Section 6B Optical

Section 6B Optical - Section 6 Optical Properties (Smith...

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MATE 210 Section 6 Optical Properties (Smith Chapter 15 – skip 15.6 & 15.8) How we can use band theory (electronic structure) to explain colors (physical properties) of some materials?
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MATE 210 E ~ 1/ λ E Electromagnetic radiation spectrum λ = c / ν C = speed of light (3x10 8 m/s) ν = frequency (cycles/sec or hertz)
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MATE 210 Absorption of photons by electron transition: • Metals have a fine succession of energy states • Near-surface electrons absorb visible light Energy of electron In c i d e n t p h o Planck’s constant (6.63 x 10 -34 J/s) freq. of incident light filled states unfilled states Δ E = h ν required! I o f r g y ν Adapted from Fig. 21.4(a), Callister 6e . OPTICAL PROPERTIES OF METALS: ABSORPTION 4.13x10 -15 eV-s
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MATE 210 Electron transition emits a photon. Adapted from Fig. 21.4(b), Callister 6e . Reflectivity = I R /I o is between 0.90 and 0.95. • Reflected light is same frequency as incident. • Metals appear reflective (shiny)! OPTICAL PROPERTIES OF METALS: REFLECTION Energy of electron filled states unfilled states Δ E I R “conducting” electron re-emitted photon from material surface
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MATE 210 Absorption by electron transition occurs if h ν > E gap •I f E gap < 1.8eV, full absorption color is black (Si, GaAs) f E gap > 3.1eV, no absorption colorless (diamond) f E gap in between, partial absorption material has color Adapted from Fig. 21.5(a),
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This note was uploaded on 04/02/2008 for the course MATE 210 taught by Professor Niebuhr during the Spring '05 term at Cal Poly.

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Section 6B Optical - Section 6 Optical Properties (Smith...

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