Channelling/Diffraction Enhanced X-ray Emission in EDS Measurements
- Practical Electron Microscopy and Database -
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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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Similar to X-ray diffraction (XRD) measurements, anomalously high X-ray intensities in EDS measurements are generated when the specimen is close to Bragg condition, because the X-ray emission is preferentially orientated emission. For an amorphous material, the X-ray emission from all elements is increased with the incident electron beam current and thus the observed X-ray ratio between different elements is not affected, while for ordered materials (e.g. crystals) significant variation in the ratio of X-ray intensities can be induced. In the later case, the variation originates from the effect of channelling enhanced X-ray emission. This phenomenon occurs when the thin, single crystal is orientated so that the specific atom sites in a crystalline compound are parallel to the incident electron beam if a parallel (not convergent) illumination is used.

In some cases we need to minimize the effects of channelling enhanced emission, e.g. in elemental quantifications and thus, measurements should be performed with the crystalline orientation far away from the exact Bragg conditions and with a highly convergent beam rather than a parallel beam. Furthermore, the use of a large convergence angle, as occurs in the STEM mode with a focused probe also minimizes the problem.

 

 

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