Prof Richard Haverkamp, of Massey University, explains how an atomic force microscope works. Includes a short animation of the basic mechanism.
Point of interest: A piconewton is unit of force equal to 10−12 newtons.
DR RICHARD HAVERKAMP
The atomic force is different from the scanning tunnelling in that you don't pass a current, you just sense force between a sharp little needle and the atoms on the surface. So you've got a little flexible bar with a sharp tip on it, and on the back its coated with gold and you shine the light on it, and you get a lever effect when the light shines on it, a little lever moves just a tiny bit, the light moves a long distance.
So you’re measuring the force between a tiny tip and a sample, and those forces are piconewtons. So an atomic microscope differs from a scanning tunneling, in that you have got a little flexible lever with a sharp tip on the end you just measure that physical force.