IBS Center for Integrated Nanostructure Physics, Institute for Basic Science, Suwon 440-746, Republic of Korea and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
Nanoscale. 2017 Feb 9;9(6):2272-2278. doi: 10.1039/c6nr08813a.
Exciton transitions are mostly responsible for the optical properties of transition metal dichalcogenide monolayers (1L-TMDs). Extensive studies of optical and structural characterization indicated that the presence of local structural defects and charge population critically influence the exciton emissions of 1L-TMDs. However, due to large variations of sample and experimental conditions, the exact mechanism of the exciton emission influenced by local structural defects and charge population is not clearly understood. In this work by using near-field scanning optical imaging and spectroscopy, we directly visualized spatially- and spectrally-resolved emission profiles of excitons, trions and defect bound excitons in CVD-grown monolayer tungsten disulfide (1L-WS) with ∼70 nm spatial resolution. We found that exciton emission is spatially uniform while emission of trions and defect bound excitons was strongly modulated by the presence of structural features such as defects and wrinkles. We also visually observe a strong correlation between local charge accumulation and the trion formation upon increased photo-excitation.
激子跃迁主要负责过渡金属二卤化物单层（1L-TMDs）的光学性质。广泛的光学和结构特性研究表明，局部结构缺陷和电荷分布的存在对 1L-TMDs 的激子发射有至关重要的影响。然而，由于样品和实验条件的巨大变化，局部结构缺陷和电荷分布影响激子发射的确切机制尚不清楚。在这项工作中，我们通过使用近场扫描光学成像和光谱学，直接可视化了 CVD 生长的单层二硫化钨（1L-WS）中激子、三激子和缺陷束缚激子的空间和光谱分辨发射谱，空间分辨率约为 70nm。我们发现激子发射是空间均匀的，而三激子和缺陷束缚激子的发射则强烈地受到结构特征（如缺陷和褶皱）的调制。我们还观察到，在增加光激发时，局部电荷积累与三激子的形成之间存在强烈的相关性。
