ENGRI111_HW5 - Yuri Andrade Sylvester November 12, 2004...

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Yuri Andrade Sylvester November 12, 2004 ENGRI 111 yas3@cornell.edu Problem Set #5 Option I 1. Compare and contrast the STM with the AFM. Include a) operating principle, b) type of materials appropriate for analysis, and c) ambient conditions required for analysis. Scanning Tunneling Microscopy works under three basic principles: the piezoelectric effect, feedback loop, and quantum mechanical tunneling. The STM functions by bringing a probe near the surface of the sample and passing an electron voltage differential across it. This piezoelectric probe, a material that forms dipoles charges when compressed, takes advantage of the wave property of light to read an electron signal across a very thin layer (sample). The “tunneling” that is created is due to the probability that the electron beam will go through the thing layer (however, the beam’s amplitude is reduced—this is what creates the tunneling effect). Finally, as the piezo head is brought close to the sample, there are two ways to create an image out of it. One is by having a fixed current and plotting the height difference of the probe, but the
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This homework help was uploaded on 02/03/2008 for the course ENGRI 1110 taught by Professor Giannelis during the Fall '07 term at Cornell University (Engineering School).

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ENGRI111_HW5 - Yuri Andrade Sylvester November 12, 2004...

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