Force Imaging
Force Modulation
Rev. D
Dimension 3100 Manual
239
Note:
You may also change the
Drive Frequency
by clicking on the
Drive
Frequency
parameter on the control monitor’s
Feedback Controls
panel, and
entering a new value.
Note:
Bimorph resonance should be between
5 kHz
and
30 kHz
. If peaks are found at
a much higher frequency, these are cantilever resonances,
not
bimorph
resonances.
o. Record the
Drive frequency
. This is the resonant frequency of your force modulation
bimorph.
9. Select
Stage
>
Locate Tip
or click the
Locate Tip
icon.
10. Select
Stage
>
Focus Surface
or click the
Focus Surface
icon.
11. Check the scan parameters
Scan speed
,
Scan size
and
Integral gain
to verify they are
reasonable for Contact Mode AFM imaging. Also, it may be desirable to readjust the detector
mirror adjustment screws if the
Vertical Difference
signal has drifted from the value
originally set.
12. For the
Channel 1
image, select
Data Type
>
Height
. Select
Data Type
>
Amplitude
for
the
Channel 2
image. The multi-image capability views both the topography data and the
force modulation (elasticity) data at the same time.
13. Reduce the
Drive Amplitude
to
0
before engaging.
14. Select
Motor
>
Engage
.
Note:
The motor moves the SPM head down towards the sample and stops once the
cantilever deflects to the chosen
Setpoint
. Under some conditions the system
may “false engage” before the cantilever actually reaches the surface. Increase
the
Setpoint
and engage again.
15. Adjust the
Integral Gain
,
Proportional Gain
,
Setpoint,
and
Scan Speed
to obtain a good
topography (
Height
) image. For force modulation operation, set the
Integral Gain
and
Proportional Gain
to values of
1
-
10
and set the
Setpoint
as low as possible using the cursor
keys (or by typing in new
Setpoint
values) until the cantilever pulls off the surface and the Z-
center voltage jumps to -
220V
.
16. Record the
Setpoint
value where the cantilever pulls off the surface (the “pull-off value”).
17. Increase the
Setpoint
until the cantilever touches the surface, and an image appears. Then
decrease the setpoint to a value just above the value where the pull-off occurred.
Note:
If you adjust the
Setpoint
very close to the pull-off value, imaging perform
with the smallest and least damaging force. However, in this condition imaging
may be more unstable, as the cantilever may pull off the surface unexpectedly.
The setpoint value affects the force modulation contrast. Examine the contrast
of the force modulation image.
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