Department of Physics, Department of Chemistry, and JILA, University of Colorado , Boulder, Colorado 80309, United States.
Department of Physics, Department of Materials Science and Engineering, University of Washington , Seattle, Washington 98195, United States.
Nano Lett. 2016 Apr 13;16(4):2621-7. doi: 10.1021/acs.nanolett.6b00238. Epub 2016 Mar 8.
Many classes of two-dimensional (2D) materials have emerged as potential platforms for novel electronic and optical devices. However, their physical properties are strongly influenced by nanoscale heterogeneities in the form of edges, twin boundaries, and nucleation sites. Using combined tip-enhanced Raman scattering and photoluminescence (PL) nanospectroscopy and nanoimaging, we study the associated effects on the excitonic properties in monolayer WSe2 grown by physical vapor deposition. With ∼15 nm spatial resolution, we resolve nanoscale correlations of PL spectral intensity and shifts with crystal edges and internal twin boundaries associated with the expected exciton diffusion length. Through an active atomic force tip interaction we can control the crystal strain on the nanoscale and tune the local bandgap in reversible (up to 24 meV shift) and irreversible (up to 48 meV shift) fashion. This allows us to distinguish the effect of strain from the dominant influence of defects on the PL modification at the different structural heterogeneities. Hybrid nano-optical spectroscopy and imaging with nanomechanical strain control thus enables the systematic study of the coupling of structural and mechanical degrees of freedom to the nanoscale electronic and optical properties in layered 2D materials.
许多二维（2D）材料已成为新型电子和光学器件的潜在平台。然而，它们的物理性质受到边缘、孪晶界和成核点等纳米级不均匀性的强烈影响。我们使用结合了尖端增强拉曼散射和光致发光（PL）纳米光谱学和纳米成像技术，研究了在通过物理气相沉积生长的单层 WSe2 中，这些相关效应对激子性质的影响。通过约 15nm 的空间分辨率，我们解析了 PL 光谱强度和与晶体边缘和内部孪晶界相关的位移的纳米级相关性，这些与预期的激子扩散长度有关。通过主动原子力针尖相互作用，我们可以在纳米尺度上控制晶体应变，并以可逆（高达 24meV 的位移）和不可逆（高达 48meV 的位移）的方式调整局部能带隙。这使我们能够区分应变的影响与不同结构异质体上 PL 修饰中缺陷的主要影响。因此，具有纳米机械应变控制的混合纳米光学光谱学和成像技术，使得对层状二维材料中结构和机械自由度与纳米电子和光学性质的耦合的系统研究成为可能。
