SPI Supplies Brand Silicon Nitride Membrane Windows for X-ray Microscopy, 10x10 mm, 3x3 mm Windows,
X-ray Windows, Si3N4:
10 mm x 10 mm Frames
Membrane Window Size: 3.0 mm x 3.0 mm
Membrane Thickness: 100 nm
The SPI Supplies brand of Silicon Nitride Membrane Windows for X-ray Microscopy provide the highest transmission possible for soft x-rays (e.g. vacuum ultra violet). In some parts of the world instead of "soft x-ray", the terms "extreme UV" or "vacuum UV" are used. We use these terms interchangeably. Synchrotron radiation is sometimes the source but laser generated x-ray plasmas (where there is a high powered laser beam focused on a target material which leads to the generation of characteristic x-rays) could also be involved. The softer the x-rays the less the penetrating layer, therefore requiring a thinner and thinner window, which unfortunately also means a higher and higher price. Thinner windows are also used when working "off axis", that is, where the membrane is at an angle to the beam so the x-rays now see a greater effective thickness.
The windows are very similar in construction to the highly successful SPI silicon nitride membrane window grids for transmission electron microscopy. For applications in x-ray microscopy the windows have the following specifications:
Frame Thickness: 200 µm standard, (381 µm on special order, 30% pricing premium, option not available in packs of 10)
Window Thickness Si3N4: 100, 150 and 200 nm available
The SPI X-ray Membrane Windows for x-ray microscopy are designed specifically for use with x-ray microscopes and other soft x-ray applications. If you are getting started in this field, then you might want to become familiar with previously published papers in this field. The typical user of the SPI Supplies x-ray windows would probably be someone making use of an x-ray port associated with a synchrotron or a laser generated x-ray plasma source.
The membrane itself is "low stress" or LS silicon nitride, as opposed to the earlier technology window that resulted in "stoichiometric" (ST) nitride layers but which were under considerable stress. The low stress products are far more robust than the earlier ST nitride layers and therefore the preferred choice.
Visually one can "see through" the windows if you view them by transmission light microscopy. There has to be some thickness beyond which the optical transparency starts to decline, but even at 200 nm thickness, they are transparent in the visible range of the spectrum. When considering optical properties, keep in mind that the absorption edge is just below 13 nm. Hence at 13 nm the transmission for a 100 nm membrane is about 44%. At 12.4 nm it drops down to about 13%. Always keep in mind where they are relative to the absorption edge when trying to estimate membrane optical properties. Our target for refraction index is approximately 2.15, but we make no gaurantees nor represent this as a specification of the product.
SPI Supplies has been careful not to offer these products as vacuum windows, although some existing customers use them this way. We don't have detailed information about vacuum compatibility but we can report the following data. If the window has the following or larger membrane thicknesses or less than or equal to the following areas, then the window will indeed survive a 1 atm pressure differential:
Membrane ThicknessWindow DimensionsPressure Differential
50 nm1.0 x 1.0 mm1 atm
100 nm1.5 x 1.5 mm1 atm
200 nm2.5 x 2.5 mm1 atm
We make no guarantees about the life expectancy of our X-ray windows under vacuum, but the windows should survive some vacuum exposure conditions.
Some Comments About Installing Your SPI Supplies Brand X-ray Windows:
Great care must be taken to not damage the window when handling. Remember that pressure must be applied so the membrane is pushed against (e.g. being pulled against) the substrate silicon and not away from it.
Some of our x-ray window customers find that having some Vacseal® Vacuum Leak Sealant near by for reducing leakage can have great value in a UVH system.
Availability of Silicon Nitride Coated Wafers:
We are now able to offer to our customers the same silicon nitride coated wafers used by SPI Supplies for the production of the membrane window product line.
Some Other Applications:
Substrates for filters such as Ti, V, Mo. Also used in x-ray optics for example as beam splitters.