Slide 4 of 12
Notes:
The liquid cell designed for these experiments is clear to allow careful probe alignment with the oil-drop anchored to a hydrophobic plate. The scanner moves the substrate, deflecting the cantilever of known stiffness up or down by repelling or attracting the sphere.
The resulting force as a function of substrate displacement is more easily understood if it can be compared on a basis of the actual separation between the sphere and deforming interface.
For a solid flat sample, this is very straightforward; we simply subtract the slope obtained at hard wall contact, i.e. a linear correction, to get a classic force profile that is normalized by the radius of the sphere.
However, the slope correction is more complicated for the drop or bubble case.