and 30 keV) in pure spinel. The variation of the semi‐logarithmic of the secondary electron emission yield (lnσ) as function of the surface density of trapped charge QT appears to be a valuable way to characterize the charging properties of an insulator surface. According to the different curves we note that when the material charged positively the slopes are the same P = 1.6 10−10 cm2/charge, whatever the primary beam energy E0 = 1.1 and 5 keV. When the material charged negatively (E0 = 15 and 30 keV) the slopes are the same P = 1.6 10−14 cm2/charge. This proves that the slope is completely intrinsic to the material, since it is independent on initial conditions (Σabs0: initial traps) and conditions of irradiation (λsource: the mean distance between electron‐hole pairs created by each