Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid–base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti4+ to form planar p-type [Ti4+n(InSe)] coordination complexes. Using this strategy, we fabricate planar p–n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B3+, Al3+ and Sn4+) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid–base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

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This work was supported by FAME, one of six centres of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA, and also supported by the MURI ARO program, grant number W911NF-11-1-0362. This work was also sponsored (at Rice and UCSB) by the Air Force Office of Scientific Research under Award Number FA9550-14-1-0268. G.B. and D.G. thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID grant number 2013/08293-7.

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Author notes

    • Sidong Lei
    •  & Xifan Wang

    These authors contributed equally to this work


  1. Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, USA

    • Sidong Lei
    • , Xifan Wang
    • , Bo Li
    • , Yongmin He
    • , Antony George
    • , Liehui Ge
    • , Yongji Gong
    • , Pei Dong
    • , Zehua Jin
    • , Gustavo Brunetto
    • , Weibing Chen
    • , Robert Baines
    • , Jun Lou
    • , Enrique Barrera
    • , Robert Vajtai
    •  & Pulickel Ajayan
  2. Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106, USA

    • Jiahao Kang
    •  & Kaustav Banerjee
  3. School of Physical Science and Technology, Lanzhou University, Lanzhou, Gansu 730000, China

    • Yongmin He
  4. Applied Physics Department, State University of Campinas, Campinas-SP, 13083-959, Brazil

    • Gustavo Brunetto
    •  & Douglas S. Galvão
  5. Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA.

    • Zuan-Tao Lin


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S.L., A.G., R.V., and P.A. conceived and supervised the experiments. S.L., A.G. and X.W. designed the experiments and analysed the data. S.L., Y.H. Z.J. and A.G. fabricated the devices and performed electronic and optoelectronic measurement and analysis. X.F and E.B. performed the chemical reaction. X.W., B.L., L.G., P.D., L.J. and E.B. performed STEM, XPS and EDS studies. J. K. and K. B. performed the DFT calculations with Atomistix ToolKit. G.B. and D.S.G. performed the DFT calculations with Quantum Espresso. W.C. and analysed the simulation data. S.L. synthesized few-layered InSe and performed Raman study. Y.G. synthesized single-layered MoS2, and MoSe2 samples. S.L., X.W., A.G., B.L., J.K. E.B., K.B., R.V. and P.A. wrote the paper. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Kaustav Banerjee or Robert Vajtai or Pulickel Ajayan.

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