Abstract
Monoatomic-layered carbon materials, such as graphene1 and amorphous monolayer carbon2,3, have stimulated intense fundamental and applied research owing to their unprecedented physical properties and a wide range of promising applications4,5. So far, such materials have mainly been produced by chemical vapour deposition, which typically requires stringent reaction conditions compared to solution-phase synthesis. Herein, we demonstrate the solution preparation of free-standing nitrogen-doped amorphous monolayer carbon with mixed five-, six- and seven-membered (5-6-7-membered) rings through the polymerization of pyrrole within the confined interlayer cavity of a removable layered-double-hydroxide template. Structural characterizations and first-principles calculations suggest that the nitrogen-doped amorphous monolayer carbon was formed by radical polymerization of pyrrole at the α, β and N sites subjected to confinement of the reaction space, which enables bond rearrangements through the Stone–Wales transformation. The spatial confinement inhibits the C–C bond rotation and chain entanglement during polymerization, resulting in an atom-thick continuous amorphous layer with an in-plane π-conjugation electronic structure. The spatially confined radical polymerization using solid templates and ion exchange strategy demonstrates potential as a universal synthesis approach for obtaining two-dimensional covalent networks, as exemplified by the successful synthesis of monolayers of polythiophene and polycarbazole.
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Change history
07 October 2024
A Correction to this paper has been published: https://doi.org/10.1038/s41586-024-08147-9
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 51532001, 52225308, 11974037, 22372048, 61327813, 51802053 and 52025025), the National Key R&D Programme (Grant No. 2017YFA0205000), the Strategic Priority Research Programme of the Chinese Academy of Sciences (Grant No. XDB36000000), the Royal Society’s Newton Advanced Fellowship scheme (Grant No. NAF\R1\180242), the Beijing Outstanding Young Scientist Programme (Grant No. BJJWZYJH01201914430039) and the Chinese Academy of Sciences Project for Young Scientists in Basic Research (Grant No. YSBR-003). This research benefited from the resources and support of the Electron Microscopy Center at the University of Chinese Academy of Sciences. We thank BL10B and BL12B in the National Synchrotron Radiation Laboratory for characterizations by synchrotron radiation. We thank Y. Li for helpful discussions and suggestions.
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L. Guo and X.Q. proposed and supervised the project. X.B., P.H., Y.Z., T.J., Z.W. and H.C. prepared the samples and spectroscopy characterization. Ang L., Aowen L., L. Gu and W.Z. performed the STEM characterization and analysis. Y.X. conducted the theoretical calculations. G.Z. performed the EFM measurements and analysis. J.K. and H.Z. carried out the soft X-ray absorption spectroscopy experiments. L. Guo, L.L., W.Z., X.Q. and L. Gu analysed data and wrote the manuscript. All authors discussed the results and commented on the manuscript. X.B., P.H., Ang L., Y.Z., Aowen L., G.Z. and Y.X. contributed equally to this work.
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Extended data figures and tables
Extended Data Fig. 1 Additional STEM-ADF images of the NAMC sample.
a, Larger field of view STEM-ADF image of NAMC (field of view 16 nm × 16 nm). b, STEM-ADF image of NAMC, showing a highly disorder atomic arrangement distinctly different from nanocrystalline graphene (field of view 6.6 nm × 5.6 nm). This image is duplicate of Fig. 1d of the main text. c, Overlay of the schematic atomic structure model on the atomic resolution STEM-ADF image in b. The 5-, 7- and 8-membered rings are highlighted with green, blue and purple, respectively. The bright atoms are impurity atoms introduced during the removal of the LDH template and TEM sample preparation. d-f, Additional atomic resolution STEM-ADF images of NAMC, all showing an amorphous structure. Pin-holes and small restacking nano-flakes can be observed from the images.
Extended Data Fig. 2 Aberration-corrected STEM-HAADF image of NAMC with the five-, six- and seven- membered rings structure crosslinked by pyrrole rings.
a, Aberration-corrected STEM-HAADF image processed by a double-gaussian filter. b, A color overlay is added for identification of 5- (green), 6- (pink) and 7- (blue) membered rings.
Extended Data Fig. 3 4D-STEM NBED characterization of NAMC.
a, STEM image of a multilayer thin flake of NAMC. b, Summed NBED pattern of the whole area in a over an area of 32 nm × 32 nm, showing diffuse halos. c, Array of the summed NBED patterns of the 16 × 16 subregions of a (The size of each subregion is 2 nm × 2 nm). d, e, Two representative pairs of adjacent NBED patterns in c, indicating that the sample features a highly disordered structure even at a scale as small as 2 nm × 2 nm.
Extended Data Fig. 4 STEM-EELS analysis of the NAMC sample.
a, The simultaneously acquired STEM-HAADF image of the sample area for STEM-EELS mapping (the same area as shown in Extended Data Fig. 1a). b, Same image as a with the contours of the monolayer regions marked with the green lines. Apart from the highlighted monolayer regions and pinholes, this sample area contains primarily re-stacked bilayers. c, The EELS spectra summed over the whole dataset (black) and the monolayer regions (green), respectively, both showing a similar nitrogen content of ~9%. The agreement of N content in both of monolayer regions and the overall sample indicates the measured N signal comes from the N atoms incorporated into the 2D amorphous carbon network, precluding the possible contribution of N species adsorbed on the surface or in contaminants.
