Lateral force microscopy (LFM) measures lateral deflections (twisting) of the cantilever that arise from forces on the cantilever parallel to the plane of the sample surface. LFM studies are useful for imaging variations in surface friction that can arise from inhomogeneity in surface material, and also for obtaining edge-enhanced images of any surface.

As depicted in Figure 4, lateral deflections of the cantilever usually arise from two sources: changes in surface friction and changes in slope. In the first case, the tip may experience greater friction as it traverses some areas, causing the cantilever to twist more strongly. In the second case, the cantilever may twist when it encounters a steep slope. To separate one effect from the other, LFM and AFM images should be collected simultaneously.

Figure 4.Lateral deflection of the cantilever from changes in surface friction (top) and from changes in slope (bottom). LFM uses a position-sensitive photodetector to detect the deflection of the cantilever, just as for AFM. The difference is that for LFM, the PSPD also senses the cantilever's twist, or lateral deflection. Figure5 illustrates the difference between an AFM measurement of the vertical deflection of the cantilever, and an LFM measurement of lateral deflection. AFM uses a "bi-cell" PSPD, divided into two halves, A and B. LFM requires a "quad-cell" PSPD, divided into four quadrants, A through D. By adding the signals from the A and C quadrants, and comparing the result to the sum from the B and D quadrants, the quad-cell can also sense the lateral component of the cantilever's deflection. A properly engineered system can generate both AFM and LFM data simultaneously.

Figure 5. The PSPD for AFM (top) and LFM (bottom).