Abstract
The properties of polycrystalline materials are often dominated by defects; two-dimensional (2D) crystals can even be divided and disrupted by a line defect1,2,3. However, 2D crystals are often required to be processed into films, which are inevitably polycrystalline and contain numerous grain boundaries, and therefore are brittle and fragile, hindering application in flexible electronics, optoelectronics and separation1,2,3,4. Moreover, similar to glass, wood and plastics, they suffer from trade-off effects between mechanical strength and toughness5,6. Here we report a method to produce highly strong, tough and elastic films of an emerging class of 2D crystals: 2D covalent organic frameworks (COFs) composed of single-crystal domains connected by an interwoven grain boundary on water surface using an aliphatic bi-amine as a sacrificial go-between. Films of two 2D COFs have been demonstrated, which show Young’s moduli and breaking strengths of 56.7 ± 7.4 GPa and 73.4 ± 11.6 GPa, and 82.2 ± 9.1 N m−1 and 29.5 ± 7.2 N m−1, respectively. We predict that the sacrificial go-between guided synthesis method and the interwoven grain boundary will inspire grain boundary engineering of various polycrystalline materials, endowing them with new properties, enhancing their current applications and paving the way for new applications.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
All data supporting the findings of this study are available in the paper and its Supplementary Information. Source data are provided with this paper.
References
Huang, P. et al. Grains and grain boundaries in single-layer graphene atomic patchwork quilts. Nature 469, 389–392 (2011).
Wei, Y. et al. The nature of strength enhancement and weakening by pentagon-heptagon defects in graphene. Nat. Mater. 11, 759–763 (2012).
Yang, S.-J., Choi, M.-Y. & Kim, C.-J. Engineering grain boundaries in two-dimensional electronic materials. Adv. Mater. 35, 2203425 (2023).
Colson, J. W. et al. Oriented 2D covalent organic framework thin films on single-layer graphene. Science 332, 228–231 (2011).
Ritchie, R. The conflicts between strength and toughness. Nat. Mater. 10, 817–822 (2011).
Galeski, A. Strength and toughness of crystalline polymer systems. Prog. Polym. Sci. 28, 1643–1699 (2003).
Evans, A. M. et al. Seeded growth of single-crystal two-dimensional covalent organic frameworks. Science 361, 52–57 (2018).
Wang, S. et al. Exfoliation of covalent organic frameworks into few-layer redox-active nanosheets as cathode materials for lithium-ion batteries. J. Am. Chem. Soc. 139, 4258–4261 (2017).
Liu, W. et al. A two-dimensional conjugated aromatic polymer via C–C coupling reaction. Nat. Chem. 9, 563–570 (2017).
Liu, K. et al. On-water surface synthesis of crystalline, few-layer two-dimensional polymers assisted by surfactant monolayers. Nat. Chem. 11, 994–1000 (2019).
Ou, Z. et al. Surfactants mediated synthesis of highly crystalline thin films of imine-linked covalent organic frameworks on water surface. Chin. J. Chem. 39, 3322–3328 (2021).
Ou, Z. et al. Oriented growth of thin films of covalent organic frameworks with large single-crystalline domains on the water surface. J. Am. Chem. Soc. 144, 3233–3241 (2022).
Qi, H. et al. Near-atomic-scale observation of grain boundaries in a layer-stacked two-dimensional polymer. Sci. Adv. 6, eabb5976 (2020).
Wang, L. et al. Superior strong and tough nacre-inspired materials by interlayer entanglement. Nano Lett. 23, 3352–3361 (2023).
Ma, T. et al. Single-crystal X-ray diffraction structures of covalent organic frameworks. Science 361, 48–52 (2018).
Yu, M. et al. Retrieving grain boundaries in 2D materials. Small 19, 2205593 (2023).
Al-Jishi, R. & Dresselhaus, G. Lattice-dynamical model for graphite. Phys. Rev. B 26, 4514–4522 (1982).
Liu, Y. et al. Weaving of organic threads into a crystalline covalent organic framework. Science 351, 365–369 (2016).
Zhan, G. et al. Observing polymerization in 2D dynamic covalent polymers. Nature 603, 835–840 (2022).
