The technique of Secondary Ion Mass Spectrometry (SIMS) is the most sensitive of all the commonly-employed surface analytical techniques - capable of detecting impurity elements present in a surface layer at < 1 ppm concentration, and bulk concentrations of impurities of around 1 ppb (part-per-billion) in favourable cases. This is because of the inherent high sensitivity associated with mass spectrometric-based techniques.
There are a number of different variants of the technique :
Statics SIMS : used for sub-monolayer elemental analysis
Dynamic SIMS : used for obtaining compositional information as a function of depth below the surface
Imaging SIMS : used for spatially-resolved elemental analysis
All of these variations on the technique are based on the same basic physical process and it is this process which is discussed here, together with a brief introduction to the field of static SIMS. Further notes on dynamic and imaging SIMS can be obtained in Section 7.4 - SIMS Imaging and Depth Profiling.
In SIMS the surface of the sample is subjected to bombardment by high energy ions - this leads to the ejection (or sputtering) of both neutral and charged (+/-) species from the surface. The ejected species may include atoms, clusters of atoms and molecular fragments