© ICSPI Corp. 2007-2021
nGauge AFM User Manual 2.0
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The highest PI values without inducing oscillations in the scan should be used. This is known as
“controller tuning”. Generally, as the scan speed increases, higher PI values are required. Also,
flatter topography (such as a flat piece of mica) will require lower PI values.
During a scan, monitor the Line Profile on the scan page: the forward and reverse lines should
overlap as much as possible. Differences between the forward and reverse lines, and forward
and reverse scans, indicate that the tip is not tracking the topography. Increase the Time Spent
at Each Point and/or the PI gains to compensate.
The Error scan should also be monitored during scanning: the goal is to have as flat an error
image as possible.
5.8.3.1.
PI Settings Example
As an example, three different PI settings are used during the scan of a calibration grating. The
line profiles of the topography are shown on the right.
P = 5
I = 5000
P = 1
I = 1000
P = 10
I = 10000
The default settings (P = 5, I = 5000) show that the sample topography is tracked well: the
image is clear, and the forward and reverse line profiles overlap well.
The low settings (P = 1, I = 1000) show that the sample topography is not tracked well: the
image is blurry, and the forward and reverse line profiles are not overlapping at all.
The high settings (P = 10, I = 10000) show a clear topography image and the line profiles
overlap well. However, inspecting the phase and error images shows that these settings
induced oscillations and the image is noisy. Although the topography image does not appear
noisy, there will be some noise in the topography image due to the controller feedback.
