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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 ...
Schemes for dynamic mode operation include frequency modulation where a phase-locked loop is used to track the cantilever's resonance frequency and the more common amplitude modulation with a servo loop in place to keep the cantilever excitation to a defined amplitude. In frequency modulation, changes in the oscillation frequency provide ...
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.
MFM images of 3.2 Gb and 30 Gb computer hard-drive surfaces. Comparison of Faraday-effect image (left) and MFM image (inset, lower-right) of a magnetic film. Magnetic force microscopy (MFM) is a variety of atomic force microscopy, in which a sharp magnetized tip scans a magnetic sample; the tip-sample magnetic interactions are detected and used to reconstruct the magnetic structure of the ...
Joule heating frequency is kept well above 20 kHz to avoid feedback response and to separate topological and thermal effects. The upper limit of the frequency is limited by the decrease of thermoelastic expansion with the inverse power of the modulation frequency and the frequency characteristics of the cantilever arrangement. [4]
The thermal diffusion length (the distance the heat spreads) is inversely proportional to the root of the modulation frequency. Consequently, the spatial resolution achieved by the early AFM-IR approaches was around one micron or more, due to the low modulation frequencies of the incident radiation created by the movement of the mirror in the ...