SPI Conductive Carbon Paste is a highly viscous formulation of micrographite
in a liquid carrier (some would say "solvent", but it is not really a solvent)
for the preparation of porous samples destined for x-ray analysis (EDS). For
samples like paper, thin fibers and fabrics, the higher viscosity of the paste
relative to the SPI Carbon Paint, results in far less potential for artifacts due
to solvent exposure and solvent "wicking" up into the sample to be studied.
Of course another alternative to consider, when mounting these kinds of samples,
would be the popular double sided conductive adhesive tapes,
sheets, and discs.
Conductivity considerations:
Obviously, the carbon paste is less conductive than silver paste, however,
when used in the SEM applications, and with micromicro amps of current, the
difference in conductivity between the silver vs. carbon paste is far less
than one might otherwise expect. What we mean is, while the silver does
give a better result, most users find the incremental improvement, while present,
is less than one might expect. We do not at the present time have actual
resistivity values for this product.
Product purity:
The carbon paste, while not spectroscopically pure, is nevertheless, pure
enough so that for most users, one does not see any impurity elements from
the paste, unless the electron beam is directly focussed onto the
paste itself.
The product, when analyzed for impurities, shows less than 10 ppm ash and in
most instances, no impurities are detectable by most energy dispersive
spectroscopy (EDS) systems. We would point out however, that we consider
the critical impurities in this kind of product, from a production
standpoint, to be silicon and sulfur. And we can report that both are
below the 10 ppm level. Other impurities, so far as we can determine,
are all at or below ppm levels in the single digits.
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