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I had a converstation with a customer using tungsten STM probes. They had a few questions regarding the oxidation probes that I was hoping you could help me with:
In your experience, how quickly do tungstem STM tips oxidize? Minutes? Hours? Days?
How critical is the oxidation towards the performance of the scan?
Is there a way to eliminate the oxidation before using the probe?
I would say Tungsten tips can stay usable for hours – typically people make Tungsten probes the same day they use them, and experiments last hours during which the tip must stay in working condition.
The oxide can eventually stop current from flowing (when for instance thicker than 1nm, but I don’t know how long it takes to form such thickness). In such case, the tip would usu. crash into the surface in the effort to reach the desired current, ending up being damaged more likely than not. Thinner oxide will cause the image to be streaky due to the instablility of the tip.
One trick is to dip the tip into dilute HF, HNO3 or NaOH solution briefly then rinse with water to remove the oxide; of course prolonged immersion can dull the tip. I have not experimented to find the best recipe, the color change from dull brownish to somewhat whiter shinier color can be used as an indicator.
Hi,
I am actually making STM in electrolyte, and I use W tips, I prepare them via Electrochemical etching by using KOH.
The tips can survive 2 days if u put the in the vacuum champer after u etch them. as I remember I got nice STM resolution with them.
Good luck