Substantial crystalline topology in amorphous silicon
J M Gibson1, M M J Treacy, T Sun
1Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
Physical Review Letters
|September 28, 2010
Summary
Unannealed amorphous silicon exhibits significant local crystallinity, with over 50% of the volume showing topological crystalline order up to 2 nm. This finding challenges previous assumptions about amorphous silicon structures.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Amorphous silicon is widely used in electronics and energy applications.
- Previous studies suggested limited local crystalline order in unannealed amorphous silicon.
- Understanding the atomic structure is crucial for optimizing material properties.
Purpose of the Study:
- To investigate the extent of local crystallinity in unannealed amorphous silicon.
- To quantify the topological crystalline order and correlation lengths.
- To challenge existing models of amorphous silicon structure.
Main Methods:
- Utilized electron correlograph analysis, a variant of fluctuation electron microscopy.
- Analyzed coherent nanodiffraction patterns from sputtered amorphous silicon.
- Compared experimental data with simulations for various structural models.
Main Results:
- Coherent nanodiffraction patterns reveal unexpected local crystallinity.
- A substantial volume fraction (>50%) of unannealed amorphous silicon is topologically crystalline.
- Observed correlation lengths of local crystalline order up to 2 nm.
Conclusions:
- Unannealed amorphous silicon possesses significantly more local crystalline order than previously assumed.
- Electron correlograph analysis is sensitive to four-body correlations, enabling the detection of local ordering.
- The findings necessitate a revision of structural models for amorphous silicon.
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