The influence of lateral forces in scanning force microscopy

A scanning force microscope using interferometric detection of the cantilever deflection is described. The interferometer uses a multimode laser diode with a short coherence length. Despite the poor coherence of the laser, shot-noise-limited detection of displacements is possible, provided that the path difference between the interfering beams is sufficiently small. It will be shown that undesired bending of the cantilever occurs if a lateral force acts on the tip. The adverse influence of this force on image formation will be demonstrated. The results presented here are particularly relevant for applications where objects with steep slopes (e.g., integrated circuits) should be imaged.