Koo Yeonjeong, Kim Yongchul, Choi Soo Ho, Lee Hyeongwoo, Choi Jinseong, Lee Dong Yun, Kang Mingu, Lee Hyun Seok, Kim Ki Kang, Lee Geunsik, Park Kyoung-Duck
Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea.
Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea.
Adv Mater. 2021 Apr;33(17):e2008234. doi: 10.1002/adma.202008234. Epub 2021 Mar 11.
The tunability of the bandgap, absorption and emission energies, photoluminescence (PL) quantum yield, exciton transport, and energy transfer in transition metal dichalcogenide (TMD) monolayers provides a new class of functions for a wide range of ultrathin photonic devices. Recent strain-engineering approaches have enabled to tune some of these properties, yet dynamic control at the nanoscale with real-time and -space characterizations remains a challenge. Here, a dynamic nano-mechanical strain-engineering of naturally-formed wrinkles in a WSe monolayer, with real-time investigation of nano-spectroscopic properties is demonstrated using hyperspectral adaptive tip-enhanced PL (a-TEPL) spectroscopy. First, nanoscale wrinkles are characterized through hyperspectral a-TEPL nano-imaging with <15 nm spatial resolution, which reveals the modified nano-excitonic properties by the induced tensile strain at the wrinkle apex, for example, an increase in the quantum yield due to the exciton funneling, decrease in PL energy up to ≈10 meV, and a symmetry change in the TEPL spectra caused by the reconfigured electronic bandstructure. Then the local strain is dynamically engineered by pressing and releasing the wrinkle apex through an atomic force tip control. This nano-mechanical strain-engineering allows to tune the exciton dynamics and emission properties at the nanoscale in a reversible fashion. In addition, a systematic switching and modulation platform of the wrinkle emission is demonstrated, which provides a new strategy for robust, tunable, and ultracompact nano-optical sources in atomically thin semiconductors.
过渡金属二硫属化物（TMD）单层中带隙、吸收和发射能量、光致发光（PL）量子产率、激子传输和能量转移的可调谐性为各种超薄光子器件提供了一类新功能。最近的应变工程方法能够调节其中一些特性，但在纳米尺度上进行具有实时和空间表征的动态控制仍然是一个挑战。在此，利用高光谱自适应针尖增强PL（a-TEPL）光谱展示了对WSe单层中自然形成的皱纹进行动态纳米机械应变工程，并对纳米光谱特性进行实时研究。首先，通过具有<15 nm空间分辨率的高光谱a-TEPL纳米成像对纳米级皱纹进行表征，这揭示了皱纹顶端的拉伸应变所改变的纳米激子特性，例如，由于激子漏斗效应导致量子产率增加、PL能量降低高达≈10 meV，以及由重新配置的电子能带结构引起的TEPL光谱对称性变化。然后，通过原子力针尖控制按压和释放皱纹顶端来动态设计局部应变。这种纳米机械应变工程允许以可逆方式在纳米尺度上调节激子动力学和发射特性。此外，还展示了一种皱纹发射的系统切换和调制平台，这为原子级薄半导体中的稳健、可调谐和超紧凑纳米光源提供了一种新策略。
