Atomic mechanism of metal crystal nucleus formation in a single-walled carbon nanotube


Knowing how crystals nucleate at the atomic scale is crucial for understanding, and in turn controlling, the structure and properties of a wide variety of materials. However, because of the scale and highly dynamic nature of nuclei, the formation and early growth of nuclei are very difficult to observe. Here, we have employed single-walled carbon nanotubes as test tubes, and an ‘atomic injector’ coupled with aberration-corrected transmission electron microscopy, to enable in situ imaging of the initial steps of nucleation at the atomic scale. With three different metals we observed three main processes prior to heterogeneous nucleation: formation of crystal nuclei directly from an atomic seed (Fe), from a pre-existing amorphous nanocluster (Au) or by coalescence of two separate amorphous sub-nanometre clusters (Re). We demonstrate the roles of the amorphous precursors and the existence of an energy barrier before nuclei formation. In all three cases, crystal nucleus formation occurred through a two-step nucleation mechanism.

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Fig. 1: Structure of Fe@SWNT and time-series AC-HRTEM images of an atomic injector.
Fig. 2: Sequential AC-HRTEM images and corresponding simulations showing the first and second stages of γ-Fe crystallite nucleation.
Fig. 3: Sequential AC-HRTEM images and corresponding image simulations showing the third and fourth stages of γ-Fe crystallite nucleation.
Fig. 4: Electron-beam-stimulated nucleation of Au crystallite from the amorphous state.
Fig. 5: Electron-beam-stimulated nucleation of Re crystallite by coalescing two amorphous sub-nanometre Re clusters.

Data availability

All data supporting the findings of this study are available in the manuscript or the Supplementary Information. The data for the electron elastic scattering cross-section that support the findings of this study are publicly available online at


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K.C. acknowledges financial support from the China Scholarship Council (CSC). J.B. and U.K. acknowledge support from the ‘Graphene Flagship’ and DFG within the project KA 1295-33 as well as the DFG and the Ministry of Science, Research and the Arts (MWK) of Baden-Wuerttemberg within the frame of the SALVE (Sub Angstrom Low-Voltage Electron microscopy) project. T.W.C. and A.N.K. acknowledge EPSRC for financial support and the Nanoscale & Microscale Research Centre (nmRC) and the Centre for Sustainable Chemistry, University of Nottingham, for access to instrumentation. E.B. acknowledges a Royal Society Wolfson Fellowship for financial support. Calculations were performed using the High Performance Computing facility at the University of Nottingham. Z.L. and K.S. acknowledge support from a JST Research Acceleration Program and the Japan Society for the Promotion of Science KAKENHI Grant JP 25107003.

Author information




R.L.M. prepared the samples. C.T.S. carried out initial analysis of the samples. T.W.C. developed the methodology of filling nanotubes with metal precursors. Z.L., J.B. and K.S. performed the EELS mapping of the sample. K.C. and J.B. investigated of the sample by AC-HRTEM and recorded the videos of nucleation. K.C., J.B., A.N.K. and U.K. discussed the results and analysed the data. E.B. and S.T.S. carried out theoretical modelling. K.C., J.B., A.N.K. and U.K. drafted the manuscript. All the authors have revised the manuscript. U.K. and A.N.K. supervised the research.

Corresponding authors

Correspondence to Andrei N. Khlobystov or Ute Kaiser.

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Supplementary information

Supplementary Information

Supplementary Section 1–8, Figs. 1–17 and references 1–25.

Supplementary Video 1

Fe crystal nuclei formed from atomic seed.

Supplementary Video 2

Au crystal nuclei formed from amorphous nanocluster.

Supplementary Video 3

Re crystal nuclei formed by coalescence.

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Cao, K., Biskupek, J., Stoppiello, C.T. et al. Atomic mechanism of metal crystal nucleus formation in a single-walled carbon nanotube. Nat. Chem. 12, 921–928 (2020).

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