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How does static secondary ion mass spectrometry map atoms and molecules on a surface?

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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.

Static secondary ion mass spectrometry (static SIMS) maps atoms and molecules on a surface by utilizing a low-density primary ion beam to analyze the topmost layers of a material without causing significant structural damage.1

In this mode, the primary ion current density is kept below $10^{- 9}$ amperes per square cm. This ensures that less than 1 percent of the surface is impacted by primary ions during the measurement process, allowing each particle to encounter an essentially unsputtered surface. When these primary ions strike the sample, they transfer momentum to the lattice, causing a process called sputtering that expels atoms, molecules, and molecular fragments from the surface.1

These expelled secondary ions are then focused by an ion lens into a mass spectrometer for identification. Because the technique is relatively nondestructive, it allows for precise mapping of both organic and inorganic species. By focusing the ion beam into a spot size as small as 0.1 micrometres, researchers can generate detailed images of surface compositions, a capability particularly valuable in fields like the microelectronics industry.12