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!