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SIMS, Secondary Ion Mass Spectrometry

Posted by mark00 On March - 23 - 2010

When a surface is bombarded with high energy ions ions and atoms are removed (sputtered) from the surface. The ions that are sputtered can be detected and analysed to determine what the actual sample consists of.

This is the basics of SIMS, Secondary Ion Mass Spectrometry. The sample is sputtered by a high energy ion beam resulting in a depth profile of the sample. The resultant erosion of the sample means that SIMS is a destructive analysis technique. The ion beam is usually oxygen or caesium as they are highly likely to ionise the atoms that are emitted from the surface, and thus be detected.

Only a very small percentage of the elements that are emitted from the surface are ionised. As the probability of ionisation in SIMS is highly variable, it is difficult to quantify SIMS data. This problem is largely solved by using another technique known as SNMS, Sputtered Neutral Mass Spectrometry.

Ionization probabilities for particles sputtered from a surface can vary between 10^-5 to 10^-1. The remaining particles are neutral and thus vary between 90% and 99.9999% which is a much smaller variation in total flux. This fact leads to much better quantitative estimations using SNMS than SIMS.

SIMS equipment