SPM Fundamentals for the MultiMode
Control Parameters and Feedback
40
MultiMode SPM Instruction Manual
Rev. B
3. The Vertical Deflection (A-B) voltage differential is sensed by the feedback electronics,
causing a dropped voltage to the Z piezo crystal—the piezo retracts. As the Z piezo retracts,
the cantilever recenters the laser beam onto the photodiode array (A = B).
4. As the tip encounters a decline in the sample topology, the tip drops. This directs more of the
beam onto the “B” portion of the photodiode array. With the “B” photodiode receiving an
increased portion of the laser light, its voltage increases while portion “A’s” decreases (A <
B).
5. Again, the Vertical Deflection (A-B) voltage differential is sensed by the feedback
electronics, increasing voltage to the Z piezo crystal—the piezo extends. As the Z piezo
extends, the tip is pushed down until the laser beam recenters on the photodiode array (A =
B).
