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A chemical-dedoping strategy to tailor electron density in molecular-intercalated bulk monolayer MoS2

Nature Synthesis volume 3, pages 67–75 (2024)Cite this article

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Abstract

Molybdenum disulfide (MoS2) is an extensively studied two-dimensional layered semiconductor with interesting electronic and optical properties. Monolayer MoS2 features strong light–matter interactions due to its direct bandgap, whereas multilayer MoS2 is an indirect bandgap semiconductor and optically inactive. The molecular intercalation of MoS2 with organic cations offers a strategy to decouple the interlayer interaction, producing a bulk monolayer material, but is usually accompanied by a heavy electron doping effect that can diminish the intrinsic semiconductor properties or induce a phase transition. Here we report a chemical-dedoping strategy to tailor electron density in molecular-intercalated MoS2, thereby retaining monolayer semiconductor properties. By introducing a poly(vinylpyrrolidone)–bromine complex during the electrochemical intercalation process, we show that bulk monolayer MoS2 thin film can be produced with decoupled interlayer interaction and reduced electron concentration. The resulting thin films display strong excitonic emission, 20 and >400 times stronger than the exfoliated monolayer and multilayer material, respectively, high valley polarization and an enhanced photoelectric response. Our study opens a scalable path to large-area bulk monolayer MoS2 thin films with monolayer-like optical properties and greatly increased optical cross-sections, presenting an attractive material platform for both fundamental photophysics studies and scalable optoelectronic applications.

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Fig. 1: Schematics of molecular intercalation and electron doping control.
Fig. 2: Structural characterizations.
Fig. 3: Electron dedoping mechanism of BM-MoS2 film with PVP-Br2 treatment.
Fig. 4: Spectroscopy of BM-MoS2 with controllable electron doping.
Fig. 5: CPL measurements.
Fig. 6: Optoelectronic properties of intercalated MoS2 thin-film device.

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Data availability

All data supporting the findings of this study are available within the article and its Supplementary Information. Source data for Figs. 2c, 3, 4, 5b–d and 6b–d are available from Figshare: https://doi.org/10.6084/m9.figshare.22827920. Source data are provided with this paper.

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Acknowledgements

The authors acknowledge the Electron Imaging Center for NanoMachines (EICN) at the California NanoSystem Institute (CNSI) and the Nanoelectronic Research Facility (NRF) at UCLA for technical support. X.D. acknowledges support from the Office of Naval Research through grant number N00014-22-1-2631. Jingyuan Zhou and D.Z. were supported by the UCLA CNSI Noble Family Innovation Fund. C.W.W. and J.H.K. acknowledge the support from the National Science Foundation, Office of Naval Research and Army Research Office on this study.

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Author notes

  1. These authors contributed equally: Boxuan Zhou, Jingyuan Zhou.

Authors and Affiliations

  1. Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, CA, USA

    Boxuan Zhou, Ao Zhang, Jingxuan Zhou, Dong Xu, Bangyao Hu & Yu Huang

  2. Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, USA

    Jingyuan Zhou, Laiyuan Wang, Dehui Zhang & Xiangfeng Duan

  3. Department of Electrical and Computer Engineering, University of California, Los Angeles, Los Angeles, CA, USA

    Jin Ho Kang & Chee Wei Wong

  4. Department of Chemistry, Purdue University, West Lafayette, IN, USA

    Shibin Deng & Libai Huang

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Contributions

X.D. and Y.H. conceived the research. B.Z. and Jingyuan Zhou designed the experiments, developed the intercalation and doping control procedure, performed X-ray diffraction characterizations, PL, Raman, reflectance spectroscopy, and analysed the data together. J.H.K. and C.W.W. performed CPL characterizations. L.W. performed AFM characterizations and contributed to discussions. A.Z. performed XPS measurements and Jingxuan Zhou performed HRTEM measurements. D.L. and D.X. contributed to the preparation of solution-processed MoS2 nanosheet thin films. B.H. contributed to some synthetic processes. S.D. and L.H. contributed to the PL characterizations. Y.H. and X.D. supervised the research. B.Z., Jingyuan Zhou and X.D. co-wrote the manuscript with inputs from all the authors. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Yu Huang or Xiangfeng Duan.

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Competing interests

A provisional patent application on the bulk monolayer materials is expected to be filed by the UCLA technology development group. The authors declare no other competing interests.

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Nature Synthesis thanks the anonymous reviewers for their contribution to the peer review of this work. Primary handling editor Alexandra Groves, in collaboration with the Nature Synthesis team.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–13.

Source data

Source Data Fig. 2

Raw data of XRD test.

Source Data Fig. 3

Raw data of PL and XPS.

Source Data Fig. 4

Raw data of PL test for intercalated BM-MoS2 with different amounts of PVP-Br2. Analysis of PL peak intensity and trion spectral weight \({{{I}}}_{{{\rm{X}}}^{-}}/{{{I}}}_{{{\rm{X}}}^{\circ}}\). Analysis of energy splitting and electron density. Raw data of off-resonance PL spectra. Raw data of Raman spectra. Raw data of reflectance spectra.

Source Data Fig. 5

Raw data of CPL spectra. Raw data of angle-dependent PL spectra. Analysis of DOP.

Source Data Fig. 6

Raw data of optoelectronic measurement.

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Zhou, B., Zhou, J., Wang, L. et al. A chemical-dedoping strategy to tailor electron density in molecular-intercalated bulk monolayer MoS2. Nat. Synth 3, 67–75 (2024). https://doi.org/10.1038/s44160-023-00396-2

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