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SPI Supplies offers apertures made from three distinctly different materials of construction, each offering its own pros and cons. Proper aperture selection requires knowing the trade-offs !
Disadvantages: Apertures will eventually "fail" due to grain growth and a saw tooth appearance around the edge resulting from repeated heating cycles and cooling. The rate of grain growth with Pt is noticeably faster than with Mo, which is a refractory metal.
Disadvantages: Cannot be cleaned in air; must be cleaned under
high vacuum, in a vacuum
evaporator, using a tungsten
boat.
Discoloration will occur over time if molybdenum is exposed to air when
hot. This is not a contamination problem and for most users at least need
not be a
concern. However, what is formed is most likely a nitride which
of course is not going to be conductive, and while we might not be able
to prove it, we just believe that starting out with a bit of
nonconductive coating on a clean aperture is just not the best practice
of electron microscopy. If you too share our concerns, we suggest you
use a platinum aperture. Or alternatively, you might want to try one of
our own SPI gold foil thin film apertures, made to a standard that is
unsurpassed.
Disadvantages: Very fragile; can only be cleaned by heating in
situ. Easily damaged by electron beam if not concentrated on "hole" of
aperture. Smallest hole size (e.g. 1 um) requires relatively clean
instruments in order to get anything approaching "reasonable" aperture
lifetimes. Useful lifetimes have been reported as being on the order of 60
minutes in diffusion pumped instruments that are thought to be
reasonably clean. However, customers who have used them seem to be very
happy since they report results just not obtainable via any other means.
There have also been reports of apertures being recleaned for reuse with
an SPI Plasma Prep II but we
here at SPI Supplies have not confirmed such rejuvenation can in fact be
done.
Pt and Mo Gold Foil
Drilled Thin Film
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Hole Dia. Tolerance Hole Dia. Tolerance
1µm +/- 0.01µm
5-10µm +/- 1 µm 2-5µm +/- 0.5µm
10-20µm +/- 1.0µm 20-500µm +/- 10% of size
30-70µm +/- 2.0µm 90-150µm +/- 5.0µm
300-1000µm +/- 1% of size
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