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Published on: May 15, 2017
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Understanding subtle changes in medium-range order in amorphous silicon.
Paule Dagenais1, Laurent J Lewis, Sjoerd Roorda
1Département de Physique et Regroupement Québécois sur les Matériaux de Pointe (RQMP), Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada.
Summary
Thermal relaxation in amorphous silicon (a-Si) can increase medium-range order. Our study shows that enhanced short-range order, not just dihedral angle changes, drives these structural modifications.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Chemistry
Background:
- Amorphous silicon (a-Si) exhibits complex structural disorder.
- Thermal relaxation is known to induce structural changes in a-Si.
- Experimental studies observe a new peak in the radial distribution function (RDF) of a-Si after annealing.
Purpose of the Study:
- To investigate the relationship between short-range atomic rearrangements and the emergence of medium-range order in amorphous silicon.
- To determine the primary cause of the observed RDF peak at 4.7 Å upon thermal relaxation.
- To analyze the correlations between dihedral and tetrahedral angles in amorphous silicon.
Main Methods:
- Detailed study of the radial distribution function (RDF) of an amorphous silicon model.
- Analysis of short-range order up to second neighbors.
- Examination of bivariate probability distributions of dihedral and tetrahedral angles.
Main Results:
- An increase in short-range order is identified as a necessary factor for the observed changes in the RDF upon thermal relaxation.
- Short-range order enhancement alone can account for the structural modifications, including the 4.7 Å RDF peak.
- Small correlations between dihedral and tetrahedral angles are found, favoring specific bond angles (around 112.5° for staggered, 120° for eclipsed conformations).
Conclusions:
- The emergence of medium-range order in amorphous silicon during thermal relaxation is significantly driven by improvements in short-range order.
- The observed experimental changes in the RDF are likely a consequence of enhanced short-range atomic correlations.
- Understanding these angle correlations provides deeper insight into the nature of disorder and ordering in amorphous silicon systems.
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