Veeco Dimension 3100, Manual

Page: 246 / 376

Force Imaging
Force Calibration (Contact Mode AFM)
226 Dimension 3100 Manual Rev. D
When the Data type is set to Height with the feedback gains set high, the tip tracks the sample
surface with nearly constant deflection of the cantilever. When the cantilever deflection is constant,
the force is constant and the force calculation above determines the contact force between the tip
and the surface over the entire scan area.
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