Crystal thickness and extinction distance determination using energy filtered CBED pattern intensity measurement and...

Area of Science:

• Materials Science
• Crystallography
• Electron Microscopy

Background:

• Conventional methods for determining single crystal thickness and extinction distance often rely on graphical analysis of fringe spacing.
• These methods can be limited in precision and applicability, particularly for unknown crystalline materials.

Purpose of the Study:

• To develop and validate a new, precise method for measuring the thickness and extinction distance of single crystals.
• To improve upon existing techniques by leveraging computed analysis of Convergent Beam Electron Diffraction (CBED) patterns.

Main Methods:

• Utilized computed adjustment of measured and calculated CBED pattern intensity profiles.
• Employed dynamical diffraction theory with a two-beam approximation, defining specimen thickness (t) and extinction distance (χig) as key parameters.
• Performed parameter refinement through minimizing the difference between experimental and calculated intensity profiles using Origin 5.0 software.

Main Results:

• The new method accurately determined specimen thickness and extinction distance with a precision of approximately 0.2%.
• Demonstrated improved precision in measured extinction distance dispersion compared to conventional Kelly and Allen techniques.
• Successfully measured the extinction distance for silicon (0 0 4 reflection) at 197 keV as 161±3 nm, closely matching theoretical values.

Conclusions:

• The developed method provides a fast, simple, and automatable approach for accurate crystal thickness and extinction distance determination.
• Offers enhanced precision and accuracy over existing methods, with improved sensitivity for thinner specimens.
• Applicable to unknown crystals without the need for prior extinction distance calculations.