The problem is there is no drop-off at all. The wire won't rupture near the surface, instead, it seems like the wire immersed in solution get etched away evenly.
The etching condition I use is 20V AC, 1.5M CaCl2, and carbon rod as one of the electrode.
So how can I get a good tip with this method?
Thanks for any help!
Hi Yanwei He ,
One option which might help is to use a circular auxiliary electrode which the Pt-Ir wire is put centrally into so there is an even etch around the wire. Some methods for etching STM tips (not necessarily of Pt-Ir) suggest putting a weight, like modelling clay, on the bottom part of the wire which is immersed in solution. Then when the etch has gone far enough the bottom half is pulled off leaving just a sharp tip and essentially stopping the etch. Otherwise you can end up with the tip being over etched.
Thanks,
Sam
Sam already suggested you how to improve uniformity of etching procedure. I would like to suggest you to move the tip slowly out of the solution during the etching process, in this way you can get rather sharp tip and you don't need to put a weight.
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