The secondary electron (SE) and backscattered electron (BSE) signals are used for high magnification, high resolution imaging, with a much lesser use of imaging using characteristic X-rays (element mapping) The ESS JEOL 733 does not easily have the capability to image cathodoluminescence (CL).
Secondary Electron Imaging (SEI)
Secondary electrons are used primarily to image 3-dimensional objects or features. As the SE detector is positioned to the right side of the sample, surfaces or edges directed toward the detector will produce a higher signal (bright on the CRT screen) then those directed away from the detector (dark on the CRT screen). These ‘edge effects’ create the 3-D appearance.
Osumilite in vug, synthetic Dacite.
Backscattered Electron Imaging (BEI)
The number of electrons ‘backscattered’ from the sample depends on the average atomic number (Z) of the sample. Thus, in multicomponent materials, like rocks, the individual minerals can be distinguished based on the fraction of electrons backscattered. Even variations in chemistry within a single mineral can be observed in BSE images.
Corona structure around anorthite feldspar in Angrite meteorite.
Although the minimum magnification of the JEOL 733 microprobe is 40x, it is possible to tile together 40x images using the GELLER software into a mosaic image of much lower magnification (ie., one can image larger areas). See an example, here.