Abstract
By combining first-principles and classical force field calculations with aberration-corrected high-resolution transmission electron microscopy experiments, we study the morphology and energetics of point and extended defects in hexagonal bilayer silica and make comparison to graphene, another two-dimensional (2D) system with hexagonal symmetry. We show that the motifs of isolated point defects in these 2D structures with otherwise very different properties are similar, and include Stone-Wales-type defects formed by structural unit rotations, flower defects and reconstructed double vacancies. The morphology and energetics of extended defects, such as grain boundaries have much in common as well. As both sp2-hybridised carbon and bilayer silica can also form amorphous structures, our results indicate that the morphology of imperfect 2D honeycomb lattices is largely governed by the underlying symmetry of the lattice.
Highlights
By combining first-principles and classical force field calculations with aberration-corrected high-resolution transmission electron microscopy experiments, we study the morphology and energetics of point and extended defects in hexagonal bilayer silica and make comparison to graphene, another two-dimensional (2D) system with hexagonal symmetry
We investigate the atomic structure and properties of point defects and grain boundaries in 2D hexagonal bilayer silica (HBS) and graphene, using a combination of aberration corrected high resolution transmission electron microscopy (AC-HRTEM) and atomistic calculations based on the density functional theory (DFT) and classical force field (CFF) approaches
In graphene the nodes are two neighbouring C atoms, in HBS four Si atoms with the neighbouring O atoms. The application of this transformation to HBS is schematically presented in Fig. 2, and we present an AC-HRTEM image of the defect in Fig. 3 with other defects and a comparison to graphene images of similar structures
Summary
By combining first-principles and classical force field calculations with aberration-corrected high-resolution transmission electron microscopy experiments, we study the morphology and energetics of point and extended defects in hexagonal bilayer silica and make comparison to graphene, another two-dimensional (2D) system with hexagonal symmetry. We investigate the atomic structure and properties of point defects and grain boundaries in 2D hexagonal bilayer silica (HBS) and graphene, using a combination of aberration corrected high resolution transmission electron microscopy (AC-HRTEM) and atomistic calculations based on the density functional theory (DFT) and classical force field (CFF) approaches. Graphene and HBS are the only 2D hexagonal materials that have been extensively studied so far, recent progress in this area, as indicated by the development of epitaxial atomically thin silicon structures[12], epitaxial hexagonal transition metal www.nature.com/scientificreports networks[13], a large number of 2D compounds with trigonal symmetry, such as h-BN and the transition metal dichalcogenides[14,15] as well as computational discoveries of new 2D compounds[16,17], suggests that other nearly free-standing hexagonal 2D materials can be created, which provides additional stimulus to study common trends in defect energetics and morphology in 2D systems
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