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Studies concerning assessment of the image quality in scanning electron microscopes and studies evaluating the detective efficiency of the secondary electron (SE) detectors in these microscopes must be based on statistics of SE emission. The vast majority of previous studies have applied Poisson statistics, although their prerequisites have not been satisfied in most cases. This paper is concerned with the limits to the applicability of Poisson statistics to SE emission. Adequate definition of a non-Poisson factor in the variance of the number of SEs emitted is discussed, and a simple formula for this factor is derived for the low yield case in which both the primary and the backscattered electron are assumed not to release more than one SE. These conditions are met with conductive specimens composed of light elements at primary electron (PE) energies of tens of keV. For the lightest specimens, such as carbon, the non-Poisson factor can even be neglected for PEs >10 keV. [ABSTRACT FROM AUTHOR]

When studying the physical properties and technological parameters of aluminum-based alloys and composites, some partial tasks, connected with the microstructure of the material bulk, pose a problem for established microscopic techniques. The topography and distribution of sub-micrometer sized precipitates and of segregations on the particle/matrix interface, for example, are difficult to observe by conventional methods of transmission and scanning electron microscopy. The introduction of a high-resolution low-energy mode into the scanning electron microscope, relying on the deceleration of an already formed and focused primary beam just in front of the specimen, enables one to browse over the full electron energy range with great ease. This method offers added value consisting of the diminished interaction volume of electrons, the favorable combination of secondary and backscattered electron signals emitted at increased yields and collected at extremely high efficiency and the availability of unconventional contrasts excited by slow electrons. Demonstration experiments have been performed on structures based on the Al-Mg-Si alloy, and oriented towards examination of the Mg-Si precipitates in the alloy and sub-micrometer spinel crystals growing on the matrix–ceramic interface in a composite filled with alumina particles. [ABSTRACT FROM AUTHOR]