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How does ion sputtering make Auger electron spectroscopy useful for depth profiling?

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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 the context of surface analysis, ion sputtering is essential to Auger electron spectroscopy (AES) because it enables the technique to perform depth profiling.

While AES is typically used to analyze the outermost layers of a material, it cannot inherently see beneath the surface. Ion sputtering solves this by using an ion beam to erode or "bore into" the surface, systematically removing successive atomic layers. By alternating between this erosion process and the rapid analytical capabilities of the finely focused electron beam used in AES, researchers can measure the chemical composition of the material at increasing depths.12

This combination is highly effective because the rapid measurement speed of AES allows for efficient data collection as the surface is progressively exposed, making it an ideal method for mapping the composition of a sample through its cross-section.1