Calculation of the deflection of a cantilever during scanning using a contact mode AFM
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Thank you very much for your instructive answers! Unfortunately, we don’t have such a signal access module. I am thinking about using the following method to calculate the deflection of the cantilever: (1) Calculate the Delta set-point, i.e., using the engagement set-point to subtract the VERT signal of the photo diode when the cantilever is just off the surface; (2) Add the value calculated from (1) to the deflection data (error signal). Does this make sense?
On the other hand, I am also using an MFP-3D Asylum AFM to do some experiments. I found some discussions regarding the calculation of true deflection (load) of a cantilever during scanning from a forum supported by Asylum Research. Briefly, some guys suggested that the actual deflection value (V) could be calculated by using the data (V) of a defection image to subtract the non-contact value (baseline, V) of a force curve that was collected immediately upon completing the collection of the deflection image. If this is true, it should be convenient for friction measurement.
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In an NS-IV, you might be best off taking force-distance curves immediately before and after your friction images. Use the "before" plot to run the Setpoint Zero function, then apply your normal force with the knowledge of what PSD output corresponds to zero load. Afterwards, take an FD to see how much you've drifted. At the very least, that will put bounds on your normal force uncertainty.
You don't need a breakout box to ramp the setpoint in the MFP-3D. I worked with AR to write a couple lines of code to change the SP on a line-by-line basis during an image. Unfortunately it's been a while since I've done this and the exact details escape me. But my discussions with Bemis et al are still up there on the AR forum. I'm sure the code is there too.