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46- “Atomic force microscopy”

Atomic force microscopy (AFM) is a very-high-resolution type of scanning probe microscopy (SPM) which is designed to measure characteristics such as height, friction and magnetism using a probe. To get an image, the probe reviews a small region of the sample and simultaneously measures the local specification. The atomic force microscope is undoubtedly the most diverse and powerful microscopic technology for studying samples at nanoscopic scale. An atomic force microscope not only provides 3D topographic images but also provides various types of surface measurements required by researchers and engineers. It can also produce atomic resolution images at angstrom’s scale with minimal surface preparation.
The AFM has a cantilever with a sharp pointed tip that runs on the surface of the sample. As the tip approaches the surface, the gravitational force between the surface and the tip causes the cantilever to be tilted toward the surface. When the cantilever gets closer to the surface so that the tip is in contact with the surface, the repulsive force will overcome and cause the cantilever to be removed from the surface. A laser beam is used to detect cantilever deviations from the surface (getting away or approaching). By reflecting the beam from the upper level of the cantilever, any deviation will cause a slight change in the direction of the beam’s reflection. By recording these changes, a surface topography can be obtained. The sensitivity of this technique is so high that can show the vertical deviations much less than 0.1 nm, so stairs with only one atom height can easily be detected. The lateral separation is also possible on this scale. Therefore AFM has a real three-dimensional atomic separation.



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