Abstract

Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials1,2,3. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility4,5,6,7,8. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures9,10,11 but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures12,13,14, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 107, along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.

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Acknowledgements

The authors acknowledge the Electron Imaging Center for NanoMachines (EICN) at California NanoSystem Institute (CNSI) and Nanoelectronic Research Facility (NRF) at UCLA for technical support. Xiangfeng D. acknowledges support by National Science Foundation DMR1508144 (materials synthesis) and Office of Naval Research through grant number N00014-15-1-2368 (device fabrications). Y.H. acknowledges support by National Science Foundation EFRI-1433541. Y.L. was supported by a Resnick Prize Postdoctoral Fellowship at Caltech. L.L. acknowledges support through the 973 grant of MOST (No. 2013CBA01604). X.H.C. acknowledges support from the National Natural Science Foundation of China (Grant No. 11534010). W.A.G. and Y.L. were also supported by DOE DE-SC0014607. W.A.G acknowledges the Extreme Science and Engineering Discovery Environment (XSEDE) supported by National Science Foundation grant ACI-1053575. Y.L. acknowledges the computational resources sponsored by the DOE’s Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory, and the Texas Advanced Computing Center (TACC). I.S. thanks the Deanship of Scientific Research at King Saud University for its funding of this research through grant PEJP-17-01.

Author information

Author notes

    • Yuanyue Liu

    Present addresses: Texas Materials Institute and Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA.

Affiliations

  1. Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, USA

    • Chen Wang
    • , Enbo Zhu
    • , Rui Cheng
    • , Nathan O. Weiss
    • , Yun-Chiao Huang
    • , Hao Wu
    • , Hung-Chieh Cheng
    •  & Yu Huang
  2. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA

    • Qiyuan He
    • , Udayabagya Halim
    • , Zhaoyang Lin
    • , Ziying Feng
    •  & Xiangfeng Duan
  3. Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA

    • Yuanyue Liu
    • , Hai Xiao
    •  & William A. Goddard III
  4. State Key Laboratory for Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, School of Physics and Electronics, Hunan University, Changsha 410082, China

    • Xidong Duan
    •  & Lei Liao
  5. Key Laboratory of Strongly Coupled Quantum Matter Physics, Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China

    • Guojun Ye
    •  & Xianhui Chen
  6. Sustainable Energy Technologies Centre, College of Engineering, King Saud University, Riyadh 11421, Kingdom of Saudi Arabia

    • Imran Shakir
  7. California Nanosystems Institute, University of California, Los Angeles, California 90095, USA

    • Yu Huang
    •  & Xiangfeng Duan

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Contributions

Xiangfeng D., Y.H. and C.W. co-designed the research. C.W. conducted device fabrication, electrical properties measurements and data analysis. C.W., Q.H. and U.H. conducted the intercalation experiments. C.W., U.H., Z.L. and Z.F. conducted structural and optical characterizations. Y.L., H.X. and W.A.G. contributed to the superlattice atomic and electronic structure calculations. E.Z. conducted the TEM studies. Q.H., Xidong D., Y.-C.H., H.W., H.-C.C., I.S. and L.L. contributed to the initial measurement system set-up, preparation of 2D materials and data analysis. R.C. contributed to the initial BP property characterization. N.O.W. contributed to the schematic drawing. G.J.Y. and X.H.C. prepared the initial BP material. Y.H. and Xiangfeng D. supervised the research. Xiangfeng D. and C.W. co-wrote the manuscript. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Lei Liao or Yu Huang or Xiangfeng Duan.

Reviewer Information Nature thanks N. Guisinger, K. Loh and Q. Xiong for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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DOI

https://doi.org/10.1038/nature25774

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