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# hw2_solution - ECE 440 Homework 2 Solution Due Friday Fall...

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ECE 440 Homework 2 Solution Fall 2009 Due: Friday, September 11, 2009 1. Gold, one of the best conductors, has a face-centered cubic lattice. The lattice constant is 4.08Å. The force holding the lattice together is the metallic bonding, i.e. an interaction between positive ion cores and surrounding free electrons in the so-called electron sea. Assume that each gold atom contributes one electron to the electron sea. Determine the free electron density in gold, and compare that to the electron density of intrinsic silicon, which is 1.5x10 10 /cm 3 . Answer: We can compute using what we know about FCC: 3 22 3 0 10 9 . 5 1 * 08 . 4 * ) 4 ( cm e atom electron A cell unit cell unit atoms n e × = = Or using the properties of gold that we know: m glyph817 glyph817 V n atom a e ρ ρ = = Where: mole atoms number Avogadro glyph817 atoms per electrons of number glyph817 m Kg mole gram Mass Atomic m a atoms 23 3 3 10 022 . 6 1 10 3 . 19 7 . 196 × = = = = × = = = ρ 3 22 23 3 3 10 9 . 5 197 . 0

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hw2_solution - ECE 440 Homework 2 Solution Due Friday Fall...

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