Observations of specimen morphology effects on near-zone-axis convergent-beam electron diffraction patterns

Area of Science:

• Materials Science
• Crystallography
• Electron Microscopy

Background:

• Convergent-beam electron diffraction (CBED) is a powerful technique for analyzing crystal structures.
• Interpreting CBED patterns typically relies on the unit cell's symmetry.
• Specimen morphology can influence diffraction patterns, but this is often overlooked.

Purpose of the Study:

• To investigate symmetry breakages in CBED patterns caused by specimen morphology.
• To demonstrate that specimen symmetry, not just unit cell symmetry, dictates CBED pattern intensity distributions.
• To establish a method for deducing nanoscale morphological information from CBED patterns.

Main Methods:

• Analysis of near-zone-axis CBED patterns from an aluminum-copper-tin alloy with nanoscale voids.
• Application of a geometric argument based on the multislice theory.
• Examination of CBED patterns where the electron beam interacts with void facets at non-perpendicular angles.

Main Results:

• Observed symmetry breakages in CBED intensity distributions that cannot be explained by unit cell symmetry alone.
• Attributed observed symmetries directly to the morphology of nanoscale voids within the aluminum matrix.
• Successfully explained diffraction pattern symmetries using specimen geometry and multislice theory.

Conclusions:

• CBED patterns can provide information about specimen morphology, particularly in the beam direction (the third dimension).
• Specimen shape and void symmetry play a crucial role in determining CBED pattern characteristics.
• This technique offers a novel approach to characterizing nanoscale features in materials using transmission electron microscopy.