Instruction manual

Force Imaging
Force Calibration (TappingMode)
Rev. B MultiMode SPM Instruction Manual 201
When the piezo turns around and begins to retract, the oscillation amplitude of the cantilever
increases until the tip is free of the surface, leveling off at the free-air amplitude (point 5).
Channel 2 (bottom) in Figure 11.5a plots average cantilever deflection (TM deflection) versus
piezo extension. The deflection signal is low-pass filtered to eliminate the high-frequency
TappingMode oscillation. Even as tip RMS amplitude dampens during its encounters with the
sample surface, the average deflection is unchanged. This condition changes once the tip is so close
to the sample that all oscillation ceases. Extending the piezo still further causes the average
deflection to increase, applying an increasing force to the sample (point 2).
At point 3 in Figure 11.5a, the cantilever begins to deflect. The region between points 3 and 4 may
be hazardous to the tip, because the tip is pressed firmly against the sample surface. Most single
crystal silicon TappingMode tips rapidly become dull in this region, depending upon the hardness
of the sample.
11.5.2 Obtaining a Force Plot (TappingMode)
When obtaining force plots in TappingMode, set up scan parameters so that the reduction of
amplitude is minimal (approximately 25 percent of the free air amplitude). If the amplitude is
reduced to zero, the tip and sample may sustain damage.
To generate a TappingMode force plot of a silicon calibration reference, complete the following
steps:
1. Verify the cantilever holder is loaded with a TappingMode tip.
2. Mount the calibration reference on the SPM stage.
3. Set the AFM mode parameter to Tapping, engage, and obtain a TappingMode image.
Note: You are now in Image mode.
4. To switch to Force Mode, click on the Realtime > View > Force Mode > Calibration or
Advanced option. At least two panels should be visible:
• Main Controls
• Channel 1 Panel
Note: Collectively, these panels control tip-sample interactions. If any panels do not
appear, pull down the Panels menu to select them. The Probe menu offers a
number of tip approach options detailed in the Command Reference Manual.
CAUTION: Use Force Calibration with caution or when it is important to
obtain experimental information shown in Force Calibration.
When using stiff TappingMode cantilevers, it is easy to blunt the
tip with excess contact force during Force Calibration
measurements.