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

Now we can offer membrane windows of silicon oxide for those needing an absence of nitrogen!

Chinese

Click here to enlarge image unperforated oxide bottom

Etched side showing the partitioning of the window into
25 individual sectors. Note the wrinkling of the membrane.

Click here to enlarge image unperforated oxide top

Membrane side of the grid showing the outside geometry,
produced to fit into a standard TEM grid holder.

Click here to enlarge image unperforated oxide close up

Close up view showing typical wrinkling of
the membrane.

Introduction:
These unique membranes of silicon oxide (SiO₂) are made using highly innovative approaches and we believe these membranes represent a unique production capability. Normal electronics industry grade silicon waters are used and presently, we have standardized with only one thicknesses of the oxide, namely 50 nm, however we do anticipate increasing the number of standard oxide thickness in the not-too-distant future.

Important note:
We have not been able to produce silicon oxide membrane windows that have the flatness we believe is being demanded by our diverse customer base. However, we believe that the flatness will be acceptable to a major part of our base of prospective customers. It is for that reason and only that reason that we now are prepared to offer this product in its present state of development. As many of our would-be customers have told us, "it is better to have something that is less than perfect than to not have it at all." In any case, we are unaware of anyone who has succeeded in making silicon oxide membranes that are more flat than these. We know that there have been many attempts in the past but so far as we know, no one has reached even the quality displayed on this website page.

Production methods:
After the wafer is patterned, the next step is to back etch through the silicon wafer to the (SiO₂) layer, thereby producing the "membrane window" effect. And while the membranes are very thin and fragile, they are sufficiently "robust" to permit one to do their experiments. The product is meant for a single use and we would not recommend trying to clean off old samples for reuse. Discriminating between the two sides with the naked eye is quite easy, the membrane side vs. the etch pit side are quite easy to tell apart. We have not yet made AFM measurements to determine surface roughness but we expect that it will be comparable to that which we achieve for our silicon nitride membranes since that roughness is a function of the roughness of the starting silicon wafer. What is so noticeably different of course, is not so much the roughness but the flatness of the membrane.

And at a thickness of 50 nm, for TEM applications there is not enough material to contribute to a diffraction pattern and the membrane itself is completely structureless and featureless. Hence, anything seen, either by diffraction or in terms of the image itself can be attributed solely to the sample and not to any structure in the support film. At this point in time, since this is a new product, we can not point to large numbers of customers successfully using silicon oxide membrane window grids. However, there are literally hundreds of researchers who do their work every day with the SPI Supplies Brand of silicon nitride membrane window grids and of course, there is a growing number now using the SPI Supplies brand of silicon oxide membrane window grids as well.

We would have every reason to believe that these silicon oxide membranes could be used without problem to at least 200 KV if not also higher.

Silicon oxide vs. silicon nitride membrane window grids:
The main attraction for SiO₂ membranes over Si3N4 membranes is for those working with nitrogen containing samples, and wanting to do EDS studies without potential confusion from nitrogen in the base membrane. The oxide membranes are also preferred by some of those who are nucleating nanofibers across holes and find that the fiber, with their process, nucleate better with the oxide than the nitride composition membrane holes.

Which side should receive the sample?
For most users, the "right" side for the sample is usually the "membrane side" of the grid as opposed to the "etch pit side". However, we have heard of the etch pit side being used in special situations. There are not intrinsic reasons why the etch pit side could not be used, except for those wanting to do AFM work on their samples, since no cantilever will go down far enough to actually get into the etch pit and "see" the membrane surface.

Who would find this product useful in their work?
Actually there are a number of instances where the SPI Silicon Oxide Membrane Windows could be useful, some times making possible the otherwise impossible, but all of them have in common the need for the absence of nitrogen (since nitrogen is in their samples):

An inert substrate that can be used at elevated temperatures to observe dynamically, reactions in situ by either TEM or SEM or in some instances, by AFM.

Use as a durable (e.g. "robust") substrate for doing "matched pairs", of the same identical area, first by TEM and then by SEM.

Use as a durable substrate for matched pairs comparing the AFM vs TEM image.

Ex-situ mounting of FIB sample but for this we would recommend the perforated membranes rather than the continuous membranes.

Many researchers studying nanoparticles, especially those with nitrogen content, would find these membrane window grids to be indispensable for their work. Those studying aerogels and/or xerogels, because of the smallness in size of the basic particles, would similarly find the SPI silicon oxide membrane window grids especially valuable for their work. We are of course extrapolating from our experience with the highly successful silicon nitride membrane window grids because the silicon oxide membranes are quite new and we don't have that much actual data on oxide membranes.

Advantages:

For SEM applications, the background is structureless and featureless.
For x-ray microscopy, there is really no other way for mounting many of the samples one would want to analyze.
Absence of nitrogen

For high temperature applications, we do not believe that the oxide membranes are as thermally stable as the nitride counterparts, which are stable to 1000°C. However the product is new enough that we have not yet had time to get "feedback" from customers telling use of their own experiences at higher temperatures. So for now, unless you really need the nitrogen free environment of the oxide membrane, for high temperature studies, we would certainly recommend the nitride over the oxide membranes.

Handling the SPI Silicon Oxide Membrane Window TEM grids:
The window, if treated with respect, can be consider surprisingly robust. On the other hand contacting it physically such as with a tool, could cause an instant failure. On the other hand, it can be picked up easily with the sharpest of our tweezers without risk to the membrane and it can be handled just like any other TEM grid.

