I aligned the AFM using the laser knobs and also had to slightly adjust the AFM head to achieve a good SUM signal. Currently, the head is slightly tilted, as this was the only way I could get acceptable SUM, VERT, and HORZ values(But not touch the piezo tube at all). However, the issue is that these signals are not stable—they fluctuate and sometimes drop to negative values. (At first VERT=0.12, HORZ=0.32, SUM=4.45)Does anyone know what might be causing this or how I can fix it? Our AFM is Bruker Multi-Mode 8
Ensuring stable SUM, VERT, and HORZ signals on a Bruker MultiMode 8 requires that the laser spot is centered on the photodetector and the cantilever is not tilted excessively. If you have to tilt the head to boost SUM, you’ve likely moved the reflected beam off the detector’s “sweet-spot,” so any slight drift or vibration will make VERT and HORZ bounce around—or even go negative when the spot crosses a quadrant boundary.
Key causes and fixes:
By restoring the head to its correct orientation, centering the beam on the detector, and then sequentially maximizing SUM and nulling VERT/HORZ, you should achieve stable, positive quadrant signals without the need for head tilt.
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