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Force Imaging

Force Modulation

240 Dimension 3100 Manual Rev. D

18. Optimize Drive amplitude for Force Modulation imaging. The amount of contrast and the

quality of both Height and Amplitude images depends on the Drive amplitude. In general,

increasing the Drive amplitude provides greater contrast in the force modulation image.

Note: It is possible to set the Drive amplitude too high. If this occurs, the Drive

amplitude no longer increases the contrast in the amplitude image. Instead, the

overall contrast in the force modulation image remains roughly constant, but

you will observe more artifacts in the image. For example, if the drive

amplitude is too high, the force modulation image becomes contaminated by

“edge effects” or “friction effects.” Operate at the lowest drive amplitude that

gives sufﬁcient contrast to examine the sample. Low drive amplitudes also help

extend the life of the cantilever tip and reduce sample damage.

Procedure for Optimizing Drive Amplitude

1. Start with a small Drive amplitude value of 50mV.

2. Increase the Drive amplitude with the right arrow keys or type in new values. The contrast

of the Amplitude (force modulation) image increases.

3. Continue increasing the Drive amplitude until sufficient contrast appears in the Amplitude

image. If the Drive amplitude increases to the point where contrast is no longer improving,

reduce the Drive amplitude slightly.

Note: Force modulation contrast also depends on the Setpoint. In general, if using a

larger Setpoint (larger tracking force) use a smaller Drive Amplitude to obtain

good force modulation images without artifacts. If it is difﬁcult to obtain a clear

force modulation image that is free of artifacts, try reducing or increasing the

Setpoint and then optimizing the Drive Amplitude.

4. Readjust gains (if necessary).

5. The value of the Drive amplitude may also affect the Contact Mode AFM image, causing

the system to go into unwanted oscillations. If the Drive amplitude changes by a large

amount, readjust the Integral gain and Proportional gain. Set the gains as high as possible

to track the sample topography, but not so high that they cause oscillation due to the bimorph

oscillation.

Sometimes an oscillation that appears in the data will be due to “aliasing” as described in the next

section. If you cannot adjust gains to eliminate unwanted oscillations without compromising the

height image’s quality, see Section 13.6.5.

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Dell 3100 Spezifikationen Seite 260