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Niobium doping induced mirror twin boundaries in MBE grown WSe2 monolayers


Mirror twin boundary (MTB) brings unique one-dimensional (1D) physics and properties into two-dimensional (2D) transition metal dichalcogenides (TMDCs), but they were rarely observed in non-Mo-based TMDCs. Herein, by post-growth Nb doping, high density 4|4E-W and 4|4P-Se mirror twin boundaries (MTBs) were introduced into molecular beam epitaxy (MBE) grown WSe2 monolayers. Of them, 4|4E-W MTB with a novel structure was discovered experimentally for the first time, while 4|4P-Se MTBs present a random permutations of W and Nb, forming a 1D alloy system. Comparison between the doped and non-doped WSe2 confirmed that Nb dopants are essential for MTB formation. Furthermore, quantitative statistics reveal the areal density of MTBs is directly proportional to the concentration of Nb dopants. To unravel the injection pathway of Nb dopants, first-principles calculations about a set of formation energies for excess Nb atoms with different configurations were conducted, based on which a model explaining the origin of MTBs introduced by excess metal was built. We conclude that the formation of MTBs is mainly driven by the collective evolution of excess Nb atoms introduced into the lattice of host WSe2 crystal and subsequent displacement of metal atoms (W or Nb). This study provides a novel way to tailor the MTBs in 2D TMDC materials via proper metal doping and presents new opportunities for exploring the intriguing properties.

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The authors thank Zhoubin Yu for fruitful discussions, Dr. Fang Lin for kindly providing the codes for two-Gaussians filtering, Degong Ding, Haifeng Wang, and Daliang He for critical comments on editing the manuscript. B.W. and C.J. acknowledged financial support from the National Natural Science Foundation of China (Nos. 51761165024, 51772265, and 61721005), the Zhejiang Provincial Natural Science Foundation (No. D19E020002), the 111 project (No. B16042) and Zhejiang University Education Foundation Global Partnership Fund. M. H. X. acknowledges the financial support from a Collaborative Research Fund (C7036-17W) and a General Research Grant (No. 17327316) from the Research Grant Cuncil, Hong Kong special Administrative Region, China. We also acknowledge the support from the NSFC/RGC joint research grant (Nos. N_HKU732/17 and 51761165024). H. P. K. acknowledges financial support from the Academy of Finland through Project No. 311058, and CSC-IT Center for Science Ltd. for generous grants of computer time. The work on electron microscopy was carried out at the Center of Electron Microscopy of Zhejiang University.

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Correspondence to Hannu-Pekka Komsa or Chuanhong Jin.

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Wang, B., Xia, Y., Zhang, J. et al. Niobium doping induced mirror twin boundaries in MBE grown WSe2 monolayers. Nano Res. 13, 1889–1896 (2020).

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  • mirror twin boundaries
  • niobium doping
  • molecular beam epitaxy
  • transition metal dichalcogenides
  • niobium
  • tungsten diselenide