Magnetic Force (MFM) Imaging
Advanced Topics
236
MultiMode SPM Instruction Manual
Rev. B
is usually not bene
fi
cial to use
Lift scan heights
much smaller than the surface roughness. Users
are encouraged to experiment for the best images on their samples.
The ultimate lateral resolution of MFM is near 20nm. Resolution is affected by properties of the tip,
including mechanical sharpness and magnetic structure. When in good condition, magnetically-
coated tips routinely give 50nm resolution, and many achieve 30nm or better.
Figure 13.6a
High-resolution magnetic force gradient image of metal evaporated tape at 30nm
Lift scan height
13.6.2 Fine Tuning Interleave Controls
Certain scanning parameters found under
Interleave Controls
can be set to values in the Interleave
(Lift) scan that differ from the values in the main scan. These parameters are enabled by clicking on
the circular
fl
ag to the immediate left of the desired Interleave control, toggling its state from “off”
(gray bullet) to “on” (green bullet). When the
fl
ag is set to “off”, the main scan control parameter
setting takes precedence. When the
fl
ag is set to “on,” the displayed Interleave scan value is active,
overriding the main scan value.
Drive amplitude
For MFM, of particular use is the Interleave
Drive Amplitude
. This parameter can affect a
magnetic force image in a variety of ways.
•
Increasing the
Drive Amplitude
can improve the signal-to-noise ratio when using phase
detection or frequency modulation. This is because intrinsic, low-level noise interferes
less when measuring the phase of a larger cantilever oscillation amplitude and hence
stronger photodetector output. As an illustration, try setting the Interleave
Drive
Amplitude
to
0
; the resulting phase image will be pure noise because measuring the
phase of a non-oscillating cantilever is meaningless.
