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An atomic force microscope using optical interferometry as the lever detection method is presented. Topographic images of graphite with 50-Å lateral resolution have been obtained using repulsive contact forces. Images of the graphite surface showing the atomic periodicity were also recorded; in this case, the image contrast does not represent surface topography, but rather variations in the lateral frictional force on the tip. Images using attractive electrostatic forces to map topographic features are shown. The instrument has also been operated as a scanning tunneling microscope while simultaneously measuring the contact force between the tip and a graphite surface.
Erlandsson et al. (Tue,) studied this question.