Recrystalize W wire for STM tip

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Recrystalize W wire for STM tip

Postby ssn » Fri Oct 16, 2009 8:55 am

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
IMG_0017.JPG (47.56 KiB) Viewed 14888 times

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.
IMG_0027.JPG (19.19 KiB) Viewed 14888 times

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.
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Joined: Sat Sep 12, 2009 7:55 pm

Re: Recrystalize W wire for STM tip

Postby jlopez » Sun Oct 18, 2009 12:40 pm

Greiner and Kruse suggest an alternative method controlling the current instead of the voltage and having the W wire in tension in a Titanium sublimation pump in the place where the filament of the TSP usually goes.

Review of Scientific Instruments 78, 026104 (2007).
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Re: Recrystalize W wire for STM tip

Postby ssn » Fri Dec 11, 2009 7:40 pm

The following is an answer to this question that I got as a pm (private message):

question:["HI,ssn, I didn't know that the W wires need to recrystalize until see you poster. I just use the poly-crystal W wires for stm tips. Do you feel the tips more stable after the annealing process?thx."]

answer:[It is argued that polycrystalline W undergoes restructuring quite ofter while scanning because of the electric field generated by the surface being scanned, and that accounts for the sudden spontaneous changes in the contrast of the images while scanning. Then, a more crystalline W tip which is thermodynamically more stable, would be less susceptible to undergo there restructuring. From my experience I have the feeling of having a more stable tip while scanning but I haven't done statistics to get quantitative data of this.]
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Joined: Sat Sep 12, 2009 7:55 pm

Re: Recrystalize W wire for STM tip

Postby maheshk1102 » Tue Nov 23, 2010 11:50 am

I used the HF after making the W tip by KOH method, which were 10x stable than the normal W etched tips.
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Joined: Tue Nov 23, 2010 11:48 am

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