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Lateral Force Microscopy (LFM)

LFM is a Derivative mode of Contact Mode AFM. The tip is constantly in contact with the sample surface. In LFM, the fast direction of the raster scanning is perpendicular to the AFM cantilever’s long axis, and the cantilever twists about this same axis as the raster scanning proceeds. As a result, in addition to the near-vertical deflection signal which is usually present during contact mode AFM, the detector can also collect a sizeable lateral defection signal from the cantilever‘s twisting motion.

The strength of the lateral deflection signal is related to the friction force between the sample surface and the tip. This is why LFM is sometimes called Friction Force Microscopy.

The LFM signal is highly susceptible to topography variations; the rougher the sample surface, the more topography convolution. To take out this convolution, to decipher the variation in friction force from the topography, two LFM images are often captured side by side. One of these two images is constructed from the detector signal during the trace of each round-trip cycle (of the raster scan). The other, during retrace. Then one of the two images is inverted and subtracted from the other. This reduces the topographic artifacts in the LFM signal.

The LFM signal is one of the those that so far has rarely been used in feedback.

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