Abstract

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.

中文翻译：

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铌掺杂在MBE生长的WSe 2单层中引起镜面孪晶边界

摘要

镜面孪晶边界（MTB）将独特的一维（1D）物理性质和特性带入了二维（2D）过渡金属二硫化碳（TMDC），但在非基于Mo的TMDC中很少观察到它们。在此，通过生长后Nb掺杂，将高密度4 | 4E-W和4 | 4P-Se镜面孪晶边界（MTB）引入分子束外延（MBE）生长的WSe ₂单层中。其中，首次通过实验发现了具有新颖结构的4 | 4E-W MTB，而4 | 4P-Se MTB则呈现出W和Nb的随机排列，从而形成了一维合金体系。掺杂和未掺杂的WSe _2的比较证实Nb掺杂剂对MTB的形成至关重要。此外，定量统计表明，MTB的面密度与Nb掺杂剂的浓度成正比。为了阐明Nb掺杂剂的注入途径，进行了关于具有不同构型的过量Nb原子的一组形成能的第一性原理计算，在此基础上建立了解释过量金属引入的MTB起源的模型。我们得出结论，MTB的形成主要是由引入宿主WSe ₂晶格中的过量Nb原子的集体演化驱动的晶体和随后的金属原子（W或Nb）置换。这项研究提供了一种通过适当的金属掺杂在2D TMDC材料中定制MTB的新颖方法，并为探索有趣的特性提供了新的机会。