Kelvin Force Microscopy
* An electrostatic force between tip and sample builds up, resulting from the charge transfer.
* Kelvin Potential equals the contact potential difference (CPD) between tip and sample.
* An alternating voltage is applied in combination with bias voltage.
Cantilever requirement :
* conductive coating
* force constant between 1 N/m (more sensitive to electrical forces but worse topography feedback) and 20 N/m (less sensitive to electrical forces but better topography feedback)
possible types : NSC18/ CrAu (made by mikromasch).
Possible results with an ac bias of 2V and 50% topography setpoint @ 2 V drive
The left picture shows the topography of the grating. the holes have a pitch of 2 µm and are positively doped with respect to the n-dopod substrate material.
The right image is the contact potential difference between sample and tip. its averga is -14V, but the mean difference between the n-doped and the p-doped region is only 170 mV +/-10 mV.