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Why do ion beams cause more surface damage than photon beams 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, ion beams are significantly more destructive than photon beams because of the physical mechanism by which they interact with a material.

While photons are generally the least destructive probe, ion beams cause damage primarily through the transfer of substantial momentum to the target atoms. When an energetic ion beam (typically 0.3–10 keV) strikes a surface, the ions penetrate the atomic or molecular lattice and are rapidly brought to a stop. This process causes considerable disruption to the lattice, leading to a phenomenon known as sputtering, where atoms, molecules, or molecular fragments are physically knocked loose and expelled from the surface.123

Because this process involves the physical removal of material, ion beams are inherently invasive. This effect is intentionally utilized for depth profiling in techniques like secondary ion mass spectrometry, where the beam effectively "eats away" the surface over time. In contrast, photon-based analysis is less destructive because it does not rely on the mechanical displacement of lattice atoms to generate a signal.123