09-4 - E45 Lecture 9/30/09 Chapter 6 - Chapter 6: Diffusion...

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Chapter 6 - E45 Lecture 9/30/09
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Chapter 6 - 2 ISSUES TO ADDRESS. .. How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for some simple cases? How does diffusion depend on structure and temperature? Chapter 6: Diffusion
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Chapter 6 - 3 Diffusion Diffusion - Mass transport by atomic motion Mechanisms Solids – vacancy diffusion or interstitial diffusion
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Chapter 6 - 4 Interdiffusion : In an alloy, atoms tend to migrate from regions of high conc. to regions of low conc. Initially Adapted from Figs. 6.1 and 6.2, Callister & Rethwisch 3e. Diffusion After some time
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Chapter 6 - 5 Self-diffusion : In an elemental solid, atoms also migrate. Label some atoms Diffusion A B C D After some time A B C D
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Chapter 6 - 6 Diffusion Mechanisms Vacancy Diffusion: atoms exchange with vacancies applies to substitutional impurities atoms rate depends on: -- number of vacancies -- activation energy to exchange. increasing elapsed time
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Chapter 6 - 7 Diffusion Mechanisms Interstitial diffusion – smaller atoms can diffuse between atoms. More rapid than vacancy diffusion Adapted from Fig. 6.3 (b), Callister & Rethwisch 3e.
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Chapter 6 - 8 Adapted from chapter-opening photograph, Chapter 6, Callister & Rethwisch 3e. (Courtesy of Surface Division, Midland-Ross.) Case Hardening : -- Diffuse carbon atoms into the host iron atoms at the surface. -- Example of interstitial diffusion is a case hardened gear. • Result: The presence of C atoms makes iron (steel) harder. Processing Using Diffusion
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Doping silicon with phosphorus for n-type semiconductors: • Process: 3. Result: Doped semiconductor regions. silicon Processing Using Diffusion magnified image of a computer chip 0.5 mm light regions: Si atoms light regions: Al atoms 2. Heat it. 1. Deposit
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This note was uploaded on 07/05/2010 for the course CHEME 140 taught by Professor Radke during the Fall '09 term at University of California, Berkeley.

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09-4 - E45 Lecture 9/30/09 Chapter 6 - Chapter 6: Diffusion...

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