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23.6 Particle Analysis
23.6.1 How Do X-ray Measurements
of Particles Differ From Bulk
Measurements?
The analysis of microscopic particles whose dimensions
approach or are smaller than the interaction volume in a
bulk target of the same composition is subject to effects simi-
lar to analyzing rough, bulk surfaces but with additional
challenges. Like the rough bulk case, the curved or locallytilted surface of a particle acts to modify electron backscat-
tering, which alters X-ray production, while deviations from
the ideal flat surface alter the X-ray path to the detector,
which modifies X-ray absorption compared to a flat bulk tar-
get. The geometry of a particle leads to additional loss of
beam electrons due to penetration through the sides and
bottom of the particle, as shown in the DTSA-II Monte Carlo
simulations in. Fig. 23.17, which depict trajectories in a
1 μm-diameter aluminum particle at different beam ener-
gies. At the highest energy simulated, E 0 = 30 keV, most tra-
jectories pass through the particle with some lateralabcBad!
Better!Best, but still compromised!aEDSEDSEDS. Fig. 23.16 Schematic illustra-
tion of orientation movements
to optimize EDS collection from
a feature of a rough, irregular
surface: a initial position gives
high absorption due to X-ray path
through bulk of specimen; b rota-
tion about a vertical axis brings
feature to directly face EDS; c
rotation about a horizontal axis
places feature perpendicular to
beam to minimize backscattering
and remote X-ray excitation
1 μm5 keV 10 keV 20 keV 30 keVAl. Fig. 23.17 DTSA-II Monte Carlo simulation of electron trajectories
in a 1-μm-diameter Al sphere on a bulk C substrate at various beam
energies; incident beam diameter = 50 nm. Trajectories inside the Al
particle are blue. Green shows trajectories that emerge from the Al par-
ticle which change to orange when they enter the C substrateChapter 23 · Analysis of Specimens with Special Geometry: Irregular Bulk Objects and Particles