Are the membrane windows hydrophilic?
The grids, as manufactured tend to be hydrophobic, so if samples are being applied from an aqueous suspension, this can cause suspended nanoparticles to appear in a nonuniform distribution across the membrane. The membranes can be made hydrophilic by treatment in a plasma etcher, such as the SPI Plasma Prep II Plasma Etcher, however the effect of the treatment is transitory, and while we have not measured it precisely, we expect that it is along the lines of longevity as carbon coated TEM grids that are treated in the same way, also to make them hydrophilic. So it is possible for us to treat the membrane window grids in this way, however we can not guarantee the longevity of the effect. This could be one of those instances where one could make the case for having this kind of etching unit handy, in their own laboratory.

Optical transparency:
We are often times asked about the optical transparency of the membrane windows. We have not yet ourselves made such measurements, although we hope to do that soon. But visually, one can indeed "see through" the windows. One can certainly see through them by transmission light microscopy.

When considering optical properties, always keep in mind where you are relative to the absorption edge of silicon oxide when trying to estimate membrane's optical properties.

Flatness of the membrane:
The silicon oxide membranes are not as flat as the silicon nitride membrane window grids. Indeed, making membranes free of wrinkles is one of the biggest challenges facing anyone trying to make them. We believe that the flatness now being achieved will be acceptable for most users but it might not be acceptable for all users. But if flatness is an issue, and if you can tolerate the presence of nitrogen, we would recommend your use of the silicon nitride version of this kind of product.

Window size:
The "standard" window size is 0.5 mm square and this dimension is more than enough for most TEM workers. Because of the tendency of the membrane to wrinkle during production, and the problem gets worse as the membrane area becomes larger, we have ended up using a "partitioned" design, one where the window itself is partitioned off into 25 smaller windows. This approach does result in membrane areas that are more flat, but still not completely flat and still not with a flatness that is comparable to what we obtain with silicon nitride membrane window grids.

If you have some special requirement for silicon oxide membrane windows, either for TEM grids or x-ray or some other kind of window, let us know your requirements. We produce a number of different custom styles for our worldwide customer base. Always keep in mind that we can process only entire wafers so that overall cost is based on the cost to process an entire wafer. We are happy to do a single wafer. However the per wafer costs start dropping dramatically as the number of wafers being processed increases.

Also, when thinking about cost, remember that the outside dimensions of the "frame" or grid determine how many units can be obtained from a single wafer. So the smaller those outside dimensions, the more pieces that can be obtained from one wafer and the cost per piece is much lower.

Cleaning of membranes before use:
The silicon oxide membrane window grids should not need further cleaning before use. There are occasionally small pieces of oxide or even of silicon from the breaking of the individual grids out of the wafer, scattered around from the snap out corners (that make the frames rounded) and the presence of such debris particles can't be prevented, but at the same time, we do not feel they should not pose any problems or interference to the user.

However, if one wants to clean them for some other reason(s), then we suggest using H₂ SO₄ : H₂O₂ (1:1) for organic and H₂O:HCl: H₂O₂ (5:3:3) for metals.

The membranes are in general not compatible with ultrasonic treatments to assist with the cleaning, as the windows have a tendency to shatter.

Adhesion of coatings to the membrane surface:
All the commonly used coating methods can be used on the membrane but there can be adhesion problems, not necessarily because they are membranes, but just because they are normal surfaces with the properties of normal surfaces. One can use vacuum evaporation, sputter coating, or any other kind of evaporative process without unexpected problems (except for spin coating, at least for now until we can master the ability to produce a smoother and flatter membrane).

Holey (perforated) membrane window grids:
We have successfully made our first perforated silicon oxide membranes using novel micro fabrication techniques. Such grids make possible the depositing of nanofibers or other samples across the holes so that data can be taken without any contribution from the support being present in the final data. Putting holes into the membrane increases the production costs and therefore the selling prices but the result is a much higher value-add membrane product since it allows one to get so much more out of a single experiment.

All orders for the SPI silicon oxide membrane window grids are shipped in an SPI Slide-A-Grid or BEEM^® grid storage box and is included in the price.

Membrane windows for spin coating:
Very often, as part of the larger protocol for using these membrane window grids, the membrane side has to be spin coated, using for example, the widely popular table-top spin coater offered by SPI Supplies, the Model KW-4A.

However, in order to spin coat successfully, there has to be a higher level of flatness to the membrane that there is at present. As we continuously perfect our production process, we anticipate that the membrane will become more and more flat. And at some point, we will be able to recommend this product for spin coating. For now, only our silicon nitride membrane products have the flatness that would be appropriate for spin coating.

Thickness of the "frames" (e.g. silicon support): The Silicon support structure, made from a silicon wafer, is 200 µm standard. A silicon support thickness of 381µm is also available on special request and at a noticeably increased cost and minimum quantities.

Package size:
Membranes are sold in packs of 10. Special pricing applies when ten packs of ten are ordered at one time (e.g. for a total of 100 membranes). We can also custom make entire wafers containing windows of special custom made designs.

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.

200 µm Thick Frames (Window Size: 0.5 mm):

Packs of 10

Thickness of membrane window	SPI #	Each Pack	Each Pack, 10+		In Stock
50 nm	4089USO-BA	$ 380.49	$ 342.44		No

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SPI Supplies® Brand Silicon Oxide Membrane Window Grids for TEM

200 µm Thick Frames (Window Size: 0.5 mm):

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