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Agreed, there is a crystalline buildup over time of aluminum at the ends of the tungsten filament ,,, I am not at all sure what the thickness OUGHT to be. I found that when I used a lot more aluminum, results were not pretty. Maybe I should experiment again... Guy Brandenburg, Washington, DC?? ============================ From: "Aurigema, Andrew N. (KSC-ESC-620)[QinetiQ North America - ESC]" To: "VacuumX@..." Sent: Thu, April 14, 2011 8:04:39 AM Subject: RE: [VacuumX] coating thickness error tolerance ? Guy, ? I don¡¯t think you can be accurate enough with volume calcs.? There is loss to the emitter itself and there is tungsten mixture losses.? I see a kind of crystalline build up near the ends of my emitters that is a tungsten aluminum kind of mess.? Is getting a thickness indicator totally out of the question ???? They are kinda pricy but if you need exactly 140 nm then I don¡¯t see how you are going to get around it.? ??Check out ¡°K. L. Lesker¡± they cary a full line of thin film indication systems.? ? Drew ? From: VacuumX@... [mailto:VacuumX@...] On Behalf Of Guy Brandenburg ? ? I am trying to figure out about depositing 140 nm on glass . ? Please recheck this for me. ? I rechecked my measurements, and my arithmetic, and it seems to me that I would need to evaporate 0.044 cm^3 of aluminum to get that thickness, which sounds kinda low. ? The distance from my coil to the mirror is 20" or 50cm. The imaginary sphere with that radius has a surface area of 4*pi*r^2 or 31416 square cm. ? ?To a decent first approximation, the thickness Of the coating will equal the volume of the aluminum being vaporized (in cc) divided by the surface area of that sphere.? ? 140 nm is 140e-9 m or 1.4e-5 cm. That thickness times the surface of 3.1416e4 cm^2 gives me a volume of 0.44 cc. ? The sg of aluminum is about 2.7g/cc. So that volume of aluminum would weigh about 1.2 grams. ? I find by weighing that 7" of my wire weighs (ok, has a mass of) about 4 grams, so 1" would weigh about .6g, which is what I've been using. So my coatings are too thin? |
