TappingMode AFM
Advanced TappingMode AFM Operation
Rev. D
Dimension 3100 Manual
147
The
Setpoint
parameter defines the desired voltage for the feedback loop. The
Setpoint
voltage is
constantly compared to the present
RMS amplitude
voltage to calculate the desired change in the
piezo position. When the gain values are high, as they should be when the
Data type
is set to
Height
, the Z piezo position changes to keep the amplitude voltage close to the
Setpoint
; therefore,
the oscillation amplitude remains nearly constant.
As discussed above, changing the
Setpoint
alters the response of the cantilever oscillation and
changes the amount of force applied to the sample surface.
The force applied by the tip on the sample increases as the setpoint is decreased. To minimize the
force on the sample:
•
Increase the setpoint using the right arrow key on the computer keyboard until the
tip is no longer interacting with the surface. This can be observed by monitoring the
trace and retrace lines in
View
>
Scope Mode
, and by monitoring the
Z Center
Position
display in the Image Monitor. When the tip is no longer interacting with
the surface, the Z Center Position will move to the retracted limit.
•
Slowly decrease the setpoint using the left arrow key on the keyboard until features
appear in the trace and retrace lines in
View
>
Scope Mode
.
The setpoint can also be adjusted by using
View
>
Force Mode
>
Calibrate
. Force calibration
mode is used to compare the amplitude of the cantilever oscillation on the surface to the free-air
amplitude. Other uses of Force Calibration include characterizing the forces on the cantilever tip,
diagnosing the performance, and calibrating the RMS amplitude voltage as a function of the
oscillation amplitude of the cantilever. The use of Force Calibration is described in
9.4.8 Surface Tune
It is often desirable to check the cantilever tune after engaging. You will notice that the
Cantilever
Tune
icon
is grayed out when the tip is engaged. However, you can still access the
Cantilever
Tune
panel by selecting
View
>
Sweep
>
Cantilever Tune
.
A warning appears indicating that cantilever tuning while engaged can result in damage to the tip or
sample. This warning prompts you to enter a
Tip
offset
. This is the distance above the sample that
the tip will be raised before displaying the tuning spectrum. Use a minimum
Tip
offset
of
100
-
200nm
.
Observe the plot of amplitude vs. driving frequency to see if the cantilever tuning curve shifted
during the engagement. The drive frequency can be adjusted to compensate for such a shift by using
the
Offset
command located above the
Cantilever
Tune
plot. The phrase response curve can be
adjusted as well.
Содержание Dimension 3100
Страница 12: ...xii Dimension 3100 Manual Rev D ...
Страница 20: ...List of Figures xx Dimension 3100 Manual Rev D ...
Страница 72: ......
Страница 106: ......
Страница 118: ......
Страница 214: ...Scanning Tunneling Microscopy STM Etching Tungsten Tips 194 Dimension 3100 Manual Rev D ...
Страница 222: ......
Страница 266: ......
Страница 274: ......