Additional Imaging Modes
5
Keysight 5500 SPM User’s Guide
5-31
Force Spectroscopy
Force Spectroscopy is an AFM-based technique to measure, and
sometimes control, the polarity and strength of the interaction between
the AFM tip and the sample. Although the tip-sample interaction may be
studied in terms of the energy, the quantity that is measured first is
always the tip-sample force. Unlike imaging, force spectroscopy is
performed mostly when the servo feedback loop is deactivated. In force
spectroscopy, the cantilever-tip assembly acts as a force sensor, as
shown schematically in
.
Figure 7-16
Schematic overview of force spectroscopy
Force spectroscopy is widely used in air, liquids, and different
controlled environments. It may involve functionalized tips to study
specific interactions of conjugated molecules or chemically-modified
surfaces.
In order to quantitatively measure interaction forces, it is necessary to
know the bending stiffness, also referred to as the spring or force
constant, of the cantilever as accurately as possible. This is described in
more detail in
The procedure described below covers general guidelines for Force
Spectroscopy in Contact Mode. It is a user-dependent choice to select
Contact vs AC Mode. The choice of scanning prior to taking force
measurements also is user-dependent.
If AC Mode is chosen, note that the
Contact Mode Sweep
check box in
the Spectroscopy window Advanced tab may be used so the imaging