Instruction manual

Force Imaging
Force Calibration (Contact Mode AFM)
Rev. B MultiMode SPM Instruction Manual 191
Motor
The Motor menu allows you to withdraw or manually control the tip position using the stepper
motor. Selecting Step Motor opens a dialog box containing the following buttons:
• Tip Up: This command moves the tip up by the SPM step size displayed inside the
window.
• Tip Down: This command moves the tip down by the SPM step size displayed inside
the window.
11.4 Force Calibration (Contact Mode AFM)
11.4.1 Obtaining a Good Force Curve
Figure 11.4a Typical Force Calibration Curve
To minimize or calculate the contact force between the tip and sample, obtain a good force curve
which shows the typical features displayed in the example curve in Figure 11.2c. However, the
force curve rarely looks “typical” immediately after invoking Force Calibration mode. This
section discusses general approach adjustments to improve force curves obtained after engaging the
microscope.
The basic approach to obtaining a good force curve entails adjusting the Z motion of the piezo
relative to the sample (with the Z scan start and Ramp size parameters) and shifting the graph
(with the Setpoint parameter) so the pull-off point of the tip displays on the graph. In general, use
the following steps to obtain a good force curve:
1. Engage and verify the tip is tracking the surface. Then switch to Force Calibration mode.
2. Maximize the Deflection Limit parameter in the Feedback Controls panel.
(Z Scan start -Ramp size)
Setpoint
Slope = Volts of Deflection/nanometers (or volts) of piezo travel
+
Cantilever Off Surface
(Z Scan start) Z Piezo Voltage
12
3
4
5
6
V
csmin
Cantilever Deflection
Voltage