SIMS

Secondary ion mass spectrometry (SIMS) builds a depth-resolved elemental or isotopic composition profile by bombarding a sample's surface with a focused primary ion beam, then directly detecting a small fraction of that same sample's own resulting sputtered material as secondary ions, with each successive sputtering cycle progressively revealing composition information from a correspondingly greater depth into that sample. This progressive-sputtering depth-revealing mechanism is specifically what gives SIMS its own genuine depth-profiling capability, letting SIMS directly measure how a sample's own elemental composition actually varies as a function of depth below that sample's original starting surface.