What is an Atomic Force Microscope (AFM)?
An atomic force microscope (AFM) is an extremely precise microscope that images a sample by rapidly moving a probe with a nanometer-sized tip across its surface. This is quite different than an optical microscope which uses reflected light to image a sample. An AFM probe offers a much higher degree of resolution than an optical microscope because the size of the probe is much smaller than the finest wavelength of visible light. In an ultra-high vacuum, an atomic force microscope can image individual atoms. Its extremely high resolution capabilities have made the AFM popular with researchers working in the field of nanotechnology. Unlike the scanning tunneling microscope (STM), which images a surface indirectly via measuring the degree of quantum tunneling between the probe and sample, in an atomic force microscope the probe either makes direct contact with the surface or measures incipient chemical bonding between probe and sample. The AFM uses a microscale cantilever with a probe tip
An AFM uses nanometer resolution actuators to scan a tiny probe on a surface while maintaining force control. Force-feedback-control loops maintain a constant deflection and therefore a constant force between the probe and the surface. Tools that do not use force feedback are not AFMs and risk increased contact force as the probe deflects over features, which can cause damage to both the sample and probe.
Because the prototype STM relied on electrical flow between tip and sample, it could only be used to examine materials that would conduct at least a small electric current. Since the early 1980s, STMs have evolved into Atomic Force Microscopes (AFMs) that are able to see a wider range of nano-scale samples. The process resembles the original one where a needle-like tip scans across a surface whose topography is read and then translated into a graphic image, but the AFM is able to see samples that are not highly conductive, such as biological samples. Rather than maintaining a constant distance between tip and sample, the tip of an AFM is attached to the end of a highly sensitive cantilevered arm and actually touches the surface of the sample to trace it and generate an image.
