Thermal expansion (TE) behavior in solid-state materials is influenced by both molecular and supramolecular structure. For solid-state materials assembled through covalent bonds, such as carbon allotropes, solids with higher dimensionality (i.e., diamond) exhibit less TE than solids with lower dimensionality (e.g., fullerene, graphite). Thus, as the dimensionality of the solid increases, the TE decreases. However, an analogous and systematic variation of the dimensionality in solid-state materials assembled through noncovalent bonds with a correlation to TE has not been studied. Here, we designed a series of solids based on dimensional hierarchy to afford materials with zero-dimensional (0D), 1D, and 2D hydrogen-bonded structures. The 2D materials are structural analogues of graphite and covalent-organic frameworks, and we demonstrate that these 2D solids exhibit unique biaxial zero TE with anisotropic and colossal TE along the π-stacked direction (α ∼ 200 MK–1). The overall behavior in the 2D hydrogen-bonded solids is similar to 2D covalent-bonded solids; however, the coefficient of TE along the π-stacked direction for these hydrogen-bonded solids is an order of magnitude higher than in 2D graphite or phosphorus allotropes. The hierarchal materials design strategy and correlation to TE properties described herein can be broadly applied to the design and synthesis of new solid-state materials sustained by covalent or noncovalent bonds with control over solid-state behaviors.
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Nano-makisu: highly anisotropic two-dimensional carbon allotropes made by weaving together nanotubes
Graphene and carbon nanotubes (CNT) are the representatives of two-dimensional (2D) and one-dimensional (1D) forms of carbon, both exhibiting unique geometric structures and peculiar physical and chemical properties. Herein, we propose a family or series of 2D carbon-based highly anisotropic Dirac materials by weaving together an array of CNTs by direct C–C bonds or by graphene ribbons. By employing first-principles calculations, we demonstrate that these nano-makisus are thermally and dynamically stable and possess unique electronic properties. These 2D carbon allotropes are all metals and some nano-makisus show largely anisotropic Dirac cones, causing very different transport properties for the Dirac fermions along different directions. The Fermi velocities in the k x direction could be ∼170 times higher than those in the k y direction, which is the strongest anisotropy among 2D carbon allotropes to the best of our knowledge. This intriguing feature of the electronic structure has only been observed in heavy element materials with strong spin–orbit coupling. These results indicate that carbon based materials may have much broader applications in future nanoelectronics.
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- NSF-PAR ID:
- 10197120
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 347 to 355
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9nr08069d
