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training with kelvin probe AFM

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  • training with kelvin probe AFM

    Hi everybody;

    I'm a PhD student (my 1 year) and with a friend, we tried to practice kelvin test using AFM, but we faced some problems and we need your assistance to understand what we got.


    Problem was that:
    We followed the manual instruction for the SKPM, and we got results as attached. ​For the topography was good but the Nap potential image unable to give any information.
    We hope you can give us some recommendations so that we can make improve our skills.

    Best Regards

  • #2
    the most likely problem is that the sample has a potential that is higher than the default voltage offset (+3V) we use to tune the probe electrically. We assume that the probe is positive relative to the sample during the electrical tune, so if it is not, the bias we apply to match the surface will have the wrong sign. When you have set the phase on the electrical tune, change the bias to -3V and see if the phase flips 180°. If it does not, then the 3V default is not high enough to make the tip relatively positive compared to the sample and you will need a larger voltage offset. I normally try 5 and then 7 volts.
    _______________

    Keith Jones
    AsylumResearch
    _______________

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    • #3
      Hello Ajoub,

      which AFM probe did you use? (Name& company, coating, resonance frequency, force constant).

      Your Drive Amplitude (for topography imaging is very high ~500 mV). Also the Meter shows more than 11 V as amplitude, isn't it? Usually one would have ~ 1-2 V free amplitude. The gain is also rather low, so for 20 um scan size the tracking of the surface is going to be difficult, I would guess.

      Maybe you had poor tracking and you were just increasing the Drive Amplitude more and more until you got good tracking? (This, you should not do.)

      One more question: what sample did you use?

      Best regards,
      Juergen





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      • #4
        Been a while since I have used this mode, but the basic troubleshooting questions are are you using the right cantilever holder? Are you using the right probe (eg/ Pt Ir coated)? Do you have the pogo out wire connected properly?
        Regards,
        Jon.

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