For many years, SPI Supplies has offered the highly popular
"Tin on Carbon" test specimens
for SEM image performance evaluation. This specimen was notable for its random
distribution of tin particles across the substrate. The substrate used is a
high quality graphite.
The use of
highly ordered pyrolytic graphic (HOPG)
results in a significantly different texture to the tin particle pattern. Instead
of a random arrangement of the tin particles, there is an alignment into "fibers"
or "strings" of particles. We are told that for the image performance evaluation
when operating in BSE mode, the tin particle alignment structure is more
convenient than when the tin particles are in a random arrangement on the substrate.
We are not sure we can explain why the tin particles self-assemble in this manner but
it must have something to do with the crystallographic structure of the underlying HOPG.
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