Page 169 - Inorganic Mass Spectrometry - Fundamentals and Applications

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Secondary ion mass spectrometry (SIMS) is a highly sensitive surface technique
for characterizing materials. The procedure is based on the mass analysis of ions
of a solid (or liquid, in a few
created when an impinging beam strikes the surface
to as the rima^
special applications). The impinging ion beam, usually referred
ion beam, is generally accelerated to energies between 0.2 and 40 keV. Figure 4.1
shows the essential elements of SIMS.
Because SMS is a mass analysis technique, it is possible to analyze for all
elements and to measure isotopic abundances of those elements having more than
one isotope. The removal of surface layers, a few atoms at a time, allows high-res-
olution depth profiling into the nanometer range. Mass imaging with x-y resolu-
tion of 4-8 nm is theoretically possible [ 1,23 and 20-nm resolution has been
achieved [3]. With the application of computerized data collection and analysis,
three-dimensional imaging is available. In general the technique is highly sensi-
tive, with detection limits extending to parts per billion in favorable cases. These
strengths have led to its application in fields as diverse as genetics, semiconduc-
tors, polymers, metallurgy, geology, and catalysts. The following discussion of
SIMS is limited to inorganic applications.

The history of SIMS began with the father of mass spectrometry, J. J. Thomson
[4], who reported the emission of “secondary Canalstrahlen” when “primary
Canalstrahlen strike against a metal plate.” Further studies on secondary ion phe-
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