AFM Workshop TT-AFM User Manual page 38

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Page 38
Appendix F: Optimizing GPID Parameters
The scan parameters such as the set-point voltage and the PIO parameters are adjusted as the line scan is
being made. The goal in adjusting the scan parameters is to have the probe track the surface. The probe is
tracking the surface when the Z error signal image has a minimal signal. Establishing the optimal conditions
requires practice and some intuition. .
'
. .
When first learning to operate an AFM, it is helpful to operate with a test sample and adjust the PIO settings to
see the effect on the Z voltage and the Z error signal, as shown in figure below.
Settings
Feedback off
Feedback
gains too low
Feedback
gains too high
Feedback
"perfect"
It
It
It
It
It
It
t
Effect
Probe bends with
the topography
~
Probe not following
lv
11-------,'hO IOPPPh'
Result on image
l,--­
Probe oscillating
Deflection
Height
Deflection
Height
Deflection
Height
Deflection
Height
t
t
t
t
t
if?)