SPI Silicon Nitride Membrane Windows™
New results validating the temperature stability of the membrane windows
We have done experiments involving the heating of individual membrane window
grids to a high temperature, which burns off any residual organic residues from
the manufacturing process. Even when done in air, and up to 1000°C/1832°F, there
is no problem with the stability of the membrane windows. We have even done
some temperature cycling experiments to further test what we believe to be a very
robust nature of the windows. And we have found that even heating and cooling
relatively quickly, for example, heating in a few minutes from room temperature
to (a few minutes from room temp to 1000°C/1832°F and then 15 minutes or so to
cool (well this is not exactly a quenching, but it is pretty fast just the same)
before opening the heating chamber door shows no sign of breakage of the membrane
windows.
The experimental set-up is both simple and unique. The heating is done in a TGA
furnace, which does seem to be ideal for this particular experiment, being very
small and controllable. Admittedly, we use it a bit differently than would be
the case for normal thermal analysis. But first the sample is inserted, then the
program is set to either ramp up to 1000°C/1832°F at 100°C/212°F/minute. Another
variation of this is to just set a direct isothermal program running
(1000°C/1832°F for 10 minutes), which ramps up as quickly as it can get there (in
about 3 minutes).
The cooling cycle can then be done by opening the chamber "a crack" to let some
air flow around it. After about 10-15 minutes the temperature has dropped to
200°C/392°F at which point it can be fully opened, exposing the membrane, which
then cools quickly to room temperature.
So we consider this to be quite remarkable because the membrane just sort of
takes this kind of abuse "in stride".
We are also quite certain that although materials being supported on the window
themselves might crystallize, the silicon nitride membrane itself remain
amorphous and does not crystallize, even up to temperatures of 1000° C.
So there have been some number of questions asked about just how robust are these
silicon nitride membrane window and as all can see, they are quite robust and are
not going to fracture very readily. Now we can not guarantee that they won't
fracture and fail in your own experimental set up, but we can only report our own
findings in our own set up using the kind of cycling and temperature range
described above.
The "proof is in the pudding" of course. The real question is just how sable are
these membranes in real use conditions with real samples. We have received
reports that several customers are using the SPI Silicon Nitride Membrane Window
Grids as lithographic substrates for e-beam type studies. They report that their
patterns start to drift at 1000° C but the membrane is very stable and does not
rupture.
Some researchers doing high temperature in situ TEM work, and who are using carbon films
for this kind of work, often times are frustrated by the migration of carbon
that can occur from the carbon support film onto the sample. We are happy
to report that no such migration from the silicon nitride membrane window
seems to be occurring, hence, the quality of the entire experiment is
improved.
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Sunday March 21, 2010
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