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Electric Techniques
Electric Force Microscopy
294 Dimension 3100 Manual Rev. D
Figure 16.2r Amplitude Detection Cantilever Tune
2. For maximum sensitivity, set the Drive frequency to the steepest part of the resonance
curve.
Note: As the tip oscillates above the sample, a gradient in the electric force shifts the
resonance frequency F
0
(see Figure 16.2q). Tracking the variations in
oscillation amplitude while in LiftMode yields an image of the electric force
gradients. You may use either side of the resonance, though we have obtained
slightly better results on the low side, as shown in Figure 16.2q.
When using Amplitude Detection, optical interference may sometimes appear in the lift (electric
force) image when imaging highly reflective samples. Optical interference appears as evenly
spaced, sometimes wavy lines with about 1–2µm spacing superimposed on the lift image. This
occurs when ambient laser light (i.e., light passing around or through the cantilever, then reflecting
off the sample) interferes with laser light reflecting from the cantilever. Interference can be
alleviated by moving the beam spot up a little along the cantilever away from the tip; about one-
third of the cantilever length from the tip usually works well. On the Dimension head, the
adjustment can be refined by carefully moving the beam spot laterally on the cantilever while
scanning until interference fringes are minimized.
Note: Optical interference is essentially eliminated by using phase detection or
Frequency Modulation, available only with the Extender Electronics Module.
Frequency Sweep
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