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information about surface potentail measurement

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BrukerApplications posted on Tue, Jul 6 2010 7:11 PM

Support Question Forward:

We would like to ask some information about the surface potential measurements by using our Veeco D3100.

Recently we have been applying KPFM to differenciate p-n junction with dosage difference of 5 order of magnitude. And the measured potential difference is near 20 mV. If the dosage difference is further decreased to 2 order of magnitude, will it be possible to differenciate the p-n junction?

What is the resolution of KPFM and the minimum measurable surface potential?

How do we calculate the steps of surface potential resolution? Would it be possible to amplify KPFM measurments?

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Answered (Not Verified) replied on Tue, Jul 6 2010 7:30 PM

You can actually determine the potential resolution by yourself. Move your tip over a conductive area that you can apply a potential to. Measure the response with your SPOM/KPFM setup. Then reduce the potential and measure again and so forth. When you plot the two values you should get a straight fit until you hit the point where you can't resolve the potential difference anymore. This point will be your potential resolution and is probably a few millivolts. If you want to get a bit fancier you can oscillate the applied potential.

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That's a pretty smart way to determine the KPFM sensitivity.  I probably should have done that a while ago :)

Do you have a ballpark estimate on what a pristine system should be able to resolve at a specific drive amplitude and lift (and material and tip...) ?

In terms of the question, did the user really gave enough information?  Wouldn't that answer depend on the material being used (abrupt/graded junction, oxide/passivation, pre/post anneal) as well as proper operation settings?

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The way Stefan suggested to determine the KPFM sensitivity works if you have a sample with uniform potential over the surface. For a non-uniform sample, what KPFM measures is the weighted average of surface potential around the tip apex. The smaller the feature of non-uniformity, the bigger the error of KPFM measurement. Furthermore, KPFM is based on long range electrostatic force. Not only the tip apex can feel the electrostatic force, but also the tip cone. So the geometry of your KPFM probe also plays an important role in the sensitivity and accuracy of potential measurement. More details on this topic can be found in the following paper: Nanotechnology, 2008, 19(23): Art No. 235704.

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I am not surprised by your KPFM results. BTW, what is the size of each doped area? Are differently doped areas adjacent to each other? You may refer to my recent post for more details.

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