An Angstrom Introduction to Atomic Force Microscopy

I don’t need an introduction, just take me to your list of microscope products!

Atomic Force Microscopy is an advanced form of scanning probe microscopy capable of viewing and manipulating particles in a sample down to an atomic scale. The AFM consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is a silicon or silicon nitride arm with a tip radius of curvature on the order of nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever according to Hooke’s law. Depending on the situation, forces that are measured in AFM include mechanical contact force, van der Waals forces, capillary forces, chemical bonding, electrostatic forces, magnetic forces,Casimir forces, solvation forces, etc.

Along with force, additional quantities may simultaneously be measured through the use of specialized types of probe. Typically, the deflection is measured using a laser spot reflected from the top surface of the cantilever into an array of photodiodes. Other methods that are used include optical interferometry, capacitive sensing or piezoresistive AFM cantilevers. These cantilevers are fabricated with piezoresistive elements that act as a strain gauge. Using a Wheatstone bridge, strain in the AFM cantilever due to deflection can be measured, but this method is not as sensitive as laser deflection or interferometry. The technology used in atomic force microscopy allows the devices to demonstrate resolutions up to 1000 times larger than the optical diffraction limit of a regular optical microscope.