1. Chapter 16: Electron Diffraction
Crystal Structure and Crystallography of Materials
Chapter 16:
Electron Diffraction

2. Electron Diffraction:
a) Accelerate through known potential
⇒ highly monochromatic
b) light, negatively changed particles
⇒ can be focused easily with magnetic lens
c) Easily detected
⇒ visible on fluorescent screen recorded on photographic film
d) High current densities
⇒ W-filament, LaB6-filament
e) Easily scattered (fe ≈ 104 fx-ray)
⇒ Absorption is strong
⇒ Need thin samples (specimen preparation is difficult)
f) Not bulk diffraction: scattering occurs only thin part of the sample

3. Electron Wave Generation:
Thermionic emission
Field-effect emission
where c is the speed of light, which is ~3 x 108 m/s. Therefore, the wavelength at 100 keV, 200 keV, and 300 keV in electron microscopes is 3.70 pm, 2.51 pm and 1.96 pm, respectively.

4. Ewald sphere construction:
∙ λ → small → Large Ewald circle
Thin sample
(hkl)
r*hkl
1/λ 2θ

5. Electron Diffraction in TEM:
λ = Å for 100KeV
In TEM, l is small while d is constant for material, therefore, has small Bragg angle
Therefore, accuracy of d-spacing determination is not as good as X-ray techniques.

6. Electron Diffraction in TEM:
r*hkl
1/λ 2θ
rhkl L T D
Photo

7. Electron Diffraction in TEM:
Alternatively,
Electron diffraction pattern is a direct representation of reciprocal lattice
Single crystal
Polycrystal

13. Phase Identification using Diffraction Pattern in TEM:

14. Phase Identification using Diffraction Pattern in TEM:

15. Convergent Beam Electron Diffraction:
Space group determination
accurate determination of lattice parameter
3-D information
Schematic diagram to show the formation of
convergent-beam electron diffraction patterns

16. FOLZ and HOLZ:

17. FOLZ and HOLZ:

18. FOLZ and HOLZ:

19. Low Energy Electron Diffraction:
Adsorption chemistry
e- : 40 ~ 120eV
LEED
Diffraction Phenomena
1) wavelength 2)
scattering 00 10 20 01 02

20. High Resolution Image (Phase Contrast Image):

21. High Resolution Image (Phase Contrast Image):

22. High Resolution Image (Phase Contrast Image):

23. High Resolution Image (Phase Contrast Image):

24. High Resolution Image (Phase Contrast Image):

25. Crystal Structure and Crystallography
THE END of
Crystal Structure and Crystallography
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