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How do photons, electrons, and ions differ in their sampling depths during surface analysis?

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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.

In surface analysis, the sampling depth—the region of a solid from which information is obtained—varies significantly depending on the type of particle used as the incident beam. This depth is determined by the penetration of the incident beam and the escape depth of the exiting beam.1

For particles with an energy of 1,000 electron volts (1 keV), the sampling depths are as follows:

Photons: Approximately 1,000 nm.1
Electrons: Approximately 2 nm.1
Ions: Approximately 1 nm.1

Because these particles interact with materials at different depths, they offer complementary capabilities for studying surface composition. For instance, techniques using photons (such as X-ray photoelectron spectroscopy) and electrons (such as Auger electron spectroscopy) are often selected based on the specific requirements of the analysis, such as the need for lateral resolution, chemical state information, or depth profiling.213