
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
, 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
0
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
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
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
).
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
0
(see
). Tracking the variations in
oscillation amplitude while in LiftMode yields an image of the magnetic force
gradients.
∆φ
Drive Frequency
90
0
180
Phase (deg)
∆
F
0
Содержание Dimension 3100
Страница 12: ...xii Dimension 3100 Manual Rev D ...
Страница 20: ...List of Figures xx Dimension 3100 Manual Rev D ...
Страница 72: ......
Страница 106: ......
Страница 118: ......
Страница 214: ...Scanning Tunneling Microscopy STM Etching Tungsten Tips 194 Dimension 3100 Manual Rev D ...
Страница 222: ......
Страница 266: ......
Страница 274: ......