Veeco Dimension 3100, Руководство пользователя

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Contact AFM
Optimization of Scanning Parameters
128 Dimension 3100 Manual Rev. D
Collect Deflection data with low feedback gains to ensure the piezo remains at a constant position
relative to the sample. In this case, the tip and cantilever are deflected by the features on the sample
surface. The output fluctuations in the cantilever deflection voltage from the top and bottom
photodiode segments are recorded as a measure of the variation in the sample surface.
Deflection
data is not automatically calibrated in units of distance. You must measure the sensitivity using the
procedures discussed in
Chapter 13 .
Deflection data collected with high feedback gains essentially equals the derivative of the height.
This is commonly referred to as the error-signal. The error-signal provides a sensitive edge-
detection technique and can be very helpful in visualizing fine details in topography that are
difficult to see in regular height data. Using two channels, you must capture both height and
deflection data simultaneously.
Deflection (error-signal) data alone does not yield quantitative
height information.
8.3.2 Gain Settings
The Integral , Proportional , and LookAhead gains in the Feedback Controls panel determine the
feedback on the piezo height. The feedback loop keeps the deflection signal constant by adjusting
the height of the piezo tube. If the gains are high, as they should be for
Height data, the piezo
height changes to keep the cantilever deflection nearly constant. If the gains are low, as they should
be for topographical
Deflection data, the cantilever deflects from its nominal position as it
encounters features in the sample.
In general, set the gain settings as follows:
1. Set the Integral and Proportional gain s to 2 - 3 to start scanning.
2. To optimize the gains for Height data, increase the Integral gain until the piezo begins to
oscillate, then eliminate the oscillations by reducing the gain with 2-3 clicks of the left arrow
key.
3. Repeat the process for the Proportional gain .
Note: Piezo oscillations typically cause high frequency wavy lines in the Realtime
image. Piezo oscillations are more easily observed in
View > Scope Mode .
4. For Deflection data, engage the microscope with the gains high, then lower them as much as
possible without losing contact with the sample once the system begins scanning.
5. Set the LookAhead gain to 0.7 initially for samples with step-like features oriented
perpendicular to the fast scan direction. Otherwise, it should be left at 0.00.
Note: The LookAhead gain includes information from the previous scan line to
determine the current gain setting.