AFMs are the most sensitive displacement sensors of all with submicron “spot” sizes. They can theoretically measure displacements down to small fractions of an Angstroms confined to areas with nanometer dimensions.
The Atomic Force Microscope uses a small cantilever with an approximately 20 nm diameter tip as its sensor probe. The usual operation of the AFM is to measure surface topology with sub-angstrom level resolution by placing the tip close to or in contact with the sample surface and monitoring the displacement of the cantilever caused by the surface as the tip is scanned across it. The control system actuates a bulk piezoelectric actuator attached to the cantilever in order to hold the cantilever at the same height above, or with the same contact force against, the sample surface. | 
