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Formation of two-dimensional transition metal oxide nanosheets with nanoparticles as intermediates


Two-dimensional (2D) materials have attracted significant interest because of their large surface-to-volume ratios and electron confinement. Compared to common 2D materials such as graphene or metal hydroxides, with their intrinsic layered atomic structures, the formation mechanisms of 2D metal oxides with a rocksalt structure are not well understood. Here, we report the formation process for 2D cobalt oxide and cobalt nickel oxide nanosheets, after analysis by in situ liquid-phase transmission electron microscopy. Our observations reveal that three-dimensional (3D) nanoparticles are initially formed from the molecular precursor solution and then transform into 2D nanosheets. Ab initio calculations show that a small nanocrystal is dominated by positive edge energy, but when it grows to a certain size, the negative surface energy becomes dominant, driving the transformation of the 3D nanocrystal into a 2D structure. Uncovering these growth pathways, including the 3D-to-2D transition, provides opportunities for future material design and synthesis in solution.

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Fig. 1: Growth and transformations of cobalt oxide and cobalt nickel oxide nanocrystals into 2D nanosheets.
Fig. 2: Tracking of cobalt oxide nanosheet development with high resolution.
Fig. 3: The interaction and attachments between two cobalt oxide nanosheets.
Fig. 4: Sequential images show the growth of nickel oxide nanocrystals.
Fig. 5: Energy evolution of cobalt oxide during the 3D-to-2D transition.

Data availability

Data are available in the online version of this paper. Data that support the findings of this study are available from corresponding authors upon reasonable request.

Code availability

Computer codes for theoretical calculations in this work are available upon request from the corresponding authors.


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This work was funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 within the in situ TEM programme (KC22ZH). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. J.Y. and J.Q. acknowledge funding support from the Natural Science Foundation of China (nos 51802251 and U1508201). J.Y. also acknowledges funding support from the China Scholarship Council (201506060073) and China Postdoctoral Science Foundation (2018M631168). This work used resources of the National Energy Research Scientific Computing Center and the Oak Ridge Leadership Computing Facility through the INCITE project. The authors thank D. Zherebetskyy (L.-W.W.'s group) for useful discussions.

Author information

Authors and Affiliations



J.Y. designed and performed the experiments and analysed the experimental data. J.K. and L.-W.W. performed the DFT calculations. Z.Z., X.Z. and C.Y. provided reagents and analysed data. S.B. carried out the measurements and calibration of liquid thickness in the liquid cells. C.C. and M.P. provided part of the TEM characterization. C.O. and K.B. helped with image processing and materials structure analyses. J.Y. and H.Z. wrote the manuscript. All authors contributed to the overall scientific interpretation and editing of the manuscript. J.Q. supervised part of the experimental work. L.-W.W. supervised the theory part of this work. All work was carried out under the supervision of H.Z.

Corresponding authors

Correspondence to Jieshan Qiu, Lin-Wang Wang or Haimei Zheng.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–24 Supplementary Tables 1–2 Supplementary video legends 1–8

Supplementary video 1

Shape evolution and the attachment of cobalt nickel oxide nanocrystals from abundant nanoparticles to the large nanosheets. The video plays 15 times faster than real time. The play rate is 3 frames s−1

Supplementary video 2

Shape evolution of cobalt nickel oxide nanocrystals from 3D nanoparticles to a 2D nanosheet. The video plays 15 times faster than real time. The play rate is 15 frames s−1.

Supplementary video 3

Shape evolution of cobalt oxide nanocrystals from 3D nanoparticles to a 2D nanosheet. The video plays 15 times faster than real time. The play rate is 15 frames s−1.

Supplementary video 4

The growth trajectories of the cobalt oxide nanosheet viewed along the [002] axis. The original video was recorded at 400 frames s−1 using a K2 IS camera. The sample drift in the original image sequence was corrected using custom developed MatLab scripts. The video plays in real time with a play rate of 10 frames s−1.

Supplementary video 5

Growth trajectories of the cobalt oxide nanosheet recorded at 400 frames s−1 using a K2 IS camera. The sample drift in the original image sequence was corrected using custom developed MatLab scripts. The video plays in real time with a play rate of 5 frames s−1.

Supplementary video 6

Growth trajectories of a cobalt oxide nanosheet viewed along the [002] axis when there is an adjacent nanocrystal. The original video was recorded at 400 frames s−1 using a K2 IS camera. The sample drift in the original image sequence was corrected using custom developed MatLab scripts. The video plays in real time with a play rate of 10 frames s−1.

Supplementary video 7

The attachment process of two cobalt oxide nanosheets recorded at 400 frames s−1 using a K2 IS camera. The sample drift in the original image sequence was corrected using custom developed MatLab scripts. The video plays in real time with a play rate of 6 frames s−1.

Supplementary video 8

The growth process of nickel oxide nanocrystals. The video plays in real time with a play rate of 5 frames s−1. The full frame is about 40 nm × 40 nm, and the cropped and enlarged region has a width of 7.5 nm.

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Yang, J., Zeng, Z., Kang, J. et al. Formation of two-dimensional transition metal oxide nanosheets with nanoparticles as intermediates. Nat. Mater. 18, 970–976 (2019).

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