Coherence between Diffracted Electron Beams in TEMs
- Practical Electron Microscopy and Database -
- An Online Book -

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This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.

 

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The influence of diffraction on the quantum wave of charged particle in electron and ion microscopes is negligibly small because the refraction index does not change significantly over the distance of several wavelength.

Therefore, in ideal EMs (electron microscopies), e.g. in point-like monochromatic TEM (transmission electron microscopy), we can assume that the electron beam is generated from a point-like source and the energy variation ΔE is zero. This electron source is fully coherent. Even though the TEM specimen can be a crystal and thus, the incident electron beam k0 is split into different Bragg-diffracted components kg, resulting in a characteristic phase shift, the phase relation between the diffracted beams is maintained (the elastic electron scattering is coherent) [1]. This coherent relationship induces an interference pattern forming a HRTEM image.

Kikuchi lines are more pronounced in CBED patterns than in SAD patterns because: i) CBED patterns arise from a smaller, and thus more uniform region than SAD patterns; and ii) The enhancement of coherent and elastic scattering in CBED.

 

 

[1] L. H. Schwartz and J. B. Cohen, (1987) Diffraction from Materials, 2nd ed., Berlin: Springer-Verlag.

 

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