Nano Labs (Lec4 AFM) - Atomic Force Microscope(AFM Nano...

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Nano Lab MAE C187L/C287L Atomic Force Microscope (AFM) Nano Labs, MAE C187L/C287L
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Nano Lab MAE C187L/C287L Atomic Force Microscope (AFM) AFM is a microscope that can “see” nanoscale surface structure through a scanning tip. An AFM includes: (1) A tip (2) An cantilever (3) A position detector
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Nano Lab MAE C187L/C287L Invention of AFM When a tip is scanning a surface, the surface will push the tip up and down, the force experienced by tip can be detected, and we “see” the surface through the force on the tip. The question is how sensitive we can measure the force? 1986 Binnig, Quate and Gerber (Swiss IBM, Stanford Univ) invented atomic force microscope (AFM)
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Nano Lab MAE C187L/C287L AFM Tip An AFM tip is a small sharp tip made from Si, carbon nanotube etc. with its end radius as small as a few nm.
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Nano Lab MAE C187L/C287L Atomic Force Typical forces between tip and sample range from 10 - 11 to 10 -6 N. Depending on the situation, forces that are measured in AFM include mechanical contact force, Van der Waals forces, capillary forces, chemical bonding, electrostatic forces, magnetic forces, etc. Van der Waals Force
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Nano Lab MAE C187L/C287L Could We Measure Atomic Force? Typical spring constants of cantilevers are between 0.001 to 100 N/m. The deflection of the cantilevers can be measured down to ~ 0.1 Å accuracy. Therefore, imaging is possible.
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Nano Lab MAE C187L/C287L Cantilever Tip Cantilever Laser Position Detector
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Nano Lab MAE C187L/C287L How is the force measured? When the force is experienced by the tip and cantilever, the cantilever will be bended, and the shift of the laser reflection spot can be detected by an optical sensor.
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Nano Lab MAE C187L/C287L Beam Deflection Detection Laser beam from a solid state diode is reflected off the back of the cantilever and collected by a position sensitive detector. The signal is collected by a differential amplifier, which is proportional to the deflection of the cantilever Detection sensitivity is < 1 A
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Nano Lab MAE C187L/C287L How To Scan? SPM scanners are made from a piezoelectric material that expands and contracts proportionally to an applied voltage Most SPMs use tube-shaped piezoceramics because they can create three-dimensional positioning. Four electrodes cover the outer surface of the tube, while a single electrode covers the inner surface.
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Nano Lab MAE C187L/C287L How To Scan? Electrodes are attached to the outside of the tube, segmenting it electrically into vertical quarters, for +x, +y, -x, and -y travel. An electrode is also attached to the center of the tube to provide motion in the z direction (not shown). The maximum scan size that can be achieved with a particular piezoelectric scanner depends upon the length of the
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