fs201f08 - EMSE 201 Introduction to Materials Science and...

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Unformatted text preview: EMSE 201 Introduction to Materials Science and Engineering 16 December 2008 Department of Materials Science and Engineering 1 of 9 Case Western Reserve University Name: SOLUTION Final Exam 180 minutes; 200 points; 9 questions; 9 pages; 20% of course grade This exam is to be taken closed-book . You may use a calculator, pencils or pens, eraser, and a straight edge. Handwritten notes on both sides of a single 8.5 11 sheet of paper are permitted. Please turn in your note page with your test. No other form of stored information is permitted. Write all answers on these pages; use the back if more space is needed. Constants : Boltzmanns constant, k B = 1.381 10-23 J K-1 = 8.620 10-5 eV K-1 gas constant, R : 8.314 J mol-1 K-1 Charge on an electron, | q e | = 1.602 10-19 C Avogadros number, N A = 6.023 10 23 mol-1 1) The unit cell of CuInSe 2 , an important photovoltaic material, resembles two unit cells of cubic zinc sulfide (ZnS) stacked on top of each other. The lattice parameters are a = b = 0.5782 nm; c = 1.1620 nm; = = = 90.000 and the actual atomic positions can be approximated as follows: Cu: 0,0,0 1 2 ,0, 1 4 0, 1 2 , 3 4 1 2 , 1 2 , 1 2 In: 0,0, 1 2 1 2 , 1 2 ,0 0, 1 2 , 1 4 1 2 ,0, 3 4 Se: 3 4 , 1 4 , 1 8 1 4 , 3 4 , 1 8 1 4 , 1 4 , 3 8 3 4 , 3 4 , 3 8 3 4 , 1 4 , 5 8 1 4 , 3 4 , 5 8 1 4 , 1 4 , 7 8 3 4 , 3 4 , 7 8 a) (6 points) How many atoms of each type are present in the unit cell? Cu: ___ 4 ___ In: ___ 4 ___ Se: ___ 8 ___ (= the # of sets of coordinates) b) (6 points) Compute the density of CuInSe 2 from the given structure information and your answers for part a). = 4(63.546) + 4(118.69) + 8(78.96) g mol 1 [ ] (0.5782 nm ) 2 (1.1620 nm )(10 21 cm 3 nm 3 )(6.023 10 23 mol 1 ) = 5.815 g cm 3 1 pt formula, 1 pt cell volume, 1 pt atomic weights, 0.5 pt ( x3 ) number of each atom per cell, 1 pt answer, 0.5 pt units. Wrong answers from part a) were inserted in the right places here no penalty. c) Sketch the arrangement of atoms on the following planes of CuInSe 2 . Clearly label the atoms in your sketches. (Note: a point with coordinates x , y , z sits on the ( hk ) plane if hx + ky + z = 1.) i) (7 points) (100) ii) (9 points) (110) EMSE 201 Introduction to Materials Science and Engineering 16 December 2008 Department of Materials Science and Engineering 2 of 9 Case Western Reserve University 1) d) (6 points) The three compound semiconductors in the table below all have the same crystal structure. In light of what you know about the trends in band structure and band-gap energy E g from C to Si to Ge to Sn, qualitatively account for the trend in E g shown by these compounds....
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fs201f08 - EMSE 201 Introduction to Materials Science and...

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