
Contact AFM
Optimization of Scanning Parameters
Rev. D
Dimension 3100 Manual
129
8.3.3 Scan Size and Scan Rate
In general, decrease the
Scan rate
as the
Scan size
increases. Use scan rates of
1.5
-
2.5 Hz
for
large scans on samples with tall features. High scan rates help reduce drift, but use high scan rates
only on flat samples with small scan sizes. When first using the system, vary the scan rate enough to
observe a change in the image quality.
8.3.4 Setpoint
The
Setpoint
parameter defines the desired voltage (and, therefore, the desired deflection or force
of the cantilever) for the feedback loop. The setpoint voltage constantly compares to the present
vertical deflection signal of the photodiode to calculate the desired change in the piezo position.
When the gain values are high, and when the
Data type
is set to
Height
, the Z piezo position
changes to keep the photodiode output signal close to the
Setpoint
; therefore, the cantilever
deflection remains nearly constant.
Adjust the
Setpoint
to increase or decrease the cantilever deflection and, therefore, the contact
force of the tip on the sample. The
Force Calibration
command in the
Realtime
>
View
menu
allows you to adjust the setpoint while viewing a graph of the tip position versus the deflection
voltage. Using this procedure, described in detail in
, minimizes the contact force of the
tip on the sample. This is especially important on soft materials such as biological samples.
8.3.5 Lowpass Filter
The
Lowpass filter
invokes a digital, one-pole, lowpass filter to remove high-frequency noise from
Realtime data. The filter operates on the collected digital data regardless of the scan direction.
Settings for this item range from
Off
through
9
.
Off
implies no lowpass filtering of the data, while
settings of
1
through
9
, successively, lower the cut-off frequency of the filter applied to the data
stream. The standard setting is
Off
.
8.3.6 Highpass Filter
The
Highpass filter
parameter invokes a digital, two-pole, highpass filter to remove low frequency
effects such as ripples caused by torsional forces on the cantilever when the scan reverses direction.
As with the
Lowpass filter
, the
Highpass filter
also operates on the digital data stream regardless
of scan direction. This parameter can be
Off
or set from
1
through
9
. Settings of 1 through 9,
successively, lower the cut-off frequency of the filter applied to the data stream. Note that in
removing low frequency information from the image, the
Highpass filter
distorts the height
information in the image. As a result, this filter must be
Off
when accurate height information is
desired. The
Highpass filter
is typically used only for atomic images.
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: ......