Taghinejad Hossein, Rehn Daniel A, Muccianti Christine, Eftekhar Ali A, Tian Mengkun, Fan Tianren, Zhang Xiang, Meng Yuze, Chen Yanwen, Nguyen Tran-Vinh, Shi Su-Fei, Ajayan Pulickel M, Schaibley John, Reed Evan J, Adibi Ali
Department of Physics , University of Arizona , Tucson , Arizona 85721 , United States.
Department of Materials Science and Nanoengineering , Rice University , Houston , Texas 77005 , United States.
ACS Nano. 2018 Dec 26;12(12):12795-12804. doi: 10.1021/acsnano.8b07920. Epub 2018 Nov 26.
Alloying plays a central role in tailoring the material properties of 2D transition-metal dichalcogenides (TMDs). However, despite widespread reports, the details of the alloying mechanism in 2D TMDs have remained largely unknown and are yet to be further explored. Here, we combine a set of systematic experiments with ab initio density functional theory (DFT) calculations to unravel a defect-mediated mechanism for the alloying of monolayer TMD crystals. In our alloying approach, a monolayer MoSe film serves as a host crystal in which exchanging selenium (Se) atoms with sulfur (S) atoms yields a MoSSe alloy. Our study reveals that the driving force required for the alloying of CVD-grown films with abundant vacancy-type defects is significantly lower than that required for the alloying of exfoliated films with fewer vacancies. Indeed, we show that pre-existing Se vacancies in the host MoSe lattice mediate the replacement of chalcogen atoms and facilitate the synthesis of MoSSe alloys. Our DFT calculations suggest that S atoms can bind to Se vacancies and then diffuse throughout the host MoSe lattice via exchanging the position with Se vacancies, further supporting our proposed defect-mediated alloying mechanism. Beside native vacancy defects, we show that the existence of large-scale defects in CVD-grown MoSe films causes the fracture of alloys under the alloying-induced strain, while no such effect is observed in exfoliated MoSe films. Our study provides a deep insight into the details of the alloying mechanism and enables the synthesis of 2D alloys with tunable properties.
合金化在定制二维过渡金属二硫属化物（TMDs）的材料性能方面起着核心作用。然而，尽管有广泛的报道，但二维TMDs中合金化机制的细节在很大程度上仍不为人知，有待进一步探索。在此，我们将一系列系统实验与从头算密度泛函理论（DFT）计算相结合，以揭示单层TMD晶体合金化的缺陷介导机制。在我们的合金化方法中，单层MoSe薄膜作为主体晶体，其中用硫（S）原子取代硒（Se）原子可得到MoSSe合金。我们的研究表明，具有大量空位型缺陷的化学气相沉积（CVD）生长薄膜合金化所需的驱动力明显低于空位较少的剥离薄膜合金化所需的驱动力。事实上，我们表明主体MoSe晶格中预先存在的Se空位介导了硫属原子的取代，并促进了MoSSe合金的合成。我们的DFT计算表明，S原子可以与Se空位结合，然后通过与Se空位交换位置在整个主体MoSe晶格中扩散，进一步支持了我们提出的缺陷介导合金化机制。除了原生空位缺陷外，我们还表明，CVD生长的MoSe薄膜中大规模缺陷的存在会导致合金在合金化诱导应变下断裂，而在剥离的MoSe薄膜中未观察到这种效应。我们的研究深入洞察了合金化机制的细节，并能够合成具有可调性能的二维合金。
