Department of Physics, University of Washington , Seattle, Washington 98195, United States.
Department of Physics and Centre of Theoretical and Computational Physics, University of Hong Kong , Hong Kong, China.
Nano Lett. 2017 Feb 8;17(2):1194-1199. doi: 10.1021/acs.nanolett.6b04944. Epub 2017 Jan 23.
Raman scattering is a ubiquitous phenomenon in light-matter interactions, which reveals a material's electronic, structural, and thermal properties. Controlling this process would enable new ways of studying and manipulating fundamental material properties. Here, we report a novel Raman scattering process at the interface between different van der Waals (vdW) materials as well as between a monolayer semiconductor and 3D crystalline substrates. We find that interfacing a WSe monolayer with materials such as SiO, sapphire, and hexagonal boron nitride (hBN) enables Raman transitions with phonons that are either traditionally inactive or weak. This Raman scattering can be amplified by nearly 2 orders of magnitude when a foreign phonon mode is resonantly coupled to the A exciton in WSe directly or via an A optical phonon from WSe. We further showed that the interfacial Raman scattering is distinct between hBN-encapsulated and hBN-sandwiched WSe sample geometries. This cross-platform electron-phonon coupling, as well as the sensitivity of 2D excitons to their phononic environments, will prove important in the understanding and engineering of optoelectronic devices based on vdW heterostructures.
拉曼散射是光与物质相互作用中的一种普遍现象，它揭示了物质的电子、结构和热性质。控制这一过程将使人们能够以新的方式研究和操纵基本材料特性。在这里，我们报告了在不同范德华（vdW）材料之间以及单层半导体和 3D 晶状衬底之间的一种新的拉曼散射过程。我们发现，将 WSe 单层与 SiO、蓝宝石和六方氮化硼（hBN）等材料相结合，可以实现传统上处于非活性或较弱状态的声子的 Raman 跃迁。当外来声子模式直接或通过 WSe 的 A 光学声子与 WSe 的 A 激子共振耦合时，这种 Raman 散射可以增强近 2 个数量级。我们还表明，在 hBN 封装和 hBN 夹在中间的 WSe 样品几何形状之间，界面 Raman 散射是不同的。这种跨平台的电子-声子耦合，以及 2D 激子对其声子环境的敏感性，将在基于 vdW 异质结构的光电设备的理解和工程中证明是重要的。
