Diffraction of Plane Wave from Multiple Point Sources
- 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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There are multiple scattering sources in a lattice structure in a TEM specimen so that the diffracted beams from each atomic plane will interfere with one another. Figure 2631 shows a periodic array of scattering centers (atoms in a crystal) and the electron wave with a specific wavelength in an electron beam is incident on each scattering center. Therefore, every atom can be considered as a new wave source and generates secondary wavelets with the same wavelength as the incident wave. These wavelets interfere, inducing a strong direct (0th order) beam and several orders of coherent (diffracted) beams scattered at different angles. Constructive interference occurs when the waves are in-phase (coherent), while destructive interference occurs when they are out-of-phase. In terms of scattering angle, the first constructive interference is a 0th order wave which proceeds in the same direction as the incident wave. The higher-order of “in-phase” waves (called a series of diffracted beams) propagate in the directions at some specific angles with respect to the incident wave, for instance, 1st order in red and 2nd order in pink in Figure 2631.

Diffraction of a plane wave from multiple point sources

Figure 2631. Diffraction of a plane wave from multiple point sources in a TEM specimen.

 

 

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