Scanning Transmission Electron Microscopy (STEM)

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STEM imaging is fundamentally different from cTEM and its related imaging modes and requires additional hardware that is not normally available on standard transmission electron microscopes. When forming a STEM image, the electron beam is focused on the specimen to a small point (frequently as small a point as possible) and moved across the specimen in a raster pattern. An image is formed by counting the scattered electrons at every point in this raster pattern, and assembing the raw electron counts into an image. The movement of the focused electron beam is controlled by additional scan coils (affecting beam shift) which operate between the C2 condensor lens and the specimen area. STEM imaging requires detectors that are very different from photographic film or CCD cameras, and that count the electrons scattered over some defined angle.