Dong, X. et al. Growth and local structures of single crystalline flakes of three-dimensional covalent organic frameworks in water. J. Am. Chem. Soc. 145, 22079–22085 (2023).
Lee, C., Wei, X., Kysar, J. W. & Hone, J. Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 321, 385–388 (2008).
Zhu, C. et al. Highly compressible 3D periodic graphene aerogel microlattices. Nat. Commun. 6, 6962 (2015).
Zeng, Y. et al. Irreversible synthesis of an ultrastrong two-dimensional polymeric material. Nature 602, 91–95 (2022).
Chen, Z., Wang, X., Bhakhri, V., Giuliani, F. & Atkinson, A. Nanoindentation of porous bulk and thin films of La0.6Sr0.4Co0.2Fe0.8O3−δ. Acta Mater. 61, 5720–5734 (2013).
Fang, Q. et al. Strong and flaw-insensitive two-dimensional covalent organic frameworks. Matter 4, 1017–1028 (2021).
Stein, J., Lenczowski, B., Anglaret, E. & Fréty, N. Influence of the concentration and nature of carbon nanotubes on the mechanical properties of AA5083 aluminium alloy matrix composites. Carbon 77, 44–52 (2014).
Dey, K., Bhunia, S., Sasmal, H. S., Reddy, C. M. & Banerjee, R. Self-assembly-driven nanomechanics in porous covalent organic framework thin films. J. Am. Chem. Soc. 143, 955–963 (2021).
Vlassak, J. J. & Nix, W. D. A new bulge test technique for the determination of Young’s modulus and poisson’s ratio of thin films. J. Mater. Res. 7, 3242–3249 (1992).
Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996).
Blöchl, P. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).
Perdew, J., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Paneff, F. Elastic Properties of Carbon Nanomembranes and Graphene: Theory and Experiment. PhD thesis, Bielefeld Univ. (2021).
Acknowledgements
We thank the National Natural Science Foundation of China (52061135103, 51873236) and Fundamental Research Funds for the Central Universities, Sun Yat-sen University (No. 23yxqntd002), for financial support. Structure characterizations were supported by the Instrumental Analysis and Research Center of Sun Yat-sen University. We acknowledge the ESRF for provision of synchrotron radiation facilities and we would like to thank O. Konovalov for assistance and support in using beamline ID10. Parts of these experiments were performed at the BL11 – NCD-SWEET beamline at ALBA Synchrotron with the collaboration of ALBA staff. We would like to thank M. Malfois for help with setting up the experiment. We acknowledge SOLEIL for provision of synchrotron radiation facilities and we would like to thank A. Hemmerle for assistance in using beamline SIRIUS.
Author information
Authors and Affiliations
Contributions
Z. Zheng initiated the project. Z. Zheng and W.L. coordinated the research. Z. Zheng and Yonghang Yang designed the experiments. Yonghang Yang and Z.L. performed most of the experimental work. X.D., J.L. and C.L. conducted the TEM tests. B.L., H.Q. and U.K. carried out AC-HRTEM and selected area electron diffraction. J.K., Yang Yang and A.G. conducted mechanical tests and analysis. M.H. and S.C.B.M. performed GIWAXS measurements and analysis. L.G., Z.L., D.L. and Z. Zhou conducted the AFM test and analysis. S.H. and X.Z. performed DFT simulations. C.W. helped with discussion. Z. Zheng, Yonghang Yang and W.L. wrote the manuscript. All authors contributed to the proofreading of the manuscript.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature thanks Yingjie Zhao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
Extended Data Fig. 1 Macroscopic 2DCOF-1 film.
a, Photograph of 2DCOF-1 films grown on the water surface of a petri dish with a diameter of 60 mm. b, c, Photographic (b) and optical microscopic (c) image of 2DCOF-1 film deposited onto a silicon substrate with a layer of 300 nm thick silicon dioxide. The position indicated by the arrow in (b) is where the tweezers caught the silicon substrate during the deposition of the film. The substrate allows angstrom level thickness detection by the eyes due to false color change. The homogeneous color of the film indicates its homogeneity in thickness. d, Photographic image of bended 2DCOF-1 film deposited onto Nafion film. The position indicated by the arrow is the bare Nafion film.
