10
JPK Instruments NanoWizard
®
Handbook Version 2.2
The qualit
y of a phase image can be strongly influenced by varying the setpoint in
intermittent contact mode. The phase should also be corrected when the cantilever
is tuned at the start of intermittent contact mode imaging. There are always some
offsets due to th
e system, which do not depend on the sample interaction. The
phase should be set so that it goes through the centre of the resonance, when the
tip is not interacting with the sample. Then when the tip and sample are brought
together, the phase shift due
to the sample can be distinguished. This operation is
described for the JPK AFM and software system in the NanoWizard® User manual.
2.6 Force adjustment in imaging modes
The force applied to the sample can strongly influence the quality of the image,
particularly on soft sam
ples. It is therefore essential to be informed about the
current force.
Contact mode
If the spring constant of the contact mode cantilever is known it is easy to get
information about the force applied to a sample during imaging. In
the JPK
NanoWizard software, the setpoint can be displayed in units of force if the
cantilever has been calibrated. With this value it is possible to adjust the current
force applied to the sample exactly.
Le Grimellec, C. et al.
75:695-703
surface of living cells by low-
contact-
microscopy”
Intermittent contact mode
In intermittent contact mode it is also possible to determine the average force
applied to the sample during imaging, using the
vertical deflection signal. A useful
reference for this can be found in:
Vié, V. et al.
82:279-
288 (2000).
"Imaging of the surface of living cells
by low-force contact-
mode atomic
force microscopy”
The typical forces applied to a samp
le strongly depend on the particular application
and the type of sample:
1-30 nN Fritz 1994,
~ 5 nN, depending on the material
Nano-manipulation < 1 nN in any case
< 50
0 pN to move molecules in
case of H-bonds
~ 100 pN to move molecules
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