SPM Fundamentals for the MultiMode
Review of TappingMode AFM
Rev. B
MultiMode SPM Instruction Manual
45
2.5.2 Optimizing the TappingMode AFM Signal after Engagement
The
fi
show the relationship between the RMS and the setpoint
voltages.
There are some basic rules to remember:
1. The setpoint voltage is always lower than the RMS voltage.
2. The difference between the RMS voltage when the tip is off the surface, and the setpoint
voltage dictates the amount of damping or “tapping force.” The larger the difference, the
greater the tapping force.
3. The RMS voltage controls the amount of energy that is in the cantilever (figs. A and D). This
is important to note because some samples are stickier than others. The tip may stick and,
therefore, be held to the sample surface if the RMS amplitude is too small.
The initial setup for TappingMode AFM is to:
4. Tune the cantilever at its resonance.
a. Select
View
>
Sweep
>
Cantilever Tune
(or click the
Cantilever Tune
icon).
For
Auto Tune Controls
, make sure the
Start Frequency
is at
100kHz
and the
End
Frequency
is at
500kHz
.
Target Amplitude
should be
2-3V
.
b. Click
Auto Tune
. A “
Tuning
...” sign should appear and then disappear once Auto Tune
is done. When done, quit the
Cantilever Tune
menu.
c. Set the
Peak Offset
to
3-10 percent
. The
Peak
Offset
is the percentage of the
cantilever’s free-air resonant frequency to be automatically offset. Peak offset is used to
compensate for changes in resonance before engagement due to the tip’s interaction
with the surface after engagement.
Range and Settings
: 0-50 percent. Positive values
offset the
Drive frequency
rightward on the graph.
5. Engage the microscope.
