Complex sentence: A scanning transmission electron microscope (STEM) is a specific sort of transmission electron microscope, where the electrons pass through the specimen, but, as in scanning electron microscopy, the sample is scanned in a raster fashion.
Split into simpler sentences: A scanning transmission electron microscope (STEM) is a type of transmission electron microscope. With it, the electrons pass through the specimen, but, as in scanning electron microscopy, the sample is scanned in a raster fashion.