Department of Materials Science and Engineering, and Shenzhen Key Laboratory of Nanoimprint Technology, South University of Science and Technology , Shenzhen 518055, P. R. China.
Department of Physics and Center for 1D/2D Quantum Materials, The Hong Kong University of Science and Technology , Clear Water Bay, Kowloon, Hong Kong, P. R. China.
ACS Appl Mater Interfaces. 2017 Jan 11;9(1):763-770. doi: 10.1021/acsami.6b13777. Epub 2016 Dec 20.
Monolayer MoS crystals with tailored morphologies have been shown to exhibit shape-dependent properties and thus have potential applications in building nanodevices. However, a deep understanding of the relationship between the shape and defect structures in monolayer MoS is yet elusive. Monolayer MoS crystals in polygonal shapes, including triangle, tetragon, pentagon, and hexagon, are grown using the chemical vapor deposition technique. Compared with other shapes, the hexagon MoS crystal contains more electron-donor defects that are mainly due to sulfur vacancies. In the triangular shapes, the defects are mainly distributed at the vertices of the shapes while they are located at the center of hexagonal shapes. On the basis of the Coulomb interaction of exciton and trion, quantitative calculations demonstrate a high electron density (∼10/cm) and high Fermi level (E - E = 15 meV) for hexagonal shape at room temperature, compared to triangular shapes (∼10/cm, E - E ≈ 30 meV). These findings verify that a much higher number of donor-like sulfur vacancies are formed in hexagonal MoS shapes. This property allows more electrons or trions to localize in such sites through the physical/chemical adsorption of O/HO, which results in a strong enhancement of the light emission efficiency in the hexagonal crystal. The findings provide a better understanding of the formation of shape-dependent defect structures of monolayer MoS crystals and are inspiring for applications in fabricating nanoelectronic and optoelectronic devices through defect engineering.
具有定制形态的单层 MoS 晶体表现出形态依赖的性质，因此在构建纳米器件方面具有潜在的应用。然而，对于单层 MoS 中的形状和缺陷结构之间的关系，我们还没有深入的了解。使用化学气相沉积技术生长出具有多边形形状的单层 MoS 晶体，包括三角形、四边形、五边形和六边形。与其他形状相比，六边形 MoS 晶体含有更多的电子给体缺陷，主要是由于硫空位。在三角形中，缺陷主要分布在形状的顶点处，而在六边形中，缺陷位于中心。基于激子和三电子的库仑相互作用，定量计算表明，与三角形相比（∼10/cm，E - E ≈ 30 meV），在室温下，六边形的电子密度（∼10/cm）和费米能级（E - E = 15 meV）更高。这些发现证实了在六边形 MoS 形状中形成了更多的类施主硫空位。这种性质允许更多的电子或三电子通过 O/HO 的物理/化学吸附定位在这些位置，从而导致六边形晶体的光发射效率得到强烈增强。这些发现提供了对单层 MoS 晶体中形状依赖的缺陷结构形成的更好理解，并为通过缺陷工程制造纳米电子和光电子器件的应用提供了启示。
