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the local interaction of the specimen and the beam. These
stray electrons and x-rays can be mostly eliminated by
proper specimen shielding and by proper design of the
column. The 400T STEM at Oak Ridge National Lab is
properly modified to minimize spurious x-ray fluorescence
through the use of top hat condenser apertures, and to
reduce sprayed, uncollimated electrons through the use of
spray apertures below the condenser lenses. Hole counts
are consequently low, in the neighborhood of 1 to 2
percent of the total elemental counts when the beam is on
the sample. A hole count spectrum was always accummulated
for each specimen and subtracted from each specimen
generated spectrum before any subsequent curve fitting and
peak deconvolution (Zaluzec, 1979).
The specimen related effects are more difficult to
assess. These effects are primarily due to absorption of
specimen generated x-rays by the specimen itself. The
most common method for quantitative analysis in the
analytical TEM follows the Cliff-Lorimer equation (Cliff
and Lorimer, 1972). This equation relates the ratio of
the concentrations of unknowns in the sample to the ratios
of the beam generated x-ray itensities:
CA/CB = (K) IA/lB,
The major assumption in the equation is that the k term,
the proportionality constant, is independent of the
specimen thickness. This assumption is not valid