Defect Coupling and Sub-Angstrom Structural Distortions in W1-xMoxS2 Monolayers
Defect Coupling and Sub-Angstrom Structural Distortions in W1-xMoxS2 Monolayers
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DOI：
10.1021/acs.nanolett.6b05045
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发表时间：
2017-05-01
期刊：
影响因子：
10.8
通讯作者：
Alem, Nasim
中科院分区：
文献类型：
--
作者：
Azizi, Amin;Wang, Yuanxi;Alem, Nasim
二维材料提供了一个非常丰富的材料平台，可以在原子水平上研究不同材料行为的起源，而掺杂则是调整此类材料功能特性的关键手段。这种掺杂剂周围的局部原子结构对决定材料的行为至关重要，因为它可以调节散射、催化活性、电子和磁性等。-在这里，使用亚埃分辨率的象差校正扫描透射电子显微镜(STEM)结合密度泛函理论计算，我们证明了Mo掺杂剂与WS2单分子膜中两种类型的缺陷之间的强烈耦合：硫单空位和晶界。虽然Mo确实占据了过渡金属晶格位置，但它并不是一个理想的替代掺杂：与STEM鉴定的S空位中80%的Mo掺杂类似，这种亲和力似乎通过部分占据的：带隙中缺陷态的对称性破缺而得到增强。虽然Mo掺杂本身不会显著扭曲WS2晶格，但它明显促进了与之配对的硫单空位的带电，从而导致了大量的晶格变形，这与第一性原理计算的结果是一致的。这种异位掺杂与空位的耦合可能被用来控制过渡金属二卤化物(TMD)中硫系空位的分布和位置，方法是将空位分成高Mo浓度的区域，这些区域被有意地放置在远离TMD器件的有源区的位置。
Two-dimensional materials offer a remarkably rich materials platform to study the origin of different material behaviors at the atomic level, and doping provides a key means of tailoring such materials' functional properties. The local atomic structure around such dopants can be critically important in determining the material's behavior as it could modulate scattering, catalytic activity, electronic and magnetic properties, and so forth.-Here, using aberration-corrected scanning transmission electron microscopy (STEM) with sub-Angstrom resolution in conjunction with density functional theory calculations, we demonstrate a strong coupling between Mo dopants and two types of defects in WS2 monolayers: sulfur monovacancies and grain boundaries. Although Mo does occupy a transition metal lattice site, it is not an ideal substitutional dopant: similar to 80% of the S vacancies identified by STEM colocalize with Mo dopants, an affinity that appears to be enhanced by symmetry breaking of a partially occupied: midgap defect state. Although a Mo dopant by itself does not considerably distort the WS2 lattice, it induces substantial lattice deformation by apparently facilitating the charging of a sulfur monovacancy paired with it, which is consistent with the results of first-principles calculations. This coupling of foreign substitutional dopants with vacancies could potentially be exploited to control the distribution and location of chalcogenide vacancies within transition metal dichalcogenides (TMD), by segregating vacancies into regions of high Mo concentration that are:purposely placed away from active regions of TMD-based devices.