二维材料中载流子产生、复合及电荷转移的超快光谱研究

Two-dimensional (2D) materials, e.g. graphene, layered transition-metal dichalcogenides, have demonstrated a wide variety of unique optical, electrical, thermal and mechanical properties, and attracted increasing attentions in recent years. Especially, van der Waals heterostructures realized by stacking various 2D materials give rise to fascinating photoelectric phenomena, providing the potential to fabricate atomic layered light-harvesting and optoelectronics device components. An in-depth understanding of ultrafast dynamics behaviors of various photo-induced carriers in 2D materials will provide necessary theoretical and experimental bases for the future design of 2D-material-based optoelectronic devices as well as photocatalytic materials. A novel ultrafast spectroscopy combining the femtosecond ultra-broadband infrared detection and microscopic technique will be developed in this project. Based on different response of photo-induced carriers on different photon energies in the infrared region, the dynamics of various kinds of excitons and free carriers in 2D materials can be specifically investigated. As a result, the detailed pathways and mechanisms of the processes such as nonradiative electron-hole recombination, ultrafast charge transfer, formation and dissociation of excitons in 2D materials can be finally revealed.

近些年来，以石墨烯、过渡族金属硫属化物等为代表的二维材料，因它们各自独特的光学，电学，热学以及机械性质等，吸引了人们越来越多的关注。特别地，将不同二维材料叠在一起所形成的范德华异质结构又因其各种迷人的光电特性，使得在将来制作出仅有几个原子层厚度的光捕集系统，光电设备等成为了可能。深入地了解二维材料内各类光生载流子的超快动力学行为，将会为人们设计各种二维光电子器件以及光催化材料等提供必要的理论依据和实验基础。本项目拟发展飞秒超宽谱带红外探测与显微成像相结合的全新超快光谱技术，利用二维材料内各种光生载流子对红外区不同能量的光子响应范围的差异，可以有针对性地研究二维材料内各类激子以及自由载流子的动力学行为。进而揭示二维材料中非辐射电子-空穴复合，超快电荷转移，以及激子态的形成、解离等过程的具体途径和机理。

目前，以石墨烯、过渡族金属硫属化物等为代表的二维材料在光电、光催化等各个领域吸引了人们越来越多的关注。在本项目中，我们着重发展了飞秒超宽谱带红外探测与显微成像相结合的全新超快光谱技术，并同时辅以其它各种超快光谱手段，用以观测二维材料内发生的各种光转换动力学过程，最终揭示其物理机制。我们通过将实验和理论的紧密结合，深入解析了二维材料内多种光生载流子及激子的超快动力学行为，并从中成功揭示了二维材料内非辐射电子-空穴复合、界面超快能量耗散、激子的形成与复合、超快电荷转移、热声子效应、热载流子弛豫等等多种过程的具体途径以及机理。上述许多成果已经在多个国际重要期刊上面发表。这些结果将会为人们将来设计以二维材料为基础的各种电子和光电子器件，例如光电探测器，太阳能电池，晶体管以及各类光催化材料等等，提供重要的理论依据以及实验基础。