Electron Microcopy

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Electron Microcopy

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

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De Brogle wavelength of electrons
100 KeV electron has 3.7 pm wavelength!
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Electron-matter interactions
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Electron-matter interactions
EDXS spectrum
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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.

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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/downl
oads/Interactions.pdf
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Interaction volumes
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Energy dependence
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Energy dependence II
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Some SEM images
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Backscattered electrons
Material contrast
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Basic TEM and SEM
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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

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De Brogle wavelength of electrons
100 KeV electron has 3.7 pm wavelength! Is this
the limit?
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Scattering and diffraction

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

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Experiment
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Braggs Law
constructive interference destructive
interference of waves
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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.

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Unit cells of a cubic crystal 3 different
Bravais lattices
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Directions in a cubic crystal
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Miller indices of crystal planes
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Examples of low index planes
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Important results for cubic systems
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Important results for cubic systems