An atomic force microscope (AFM), also known as a scanning force microscope, is powerful type of scanning probe microscope that measures the local property of the inspected surface in order to give values for height, optical absorption, and magnetic properties. It is able to view images within fractions of a nanometer and is 1000 times more powerful than the optical diffraction limit. An AFM does this by employing a probe that is positioned very close to the surface of the object and then achieves the measurements.
Atomic force microscopes have two different modes of operation: static (contact) mode imaging and dynamic (non-contact) mode imaging. Static mode uses a soft cantilevered beam with a sharp tip at its end. When this is brought in contact with the sample surface, the forces between the tip and the sample deflect the cantilever beam. The deflection is measured by light that reflects from a laser diode from the back of the beam to a pair of photodetectors. This beam is what is used by the AFM in order to retrieve the information on the sample’s surface.
Dynamic mode imaging uses a piezo element rather than a sharp tip. This causes the cantilever beam to oscillate at its exact resonance frequency. When it is brought within 10 to 100 nm from the surface of the sample, the oscillation is then modified by interaction forces between the sample and the piezo tip. The changes caused by the wavering of the beam allow the AFM to generate a map, characterizing the sample beyond just two-dimensional images.
An atomic force microscope has many advantages when compared to a scanning electron microscope. For instance, it provides a pure three-dimensional profile of the surface while the electron microscope can only give a two-dimensional image. Also, the sample for an AFM does not require any treatment like those viewed by an electron microscope, which also prevents it from any possible damage.
There are, however, some disadvantages using an atomic force microscope. A scanning electron microscope can view areas on the order of millimeter by millimeter, but an AFM can only achieve its maximum height on the order of micrometers. Also, a bad selection of tip can cause image artifacts for an AFM, while this is not a problem for an electron microscope.