TappingMode AFM
Advanced TappingMode AFM Operation
146
Dimension 3100 Manual
Rev. D
9.4.4 Optimization of Scanning Parameters
The user is encouraged to review
which discusses parameter optimization for Contact
AFM.
9.4.5 Data Type
Data type
is the first parameter to set because the values of other parameters depend on it. The
Data type
parameter in the
Channel 1
,
Channel 2
and
Channel 3
panels selects the type of data
collected by the system.
Height
data corresponds to the change in piezo height needed to keep the
amplitude of the cantilever constant.
Amplitude
data measures the change in amplitude relative to
the amplitude setpoint.
The scan parameters required to collect good
Height
data
are different than the optimal parameters
for
Amplitude data
. To collect
Height
data
while tracking the sample surface with minimal
change in the tip’s oscillation amplitude, the feedback gains must be high.
Amplitude data
collected with high feedback gains is the derivative of the height.
Amplitude
mode
provides a sensitive edge detection technique. With the dual screen mode it is possible to
capture both
Height
and
Amplitude data
simultaneously.
9.4.6 Gain Settings
The
Integral
and
Proportional
gains
on the
Feedback Controls
panel must be high enough to
force the feedback system to track the sample surface. When scanning in TappingMode, set the
Integral
and
Proportional
gains
to lower values than those values used in Contact mode. The
Proportional gain
can usually be set 30%-100% higher than the
Integral gain
. To optimize the
gains, increase the
Integral gain
until the piezo begins to oscillate (feedback oscillation usually
occurs with
Integral gains
of
1
-
2)
, then eliminate the oscillations by reducing the gain with two or
three clicks of the left arrow key. Repeat the process for the
Proportional gain
.
9.4.7 Scan Size, Scan Rate, and Setpoint
The
Scan size
,
Scan rate
, and
Setpoint
values effect data output differently. As in Contact mode,
decrease the
Scan rate
as the
Scan size
is increased. Use
Scan rates
of
0.5
-
1.0 Hz
for large scans
on samples with tall features. High scan rates help reduce drift, but only use them on flat samples
with small scan sizes.
CAUTION:
Do not conduct TappingMode microscopy with low feedback gain
values, as this will cause damage to both the tip and sample. The
maximum amplitude of the cantilever oscillation is not sufficient to
track tall features.
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