Selecting A Force Modulation Tip - Veeco Digital Instruments Dimension 3100 Manual

Force Imaging
Force Modulation continued...
Force modulation requires the use of a special optional cantilever holder,
shown in Figure 13.7a. This cantilever holder uses a piezoelectric bimorph to
oscillate the cantilever against a sample surface. The force modulation
cantilever holder is similar to the standard cantilever holder; however, it does
not have a piezo stack used for Tapping Mode operation.
Figure 13.7a Force Modulation Cantilever Holder

13.7.2 Selecting a Force Modulation Tip

The key consideration when selecting a force modulation cantilever is its
spring constant. Ideally, the cantilever must have a spring constant which
compliments the pliancy of the two contrasting materials (or close to the
pliancy of one, but not the other). This way, the tip indents into one material
more than the other providing good force modulation image contrast. If the
tip is so stiff that it indents equally into both materials, or so soft that it
indents neither material, then you will not see contrast (elasticity) in the
force modulation image. Instead, the image will consist primarily of edge
and frictional artifacts. It may take experimentation to find a cantilever that
matches the sample's requirements. For rubber and plastic samples Digital
Instruments Veeco recommends using 225 µm long force modulation (Model
# FESP) silicon cantilevers. For more delicate, biological samples, use 450
µm long silicon cantilevers or silicon nitride cantilevers. For extremely hard
materials, use stiffer ("harder") tips like the 225 µm single crystal silicon
Tapping Mode tips.
13-260 Dimension 3100 Manual Rev. C