SPI Diamond Knives
Everything you wanted to know about diamond knives but did not know who to ask.
Diamond knives for ultramicrotomy are an extremely sharp and precise
diamond edges mounted on a "shank" which is itself mounted in a
precision made metal holder called the "boat". Diamond knives are used
for producing extremely thin specimen sections (or "slices") which can
be observed in either electron or light microscopes depending on the
size of the features to be observed.
In addition, when the last section is taken from a sample, what remains,
which is called the "faced off piece" or the "faced off block" itself
can make for very worthwhile and productive viewing either by SEM and/or
EDS, LM, or more recently even by confocal, AFM, micro-FT/IR or micro-
Raman spectroscopy. This "second opinion" or independent viewing of the
same sample, but in a different form, often times permits a level of
validation and confirmation of what is being seen but with some element
of uncertainty by TEM via the thin sections.
Sometimes the smoothness of the "faced off block" is so perfect that
it is the very best way to make any kind of cross section of some
samples. Indeed at times it can be so smooth that
there is so little surface topography that there is insufficient
contrast to resolve anything by SEM. Consequently some times in order
to see such contrast by SEM, a short exposure to plasma etching with the
SPI Plasma Prep II Plasma Etcher
is necessary, making it possible to see dispersed phases
of inorganics or even dispersed phases of polymers in polymers but which
have already been stained with osmium tetroxide or some other heavy
metal staining system (to alter the etching rate).
Indeed, some researchers using the SPI Supplies Diamond Knives
(Materials Science) only for the generation of faced off blocks for
characterization of the specimens by SEM/EDS or to make the kind of high
quality cross sections needed to examine certain types of samples by
micro-FT/IR or micro-Raman spectroscopy or even AFM. The introduction
of plasma etching seems to be required only for SEM and/or EDS
examination and does not seem to be needed for micro-FT/IR or micro-
Raman applications.
While one might quibble about just what is the radius of curvature of
an SPI Supplies Diamond Knife, some measurement suggest it is about 2 nm
or only 12 carbon atoms! However we do know that the ultimate radius of
curvature that can be given to any material is a function of its
hardness, the greater the hardness, the smaller the theoretical limit on
radius of curvature. And diamond being the hardest material known to
man has the potential for being given the very smallest radius of
curvature of any material. Therefore the attraction of diamond over all
other materials including glass and even sapphire. Nothing comes close
to diamond in hardness.
Another point not often times considered is why one needs the smallest
possible radius of curvature and to put it quite simply, the smaller the
radius of curvature, the greater the "sharpness" and the lower the
amount of force that is needed to make a cut. Putting it another way,
the sharper the knife the lower the force needed to make a cut, and
therefore also, the lower the distortion. The attention being paid to
the very smallest possible radius of curvature means that an SPI Diamond
Knife will cut with the very smallest possible force, resulting in the
very lowest amount of specimen distortion. Without this very smallest
of radius of curvatures, one could not cut sections we estimate to be
down to the 25 nm range.
All SPI Supplies diamond knives are given the ultimate quality
inspection, that is, they are used to cut a plastic block which is then
inspected by TEM to inspect for the presence of striations. Life
science diamond knives are given the very highest level of inspection
since no striations are tolerated.
For the SPI Supplies Materials Science Diamond Knives, some population
of the finest striations are in fact tolerated since for most materials
science samples, the hardness of the samples being cut, on the first
"slice" will impart to the diamond edge larger striations than the fines
ones we are talking about removing! It is not rocket scientist logic to
appreciate that the removal of the very last of the fine
striations also imparts higher costs and it has never made sense to us to
expect our customers to pay for a life science diamond knife when in
fact, after the first few slices it is going to be no better than a
"Materials Science" diamond knife which is much cheaper to begin with!
For the light microscopy diamond knives, the specifications are even
less "tight" because some striations clearly can be tolerated if they
are smaller than what could be reasonably be expected to be resolved by
LM. For laser Raman or FT/IR applications, we recommend the "light
microscopy" diamond knives because after all, why force someone to pay
for a quality that is far beyond what would otherwise be needed?
The entire range of the SPI Supplies diamond knives are actually made
from "gem quality" diamonds. They are carefully selected using a
process of "diamond pickers", person who have that difficult to define
Mintuition as to just which uncut diamonds are going to have the
potential to be crafted into a diamond knife meeting the high standards
of SPI Supplies. Stones of lower quality are just not acceptable
because the same features (actually defects) that would reduce their
value as an item of jewelry would also reduce their value as a diamond
for eventual use in ultramicrotomy.
Therefore once the stone is selected, skilled craftsmen do the cleaving
along natural lattice planes and are then further screened at the LM
level so that only those that are of the highest quality (e. g.
exhibiting no defects at that magnification) are eventually purchased
to be converted into an SPI Supplies diamond knife.
