Force Imaging
Force Calibration (TappingMode)
Rev. B
MultiMode SPM Instruction Manual
199
11.5 Force Calibration (TappingMode)
Force Mode
allows the imaging of forces between the tip and surface, including chemical bonds,
electrostatic forces, surface tension and magnetic forces. In TappingMode, you can observe forces
by measuring changes in tip RMS amplitude, phase, or TM de
fl
ection. The user may collect force
plots in one of two forms:
Force Plot
and
Force Volume
. The two forms are similar, with
Force
Volume
generating a map of many individual force plots. To produce high-quality force plots, it is
necessary to precisely control tip position relative to the surface.
11.5.1 Force Plots
When performing
Force Plot
in TappingMode, the piezo moves to the center of the current X-Y
scan, then turns off the X-Y scan motion. Next, a triangular waveform is applied to the Z electrodes
of the piezo tube resulting in the sample moving up and down relative to the oscillating tip. The
same Z-axis piezo motion occurs in Contact Mode AFM force plots. However, in TappingMode, the
force plot is a graph of the piezo’s extension versus oscillating tip amplitude, phase or TM
de
fl
ection, instead of de
fl
ection or friction.
Uses of
Force Calibration
in TappingMode include characterizing forces on the cantilever tip,
diagnosing SPM performance, calibrating the RMS amplitude or TM de
fl
ection, and con
fi
guring
Lift
Mode
. For example, as the oscillating tip is brought closer to the surface, tip motion is
dampened, which shows as an immediate drop in amplitude. When plotted, the graph resembles
.
CAUTION:
Because TappingMode cantilevers are relatively stiff,
Force Mode
can potentially damage the tip and/or surface. Before using Force
Calibration, read and understand the following section.
