175x Filetype PPT File size 0.26 MB Source: sjctni.edu
Atomic Force Microscope (AFM) Introduction The atomic force microscope (AFM) was invented in1986 by Binnig, Quate and Gerber. The AFM raster scans a sharp probe over the surface of a sample and measures the changes in force between the probe tip and the sample. 2 Working Concept The physical parameter probed is a force resulting from different interactions. Thus, an AFM image is generated by recording the force changes as the probe (or sample) is scanned in the x and y directions. The sample is mounted on a piezoelectric scanner, which ensures three-dimensional positioning with high resolution. The force is monitored by attaching the probe to a pliable cantilever, which acts as a spring, and measuring the bending or "deflection" of the cantilever. 3 Principle • The AFM consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. • The cantilever is typically silicon or silicon nitride with a tip radius of curvature on the order of nanometers. • When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever according to Hooke's law. • Depending on the situation, forces that are measured in AFM include mechanical contact force, van der Waals forces, capillary forces, chemical bonding, electrostatic forces. 4 Working concept of AFM 5 Basic set-up of an AFM The ability of an AFM to achieve near atomic scale resolution depends on the three essential components: (1) a cantilever with a sharp tip, (2) a scanner that controls the x-y-z position, and (3) the feedback control and loop. 6
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