单层二硫化钼中谷自由度的调控和输运研究

The intrinsic degrees of freedom (DoF), valley, of an electron can be used as the information carrier of new generation devices. Valley-selective circular dichroism of monolayer molybdenum disulphide makes it as one of the most important materials for valletronics. Now, the most critical thing is how to efficiently produce the valley-polarized current which can be easily controlled and detected. In this project, the non-equilibrium Green’s function with density functional theory are used as the simulate tool, the system Hamiltonian will add the description of electron-photon interaction to simulate the illumination, and the metallic 1T phase monolayer molybdenum disulphide is used as the electrode. The core issue is to figure out that how to control and manipulate the valley DoF in monolayer molybdenum disulphide. Based on two important criteria, momentum dependence of circular dichroism and the valley photocurrent, this project will implement a comprehensive study on the factors, strain, electric field, defect and van der Waals heterojunction, which can affect the valley DoF. The regulating mechanism of valley DoF will be obtained based on one of these factors. Moreover, according to the relevance of these various factors, we will try to explore the filter effect using the stress and defects in the monolayer molybdenum disulphide, and the dynamic control mechanism and multi-dimensional transport mechanism based on the electric field coupling van der Waals heterojunction. A theory solution will be found to keep the optical selectivity and get high valley polarization current. The project aims to provide a theoretical guidance for valleytronics of monolayer molybdenum disulphide.

电子的内禀谷自由度可作为新一代的信息载体。单层二硫化钼具有谷依赖的旋光选择性，是谷电子学器件最重要的候选材料之一。如何高效率产生谷极化电流并对其进行调控和检测是谷电子器件应用的前提条件和研究重点。本项目拟采用密度泛函微扰理论结合非平衡格林函数电子输运理论，引入电子-光子相互作用哈密顿量，围绕单层二硫化钼谷自由度调控这一核心问题，从静态圆二色性和动态谷电流输运两个层次，选取二硫化钼金属相为电极，系统全面梳理谷自由度的影响因素（应变、电场、缺陷、范德瓦尔斯异质结），获取单层二硫化钼中的谷自由度单因素调控机制。根据各因素的关联性，探索应力和缺陷对谷自由度的过滤效应；基于对称性破坏和层自由度的耦合，研究范德瓦尔斯异质结中谷自由度的动态电场控制机制和多维度输运机制。目的是在保持旋光选择性的前提下获取易检测的高谷极化电流的理论方案，为单层二硫化钼谷电子器件的设计开展前期探索及提供理论指导。

二维层状过渡金属硫化物(TMDs)是一类非常具有前景的功能材料，其中二硫化钼是典型代表。为了对单层二硫化钼基电子器件的设计开展前期探索和理论分析，基于密度泛函理论结合非平衡格林函数电子输运理论，本项目系统研究了二硫化钼材料中的应变、界面、掺杂、缺陷及非对称效应，重要结论如下(1)界面应力的存在会导致界面电子态的增加，进而改善界面的电学输运，这也给出了应力不同是实验获得的二硫化钼电学差异较大的可能原因之一；(2)高K介电屏蔽层可提升晶体管的电流开关比、降低亚阈值摆幅，进而可以改善晶体管的性能；(3)得益于在边缘位置的面内悬挂键，金属性1T二硫化钼可以边缘接触的方式用作半导体性2H二硫化钼的电极，边缘接触模型是欧姆接触，可使界面势垒消失；(4)Ni掺杂的方式可以调控单层二硫化钼析氢反应活性，源于Ni掺杂对电荷分布具有动态间接调控作用；(5)通过构造Janus 1T-MoSX，建立非对称引起的内建电场，可以方便获得高性能析氢反应催化活性。据此进行了电极设计、输运优化，探讨了二硫化钼类材料在催化等领域的应用。通过总结共性规律，我们还在其他相关类二硫化钼材料进行了分析探讨、推演类比，并结合实验研究验证了部分规律。项目组目前在国际有影响的学术期刊上已经发表SCI论文19篇，培养具有一定科研能力的硕士研究生6名。项目研究结果受到了同行的广泛关注，目前总计被引用150余次。