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Electron Microcopy

Electron Microcopy. 180/198-334 Useful info – many websites. Images here from www.microscopy.ethz.ch/elmi-home.htm. De Brogle wavelength of electrons. 100 KeV electron has 3.7 pm wavelength!. Electron-matter interactions. Electron-matter interactions. EDXS spectrum. Elastic interactions.

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Electron Microcopy

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  1. Electron Microcopy 180/198-334 Useful info – many websites. Images here from www.microscopy.ethz.ch/elmi-home.htm

  2. De Brogle wavelength of electrons 100 KeV electron has 3.7 pm wavelength!

  3. Electron-matter interactions

  4. Electron-matter interactions EDXS spectrum

  5. Elastic interactions No energy is transferred from the electron to the sample. The electron either passes without any interaction (direct beam) or is scattered by the positive potential inside the electron cloud. These signals are mainly exploited in TEM and electron diffraction.

  6. Inelastic Interactions Energy is transferred from the incident electrons to the sample: secondary electrons, phonons, UV quanta or cathodoluminescence are produced; shooting out inner shell electrons leads to the emission of X-rays or Auger electrons. These signals are used in analytical electron microscopy. Excellent manuscript: www.microscopy.ethz.ch/downloads/Interactions.pdf

  7. Interaction volumes

  8. Energy dependence

  9. Energy dependence II

  10. Some SEM images

  11. Backscattered electrons Material contrast

  12. Basic TEM and SEM

  13. Which EM to use? The method that is needed is determined by the question to be solved: Structure (High-Resolution) Transmission Electron Microscopy Scanning Transmission Electron Microscopy (STEM) Electron diffraction (ED) Composition Energy-dispersive X-ray spectroscopy (EDXS) Electron Energy Loss Spectroscopy (EELS) Morphology Scanning Electron Microscopy (SEM) Elemental mapping Electron Spectroscopic Imaging (ESI) STEM + X-ray spectroscopy / EELS SEM + X-ray spectroscopy

  14. De Brogle wavelength of electrons 100 KeV electron has 3.7 pm wavelength! Is this the limit?

  15. Scattering and diffraction • Experiment • Basic structures and how to label them • X-ray diffraction

  16. Experiment

  17. Bragg’s Law constructive interference destructive interference of waves

  18. Crystal symmetries: finite number! 7 crystal systems: The crystal systems are a grouping of crystal structures according to the axial system used to describe their lattice. Each crystal system consists of a set of three axes in a particular geometrical arrangement. Cubic, hexagonal, tetragonal, rhombohedral (also known as trigonal) orthorhombic, monoclinic and triclinic. 14 Bravais lattices: When the crystal systems are combined with the various possible lattice centerings, we arrive at the Bravais lattices. They describe the geometric arrangement of the lattice points, and thereby the translational symmetry of the crystal.

  19. Unit cells of a cubic crystal 3 different Bravais lattices

  20. Directions in a cubic crystal

  21. Miller indices of crystal planes

  22. Examples of low index planes

  23. Important results for cubic systems

  24. Important results for cubic systems

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