Realtime Operation
36
Scanning Probe Microscope Training Notebook
Rev. F
16.0 Realtime Operation
The Realtime parameters are located in the control panels which are available in the Panels pull
down menu. The main control panels for topographic imaging are “Scan controls,” “Feedback
Controls,” “Other Controls,” and “Channel 1.”
There are three primary feedback parameters that need adjusting every time you engage the
microscope to capture an image in TappingMode AFM or Contact Mode AFM:
Setpoint
,
Integral
Gain
, and
Scan Rate
.
To demonstrate how these parameters affect the image, examples of TappingMode operation on the
10µm x 10µm pitch calibration grating will be shown. These examples were acquired by viewing
the
Scope Mode
(in the
View
menu), which displays a two-dimensional view (X vs. Z) of the Trace
(left-to-right) and Retrace (right-to-left) scan lines being acquired in Realtime.
Scope Mode
may be used to diagnose how well the tip is tracking the surface. If the feedback
parameters are adjusted optimally, the trace and retrace scan lines should look very similar, but may
not look completely identical.
An optimized scope trace of a 40µm TappingMode scan across the pits of the grating is shown
below.
Figure 16.0a
Scope Trace with Optimized Realtime Parameters
16.1 Setpoint
The Setpoint parameter tells the feedback loop what amplitude (TappingMode) or deflection
(Contact Mode) to maintain during scanning.
Set this parameter so that the smallest amount of force is applied during scanning while still
maintaining a stable engagement on the surface.
If the setpoint is too close to the free air amplitude (TappingMode) or free air deflection (Contact
Mode) of the cantilever, the tip will not trace the topography properly.
This problem will be more pronounced on downward slopes with respect to the scan direction. An
example of this is shown below.