We use a platinum-irididum wire to fabricate our STM tips. And by "fabricate" I mean to cut it with really sharp pliers or scissors. Sometimes we get good tips but most of the time they are not usable especially when you need a high aspect ratio and a sharp tip with preferably only "one atom" where the tunneling current goes through.
Therefore my question:
How could one process a platinum-iridium wire to get a really sharp tip? (Besides using chemicals to etch it) Here are some characteristics of the pt80ir20 wire that we use: http://shjmjs.en.b2b168.com/shop/supply/13658861.html The melting point is around 1800 ° C. And by "sharp" and "high aspect ratio" I mean a geometry like this: