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The cantilever in the AFM is a reference electrode that forms a capacitor with the surface, over which it is scanned laterally at a constant separation. The cantilever is not piezoelectrically driven at its mechanical resonance frequency ω 0 as in normal AFM although an alternating current (AC) voltage is applied at this frequency.
Diagrams showing the effect of cantilever movement with the photodetector represented by the square with quadrants labelled A, B, C and D. Torsional bending of the cantilever (left) leads to a change in lateral deflection and (right) vertical displacement of the cantilever leads to a change in vertical deflection
A change in the force applied to a cantilever can shift the resonance frequency. The frequency shift can be measured with exquisite accuracy using heterodyne techniques and is the basis of ac-coupled cantilever sensors. The principal advantage of MEMS cantilevers is their cheapness and ease of fabrication in large arrays.
The qplus sensor-based cantilevers are much stiffer than regular silicon cantilevers, allowing stable operation in the negative force regime without instabilities. [33] An added benefit of the stiff cantilever is the possibility to measure STM tunneling current while performing the AFM experiment, thus providing complementary data for the AFM ...
Bimorph cantilevers used as micromechanical linear actuator: 1 - substrate 2 - piezoelectric layer 3 - passive layer 4 - mechanical contact area 5 - track
The prior art includes an RF MEMS frequency tunable fractal antenna for the 0.1–6 GHz frequency range, [18] and the actual integration of RF MEMS switches on a self-similar Sierpinski gasket antenna to increase its number of resonant frequencies, extending its range to 8 GHz, 14 GHz and 25 GHz, [19] [20] an RF MEMS radiation pattern ...
In this mode the cantilever is oscillated at a resonant frequency of the cantilever and the AFM tip is held such that it only senses with long range electrostatic forces without entering the repulsive contact regime. In this non-contact regime, the electric force gradient causes a shift in the resonance frequency of the cantilever.
Figure 3. In the flat region, the sensor can be modeled as a voltage source in series with the sensor's capacitance or a charge source in parallel with the capacitance. Piezo sensors typically use the flat region of the frequency response (the "usable region" in Figure 1) between the high-pass cutoff and the resonant peak.