Monolayer transition-metal dichalcogenides (TMDCs) have been extensively studied due to their wide range of physical properties and applications. It has been demonstrated that the electron beam in a transmission electron microscope (TEM) or scanning TEM (STEM) generates chalcogen vacancies that agglomerate into dispersed linelike or holelike defects. Here we employ a STEM electron beam and demonstrate that, in $\mathrm{W}{\mathrm{Se}}_2$, beam-induced chalcogen vacancies initially form certain dispersed multivacancy structures, as seen in TMDCs in prior work. However, with suitable control of the STEM focused electron beam, these multivacancies gradually evolve into a dense network of ten-, 12-, 14-, and 16-member ring round holes, whereas the same process leads predominantly to chalcogen-vacancy line defects in other trigonal-prismatic TMDCs. Density functional theory calculations find that the underlying atomic-scale processes lead preferentially to defect structures that lower the total energy so that we are able to track the formation of the observed multivacancy complexes, which then lead to the formation of dense large round holes in $\mathrm{W}{\mathrm{Se}}_2$. The same processes in $\mathrm{W}{\mathrm{S}}_2$, however, are energetically unfavorable, while linear multivacancy defects are preferred, as observed. The demonstrated control of the formation of unique high-density round holes in $\mathrm{W}{\mathrm{Se}}_2$ has potential for applications such as atomic and molecular sieving.

中文翻译：

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电子束辐照在单层WSe2中形成优先孔缺陷

由于单层过渡金属二卤化物（TMDC）的广泛物理特性和应用，因此已进行了广泛的研究。已经证明，透射电子显微镜（TEM）或扫描TEM（STEM）中的电子束产生硫族元素空位，其聚集成分散的线状或孔状缺陷。在这里，我们使用了STEM电子束，并证明了$\mathrm{w\; ^}{硒}_{\mathrm{2个}}$，束流激发的硫族元素空位最初形成某些分散的多空位结构，如在先前工作中的TMDC中所见。但是，在适当控制STEM聚焦电子束的情况下，这些多空位逐渐演变成由10、12、14和16元环孔组成的密集网络，而同一过程主要导致硫族元素空位线缺陷在其他三角棱柱型TMDC中。密度泛函理论计算发现，潜在的原子尺度过程优先导致缺陷结构降低了总能量，因此我们能够跟踪观察到的多空位络合物的形成，然后导致形成密集的大圆孔。$\mathrm{w\; ^}{硒}_{\mathrm{2个}}$。相同的过程$\mathrm{w\; ^}{\mathrm{小号}}_{\mathrm{2个}}$然而，如观察到的那样，在能量上是不利的，而线性多空位缺陷是优选的。经证明可控制形成独特的高密度圆孔$\mathrm{w\; ^}{硒}_{\mathrm{2个}}$ 具有原子和分子筛等应用的潜力。