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Chapter 10 & 11

Chapter 10 & 11. Molecular Bonds & Band Structure Semiconductors Superconductivity Lasers. Harris, “Modern Physics” Eisberg & Resnick, “Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles ”. Outline. 10.1 Molecular Bonding (~2 atoms together) pages 334-342

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Chapter 10 & 11

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  1. Chapter 10 & 11 Molecular Bonds & Band Structure Semiconductors Superconductivity Lasers Harris, “Modern Physics” Eisberg & Resnick, “Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles”

  2. Outline • 10.1 Molecular Bonding (~2 atoms together) • pages 334-342 • 11.1 Band Theory (~1023 atoms together) • pages 387-392 • 11.2 Semiconductor Theory • mainly pages 395-398 • 10.5 Superconductivity • pages 362-381 • 10.2 Stimulated Emission & Lasers • mainly pages 342-347

  3. MOLECULES(~2 atoms together)Ionic & Covalent BondsMolecular ExcitationsRotation, Vibration, Electric

  4. Ionic Bonds RNave, GSU at http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html#c4

  5. Ionic Bond Energy Balance

  6. Covalent Bonds RNave, GSU at http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html#c4

  7. Covalent Bonding SYM ASYM spatial spin ASYM SYM spatial spin space-symmetric tend to be closer Ref: Harris

  8. Ionic Characteristics Crystalline solids High melting & boiling point Conduct electricity when melted Many soluble in water, but not in non-polar liquids Covalent Characteristics Gases, liquids, non-crystalline solids Low melting & boiling point Poor conductors in all phases Many soluble in non-polar liquids but not water Ionic vs Covalent Bond Properties

  9. Molecular ExcitationsRotational Spectra w moment of inertia rotational A.M.

  10. Rotational Spectra Ref: Harris

  11. Molecular ExcitationsVibration

  12. Vibration (in an Electronic state)

  13. Ocean Optics: Nitrogen N2 ~ 0.3 eV ~ 0.4 eV http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/atspect.html

  14. Electronic + Vibration Ref: Harris

  15. Electronic + Vibration + Rotation 2.550 eV 2.656 eV electronic excitation gap vibrational excitation gaps Ref: Eisberg&Resnick

  16. Electronic + Vibration + Rotation Vibrational Well Vibrational Well 2.656 eV depth ~ 0.063 eV electronic excitation gap vibrational excitation gaps Ref: Eisberg&Resnick

  17. Electronic, Vibration, Rotation Electronic ~ optical & UV ~ 1 – 3 eV Vibration ~ IR ~ 10ths of eV Rotation ~ microwave ~ 1000ths of eV Harris 9.24

  18. Some Molecular Constants Notes: a) vibrational frequency in table is given as f / c b) moment of inertia in table is given as hbar2/(2I) / hc

  19. SOLIDS(~10x atoms together)

  20. Isolated Atoms

  21. Diatomic Molecule

  22. Four Closely Spaced Atoms conduction band valence band

  23. Two atoms Six atoms Solid of N atoms ref: A.Baski, VCU 01SolidState041.ppt www.courses.vcu.edu/PHYS661/pdf/01SolidState041.ppt

  24. Sodium Bands vs Separation Rohlf Fig 14-4 and Slater Phys Rev 45, 794 (1934)

  25. Copper Bands vs Separation Rohlf Fig 14-6 and Kutter Phys Rev 48, 664 (1935)

  26. Differences down a column in the Periodic Table: IV-A Elements same valence config Sandin

  27. Conductors vs insulators vs semiconductors

  28. Conductors & Insulators at T=0 Harris9.35a

  29. Conductors & Insulators at T>0 Harris9.35b

  30. Semiconductors&Superconductors Rex Thorton p 395-398 p 362-381

  31. Two atoms Six atoms Solid of N atoms ref: A.Baski, VCU 01SolidState041.ppt www.courses.vcu.edu/PHYS661/pdf/01SolidState041.ppt

  32. Temperature Dependence of Resistivity

  33. Conductors & Insulators at T=0 Harris9.35a

  34. Conductors & Insulators at T>0 Harris9.35b

  35. Conductors Resistivity r increases with increasing Temp Temp t but same # conduction e-’s r Semiconductors & Insulators Resistivity r decreases with increasing Temp Temp t but more conduction e-’s r

  36. Semiconductors ~1/40 eV gap • Types • Intrinsic – by thermal excitation or high nrg photon • Photoconductive – excitation by VIS-red or IR • Extrinsic / Doped • n-type • p-type ~1 eV gap ~1-4 eV gap ~0.01 eV gap with adjustable charge carrier density

  37. Intrinsic Semiconductors Silicon Germanium RNave: http://hyperphysics.phy-astr.gsu.edu/hbase/solcon.html#solcon

  38. Doped Semiconductors lattice p-type dopants n-type dopants

  39. 5A doping in a 4A lattice Almost free, but not quite Sandin, “Modern Physics” 5A in 4A lattice 3A in 4A lattice

  40. Bands in n-doped Semiconductor 9.44

  41. Bands in p-doped Semiconductor 9.45

  42. Superconductivity First observed Kamerlingh Onnes 1911

  43. Note: The best conductors & magnetic materials tend not to be superconductors (so far) Superconductors.org Only in nanotubes

  44. Discovery of “Type II” --- CuxOy

  45. Superconductor Classifications • Type I • tend to be pure elements or simple alloys • r = 0 at T < Tcrit • Internal B = 0 (Meissner Effect) • At jinternal > jcrit, no superconductivity • At Bext > Bcrit, no superconductivity • Well explained by BCS theory • Type II • tend to be ceramic compounds • Can carry higher current densities ~ 1010 A/m2 • Mechanically harder compounds • Higher Bcrit critical fields • Above Bext > Bcrit-1, some superconductivity

  46. Superconductor Classifications

  47. Type I Bardeen, Cooper, Schrieffer 1957, 1972 “Cooper Pairs” e- e- Symmetry energy ~ -0.01 eV Q: Stot=0 or 1? L? J?

  48. Popular Bad Visualizations: correlation lengths Sn 230 nm Al 1600 Pb 83 Nb 38 Pairs are related by momentum ±p, NOT position. Best conductors  best ‘free-electrons’  no e- – lattice interaction  not superconducting

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