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ema 4125 HW -3 2011

# ema 4125 HW -3 2011 - EMA 4125 Homework#3 Due September...

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EMA 4125: Homework #3 Due September 28 th , 2011 Q1. Write down the Fick’s first law of diffusion. Show the units for each quantity. Write down the assumptions used to derive the first law Q2. For materials engineers it is necessary to understand the implications of the various diffusion mechanisms. Explain the following terms and identify the materials conditions (e.g pristine material, alloys, etc.) that these terms may be applicable a) Self diffusion b) Intrinsic diffusion c) Inter diffusion coefficient d) Vacancy diffusion e) Interstitial diffusion Q3. In crystalline silicon the diffusion coefficients of boron (p– type dopant) and bismuth (n- type dopant) in single crystal silicon are 2.5 * 10^-17 m 2 /sec. and 1.8 * 10^-20 m 2 /sec., respectively at 1250 K. At 1666 K their diffusion coefficients increase to 1* 10^-14 m 2 /sec. and 1 x 10^-15 m 2 /sec., respectively. Assuming Arrhenius equation can be used to determine the diffusivity as a function of temperature- (i) Calculate the activation energy and frequency factor for each dopant in crystalline silicon.

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ema 4125 HW -3 2011 - EMA 4125 Homework#3 Due September...

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