It is not necessary to prepare ultra-thin sections for examinations under the scanning electron microscope because the electron beam does not penetrate the object, in contrast to transmission electron microscope (TEM).
The SEM image is created directly by a point-to-point visualization of the surface details of the specimen. To achieve this effect, a very thin electron beam scans the surface of the specimen line by line. Each surface point emits secondary electrons whose different intensities are measured by a detector.
When preparing tissue specimens for a scanning electron microscopic examination, the specimens are dried instead of embedded and sliced after fixation and dehydration.
The dehydration technique commonly used today is critical-point drying. The dried specimens are then coated with gold in a vacuum, the so-called sputtering apparatus. This covers the specimen with a surface which can emit secondary electrons.