MT1-Review - Midterm 1 Review Solid State Physics Solid...

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Midterm 1 Review
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Solid State Physics ± Solid matter forms can form in random (amorphous) or orderly (crystalline) fashion. ± Crystalline matter can be classified by the types of bonds they form. ² Metallic, ionic, covalent, atomic, molecular. ± The bonds determine the electronic energy structure of the crystal.
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Band Structure ± As individual atoms or molecules form bonds and larger crystals, their discrete energy levels split finer and finer until they form virtual continuums (energy bands) separated by prohibited levels (energy gaps). ± The available electrons of the atom fill these bands with the ones tightest bound to the nucleus having the lowest energy. ± The electrical and optical properties of the material is determined by the higher energy electrons and whether they fill the highest occupied band (valence band) completely or partially.
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Semiconductors ± If the valence band is only partially filled we have a conductor. ± If it is completely filled we have an insulator or a semiconductor. ± Semiconductors are insulators with smaller band gaps and can be controllably doped with an acceptor (p-type) or donor (n-type) to change their conduction and the type of carriers. ± p- and n-type semiconductors can be put together to form diodes, LEDs, transistors or solar cells.
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Defects ± Many electrical, optical, mechanical and thermal properties of materials are determined by the defects they have. ² Vacancies (point defects) are thermal in nature. ² Edge dislocations (line defects) arise from film growth problems. ² Grain boundaries (surface defects) are seen in polycrystalline films.
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Thermodynamics ± The possibility of a chemical reaction is determined by thermodynamics. ² If ' G > 0, the process is forbidden. ² If G < 0, it is allowed. ² If G = 0, there is equilibrium. ± In a chemical reaction involving three substances, in most cases, the Gibbs Free Energy can be taken as, STH G ' ±' ' where G is the change in the Gibbs Free Energy, H is the change in the enthalpy, S is the change in entropy ° ¿ ° ¾ ½ ° ¯ ° ® ­ ' ' b eq B a eq A c eq C aa a RT G G ,, , 0 ln where where the a i ³s are the activities (kind of a thermodynamic concentration) and G 0 is the standard state value of G .
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Example ± Ellingham Diagrams ² Plots of ' G 0 vs. T can be used to determine a preferred reaction. ² Consider the choice of depositing either Al or Cu on SiO 2 at 400 K. T G 0 (kcal) 32 3 2 2 3 4 O Al O Al o ± 2 2 SiO O Si o ± CuO O Cu 2 2 2 o ± 400 -230 -175 -45 To get the relevant reduction equations for Si, add either the Al or Cu equation to the Si equation and algebraically eliminate O 2 . Apply the same factor to the free energy.
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MT1-Review - Midterm 1 Review Solid State Physics Solid...

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