Chapter_12-Materials

Chapter_12-Materials - Ch.12.Materials Materials...

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Materials Ch.12.Materials
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Classification of materials Ch.12.Materials By … properties electrical insulators semiconductors conductors mechanical strength elasticity - etc, etc… optical transparency selective wavelength absorption refraction index magnetic diamagnetic paramagnetic ferromagnetic
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Classification of materials Ch.12.Materials We classify materials according to our needs. Often an unusual combination of properties is needed. Example: transparency and electric conductivity are combined in Indium Tin Oxide (ITO) widely used in LCD displays, plasma screens etc. Example: electric insulation and high thermal conductivity are combined in diamond.
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How the electronic structure of atoms becomes the electronic structure of materials Ch.12.Materials When many atoms interact, then we talk not about orbitals structure, but about electronic band structure. Example of hydrogen atoms: The more modal planes the more antibonding an orbital is.
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Conductivity of metals, semiconductors and insulators Ch.12.Materials The larger is band gap the less electrons can jump up to conductivity band, the lower is conductivity. Conduction band (made out of antibonding orbitals) Valence band (made out of bonding orbitals) Band gap >~3eV means insulator.
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Semiconductors Ch.12.Materials Elemental semiconductors (only four exist at room temperature): C, Carbon (graphite) Si, Silicon Ge, Germanium Sn, Tin (“gray tin” allotrope) Compound semiconductors: GaAs, Gallium Arsenide InP, Indium Phosphide CdTe, Cadmium Telluride ZnSe, Zinc Selenide etc Note: “white tin” allotrope is a metal.
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Chapter_12-Materials - Ch.12.Materials Materials...

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