Force Adjustment In Imaging Modes - JPK instruments nanowizard afm Handbook

The quality 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 the 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 samples. 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.
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.
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:
The typical forces applied to a sample strongly depend on the particular application
and the type of sample:
Scanning of living cells 100 pN
1-30 nN
Nano-scribing ~ 5 nN, depending on the material
Nano-manipulation < 1 nN in any case
< 500 pN to move molecules in
case of H-bonds
~ 100 pN to move molecules
10 JPK Instruments NanoWizard
75:695-703 (1998). "Imaging of the
In the JPK
"Imaging of the surface of living cells
le Grimellec, 1998
Fritz 1994,
Radmacher 1997
®
Handbook Version 2.2
Le Grimellec, C. et al. Biophys. J.
surface of living cells by low-force
contact-mode atomic force
microscopy"
Vié, V. et al. Ultramicroscopy
82:279-288 (2000).
by low-force contact-mode atomic
force microscopy"