Abstract

We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe2. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe2 and MoS21,2,3,4,5,6,7. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent density of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.

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Acknowledgements

We acknowledge P. Hapala for assistance with the nc-AFM image simulations. We thank our colleagues at the Molecular Foundry for stimulating discussion and assistance. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231 (user proposal #3282) (STM imaging, STM spectroscopy, theoretical simulations, and analysis). A.W.-B. and S.W. were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Scientific User Facilities Division (NSRCs) Early Career Award. S.B. acknowledges fellowship support by the European Union under FP7-PEOPLE-2012-IOF-327581. ALS and SIMES were supported by Office of Basic Energy Science, US DOE, under contract numbers DE-AC02-05CH11231 and DE-AC02-76SF00515, respectively. H.R. acknowledges support from the Max Planck Korea/POSTECH Research Initiative of the NRF under Project No. NRF-2011-0031558. M.B.S. was supported by the Division of Materials Science and Engineering through the Chemical and Mechanical Properties of Surfaces and Interfaces Program. Portions of the computational work were done with NERSC resources. M.F.C. acknowledges support from National Science Foundation grant EFMA-1542741 (sample surface preparation development).

Author information

Author notes

    • Sara Barja
    •  & Sebastian Wickenburg

    These authors contributed equally to this work.

Affiliations

  1. Molecular Foundry, Lawrence Berkeley National Laboratory, California 94720, USA

    • Sara Barja
    • , Sebastian Wickenburg
    • , Zhen-Fei Liu
    • , Ed Wong
    • , D. Frank Ogletree
    • , Jeffrey B. Neaton
    •  & Alexander Weber-Bargioni
  2. Materials Sciences Division, Lawrence Berkeley National Laboratory, California 94720, USA

    • Sara Barja
    • , Sebastian Wickenburg
    • , Zhen-Fei Liu
    • , Ed Wong
    • , Miquel B. Salmeron
    • , Feng Wang
    • , Michael F. Crommie
    • , D. Frank Ogletree
    • , Jeffrey B. Neaton
    •  & Alexander Weber-Bargioni
  3. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Yi Zhang
    • , Hyejin Ryu
    • , Zahid Hussain
    •  & Sung-Kwan Mo
  4. National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China

    • Yi Zhang
  5. Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA

    • Miguel M. Ugeda
    • , Miquel B. Salmeron
    • , Feng Wang
    • , Michael F. Crommie
    •  & Jeffrey B. Neaton
  6. CIC nanoGUNE, Donostia-San Sebastián 20018, Spain

    • Miguel M. Ugeda
  7. Ikerbasque, Basque Foundation for Science, Bilbao 48013, Spain

    • Miguel M. Ugeda
  8. Stanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA

    • Zhi-Xun Shen
  9. Department of Materials Science and Engineering, University of California Berkeley, California 94720, USA

    • Miquel B. Salmeron
  10. Kavli Energy NanoSciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Feng Wang
    • , Michael F. Crommie
    •  & Jeffrey B. Neaton

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Contributions

S.B., S.W. and A.W.-B. conceived the work and designed the research strategy. S.B. and S.W. measured and analysed the STM/STS and nc-AFM data. Z.-F.L. performed the theoretical calculations. Y.Z. and H.R. performed the MBE growth and characterization of the samples. S.-K.M., Z.H. and Z.-X.S. supervised the MBE growth and sample characterization. J.B.N. supervised the theoretical calculations. M.M.U., E.W., M.B.S., F.W., M.F.C. and D.F.O. participated in the acquisition and interpretation of the experimental data. A.W.-B. supervised the STM/STS and nc-AFM measurements. S.B. wrote the manuscript with help from S.W., Z.-F.L., D.F.O., J.B.N. and A.W.-B. All authors contributed to the scientific discussion and manuscript revisions.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Sara Barja or D. Frank Ogletree or Alexander Weber-Bargioni.

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DOI

https://doi.org/10.1038/nphys3730

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