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How does scanning electron microscopy create a detailed image of surface topography?

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Moon rock crystals — surface analysis A scanning-electron-microscope photograph of pyroxene and plagioclase crystals (the long and the short crystals, respectively) that grew in a cavity in a fragment of Moon rock gathered during the Apollo 14 mission.

Scanning electron microscopy (SEM) creates detailed images of surface topography by scanning a finely focused beam of electrons across the surface of a specimen in a regular pattern.12

As the electron beam interacts with the sample, it stimulates the emission of secondary electrons and high-energy backscattered electrons from the surface. These emitted electrons are collected and analyzed to construct a physical image of the surface's topography. Because the electron beam can be focused to a very fine scale—often on the order of nanometers—the technique is capable of providing a high level of topographical detail.12

In traditional SEM, samples are often coated with a thin layer of conductive material, such as gold or carbon, to prevent surface charging caused by the electron beam. More recent techniques utilize lower-energy electron beams, which can eliminate the need for such coatings and allow for surface analysis at very low incident energies. While SEM is primarily a topographic technique, it can be combined with an energy-dispersive (EDX) analyzer to obtain elemental mapping of the surface layer by detecting X-rays generated by the electron beam.12