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Hi All,
I'm looking to shorten some fabricated carbon nanotube probes using the electrical discharge method, where electrical pulses of up to 60V are applied to the tip whilst tapping the surface.
My question is how this might be achieved using a multimode AFM.
Currently we have a new Multimode 8, however I'm fairly sure that we don't have any of the extender modules meaning that the bias can't be applied using the AFM. There are papers which mention using the signal access module and an external pulse generator to do this, which we do have.
Is the application of this bias to the probe possible using the instrumentation avaliable or would we require other components?
Kind Regards,
Ash
Hi Shuo,
The 10mA limit is spelled out in the manual for the Signal Access Module. It is a safe limit to protect all parts in the signal path. 10mA is actually quite a big current for an AFM.
Stefan
On Multimode, we do not recommend to apply votage above +/-12V. If you want to try anything above +/-12V, make sure you have a current limiting resistor in series to make sure current is kept below 10mA.
A safer way to do this is isolate the sample disk from the piezo cap (for instance using scotct tape), and make the electrical connection between the sample disk and the voltage source. You do not need addition components this way.
Chunzeng
Thanks Chunzeng,
After reading some more papers on this process, it seems that people can achieve this oxidative shortening at or below 12V DC.
Connecting to the sample should be relatively simple, however I'm not sure how to make a connection to the cantilever using a standard TM AFM tip holder.
We have a tip holder which has a wire attached that we used for oxidising surfaces with our older Multimode III setup, however I'm not sure if this will work with the new multimode 8 head.
What we are most concerned with is whether the application of a bias could damage the components of the AFM. It seems that if a bias were to be applied to the tip, then it could quite easily travel through the AFM head, given that it is all metal.
Is this a typical procedure, or would we be pushing the instrument beyond the safe operating limits.
Ashley,
If you are using a tip holder that isolates the tip from the chassis you will be fine. To convince yourself you can use a simple voltmeter to check it.
Best,
Hi Dr. Li,
I have a related question: our lab has an old multimode AFM (MMAFM-2, with Nanoscope IIIa controller and signal access module). We have a tip holder for electrical measurements. I wonder if the current limit is also 10 mA? Thank you very much for your help.
-Shuo
Hi Dr. Kaemmer,
Thanks a lot for your prompt reply. It is very helpful. Yeah, I finally found it on the manual. Thanks again. Have a nice day!
Shuo