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Force Imaging

Force Calibration (TappingMode)

230 Dimension 3100 Manual Rev. D

the sample surface, the oscillation amplitude of the cantilever decreases as the piezo is extended.

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 13.5a 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 13.5a,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.

13.5.2 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

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.

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