Extended Data Fig. 2 Crystallinity and structure of 2DCOF-1 film.
a, TEM image of 2DCOF-1 film suspended over holey copper grids. Selected area electron diffraction patterns at different areas ((c), (d), (e), (f)) indicated the single crystallinity of the 2DCOF-1 film. f, Near-atomic structure of 2DCOF-1 film visualized by AC-HRTEM. Inset, corresponding Fast Fourier transform pattern.
Extended Data Fig. 3 Reaction time dependent GIWAXS images of 2DCOF-1 film.
GIWAXS images of 2DCOF-1 films deposited onto silicon squares with a diameter of 1.5 cm at synthesis times of (a) 6 h, (b) 7 h, (c) 16 h, and (d) 6 days.
Extended Data Fig. 4 Reaction time dependent AC-HRTEM images of 2DCOF-1 film.
AC-HRTEM images of 2DCOF-1 films deposited onto holey copper grids at synthesis times of (a) 6 to 8 h (the inset shows a selected area electron diffraction pattern of the film), (b) 14 h, (c) 16 h, (d) 2 days, (e) 6 days, and (f) 7 days.
Extended Data Fig. 5 Reaction time dependent AFM images of 2DCOF-1 film.
AFM topographic images of 2DCOF-1 films on mica with synthesis times of (a) 6 to 8 h, (b) 9 h, (c) 10 h, (d) 12 h, (e) 14 h, (f) 16 h, (g) 2 days, (h) 6 days, and (i) 7 days.
Extended Data Fig. 6 Morphology and structure 2DCOF-1-A film.
a, Photographic image of the film on water surface of a petri dish with a diameter of 60 mm. b, GIWAXS patterns of 2DCOF-1-A film with a synthesis time of 7 days on silicon substrate. c, AFM topographic image of the film on mica (upper) and its corresponding roughness at the white dashed line. d, Scanning electron microscopic image of the 2DCOF-1-A film over 47-µm-diameter-sized circular hole in a copper grid. e, Wiener filtered AC-HRTEM image of the grain boundary structure of the film. f, Optical image of the 2DCOF-1-A film over 47-µm-diameter-sized circular holes in a copper grid.
Extended Data Fig. 7 Morphology of 2DCOF-2 film.
a, Photograph of the film grown on the water surface of a petri dish with a diameter of 60 mm. b, Optical microscopic image of the film deposited onto a silicon substrate with a layer of 300 nm thick silicon dioxide. c, AFM topographic image of the film on mica. d, Scanning electron microscopy image of the 2DCOF-2 film suspended over 47-µm-diameter-sized circular hole in a copper grid. e, Scanning electron microscopic image of the 2DCOF-2 film at higher magnification.
Extended Data Fig. 8 Morphology of 2DCOF-2 film.
a, GIWAXS patterns of 2DCOF-2 film on silicon substrate. b, Near-atomic structure of 2DCOF-2 film visualized by AC-HRTEM. Inset shows the corresponding Fast Fourier transform pattern. c, AFM topographic image of 2DCOF-2 on mica and d, corresponding height profile along the white line in (c).
Extended Data Fig. 9 Bulge test of 2DCOF-1 film.
a, Optical images of film bulging under different pressures. b, The load and unload curves and their fitted curves. AFM image of the 2DCOF-1 film at a deflection of 2.6 µm (inset).
Extended Data Fig. 10 Mechanical properties of 2DCOF-2 film.
a, Force-displacement curves of 20 cycles of loading (upper) and unloading of AFM tips with a radius of ~ 100 nm at the same position under constant rate. b, Rupture force-displacement curves of 2DCOF-2 film at the same indentation position as in (a).
Supplementary information
Supplementary Information
This file contains Supplementary Figs. 1–21, Tables 1–5 and references.
Rights and permissions
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
About this article
Cite this article
Yang, Y., Liang, B., Kreie, J. et al. Elastic films of single-crystal two-dimensional covalent organic frameworks. Nature 630, 878–883 (2024). https://doi.org/10.1038/s41586-024-07505-x
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41586-024-07505-x
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.
