石墨烯中超快载流子弛豫与输运动力学的飞秒吸收光谱研究

石墨烯是单层碳原子密堆积成蜂窝结构形成的二维薄膜，具有极大的载流子迁移率，有可能成为开发超高速场效应晶体管和光电子器件的理想材料。石墨烯的超快热载流子动力学已成为近几年来的研究热点，有较多的超快动力学报道，揭示出超快热载流子动力学的多样性。然而，对超快热载流子动力学的多样性的物理起源目前尚不清楚，甚至载流子的复合时间尺度目前也存在争议。另外，少量的实验观测到的载流子扩散系数远大于基于爱因斯坦关系和测量的迁移率计算的扩散系数，似乎显示在石墨烯中爱因斯坦关系可能不成立。本课题组最近还发现了一种类线性二色瞬态吸收效应，基于目前的石墨烯理论尚无法解释。本项目拟系统、深入研究不同方法制备的单层石墨烯中超快热载流子弛豫和输运动力学及其随吸附杂质浓度和类型的变化，弄清超快动力学多样性的起源，载流子复合寿命的时间尺度，验证爱因斯坦关系是否成立。结合第一性原理计算，弄清类线性二色瞬态吸收效应的起源。

Graphene is a two-dimensional thin film with a honeycomb lattice structure composed of a single layer of carbon atoms, has a extremely large mobility of carriers and is possible to become an ideal material for making ultrahigh speed field effect transitors and photoelectronic devices. Ultrafast dynamics of hot carriers in graphene has become a active topic in recent years. Many ultrafast dynamics have been reported, revealing the diversity of ultrafast dynamics of hot carriers. However, the physical origin of the diversity has not been understood so far, and even time scale of carrier recombination is aslo controversial. On the other hand, it is found that the diffusivity of hot carriers observed in sparse experiments is much larger than the calculated one based on Einstein relation and the observed mobility, which seems to show the invalidity of Einstein relation in graphene. A linear dichroism-like transient absorption effect is observed recently by our group, which is beyond the current knowledge on graphene. In this project, ultrafast dynamics of relaxation and transport of hot carriers in monolayer graphene prepared by different methods and their dependence on the density and type of adsorbed impurities will be investigated deeply and systematically to understand the origin of the diversity of ultrafast dynamics and the time scale of carrier recombination lifetime as well as to test the validity of Einstein relation. In conjunction with the first-principle calculation, we attempt to understand the origin of linear dichroism-like transient absorption effect.