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Unformatted text preview: Q1. Zone refining is used in semiconductor industry to obtain high purity materials by remelting thin zones of an initial bar. What is the purity of the semiconductor bar after remelting if the initial bar has 0.1 % impurity and k = 0.12. (5 points) Zone refining is a method for purifying the crystals where a narrow region of the crystal is molten and this zone is moved through the crystal, The segregation coefficient, k, is the ratio concentration of an impurity in the solid phase after the zone melting to the concentration of impurity present initially in the liquid phase. (2 points) K= X final /X initial (2 points) X final =k*X initial = 0.12 * % 0.1= 0.012% impurity is present in the solid after the zone melting process. 1 point for showing work Q2. Same as Problem 4.2 in textbook but for spherical clusters containing (a) 5 atoms and (b) 200 atoms. Comment on the frequency of forming such clusters in the liquid. ( 10 points) From the question: V atom = 1.6* 10-29 m 3 SL =0.177 J/m 2 k=1.38*10-23 J/K T m =1356 K N c = 5 and 200 atoms n r = n * exp(-G r /kT m ) where n r is the number of clusters with the radius r, n is the total number of atoms given in that particular volume, G r is the excess free energy associated with the cluster, k is the Boltzmanns constant and T is the melting temperature. (2 points) Volume we are looking at is 1 mm3. If volume of 1 atoms is equal to 1.6 * 10Volume we are looking at is 1 mm3....
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- Spring '10