Instruction manual

Force Imaging
Force Calibration Mode
Rev. B MultiMode SPM Instruction Manual 179
As a result of the applied voltage, the sample moves up and down as shown in Figure 11.2c. The Z
scan start parameter sets the offset of the piezo travel, while the Ramp size parameter defines the
total travel distance of the piezo. Therefore, the maximum travel distance is obtained by setting the
Z scan start to +220V, with the Scan size set to 440V.
Figure 11.2b represents a tip-sample-piezo relationship on a MultiMode system. The piezo
positions the sample below the tip, then extends a known distance closer to the tip (the Scan size).
Figure 11.2b Relationship of Z Scan Start and Scan Size
As the piezo moves the sample up and down, the cantilever-deflection signal from the photodiode is
monitored. The force curve, a plot of the cantilever deflection signal as a function of voltage applied
to the piezo tube, shows on the display monitor. The control panel detailing parameters for
controlling the microscope in Force Calibration mode displays on the control monitor.
Force Calibration mode is frequently used to adjust and calculate contact forces between the
cantilever and the sample. Other uses of Force Calibration mode include characterization of the
forces on the cantilever tip, diagnosing AFM performance, and determination of the sensitivity of
the cantilever deflection voltage in terms of voltage applied to the piezo. If used correctly, Force
Calibration mode provides a variety of useful information.
Z scan start
Ramp size
Tip
distance fixed
by adjustment
screws
Z = Z Scan Start - Ramp Size Z = Z Scan Start