Experimental methods
One of the most powerful
microanalytical methods for the characterization of diamond zoneation
and inclusion chemistry is Secondary Ion Mass Spectrometry
(SIMS). This technique is one of the more direct and sensitive
spectrometric methods for the analysis of earth materials.
Whereas the electron probe relies upon excitation of the sample to
produce a characteristic emission spectra, SIMS uses an ion beam to
physically desorb atoms from the surface of the material which are then
channeled into a mass spectrometer for direct analysis. The
emitted atoms are ionized (they are the secondary ions) which allows
them to be collected and focused electromagnetically. There are
various primary ions which can be used for the incident beam based on
the requirements of the material. Both low energy and high energy
ions may be used. Depending on the source, beam diameters as small
as 0.1µm are possible, although the zone of interaction in the material
will be somewhat larger than this. Probe resolution is a function
of beam current and beam brightness. Due to the variable ion
yields of different species, which is a function of the atomic
environment, it is neccesary to calibrate the measurement using a
standard sample, (Murr, 1991).
The
figure below (modified
from Woods Hole Oceanographic Institution website) shows a schematic of
a typical SIMS apparatus.
