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On-liquid-gallium surface synthesis of ultrasmooth thin films of conductive metal–organic frameworks

Abstract

Conductive metal–organic frameworks (MOFs) are emerging electroactive materials for (opto)electronics; however, it is challenging to achieve MOF-based devices using existing synthesis methods. Here we develop an on-liquid-gallium surface synthesis (OLGSS) strategy under chemical vapour deposition conditions for the controlled growth of two-dimensional conjugated MOF (2D c-MOF) thin films, which gives a tenfold improvement in surface flatness compared with traditionally synthesized c-MOFs. The basis for constructing these flatter surfaces is a layer-by-layer chemical vapour deposition growth mode, which is triggered by the high adhesion energy between gallium and aromatic ligands. We demonstrate the generality of the OLGSS strategy by reproducing flat surfaces for nine different 2D c-MOF films with variable thicknesses (2–208 nm). Compared to traditionally synthesized MOF films, the resultant ultrasmooth films enable the formation of high-quality electrical contacts with contact resistance reduced by over 13-fold. Furthermore, due to the efficient interfacial interaction, the prepared van der Waals heterostructure of OLGSS c-MOF and MoS2 shows intriguing photoluminescence enhancement, photoluminescence peak shift and work function modulation. This robust OLGSS method provides the opportunity to develop MOF electronics and shows promise for the construction of multicomponent MOF-based heterostructure materials.

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Fig. 1: Schematic illustration of the synthesis of 2D c-MOF films on different substrates by CVD.
Fig. 2: OLGSS 2D c-MOF thin films with an ultrasmooth surface.
Fig. 3: Surface evenness of 2D c-MOF thin films synthesized by different methods.
Fig. 4: Growth mechanism behind the OLGSS strategy with O-Cu-BHT 2D c-MOF as a typical example.
Fig. 5: Interfacial contact of microelectronic devices based on various 2D c-MOF thin films.
Fig. 6: OLGSS thin-film-based vdWHs.

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The data supporting the findings of the study are available in the paper and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

This work was financially supported by National Natural Science Foundation of China (22272092), ERC starting grant (FC2DMOF, number 852909), ERC Consolidator grant (T2DCP), SFB-1415 (number 417590517), GRK2861 (number 491865171), EMPIR-20FUN03-COMET, and by the German Science Council, Center for Advancing Electronics Dresden (CFAED). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC grant agreement number 714067, ENERGYMAPS). We acknowledge the European Synchrotron Radiation Facility (ESRF) for provision of synchrotron radiation facilities and we thank O. Konovalov for assistance and support in using beamline ID10. We acknowledge Elettra Sincrotrone Trieste for providing access to its synchrotron radiation facilities and for financial support under the IUS internal project. We thank L. Barba for assistance in using beamline XRD1. We acknowledge Dresden Center for Nanoanalysis (DCN) at TUD. R.D. thanks the Taishan Scholars Program of Shandong Province (tsqn201909047) and the Natural Science Foundation of Shandong Province (ZR2023JQ005). We thank Z. Wang for his help with TEM measurements. J.L. gratefully acknowledges funding from the Alexander von Humboldt Foundation.

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Authors

Contributions

R.D. and X.F. conceived this project. J.L. and Y.C. carried out the CVD growth experiments and the Raman, PL, AFM and SEM measurements, and the device fabrication. X.H. provided the BHT ligand. Y.R., D.B., A.D., J.G. and G.C. conducted the DFT calculations. M.D., F.Z, J.H. and Y.V. performed the XPS and UPS measurements and analysed the spectra. D.P., F.Z., X.L., B.Z. and Z.L. performed the TEM measurements. M.L. contributed to the SEM measurements. M.H. and S.C.B.M. performed the GIWAXS measurements and also contributed to the device measurements. J.L., Y.C., R.D. and X.F. co-wrote the manuscript with contributions from all the authors.

Corresponding authors

Correspondence to Junfeng Gao, Xinliang Feng or Renhao Dong.

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Nature Synthesis thanks Mark Allendorf, Ning Huang, Grigorii Skorupskii and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Alison Stoddart, in collaboration with the Nature Synthesis team.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–55 and Tables 1–3.

Source data

Source Data Fig. 3

Statistical source data of film roughness and thickness.

Source Data Fig. 5

Source sata of lateral and vertical devices.

Source Data Fig. 6

Source data of PL, UPS and c-AFM curves.

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Liu, J., Chen, Y., Huang, X. et al. On-liquid-gallium surface synthesis of ultrasmooth thin films of conductive metal–organic frameworks. Nat. Synth 3, 715–726 (2024). https://doi.org/10.1038/s44160-024-00513-9

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