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Effect of electron beam parameters on simulated CBED patterns from edge-on grain boundaries
R M Bokel1, F D Tichelaar, F W Schapink
1Laboratory of Materials Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, The Netherlands.
Journal of Microscopy
|January 5, 2000
Summary
Subnanometer probe convergent beam electron diffraction (CBED) reveals grain boundary symmetry and structure. Electron beam geometry, including probe size and convergence, significantly influences CBED patterns, impacting interface analysis.
Area of Science:
- Materials Science
- Solid-State Physics
- Electron Microscopy
Background:
- Convergent beam electron diffraction (CBED) is a powerful technique for analyzing crystal symmetry and structure.
- Subnanometer probes in CBED enable detailed investigation of localized regions, such as grain boundaries.
- Vertical grain boundaries, oriented parallel to the electron beam, are amenable to CBED analysis for symmetry determination.
Purpose of the Study:
- To investigate the influence of electron beam geometry on convergent beam electron diffraction (CBED) patterns at vertical grain boundaries.
- To understand how imaging conditions affect the symmetry determination of bicrystals and the structure of interface regions using subnanometer probes.
- To identify factors that can lead to deviations from theoretically predicted symmetries in CBED patterns.
Main Methods:
- Simulations of coherent CBED patterns using the multislice algorithm.
- Analysis of the dependence of CBED patterns on defocus distance, probe size, and beam-convergence angle.
- Investigation of the impact of spherical aberration and accelerating voltage on pattern symmetry.
Main Results:
- Subnanometer-probe CBED patterns are significantly influenced by electron beam geometry, including probe size and convergence angle.
- The defocus distance between the probe and specimen midplane critically affects the CBED pattern of edge-on interfaces.
- Spherical aberration, especially at lower accelerating voltages and with increased beam convergence, can reduce the observed pattern symmetry compared to theoretical predictions.
Conclusions:
- Accurate determination of interface structure using subnanometer-probe CBED requires careful consideration and control of imaging conditions.
- Electron beam geometry parameters, such as probe size, convergence, and defocus, play a crucial role in the interpretation of CBED patterns.
- Deviations from expected symmetry due to aberrations highlight the importance of optimizing experimental setups for reliable structural analysis.