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Lattice-resolution contrast from a focused coherent electron probe. Part II
S D Findlay1, L J Allen, M P Oxley
1School of Physics, University of Melbourne, Parkville, Vic. 3010, Australia.
Ultramicroscopy
|March 8, 2003
Summary
This study refines scanning transmission electron microscopy (STEM) by matching probe wave functions to crystal wave functions. This improves computational efficiency and offers insights into convergent probe physics in perfect crystals.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Electron Microscopy
Background:
- Previous work matched probe and crystal wave functions in STEM by equating the entire wave function.
- Existing Bloch wave formulations use plane wave boundary conditions, which may not fully capture probe characteristics.
Purpose of the Study:
- To link the whole wave function matching approach to Bloch wave formulations.
- To investigate the physics of convergent probes in perfect crystals using an improved computational model.
- To compare different simulation methods for STEM imaging.
Main Methods:
- Matching the entire wave function across the boundary between probe and crystal.
- Employing a fine reciprocal space mesh to accommodate transverse momentum components of the probe.
- Developing a structure matrix (A) that accounts for probe characteristics.
- Block diagonalizing the A-matrix for perfect crystals to enhance computational efficiency.
Main Results:
- The refined method provides insights into reciprocity in coherent imaging and the small aperture limit for contrast.
- Numerical equivalence was demonstrated between the Bloch wave method and the multislice method for incoherent lattice contrast.
- The study sets the stage for comparing Bloch wave, multislice, and frozen phonon models.
Conclusions:
- The whole wave function matching approach, when combined with a fine reciprocal space mesh, offers a computationally efficient and physically insightful model for STEM.
- This method provides a unified framework for understanding convergent probe behavior in STEM simulations.
- Further comparisons with established methods like the frozen phonon model are warranted.