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HAADF-STEM imaging with sub-angstrom probes: a full Bloch wave analysis
Yiping Peng1, Peter D Nellist, Stephen J Pennycook
1Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6030, USA.
Journal of Electron Microscopy
|August 31, 2004
Summary
Researchers used advanced calculations to understand how images form in scanning transmission electron microscopy (STEM) with tiny probes. They discovered a new imaging mode that can reveal 3D atomic structures, paving the way for future STEM advancements.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Electron Microscopy
Background:
- High-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM) is crucial for atomic resolution.
- Understanding image formation with sub-angstrom probes is essential for advancing STEM capabilities.
Purpose of the Study:
- To investigate high-angle annular dark-field image formation for sub-angstrom probes in STEM.
- To explore the transition from projection imaging to depth-slicing imaging in STEM.
Main Methods:
- Full coherent Bloch wave calculation was employed.
- Analysis of image contributions from different atomic depths within a crystal.
Main Results:
- The contribution of 1s bound states and high-angle plane wave states to image formation was analyzed with increasing illumination angle.
- An oscillatory behavior in image contributions from different depths was observed due to the beating between 1s and non-1s states.
- A decrease in oscillation period with decreasing probe size indicates a changeover to a depth-slicing imaging mode.
Conclusions:
- The study reveals a novel depth-slicing imaging mode in STEM.
- This depth-slicing mode has the potential to resolve three-dimensional atomic structures.
- Future aberration-corrected STEM instruments could leverage this mode for advanced structural analysis.