Silicon nitride was widely adopted as the most popular material for x-ray microscopy because of its wide availability and simplicity of processing into free-standing membranes. Silicon nitride traditionally has a stoichiometry of Si3N4 and the intrinsic stress is circa 1 GPa. In 1982 Sekimoto et. al from NTT proposed a way to reduce the intrinsic stress by altering the ratio of dichlorosilane to ammonia in the LPCVD deposition process. This material is now most commonly referred to as silicon-rich nitride (SiRN) and is the default material for Silson silicon nitride membranes, with typical stress of 300 – 400 MPa. Silicon nitride membranes are incredibly strong in relation to their thickness but the SiRN option further extends the size and thickness permutations from which membranes can be manufactured.
Membranes are available in Si3N4 with thickness, 10, 20, 30, 50, 75, 100, 150, and 200 nm. SiRN membranes are not produced in 10 nm and 20 nm options but are available with all the other standard thicknesses and additionally 350, 500 and 1000 nm. Due to interference effects, this produces a wide range of frame colours which is very useful for rapid thickness determination.
Standard frame sizes for silicon nitride membranes are TEM, 5.0, 7.5, 10.0, 12.5, 14.0, 17.5 and 23.5 mm. Standard membrane sizes vary from 20.0 microns to 19.0 mm but Silson can respond to requests for custom designs very quickly and they are very popular.
In addition to the standard square membranes in square frames, rectangular frames and membranes are produced and also windows consisting of multiple membranes on single frame, either for experimental compartmentalisation or to increase the stability of large area membranes.
Membranes are produced on silicon wafers with three standard thicknesses, 200, 381 and 525 µm. 100 µm thick frames are also available to special order.
Every membrane is inspected for ultimate quality assurance and packaged in individual capsules for the best protection during transportation.
Standard wafers are prime, p-type boron-doped with resistivity from 0 – 30 ohm-cm. The roughness is <5Å rms.
Silson recommends the CXRO database for calculations of the transmission of their thin membranes. You can find this page here.
Membrane thickness: nm Frame Thickness: μm