Tapping AFM
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Template:Context Tapping AFM is one of several different modes of operation in Atomic force microscope analysis. Atomic Force Microscopy is an imaging technique used frequently to visualise extremely small surface structures. It is possible to image a surface down to Angstrom levels, (that is 10,000,000,000 smaller than a meter!) and generates a 3D map of the sample surface.
The AFM scanning head is a known as cantilever,due to the fact that most of them look like a rectangular lever some hundred of micrometres long and few micrometres thick (several different shapes and sizes are available). One end of the cantilever is steady fixed to a bigger (close to mm size) base, usually called "chip", which has to be fixed to the AFM tip holder. The opposite side of the cantilever is completely free. At this free side a very fine tip comes out from the surface perpendiculary to the cantilever longitudinal axe toward the sample surface that lies below it. Generally the operating distance of the AFM tip is achieved with two subsequent stages. In the first step the AFM tip is approached to the sample by moving it over X-Y-Z directions with very precise stepping motors embedded in the device. After this coarse movement a second and final approaching step is adopted by moving the sample, lying over a piezoelectric actuator, up toward the tip above. At this stage, due to the extremly small distance between the tip and the sample surface, one could clearly see the repulsive/attractive atomic forces effects that give the name to this device.
Instead to be used as a nano-profilometer, as in the classical contact mode in tapping mode the cantilever is let free to oscillate up and down at its resonant frequency. This is due to the effect of the specific forces acting on the cantilever when the tip is extremly close to the surface, Van der Waals force or dipole-dipole interaction. A Tapping AFM evaluation image is therefore provided by a subsequent theory of smooth contacts of the tip with the sample surface. This is an improvement on contact AFM which just dragged the cantilever across, as Tapping AFM will do less damage to the surface and any nanostructures thereon.