Instruction manual

Magnetic Force (MFM) Imaging

Advanced Topics

236 MultiMode SPM Instruction Manual Rev. B

is usually not beneﬁcial 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 ﬂag to the immediate left of the desired Interleave control, toggling its state from “off”

(gray bullet) to “on” (green bullet). When the ﬂag is set to “off”, the main scan control parameter

setting takes precedence. When the ﬂag 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.