Frequency Modulation

For certain applications you may need to use the frequency modulation LiftMode techniques. This activates a feedback loop, which modulates the Drive Frequency to keep the cantilever phase lag at 90 degrees relative to the drive, corresponding to resonance. The frequency Data Type displays the resulting shift in Drive Frequency in Hz, and gives the most direct, quantitative image of force gradients.

To enable frequency modulation, the procedure is the same as for obtaining an MFM image with Phase Detection, with the following modifications:

1. Input Feedback (Interleave panel): Frequency
2. Channel 2 Image Data Type: Frequency

Try a Data scale (frequency shift) of approximately 10 Hz.

3. If necessary, adjust the frequency modulation gains in the Interleave panel.

As with topography gains, the scan can be optimized by increasing the gains to maximize feedback response, but not so high that oscillation sets in.

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