An atomic force microscope (AFM) uses a nanometer-sized probe to view a sample by direct contact or measuring chemical bonds. It offers higher resolution than a light microscope and can view individual atoms. AFMs can operate in a liquid or gaseous environment and are popular in nanotechnology research. They use a microscale cantilever with a probe tip and operate in static or dynamic mode. AFMs require a high vacuum environment and a rigid cantilever for high resolution. They have similar resolution to scanning tunneling microscopes in ultra-high vacuum.
An atomic force microscope (AFM) is a highly accurate microscope that views a sample by rapidly moving a probe with a nanometer-sized tip across its surface. This is very different from a light microscope which uses reflected light to image a specimen. An AFM probe offers a much higher degree of resolution than a light microscope because the size of the probe is much smaller than the finest wavelength of visible light. In an ultrahigh vacuum, an atomic force microscope can view individual atoms. Its extremely high resolution capabilities have made AFM popular with researchers working in the field of nanotechnology.
Unlike the tunneling microscope (STM), which visualizes a surface indirectly by measuring the degree of quantum tunneling between the probe and the sample, in an atomic force microscope the probe makes direct contact with the surface or measures the incipient chemical bond between probe and sample.
AFM uses a microscale cantilever with a probe tip whose size is measured in nanometers. An AFM operates in one of two modes: contact (static) mode and dynamic (oscillating) mode. In static mode the probe remains stationary, while in dynamic mode it oscillates. As the AFM is approached or contacts the surface, the cantilever deflects. Usually, above the cantilever is a mirror which reflects a laser. The laser reflects off a photodiode, which precisely measures its deflection. As the wobble or position of the AFM tip changes, it is recorded in the photodiode and an image is created. More exotic alternatives are sometimes used, such as optical interferometry, capacitive sensing, or piezoresistive (electromechanical) probe tips.
Under an atomic force microscope, individual atoms look like fuzzy blobs in a matrix. To provide this degree of resolution requires a very high vacuum environment and a very rigid cantilever, which prevents it from sticking to the surface at close range. The disadvantage of a rigid cantilever is that it requires more accurate sensors to measure the degree of deflection.
Scanning tunneling microscopes, another popular class of high-precision microscopes, usually have better resolution than AFMs, but one advantage of AFMs is that they can be used in a liquid or gaseous environment whereas an STM needs to operate top empty. This allows imaging of wet samples, especially biological tissue. When used in ultra-high vacuum and with a rigid cantilever, an atomic force microscope has similar resolution to an STM.
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