Instruction manual

Force Imaging
Force Calibration (Contact Mode AFM)
Rev. B MultiMode SPM Instruction Manual 197
Force calculations are not as straightforward on images captured with the Data type set to
Deflection. When collecting deflection data, the feedback gains are ideally set low so the sample
stays at a nearly constant position relative to the cantilever holder. In this case, the cantilever
deflection (and therefore the force applied to the sample) varies as features on the surface are
encountered. The contact force can be calculated by adding the deflection data from the image to
before multiplying by the spring constant: F = k (deflection image data + d). Note that the
Sensitivity parameter must be accurate—that is, previously determined and entered—before the
deflection data will be accurate.
A simple alternative to calculating force is to follow these five steps:
1. Set sensitivity using the mouse.
2. Change units to metric.
3. Count vertical units from Setpoint to VCS min.
4. Multiply by Deflection Scale (adjacent to plot).
5. Multiply by the spring-constant, k.
d