= Solution
In <tapping-mode atomic force microscopy>, the cantilever is driven near a <resonance> and its <oscillation> <amplitude> is monitored. Tip-surface interaction changes that <amplitude>. A controller compares it with a chosen setpoint and moves the vertical piezoelectric actuator to reduce the error. The recorded actuator <displacement> supplies the topography channel. A smaller <amplitude> during approach commonly triggers withdrawal and an increased <amplitude> during separation triggers approach, with the actual feedback sign set by the instrument's operating convention. Correct tracking requires enough response <bandwidth> without destabilizing the loop.
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