Atomic Force Microscopy (AFM)
Atomic Force Microscopy (AFM) uses an optical lever technique to amplify the motion of the cantilever and tip as they are raster-scanned across a surface. Light from a laser reflects off the end of the cantilever and strikes a detector. This light moves on the detector as the cantilever moves over the surface of the sample. The result is great magnification of the tip motion (~2000 fold).
In AFM, the tip is mounted on a piezo-electric scanner (see figure below). When a voltage is applied to a piezo-electric material, it produces a mechanical pressure that is directly proportional to the magnitude of the voltage. This gives the user very precise control over the movement of the tip. Then, a controller can be used to apply constantly changing potentials to the X, Y and Z piezos to cause the cantilever to raster scan a small area of the sample. During this process, a feedback loop acts to minimize changes in deflection of the cantilever by causing the z-piezo (see below) move up and down. This movement of the z-piezo yields the height information in the AFM image.