Chapter 10 & 11

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

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

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

33. Temperature Dependence of Resistivity

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

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

36. 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

37. 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

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

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

40. 5A doping in a 4A lattice Almost free, but not quite Sandin, “Modern Physics” 5A in 4A lattice 3A in 4A lattice

41. Bands in n-doped Semiconductor 9.44

42. Bands in p-doped Semiconductor 9.45

44. Superconductivity First observed Kamerlingh Onnes 1911

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

46. Discovery of “Type II” --- CuxOy

47. 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

48. Superconductor Classifications

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

50. 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