Once cleaved, each "slice" is welded, using a special high technology
titanium alloy to a steel shank, forming a high strength bond between
diamond and metal, making certain that there is good stability during
sectioning. The very latest USA developed laser technology is used to
align the diamond along the precise crystal orientation that provides
maximum edge strength, durability, as well as lifetime.
The real manufacturing process can start now that the diamond slice is
welded to the steel shank, and it can be precisely positioned for the
various procedures using not just the above mentioned laser technology
but other micropositioning and micro measuring technologies.
In order to insure the very highest quality and reproducibility of
quality, knife to know, and SEM is often times called into service.
When the SEM does not provide an answer, the SPI Supplies knives even
have the potential for examination using the very latest in AFM
instrumentation. It is actually via the AFM that we are so certain
about the ultimate radius of curvature at the edge of an SPI Supplies
diamond knife.
While the manufacturing and inspection process is kept secret by us, we
can state that the heart of the production process from this point on is
a combination of polishing steps, each one designed to bring the radius
of curvature closer and closer to the desired figure and also, to do it
in a way that when it is all over, there will be a defect-free edge, an
absolute necessity to produce a striation free section.
Ultimately, when it appears the knife is ready for final inspection, it
is tested by cutting with an ultramicrotome, sections down to the gray or
silver range followed by inspection of the qulity of the cut for the
entire width of the knife edge. Only those knives that "pass" this step
are permitted to continue down the path to becoming a finished knife
product, and ready to ship to a customer. Remember that at this point,
the knife is still just a sharpened diamond slice welded to the steel
shank.
The next step in the production process is for the shank and diamond to
be attached to the proper "boat", again calling into use the very latest
in laser positioning technology to insure perfect alignment. A special
bonding agent is used to fasten the shank to the boat. It is important
that this bonding agent, and it's composition is another one of our
secrets, is very inert and insoluble in most solvents. This allows the
use of various solvents and solvent solutions to be used on the knife
without the fear that this polymeric bonding agent will be dissolved
away. One special note: We are talking about room temperature solvents
and also, diamond knives should not be used in ultrasonic cleaners.
While the polymeric bonding agent is a good one, like with everything
else there are limits and we would not want to risk exceeding them.
Another important and potentially interesting bit of information has to
do with the process by which the edge is made hydrophilic. After all,
if water will not "wet" the diamond, there will be difficulties in
getting the knife to cut acceptably. Therefore all SPI Supplies diamond
knives are subjected to a process by which the edge is will indeed by
highly hydrophilic. In addition, a hydrophilic agent inside the boat
attracts water in the boat toward the edge making it far easier to
maintain the proper water level and meniscus for optimum sectioning
conditions.
We are now at the end of the production line. After the product is
completely assembled, that is, the shank and diamond are bonded to the
boat, a final sectioning test is performed. The entire length of the
edge is examined and sections are produced and examined by TEM in order
to make sure that there are no any defects present that might not be
seen at the LM level. Only if the knife passes this final test will it
proceed for final packaging into the distinctive SPI wooden case and
sending to the inventory area for future shipment to a customer. Knives
that do not pass are sent back to the production area for either
disassembly and further processing, if not into a life science knife
then into either a materials science or a light microscopy level knife.
Every SPI Supplies diamond knife is shipped with a Certificate of
Quality, indicating the parameters of the final test, such as resin type
, speed, section thickness, etc. This is signed and dated by the
microtomist performing the test. Of course, as we say here in
Pennsylvania, the truth comes out where the tire hits the pavement.
Does the SPI Supplies Diamond Knife work or not and how does it work
when compared to other knives.
There are only several major manufacturers of diamond knives in the
world, and we are confident that the quality of the SPI Supplies diamond
knives will equal or exceed the expectations of the most exacting
researcher or engineer doing the very finest ultramicrotomy. The SPI
Supplies diamond knives are made in the USA and take advantage of some
of the very latest aerospace industry inspired measuring tools to
produce these high quality knives at lower cost than just about anyone
else. Furthermore, knives made in countries out side of the USA are
priced in foreign currencies which at the moment, are very "strong" when
compared to the US dollar, or putting it another way, for the same money
, the purchaser of an SPI Supplies diamond knife gets a whole lot more
money's worth!
Besides, how can a customer lose? We guarantee complete satisfaction
and will return any knife that does not live up to a customer's
expectations with either a replacement knife or a full refund of monies
paid. There are two qualifiers on the SPI guarantee however:
a) It is the responsibility to do a "test" of the knife immediately upon
receipt because the offer of return and replacement expires thirty days
after receipt of the knife and
b) This guarantee does not apply to persons trying to cut hard
materials science samples who then find out that such samples can not
be cut with a diamond knife (or else they do not have the required
technique to do the cutting). SPI Supplies can not be in the position
of funding a researcher's research program!
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Saturday October 11, 2008
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