Extended Data Fig. 5 Structural models for formation energy calculations of N doping in graphene and amorphous monolayer carbon.
a, b, Structural models for graphene (a) and N-doped graphene (b). c, d, Structural models for amorphous monolayer carbon (c) and NAMC (d). Blue and grey balls stand for N and C atoms, respectively. The formation energy of N-doping atoms was calculated by the equation: Ef = EN-doped − Epure − nEN + nEC, where EN-doped and Epure represent the total energies of the N-doped structure and the pristine structure, respectively. EN and EC correspond to the energy per N atom in N2 gas and the energy per C atom in graphene, respectively. Meanwhile, n stands for the total number of doping atoms. The pristine structural model for either graphene or amorphous monolayer carbon contains 100 C atoms, and the N-doped model contains 90 C atoms and 10 N atoms, corresponding to 10 at% N doping in both graphene and amorphous monolayer carbon. First-principles calculations indicate that the formation energy of N doping in amorphous monolayer carbon is lowered to 0.60 eV per N as compared to that of N-doped graphene (0.92 eV per N), making it potentially easier to incorporate nitrogen into the strained disordered carbon lattice.
Extended Data Fig. 6 Calculated electronic structures of NAMC with a planer model structure using HSE06 functional.
a, Density of states. There is a pseudo-gap of 0.4 eV between the highest occupied molecule orbital (HOMO) and the lowest unoccupied molecule orbital (LUMO). b, c, Illustration of HOMO (b) and LUMO (c), respectively. The size of the model structure is about 20 Å × 20 Å, consisting of the 5-, 6- and 7- rings. The isosurface is 0.0015 e/Å3. H: white, C: brown, N: blue.
Extended Data Fig. 7 Optical bandgap measurement of NAMC.
a, UV-Vis-NIR absorption spectrum of NAMC. b, Tauc plots derived from the absorption spectrum. The red line indicates linear extrapolation of the absorption edge.
Extended Data Fig. 8 Characterizations of the 2D monolayer PTH.
a, XRD profiles of LDH, LDH-S2O82− and LDH-PTH. Similar to the ion-exchange and confined polymerization process of NAMC, the interlayer distance of LDH increases from 7.47 Å to 9.07 Å after the intercalation of S2O82−, and shrinks to 8.60 Å upon the decomposition of S2O82− to produce LDH-PTH. b, TEM image and SAED pattern of PTH. c, AFM image and the corresponding height profile of monolayer PTH. d, Atomic resolution STEM-ADF image of monolayer PTH. e, Overlay of the schematic atomic structural model on d. The 5-, 7- and 8-membered rings are highlighted with green, blue and purple, respectively. f, EELS spectrum acquired over a 32 nm × 32 nm sample area. The S content is approximately 6% as quantified from the EELS spectrum. g, STEM-ADF image of a PTH nanosheet. h, Summed NBED pattern of the whole area in g over an area of 32 nm × 32 nm, showing diffuse halos characteristic of an amorphous structure. i, Array of the NBED patterns of the 16 × 16 subregions of g. The size of each subregion is 2 nm × 2 nm. j, k, two representative pairs of adjacent NBED patterns in i, all showing diffuse halos, suggesting that the sample features a highly disordered structure even at a scale as small as 2 nm × 2 nm.
Extended Data Fig. 9 Characterizations of the 2D monolayer PCZ.
a, XRD profiles of LDH, LDH-S2O82− and LDH-PCZ. Similar to the ion-exchange and confined polymerization process of NAMC, the interlayer distance of LDH increases from 7.47 Å to 9.07 Å after the intercalation of S2O82−, and shrinks to 8.66 Å upon the decomposition of S2O82− to produce LDH-PCZ. b, TEM image and SAED pattern of PCZ. c, AFM image and the corresponding height profile of monolayer PCZ. d, Atomic resolution STEM-ADF image of monolayer PCZ. e, Overlay of the schematic atomic structural model on d. The 5-, 7- and 8-membered rings are highlighted with green, blue and purple, respectively. f, EELS spectrum acquired over a 32 nm × 32 nm sample area. The N content is approximately 4% as quantified from the EELS spectrum. g, STEM-ADF image of a PCZ nanosheet. h, Summed NBED pattern of the whole area in g over an area of 32 nm × 32 nm, showing diffuse halos characteristic of an amorphous structure. i, Array of the NBED patterns of the 16 × 16 subregions of g. The size of each subregion is 2 nm × 2 nm. j, k, two representative pairs of adjacent NBED patterns in i, all showing diffuse halos, suggesting that the sample features a highly disordered structure even at a scale as small as 2 nm × 2 nm.
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Bai, X., Hu, P., Li, A. et al. Nitrogen-doped amorphous monolayer carbon. Nature 634, 80–84 (2024). https://doi.org/10.1038/s41586-024-07958-0
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DOI: https://doi.org/10.1038/s41586-024-07958-0
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