TappingMode AFM
Advanced TappingMode AFM Operation
Rev. D
Dimension 3100 Manual
143
9.4
Advanced TappingMode AFM Operation
This section discusses the more subtle aspects involved in operating the Dimension 3100 in
TappingMode.
9.4.1 Resonating Techniques
Without a thorough understanding of principles associated with cantilever resonating techniques,
you may generate distorted data. Understanding the
Cantilever Tune
process and the effects of
real-time scan parameters is critical for effective operation of the microscope. It is also important to
understand similarities and differences between
Force Calibration Mode in Contact AFM
and
Force Calibration Mode in TappingMode
9.4.2 Cantilever Oscillation
The response of the cantilever to inputs plays an important role in the operation of the Dimension
3100 SPM while in TappingMode. There is an important trade-off between the response time of the
cantilever and the force applied to the sample. The cantilever does not respond instantly to
perturbations in oscillation amplitude. The cantilever drive system pumps energy gradually into the
cantilever oscillation.
illustrates a typical response curve of the cantilever amplitude as
a function of time. To demonstrate the conflicting requirements, the performance of the system is
analyzed at two operating points.
Figure 9.4a
Cantilever Response Curve
At Setpoint 1 the operating point is only slightly lower than the free oscillation amplitude. This has
the advantage of dissipating very little energy to the sample surface. The disadvantage is that the
system takes longer to recover from a given perturbation in the amplitude. Consider the situation
where the tip travels off a step with a height of
∆
x. At Setpoint 1 it takes longer for the amplitude of
the cantilever oscillation to increase; therefore, the feedback system is slow in responding to the
error created by going off of the step. At operating Setpoint 2 the cantilever amplitude builds up
∆
x
∆
x
Free Amplitude
∆
t
2
∆
t
1
Time
Cantilever Vibration Amplitude
Setpoint 1
Setpoint 2
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