Appendix I: Analyzing Force/Distance Curves - AFM Workshop LS-AFM User Manual

Appendix I - Analyzing Force/Distance Curves
A force/distance curve is a graph that shows the amount a cantilever tip bends as it is sys-
tematically pushed into a sample. The probe may be lowered onto the surface, or the surface
may be raised into the probe.
What is actually measured is the deflection of the cantilever, or the Top - Bottom (T-B) signal
of the photo-detector.
The deflection of the cantilever can be converted to Force using Hook's law:
Force = - K * d
K = force constant
d = deflection of the cantilever
In a light lever AFM, the user must convert the T-B signal into the cantilever deflection. This
is achieved by measuring the change in the T-B signal as the sample is directly pushing
against the probe. This is labeled slope data in the first figure above. The force constant for
the cantilever is supplied by the manufacturer.
Appendix I-1
V 1.1 / LS-AFM Users Guide