SPI Supplies^® Brand Perforated Silicon Oxide Membrane Window Grids for TEM

Use this nitrogen free membrane for work requiring an absence of nitrogen.


SEM view of the 2µm perforations on 4 µm centers. Note the flatness, or perhaps absence of flatness at elevated magnification. But for some types of work, these grids seem to be acceptable.

Introduction:
SPI Supplies has been offering since July 2000 a full range of silicon nitride membrane windows for TEM grid and x-ray microscopy window applications. During this time, we have had many requests not only for silicon oxide membrane grids (unperforated) but also perforated membrane window grids (e.g. grids with holes, or "holey" membranes). The high precision drilling of some holes in the membranes, using the same technology that is used for the production of the SPI Supplies Brand of apertures for electron microscopy, individual or multiple holes could be drilled and offered to customers. However, the drilling operation is very expensive and the yield at times not very high since the membranes during the drilling have a tendency to rupture.

We have even tried using the techniques of FIB (focussed ion beam) microscopy, but there have always been at least some kind of disadvantage in the end result, either in hole roundness or material build up around the circumference of the holes or both.

Membranes now available in silicon dioxide:
Using the very latest MEMs technology and processing techniques, we have been able to greatly reduce the costs for making the perforations and can now offer in essence an array of holes, 2 µm in diameter on 4 µm centers. However, because of compressive stresses in the silicon oxide membrane, wrinkling is prevalent, and presenting a difficult technical challenge, one we have not yet been able to fully conquer. Therefore in order to minimize the wrinkling that would otherwise occur, we have made these membranes with "reinforcing bars" left in from the original silicon wafer. Hence instead of having a single continuous window that is 500 µm, there are 25 separate windows, with dimension of 75 µm on a side, bordered by "bars" that are 25 µm wide. Although some wrinkling is present, this does, for now represent the best we can do. We have tried to photograph for this presentation, not the "best" that we could find but the worst; hence you can be sure that any silicon oxide membranes you do purchase will be no worse than presented here.

Description of the holey areas:
The entire area of the membrane window, with the exception of the bars is in essence "holey" and the the array of holes cover the membrane area in its entirety. Quantitatively, in each of the 25 sectors, there are 16 rows and 16 columns of perforations (2 µm holes on 4 µm centers) for a total of 256 perforations per sector, or 256 x 25 sectors for a total of 6400 perforations on each grid. The outside frame of course will fit comfortably in any TEM grid holder that has been designed for 3.05 mm diameter grids.

We can produce other hole sizes and other hole densities, in the silicon oxide membranes, however there are some large set up costs to make the first complete wafer. Just let us know your requirements and we can get back to you with firm pricing.

Potential major impact on nature of experiments:
For those applications involving the nucleation of nanofibers across the holes, compared to membranes that have only one or two or some small number of holes, these new SPI perforated membranes open up a whole new way of doing experiments since the population of holes is increased enormously. It is amazing to think how much more data can be obtained, potentially, from just one of these new perforated SiO₂ membrane window TEM grids.

Light microscope view of the grid showing the indexing features

Also an index grid:
We have built into the silicon oxide perforated membrane window grid an indexing system so that the same sector can always be relocated for further study, as shown to the right. Each sector can be described with its own unique set of indexing marks.

Flatness of the membranes:
Put bluntly, these membranes do not have the flatness, at least not presently, as do the silicon nitride counterparts. However when viewed on the scale of the holes, the membranes at least appear to be flat. We think of the development work to make better and better membranes to one of those proverbial "works in progress" and we are constantly striving to improve the membrane flatness. We can state however, that you can consider the observed waviness to be a "worst case scenario". At higher magnification on the scale of the holes, the membrane does have at least the appearance of being flat. But just so we don't give anyone unrealistic expectations, note what we consider the worst case scenario as to the wrinkling of the membrane.

Note before use:
The typical TEM grid has a thickness of 30-50 µm whereas these membrane window grids are 200 µm thick. For most TEM users, this larger thickness presents no problems whatsoever. However, for the first time user, make sure you do not "force" the holder too tight. If you should be one with a holder that is just "too snug", we would suggest contacting your TEM vendor supplier since they would have information about how the holder could be modified to more comfortably "take" this thicker grid. But as mentioned earlier, most users report no difficulties in the use of these somewhat thicker grids (that experience being with those using the nitride counterparts, not the silicon oxide grids).

Coming products:
We are presently deciding upon other standard products with other hole sizes and densities. Can we make smaller holes? Yes, but they are made using a different technology and one that is significantly more expensive. These smaller holes are done by mechanical drilling. If you have such an interest in smaller holes that would be mechanically drilled, remember that the thinner the membrane, the lower the cost. The drilling of a hole in a 30 nm membrane is roughly half the cost of drilling a hole in a 60 nm membrane.

Product availability:
Our first commercially produced silicon oxide membranes are now in stock and ready for immediate shipment from stock. Naturally we cannot guarantee that such stock would be available at some time in the future since its stock availability is always going to be subject to prior sale to some other customers.

Specifications of the perforated membrane window grids:
Frame thickness: 200 µm
Membrane size: 0.5 x 0.5 mm (500x500 µm)
Membrane thickness: 50 nm
Holes: 2 µm holes on 4 µm centers
Total number of holes: 6400

What other customers order when ordering silicon nitride membrane window grids:
A substantial number of membrane grid customer order tweezers (to safely pick them up). and additional grid storage boxes for storing the prepared grids.

Packaging: 10 grids per pack shipping in an SPI Twist-A-Grid™ or BEEM^® grid box

Perforated silicon oxide membrane window grids for TEM:

	SPI #	Pack of ten grids		In Stock
	4089PSO-BA	$ 434.85		Yes

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SPI Supplies® Brand Perforated Silicon Oxide Membrane Window Grids for TEM

SPI Supplies^® Brand Perforated Silicon Oxide Membrane Window Grids for TEM