 | For those new to surface analysis we include here a brief outline of the methods and capabilities of the principal techniques. There are many excellent reviews and tutorial articles available over the world wide web - perhaps the best place to start to look for those is at one of the sites related to a national User Group such as the UK Surface Analysis Forum (UKSAF formerly UK ESCA UG) site - a body which has close relationships with LSA First, something about SIMS.... |
SIMS
Secondary Ion
Mass
Spectrometry
In SIMS (secondary ion mass spectrometry) the surface of a sample is bombarded by a (focussed) beam of ions. The eroded - or "sputtered"- material is partly ionised. The ionised component is analysed in a mass spectrometer.
SIMS has two main variant techniques - STATIC SIMS and DYNAMIC SIMS
In static SIMS a very low ion beam current density is used and less than 1% of the original surface of the sample is consumed during the course of the analysis. The material sputtered from the surface is mainly in the form of molecular fragments that reflect the surface chemistry of the sample. Thus it is possible to identify surface contaminants by their molecular fragment patterns.
In dynamic SIMS a much higher primary ion beam current density is used. The surface of the sample is continuously etched away during the course of the analysis. By monitoring the signals from elements of interest as a function of time depth profiles for those elements are produced. Normally the primary ion beams used are oxygen or caesium since these species maximise the secondary ion yields of electropositive and electronegative species respectively.
It is also possible to image the distribution of species across a surface as well as in depth, thus providing a three dimensional analysis of the sample.
As SIMS is a mass spectrometric technique, it is capable of detecting all elements and isotopes, from hydrogen to uranium. It has no inherent background and so is very sensitive, capable of detection limits in the parts per million to parts per billion range.
