Research Article


2020, 13(7): 1889–1896


Niobium doping induced mirror twin boundaries in MBE grown WSe2 monolayers

Bo Wang1,2, Yipu Xia3, Junqiu Zhang3, Hannu-Pekka Komsa4 (*), Maohai Xie3, Yong Peng1, and Chuanhong Jin2,1,5 (*)

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1 Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China
2 State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310024, China
3 Physics Department, The University of Hong Kong, Pokfulam Road, Hong Kong 999077, China
4 Department of Applied Physics, Aalto University, 00076 Aalto, Finland
5 Hunan Institute of Advanced Sensing and Information Technology, Xiangtan University, Xiangtan 411201, China

Keywords: mirror twin boundaries, niobium doping, molecular beam epitaxy, transition metal dichalcogenides, niobium, tungsten diselenide
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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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Niobium doping induced mirror twin boundaries in MBE grown WSe2 monolayers. Nano Res. 2020, 13(7): 1889–1896

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