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KPFM (Kelvin Probe Force Microscopy) measurements can be done with this AFM Icon. It is best for mapping the surface potential on a sample with nanometer resolution but it can also be calibrated to give quantitative values.

Here I shortly explain how to calibrate to get 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

For reference I prefer using the gold as the two other materials form oxides and I think the uncertainty of the values are higher. But even for gold you can find several different values for the work function. Take a look at these references: [1], [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.

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 is the work function difference between the tip and the sample.

Measured surface potential = Work funtion (Tip) - Work function (sample)