Block diagram of FM-AFM, displaying the cantilever above the sample, the self-oscillation feedback loop, and the amplitude, phase, and frequency detector. Adapted from Ref. 2.
Block diagram of the electronics for the amplitude, phase, and frequency detector (see text).
(a) Amplitude detection as a function of the center frequency of the carrier oscillation. (b) The detected phase modulation for an input signal that is (±10°) phase-modulated with a modulation frequency .
Frequency step-response. (a) Second order PLL with , for (solid line), (dashed), (dotted). (b) Fourth order PLL with theoretical settings (solid) and with second-order settings for and (dashed). (c) Second-order settings for and , with (solid) and (dashed), compared to the equivalent settings (short dash and dotted). (d) Step-response of a commercial frequency detector (Nanosurf EasyPLL).
FM-AFM topograph of the surface of cleaved mica in aqueous solution. The Nanosensors PPP-NCH cantilever (spring constant 42 N/m) was kept at a constant amplitude of 0.6 nm and at a constant frequency shift of with respect to its resonance away from the surface (158 kHz). The tip velocity was 61 nm/s.
Theoretical parameter settings for PI feedback and filters to yield 1 kHz modulation bandwidth with a second and fourth order PLLs (see text). For other bandwidths, note that is inversely proportional, and and are proportional to .
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