I am using Nanoscope 4 Multimode AFM. The laser clearly reaches (after reflection from cantilever) the photodiode, but SUM signal is always zero. Also Vertical and Horizontal signals do not change. Vertical signal stays around 9 and horizontal signal stays around 3.5. All cable connections are checked. They are good.
Is it possible that you focussed the laser not onto the cantilever, but actually the holder? This can be checked by detuning it perpendicular to the cantilever direction, if there is not much change, it's not on the cantilever.
Try to approach the cantilever to the surface controlling it with the camera. When it is pretty close, it is possible to check the position of the laser and move it precisely to the cantilever. Most likely, it is focused to something else, e.g. to the edge of the chip. In addition, try to play with the mirror tilt.
Good luck!
Thank you Jürgen and Denis for your recommendations. I am sure that laser is focused on the tip of cantilever. I checked by inserting a piece of paper close to photodiode location that laser spot definitely reaches to the photodiode. By tilting mirror, laser reflection from the mirror also varies. However, signals from diode don't change. I am guessing problem is with photodiode connections or inside the AFM base. Nanoscope 4 is too old to get it repaired. So I look forward if someone had such experience and knows about the circuit connections inside AFM base.
Do you know how the SUM, Vert and Horz signals on AFM base display are calculated? I mean are they calculated within the AFM base and displayed there or they are send from the controller to the AFM base display?
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