Paul: We use thin Si all the time inour crystal optics for fluorescence analyzers and for beam cleaners. The really thin wafers are quite bendable. We bend them to 200mm radii with no problem. You can find single sided polished wafers of about 125um thickness for 2" diameter wafers. These would be quite flexible and wouldn't absorb too much. Carlo On Wed, 28 Apr 2004, Paul Fons wrote:
I have still not decided on the final substrate material, but I have a couple of samples coming from Dupont of polyimide (same composition as Kapton) material called vespel. It is essentially inert as one would expect (like Kapton), but due to differences in manufacture I understand it is hydroscopic. From this I assume that the reaction for making Kapton is diffusion limited and Vespel is essentially a "polycrystalline" -- in the sense there are grains between which water can absorb -- form of Kapton. The energy in question is 11.6 keV (the Ge edge). Si is an interesting idea but the loss for a 200 micron thick substrate is essentially 1/e. It is certainly worth considering for higher energies though! The 1/e value for polyimide is about 3500 microns in contrast, while the 1/e value for MgO is about 300. As in my experiment I want to create biaxial stress in a thin film on the substrate, I worry that the stress/strain curves for MgO are too stiff. On the other hand, thin Si is a real possibility (darn, Si technology is everywhere!). I like the Si idea and might try that in parallel. Has anyone tried using thinned Si wafers (Virginia Technology ? sells mechanically thinned wafers I think -- I saw them at a MRS booth a long time ago). How fragile are the wafers?
-- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@agni.phys.iit.edu http://www.iit.edu/~segre