论文标题
室温微型和纳米光致发光揭示的夹心单层WSE2中的深色激子相关发射的辐射衰变
Radiative Decay of Dark Exciton Related Emission in a Sandwiched Monolayer WSe2 Revealed by Room Temperature Micro and Nano Photoluminescence
论文作者
论文摘要
近年来，TMDC由于其独特的间接间接而引起了很多关注，因为它们独特地直接从散装到单层厚度进行了频段差距过渡。平面外向的强限制会增强带电颗粒（E-H对）之间的库仑电势，从而大大增加了激子结合能。单层中的晶格反演不对称产生了两个非等效的（但在能量中退化）带有伪旋转的时间反向极化保护的条带边缘。然而，在价带中存在强旋轨道耦合和传导带中的弱自旋分解导致WX2（x = s，se）在WX2（x = s，se）中的最低激子被禁止旋转和光学上的黑暗。由于它们的寿命长，深色激子（XD）对于量子光学和光电应用非常有吸引力。迄今为止，研究XD排放仅限于低温温度或需要在室温（RT）下观察它们的非常复杂的实验构型。在这里，我们展示了RT在RT上由Micro和Nano PL研究的1L-WSE2中XD相关排放的辐射衰减的新方法。 1L-WSE2薄片被贵金属（AU或Ag）底物和PDMS纳米点夹住，可提供与2D平面相对于2D平面的局部局部外偶极矩。这种强的偶极矩不仅增强了WSE2中的XD，还会由于RT可见的外部电荷缺陷而产生结合的激子。通过TEPL研究了这些相关排放的空间分布，其空间分辨率<10 nm，确认了这些激子在PDMS纳米斑点中的限制。最后，通过从薄片顶部删除纳米斑，我们能够在1L-WE2中恢复明亮的激子。我们的方法为在低维半导体中的深刻理解和利用激子特性铺平了道路，从而为量子光学元件提供了平台。
TMDCs have attracted a lot of attention in recent years due to their unique indirect to direct band gap transition from bulk to monolayer thickness. Strong confinement in the out-of-plane direction enhances the Coulomb potential between the charged particles (e-h pairs) and thus increases the exciton binding energy dramatically. The lattice inversion asymmetry in a monolayer creates two non-equivalent (but degenerate in energy) band edges protected by time reversal polarisation via pseudo-spin. However, the presence of strong spin-orbit coupling in the valence band and weak spin-splitting in the conduction band results in the lowest lying exciton in WX2 (X = S, Se) being spin forbidden and optically dark. Because of their long life times, dark excitons (XD) are highly attractive for quantum optics and optoelectronic applications. To date studying XD emission is limited to cryogenic temperature or required very complex experimental configurations to observe them at room temperature (RT). Here, we demonstrate a novel approach of radiative decay of XD related emissions in 1L-WSe2 studied by micro and nano PL at RT. 1L-WSe2 flakes were sandwiched by noble metal (Au or Ag) substrates and PDMS nano-patches providing a strong local out-of-plane dipole moment with respect to the 2D plane. This strong dipole moment not only enhances the XD in WSe2, it also produces bound excitons due to extrinsic charge defects visible at RT. The spatial distributions of these XD related emissions were studied by TEPL with a spatial resolution < 10 nm confirming the confinement of these excitons within the PDMS nano-patches. Finally, by removing the nano-patches from the top of the flakes we are able to recover the bright excitons in the 1L-WSe2. Our approach paves the way for deep understanding and to harness excitonic properties in low dimensional semiconductors, thus offering a platform towards quantum optics.
