Veeco 004-210-000, Instruction Manual

Page: 225 / 358

Force Imaging
Force Modulation
Rev. B MultiMode SPM Instruction Manual 205
11.6.2 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 in the force modulation image. Instead, the image will consist primarily of edge and
frictional artifacts. It may take experimentation to
fi nd a cantilever that matches the sample's
requirements. For rubber and plastic samples Veeco recommends using 225µm long force
modulation (Model # FESP) silicon cantilevers. For more delicate, samples, use 450µm long silicon
cantilevers or silicon nitride cantilevers. For hard materials, use stiffer tips like the 125µm single
crystal silicon TappingMode tips.
Veeco offers cantilevers with a wide range of spring constants (see Table 11.6a ). Choosing a tip
depends upon how stiff the sample is For samples of unknown hardness, start with a force
modulation cantilever (Model FESP) and determine whether the tip is suf
fi ciently stiff then adjust
accordingly.
Table 11.6a Force Modulation Tips
Cantilever
Model
No.
Cantilever
Length
Spring
Constant
Standard Silicon Nitride NP, DNP 100—200
µ
m 0.01—0.6 N/m
Oxide-sharpened
Silicon Nitride NP-S,
DNP-S 100—200
µ
m 0.01—0.6 N/m
Contact AFM
Etched Silicon ESP 450
µ
m 0.02—0.1 N/m
Force Modulation
Etched Silicon FESP 225
µ
m 1—5 N/m
TappingMode
Etched Silicon LTESP 225
µ
m 20—70 N/m
TappingMode
Etched Silicon TESP 125
µ
m 20—100 N/m
SOFTER
HARDER