If a surface is bombarded with high energy ions, then ions and atoms from the sample will be sputtered from the surface. The ions can be detected and mass analysed to determine what the sample is made of. This is the basis of the SIMS technique. The erosion of the sample by the ion beam can provide a depth profile of the sample, and the ion beam can be rastered over the surface to provide an image of the presence of particular elements or molecules on the surface. The eroding nature of the beam makes SIMS a destructive technique. The incident ions are usually oxygen or caesium. These elements are more likely to ionise the atoms emitted from the surface, and thus be detected. Only a small proportion of the elements emitted from the surface are ionised. Post-ionisation by various means leads to the technique of SNMS. As the probability of ionisation in SIMS is highly variable, it is difficult to quantify SIMS data. This problem is largely overcome in SNMS.

SIMS has to be carried out in UHV conditions.