Li Yujie, Chen Yuzhong, Zhou Hongzhi, Zhu Haiming
State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China.
ACS Nano. 2021 Mar 23;15(3):5495-5501. doi: 10.1021/acsnano.1c00243. Epub 2021 Mar 9.
Controlling the optical response of two-dimensional (2D) layered materials is critical for their optoelectronic and photonic applications. Current transient optical modulation of 2D semiconductors is mainly based on the band filling effect, which requires internal exciton/charge occupation from photoexcitation or charge injection. However, 2D atomically thin layers exhibit a strong excitonic effect and environmental sensitivity, offering exciting opportunities to engineer their optical properties through an external dielectric or electronic environment. Here, using femtosecond transient absorption spectroscopy as a tool and transition-metal dichalcogenide (TMD) van der Waals heterostructures with type I band alignment, we show the transient absorption modulation of the TMD layer by excitons at ultimate proximity without direct photoexcitation or exciton/charge occupation. Further layer-dependent study indicates the presence of excitons reduces the exciton oscillator strength in adjacent layers through the electric field effect because of environmental sensitivity and proximity of 2D materials. This result demonstrates the transient optical modulation with decoupled light absorption and modulation components and suggests an alternative approach to control the optical response of 2D materials for optoelectronic and photonic applications.
控制二维（2D）层状材料的光学响应对于其光电和光子应用至关重要。目前二维半导体的瞬态光学调制主要基于能带填充效应，这需要光激发或电荷注入产生的内部激子/电荷占据。然而，二维原子薄层表现出强烈的激子效应和环境敏感性，为通过外部介电或电子环境调控其光学性质提供了令人兴奋的机会。在此，我们使用飞秒瞬态吸收光谱作为工具，并利用具有I型能带排列的过渡金属二硫属化物（TMD）范德华异质结构，展示了在没有直接光激发或激子/电荷占据的情况下，激子在极近距离对TMD层的瞬态吸收调制。进一步的层依赖研究表明，由于二维材料的环境敏感性和近距离，激子的存在通过电场效应降低了相邻层中的激子振子强度。这一结果证明了光吸收和调制成分解耦的瞬态光学调制，并为控制二维材料在光电和光子应用中的光学响应提供了一种替代方法。
