Technology

972 B3102005 Diffraction Direction

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1. Diffraction: directions of diffraction <ul><li>For a set of plane (hkl), an incident x-ray </li></ul><ul><li>beam with wavelength…
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  • 1. Diffraction: directions of diffraction <ul><li>For a set of plane (hkl), an incident x-ray </li></ul><ul><li>beam with wavelength  will be diffracted when </li></ul><ul><li>incident, diffracted and plane normal are coplanar </li></ul><ul><li>incident and diffracted beams both make a Bragg angle  B with the (hkl) plane, where  =2d sin  B </li></ul><ul><li>Provided the structure factor for (hkl) plane F(hkl) is not zero </li></ul>
  • 4. Summation over all atoms in a unit cell with positions [x n , y n , z n ] and atomic scattering factor f n (to be defined later).
  • 5. Difference between powder and single crystal diffraction <ul><li>For a single crystal sample, the whole sample is a large, continuous crystal </li></ul><ul><li>A powder sample is an assembly of randomly or partial randomly oriented tiny crystals called grains, it may be in a form of true powder or a piece of solid bulk. </li></ul><ul><li>For single crystal diffraction, both background and characteristic radiations from an x-ray tube are diffracted. </li></ul><ul><li>In powder diffraction, only characteristic radiations are considered because diffraction of weak background radiations by small grains is usually negligibly weak. </li></ul>
  • 6. Single crystal diffraction-Laue method
  • 7. Laue camera
  • 9. (a) Transmission (b) back-reflection Laue W radiation, 30kV, 19mA
  • 10. Powder diffraction
  • 11. Powder diffraction: poles of plane normals for (hkl) planes of all grains distribute uniformly on the surface of the reference sphere
  • 13. Powder diffraction-Pinhole camera
  • 14. Powder diffraction-Hull/Debye-Scherrer camera
  • 15. Powder diffraction-Hull/Debye-Scherrer camera
  • 19. Homework assignment <ul><li>Cullity 3-1 </li></ul><ul><li>Cullity 3-3 </li></ul>
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