强耦合杂化态对二维纳米材料功能调控的超快光谱研究

Two-dimensional transition metal disulfides of semiconductors (TMDCs) possess large natural band gap, and can form van der Waals heterojunctions by simple stacking single layers. These advantages make it ideal candidates for the fabrication of ultrathin, transparent and flexible nano-electrooptical devices. However, due to the limited absorption capacity of light by monolayer materials and the limitation of carrier mobility compared with other traditional semiconductors, the efficiency of TMDCs nano-optoelectronic devices is still low, and there is still a long way to the practical application. In this project, the surface plasmon-TMDCs strong coupling hybrid system is constructed, and the multi-characteristics of the strongly coupled hybrid state are used to enhance the modulation of TMDCs material functionalities, which include: to control the band structure of TMDCs monolayers and expand the band-edge absorption range and capacity, to enhance the carrier mobility via the delocalization characteristics of the hybrid state, to construct an effcient and ultrafast charge/energy transfer pathway in the TMDCs heterojunction by the middle hybrid state under multi-strong coupling hybrid systems. To elucidate the physical mechanism of the strong coupling effect on the function control of TMDCs, the generation and evolution of strong coupled hybrid states will be detected by time-resolved spectroscopy, and therefore to provide theoretical basis for improvement of the efficiency of TMDCs nano-optoelectronic devices.

半导体性的二维过渡金属硫化物（TMDCs）具有较大的天然带隙，单层TMDCs材料还可以通过简单堆叠形成范德华异质结，为超薄透明柔性纳米光电器件的制备提供了新方案。然而，由于单层材料对光的吸收能力有限、载流子迁移率相较于传统半导体仍然较低等材料自身特性的限制，TMDCs纳米光电器件的效率仍然偏低，距离实际应用还有很大差距。本项目将通过构筑表面等离激元-TMDCs材料强耦合体系，利用强耦合杂化态所具有的多重特性实现对TMDCs材料功能的增强调控，具体包括：对TMDCs单层材料的能带结构进行调控，拓展带边吸收范围；利用杂化态的离域化特性，提升载流子迁移率；通过多重强耦合杂化下的中间能态建立TMDCs异质结中电荷转移/能量传递的快速通道。并采用时间分辨光谱技术对强耦合杂化态的产生和演化过程进行探测，阐明强耦合作用对TMDCs材料功能调控的物理机制，为TMDCs纳米光电器件效率的提升提供理论基础。

新型二维过渡金属硫化物凭借其优异的光电特性，在纳米光电器件、清洁能源等领域展现出了广阔的应用前景，特别是由于其具有较大的天然带隙，为很多新奇物理问题的研究提供了崭新的平台，构筑强耦合杂化态并实现对其功能的定向光调控便是其中之一。近年来，研究者们已经构筑出了多种光场-二维材料强耦合杂化体系，然而对于这些体系的产生和演化过程的研究还未展开，而这些信息对于基于强耦合的二维材料纳米光电器件的设计及性能优化起着至关重要的作用。本项目通过理论计算对能够产生特定表面等离激元的金属纳米结构进行设计，综合利用多种纳米加工技术，构筑了表面等离激元与二维材料及其异质结间的强耦合杂化体系；并运用超快光谱技术对构筑出的强耦合杂化态的产生和演化过程进行了时间分辨探测。具体包括：利用多种金属光栅结构对单层WS2能谷的超快调制；利用银纳米柱阵列激发表面等离激元实现了其与单层MoS2间的多重强耦合的动力学研究；构筑了微腔与单层WS2强耦合杂化体系，实现了对单层WS2材料中A、B激子以及里德伯激子态发光的增强调控；另外，我们借助宽带超快光谱技术，探究了应力和层数对异质结界面电荷转移速率的影响，接着对电荷转移和层间激子转移的过程进行了详细研究，最后研究了不同异质结的能谷自旋退极化过程，为强耦合作用对二维材料异质结间的电荷转移过程调制提供了研究基础。目前项目总计发表SCI论文12篇,圆满完成项目工作。