Department of Materials Science and Engineering, Izmir Institute of Technology, 35430 Izmir, Turkey.
Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.
J Chem Phys. 2018 Aug 28;149(8):084707. doi: 10.1063/1.5043207.
Using first principles calculations, we study the structural and phononic properties of the recently synthesized Janus type single layers of molybdenum dichalcogenides. The Janus MoSSe single layer possesses 2H crystal structure with two different chalcogenide sides that lead to out-of-plane anisotropy. By virtue of the asymmetric structure of the ultra-thin Janus type crystal, we induced the out-of-plane anisotropy to show the distinctive vertical pressure effect on the vibrational properties of the Janus material. It is proposed that for the corresponding Raman active optical mode of the Janus structure, the phase modulation and the magnitude ratio of the strained atom and its first neighbor atom adjust the distinctive change in the eigen-frequencies and Raman activity. Moreover, a strong variation in the Raman activity of the Janus structure is obtained under bivertical and univertical strains. Not only eigen-frequency shifts but also Raman activities of the optical modes of the Janus structure exhibit distinguishable features. This study reveals that the vertical anisotropic feature of the Janus structure under Raman measurement allows us to distinguish which side of the Janus crystal interacts with the externals (substrate, functional adlayers, or dopants).
我们运用第一性原理计算研究了最近合成的 Janus 型单层二硫化钼的结构和声子性质。Janus MoSSe 单层具有 2H 晶体结构，两侧具有两种不同的硫属元素，导致面外各向异性。由于超薄 Janus 型晶体的不对称结构，我们引入了面外各向异性，从而对 Janus 材料的振动特性表现出独特的垂直压力效应。我们提出，对于 Janus 结构的相应 Raman 活性光学模式，相位调制和应变原子及其第一近邻原子的大小比可以调节本征频率和 Raman 活性的显著变化。此外，在双垂直应变和单垂直应变下，Janus 结构的 Raman 活性得到了强烈的变化。不仅本征频率的移动，而且 Janus 结构的光学模式的 Raman 活性都表现出可区分的特征。本研究表明，在 Raman 测量下，Janus 结构的垂直各向异性特征允许我们区分 Janus 晶体的哪一侧与外部（衬底、功能覆盖层或掺杂剂）相互作用。
