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Band structure information from soft x-ray spectroscopy

Band structure information from soft x-ray spectroscopy. Andrew Preston andrew@preston.co.nz. Materials World Network. NML at BU. NML at BU. Novel materials Nitrides: Rare-earth nitrides, III-V Oxides: TCO, SOFC, low dimensional Organics X-ray spectroscopy Absorption (XAS)

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Band structure information from soft x-ray spectroscopy

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  1. Band structure information from soft x-ray spectroscopy Andrew Preston andrew@preston.co.nz

  2. Materials World Network

  3. NML at BU

  4. NML at BU • Novel materials • Nitrides: Rare-earth nitrides, III-V • Oxides: TCO, SOFC, low dimensional • Organics • X-ray spectroscopy • Absorption (XAS) • Emission (XES) • Resonant emission (RXES, RIXS) • Photoemission (XPS) • Angle resolved photoemission (ARPES)

  5. NML at BU • Synchrotron based • National Synchrotron Light Source – X1B • Advanced Light Source – BL7, BL12 • MAXlab – 5II

  6. Spectroscopy

  7. Spectroscopy

  8. X-ray absorption (XAS) Empty Ef Filled

  9. X-ray absorption (XAS) Empty Ef Filled

  10. Site selectivity

  11. Typical XAS

  12. Curtain! XAS Kotani, Shin Rev. Mod. Phys. 73, 203 (2001)

  13. ZnO XAS

  14. Zinc oxide

  15. Zinc oxide • Zn = [Ar]3d104s2 O = [He]2s22p4

  16. ZnO electronic structure • Density functional theory • HSE03 XC functional • GW correction • Essential for correctly locating the Zn 3d electrons, bandgap

  17. ZnO electronic structure

  18. Zinc oxide

  19. ZnO electronic structure

  20. Dipole approximation • Orbital selection • Δl = ±1 • s -> p

  21. ZnO electronic structure

  22. ZnO electronic structure

  23. ZnO XAS

  24. ZnO anisotropy

  25. ZnO anisotropy O p orbitals ZnO crystal

  26. Orbital selection

  27. ZnO anisotropy

  28. ZnO XAS

  29. X-ray emission (XES) Empty Ef Filled

  30. Curtain! XES Kotani, Shin Rev. Mod. Phys. 73, 203 (2001)

  31. Dipole approximation • Orbital selection • Δl = ±1 • p -> s

  32. ZnO XAS and XES

  33. ZnO XAS and XES

  34. ZnO XAS and XES

  35. XES anisotropy?

  36. XES and XPS

  37. XAS and XES • Optical processes (photon in/photon out) • Magnetic fields • Insulators • Dirty surfaces • Capping layers • Advantages over photoemission in some domains

  38. Selection rules • Site selection • Orbital selection • Dipole selection rule (conservation of angular momentum) • Orbital selection 2 • Linear polarization + crystalline anisotropy • Dispersion?

  39. Resonant x-ray emission (RXES) Empty Ef Filled

  40. RXES • Kramers-Heisenberg • Coherent 2nd order process • XAS from |i> to |m>, followed by XES from |m> to |f> • Selection rule: conservation of crystal momentum!

  41. RXES = coherent and incoherent XES

  42. RXES

  43. RXES

  44. RXES Kotani, Shin Rev. Mod. Phys. 73, 203 (2001)

  45. ZnO anisotropy

  46. ZnO RXES

  47. ZnO RXES

  48. ZnO RXES

  49. ZnO pxy band structure

  50. ZnO pz band structure

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