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Schematic of the modified KFM setup. For topography feedback, the cantilever is excited at a constant frequency ωd close to resonance. Lock-in amplifiers at ωd ± ωm and ωd ± 2ωm detect sidebands of the cantilever oscillation which contain information about the surface potential and tip–sample capacitance. Both contributions are used by the Kalman-KFM controller for the CPD estimate.
