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Specific Process Knowledge/Characterization/AFM: Atomic Force Microscopy/KPFM: Difference between revisions

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To get the potential/work function: set the Interleave mode to "Lift" while scanning with the KPFM workspace
To get the potential/work function: set the Interleave mode to "Lift" while scanning with the KPFM workspace
   
   
===Here I shortly explain how to calibrate to get work function values===
===Here is shortly explained how to calibrate to get the work function values===


To get a quantitative value for the work function of a sample material you need to calibrate the AFM tip you are using. This is done by measuring a material with a known work function. We do not have a certified sample for this but we are using a sample that came with the system. It has some lines of Au-Si-Al right next to each other. The below image is from the Bruker application note: AN10-RevA1-PeakForce_KPFM-appNote.pdf
To get a quantitative value for the work function of a sample material you need to calibrate the AFM tip you are using. This is done by measuring a material with a known work function. We do not have a certified sample for this but we are using a sample that came with the system. It has some lines of Au-Si-Al right next to each other. The below image is from the Bruker application note: [[File:PeakForce-Kelvin-Probe-Force-Microscopy-App-Note-BRUKER.pdf]] - used with permission
[[File:AN10-RevA1-PeakForce_KPFM-appNote.pdf]]


[[File:KPFM workfunction Au Si Al.jpg|400px]]
[[File:KPFM workfunction Au Si Al.jpg|400px]]


For reference I prefer using the gold as the two other materials form oxides and I think that using the values for Si and Al are then less accurate.
For reference I prefer using the gold as the two other materials form oxides and I think that using the values for Si and Al are then less accurate.
But even for gold you can find several different values for the work function. Take a look at this reference: [https://en.wikipedia.org/wiki/Work_function#Work_functions_of_elements[11]]. The work function value range for gold seems to be from 5.10eV to 5.47eV. 5.10eV for poly crystaline gold and the higher values for single crystalline gold. I believe I do not have single crystalline gold, so I will use the 5.10eV as the reference value for the sample.
But even for gold you can find several different values for the work function. Take a look at this reference: [https://en.wikipedia.org/wiki/Work_function#Work_functions_of_elements[11]]. The work function value range for gold seems to be from 5.10eV to 5.47eV. 5.10eV for poly crystalline gold and the higher values for single crystalline gold. I believe I do not have single crystalline gold, so I will use the 5.10eV as the reference value for the sample.


To get the work function of the your sample of interest, you need to find the work function of the tip as what you measure with KPFM is the work function difference between the tip and the sample.
To get the work function of the sample of interest, you need to find the work function of the tip because what you measure with KPFM is the work function difference between the tip and the sample.


  Measured surface potential = Work function (Tip) - Work function (sample)
  Measured surface potential = Work function (Tip) - Work function (sample)
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  Work function (Tip) = -0.514 V * e + 5.10 eV = 4.586 eV
  Work function (Tip) = -0.514 V * e + 5.10 eV = 4.586 eV


The value can be typed into the workspace and after that the potential window will show you the work function.  
The value can be typed into the workspace and after that the potential window will show you the work function of your material.  


'''The accuracy of your results are limited by'''  
'''The accuracy of your results are limited by'''  
*the accuracy of the value you use for calibration.  
*the accuracy of the value you use for calibration.  
*It is also limited by the state of the tip. If the tip radius change after the calibration this will affect your results and the tip should be calibrated again.  
*It is also limited by the state of the tip. If the tip radius change after the calibration this will affect your results and the tip should be calibrated again.  
*Other things to consider is that the sample surface must be grounded to the stage. Here you can use Al-tape from the surface of the your sample (be very careful not to hit the tape with the AFM probe.
*Other things to consider is that the sample surface must be grounded to the stage. Here you can use Al-tape from the surface of the your sample (be very careful not to hit the tape with the AFM probe).
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