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
. The
Z
scan start
parameter sets the offset of the piezo travel, while the
Ramp size
parameter de
fi
nes 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
.
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-de
fl
ection signal from the photodiode is
monitored. The force curve, a plot of the cantilever de
fl
ection 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 de
fl
ection 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
