SPI Supplies® Brand Diamond Grids
For those doing ion milling and analytical TEM
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Diamond Grid, 100 mesh
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Surface morphology of diamond
grids viewed by SEM
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Grids made out of diamond? This is no joke! SPI Supplies is offering these
innovative grids made using the latest diamond thin film technology right
out of the aerospace industry. Specifically, the process used is called
'activated chemical vapor deposition (CVD)'. Diamond is grown on
a silicon wafer followed by a complete removal of the Si to get a free
standing diamond film and eventually then, the grids. These grids are made
of solid diamond and there is nothing else involved.
Everyone knows about diamond, from the fact that diamond is the hardest
material known to man all the way to the fact that they are known to be a
lady's best friend. Diamonds are also supposed to be "forever". Well,
nothing in this life is really "forever" but did you know that diamond has
another unique physical characteristic? Diamond has a thermal conductivity
approximately four times higher than that of copper. Translated, this means
that diamond can carry away heat four times more efficiently than copper!
Diamond is very rigid compared with other materials of the same thickness.
It is also the hardest material known and has a very low sputter rate.
Diamond is chemically inert and samples mounted on the SPI Diamond Grids can
be easily cleaned or etched prior to examination in the TEM.
For ion milling
So just what does this mean for an EM user? For those samples being ion
milled, and for which the milling rate must be slowed down to prevent
overheating, with the higher thermal conductivity of diamond support rings,
there is the possibility that ion milling rates can be increased
substantially!
In addition, diamond is highly resistive to being ion milled itself, thereby
resulting in a cleaner ion milling environment and less deposition of
material on the sample itself.
For high resolution TEM work
For TEM experiments requiring very long exposure times, the thermal
conductivity of a diamond means that there will be far less heating of
certain specimens and therefore less thermal drift. But that is not all!
A sample supported on a diamond grid has a rigid carrier with low thermal
expansion as well as high thermal conductivity. Under the kinds of
conditions that a carbon film will go "limp" on a copper or other metal
grid (which shrinks as it is cooled), diamond has virtually zero contraction
and any carbon film will remain highly taught.
And for those working in the semiconductor field, samples mounted on diamond
have the ideal support while chemical etching is being performed.
Electrical conductivity: We are often times asked about how diamond
grids could be used in this application because, as everyone knows, diamond,
while thermally conductive, is quite nonconductive electrically. Clearly,
a nonconductive diamond, according to conventional wisdom would charge up in
any application in a TEM. But in this case, such conventional wisdom is not
correct, and the grid does not charge up in the beam.
While it is quite correct that the original diamond wafers are not
conductive (resistivity: 104 - 10
5 Ohm-cm), however, during the laser cutting,
as luck would have it, a small amount of graphite that is formed settles
onto the surface of the diamond grid, and quite miraculously, making them
conductive, or at least conductive enough for use in a TEM! Now we have not
actually made measurements of the resistivity of the laser cut grids but we
do know that they are conductive and do not charge up under the electron
beam in a TEM.
Low Bremsstrahlung radiation:
Diamond, unlike other forms of carbon, such as graphite,
exhibit extremely low levels of Bremsstrahlung radiation
and therefore sensitivity on an EDS spectrum will be maximum when using these grids. The level of Bremsstrahlung
radiation is comparable to what is observed when using beryllium grids.
For safety reasons
While we ourselves do not believe there is any danger from the use of
beryllium grids (for low background) many researchers are working in
organizations that forbid beryllium products into the laboratory, diamond
grids represent a possible alternative to beryllium grids.
Special Notice:
Because of corporate downsizings and divisional take-overs by other companies, we have lost our ability
(we hope temporarily) to produce the 200 mesh diamond grid. So while the slot and ring style grids
continue to be manufactured by SPI Supplies, we have had to temporarily suspend the offering of the mesh
type grid. For those requiring "clean" EDS spectra and also low Bremsstrahlung background radiation, select
as an alternative, the SPI Supplies® Brand beryllium grids.
Available geometries:
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Wednesday May 14, 2008
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