Marcus Lay

Associate Professor of Chemistry

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.