Tungsten wire recrystallization
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I am using the following method that a friend suggested to recrystallize a polycrystalline tungsten wire to use it afterwards to make a better STM tip, since it has been reported in the literature that more crystalline wires give more stable tips.
I put together a small chamber like the one in this the pic
that gets to a pressure of ~5x10-7 torr with a turbo pump. Then I attach a 0.25mm W wire to the two ends of a feedthrough with a 2kg weight hanging from the wire to have it in tension in the axial direction. Close the chamber, pump it and run some current through the W wire by connecting a variable transformer to the outer connectors of the feedthrough until the wire begins getting whiteish.
Let it degas overnight and then increase the current very slowly until the wire breaks.
I haven't taken x-ray diffraction of the wire to see how crystalline it is but I can tell you that it gets extremely brittle after the treatments and the tips I get using this wire have been working quite well.
Let me know if you have suggestions to improve the method of if there are other alternatives for doing the recrystallization.