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Magnetic Force Microscopy

Basic MFM Operation

260 Dimension 3100 Manual Rev. D

To correctly track the cantilever phase, the Phase offset parameter must be adjusted. This

automatically occurs in AutoTune; alternatively, Zero Phase can be selected from the Channel 2

panel. The phase curve should appear as in Figure 15.2a, decreasing with increasing frequency and

crossing the center line (corresponding to a 90° phase lag) at the peak frequency. The phase curve

then measures the phase lag between the drive voltage and the cantilever response. Again, vertical

gradients in the magnetic force cause a shift ∆f

in the resonance frequency. In this case, resonance

shifts give rise to phase shifts ∆φ which then give an image of the magnetic force gradients (see

Figure 15.2b).

Note: The Extender electronics give a measure of the phase lag of the cantilever

oscillation relative to the piezo drive. This measurement is monotonic versus

frequency as is the true phase lag in degrees. The Extender measurement has

slightly different nonlinear characteristics vs. frequency. The measurement

technique allows optimal signal-to-noise ratios; however, absolute values of

phase data should be taken as approximate. Users requiring quantitative

measures of force gradient are advised to use frequency modulation (see

Frequency Modulation: Page 263).

Figure 15.2b Shift In Phase at Fixed Drive Frequency

Setting a Drive Frequency for Amplitude Detection

1. Use the AutoTune feature to find the resonance peak.

2. Select the Offset function under the Cantilever Tune pop-down menu to manually move the

drive frequency to the side of the resonance (see Figure 15.2b).

3. Set the Drive Frequency to the steepest part of the resonance curve for maximum

sensitivity.

Note: As the tip oscillates above the sample, a gradient in the magnetic force will

shift the resonance frequency f

(see Figure 15.2c). Tracking the variations in

oscillation amplitude while in LiftMode yields an image of the magnetic force

gradients.

∆φ

Drive Frequency

180

Phase (deg)

∆F

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Dell 3100 Spezifikationen Seite 280