Force Imaging
Force Modulation
Rev. D
Dimension 3100 Manual
235
Table 13.6a
Force Modulation Tips
13.6.3 Operating Principle
Force modulation mode is very similar to Contact Mode AFM. The NanoScope system scans the
cantilever over the sample surface while trying to keep the cantilever deflection constant. The
deflection setpoint determines the average deflection during operation. In addition, the cantilever is
oscillated up and down by a piezoelectric bimorph in the tipholder so that the tip indents slightly
into the sample surface as it is scanned across the surface. The NanoScope system records the
amplitude of the cantilever, motion, which indicates the relative indentation of the tip into the
surface. For softer samples the tip penetrates further into the surface resulting in a smaller change in
the angle of the cantilever. A small change in angle results in a small measured amplitude which
displays as a bright area on the image. For harder samples the tip penetrates less into the surface
resulting in a larger change in angle of the cantilever. A large change in angle causes a large
measured amplitude which displays as a dark area on the image.
13.6.4 Force Modulation Procedure
This section gives instructions for operating in
Force Modulation
mode.
1. Choose the
Force Modulation
profile under
Microscope
>
Profile
.
2. Verify that the
Microscope
mode parameter in the
Other Controls
panel is set to
Tapping
and the
SPM Feedback
in the
Feedback Controls
panel is set to
TM Deflect
.
3. Load the special force modulation cantilever holder with a cantilever. The procedure for
loading a cantilever is exactly the same as for operation with the standard air cantilever
holder.
Note:
earlier in this chapter to help you choose
an appropriate cantilever.
Cantilever
Model
No.
Cantilever
Length
Spring
Constant
Standard Silicon Nitride
NP, DNP
100—200µm
0.01—0.6 N/m
Oxide-sharpened
Silicon Nitride
NP-S,
DNP-S
100—200µm
0.01—0.6 N/m
Contact AFM
Etched Silicon
ESP
450µm
0.02—0.1 N/m
Force Modulation
Etched Silicon
FESP
225µm
1—5 N/m
TappingMode
Etched Silicon
LTESP
225µm
20—70 N/m
TappingMode
Etched Silicon
TESP
125µm
20—100 N/m
SOFTER
HARDER
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