石墨烯类材料的缺陷动力学与功能性研究

The study of defects has long been a important topic in the communities of materials, physics and mechanics. Two-dimensional (2D) materials, whose thickness spans just one or several atoms, have no exception in this realm. In 2D materials, defects are strictly confined in a 2D space and have all their atoms located on the surfaces; thus the structures and properties of defects are anticipated to be qualitatively different from those in bulk materials. Existing studies of defects in 2D materials are primarily focused on structures, leaving the dynamics that is fundamentally important to material deformation largely unexplored. In the newly emerged 2D MoS2 and phosphorene, the binary composition and highly buckled crystal structures will enrich the defect structures and dynamics; yet the related scientific issues are more complicated. In this project, we plan to develop a physical mechanics method for carrying out large-scale modeling of defect structures in 2D materials, and then combine this method with atomistic computations to investigate the dynamics and functionality of point and topological defects in graphene, h-BN, MoS2 and phosphorene etc. Special attention will be paid to structural evolution and dynamics of coupled point and topological defects, aiming to reveal new mechanism of dislocation motion and attain in-depth understanding into plastic deformation of various 2D materials. We will also examine how the defects influence mechanical, electronic and magnetic properties of these materials; the results will be further analyzed to establish defect-driven structure-functionality relationships and to develop defect-based band engineering for 2D materials. The outcomes of this project are expected to provide advanced principles and technological base for potentially boosting 2D materials into device applications.

以石墨烯等为代表的二维材料具有丰富的结构缺陷。这些缺陷严格局限于二维空间中，且暴露于材料表面，导致它们的结构和功能性与宏观材料情况截然不同。现有相关工作主要集中于缺陷结构研究，而对二维材料变形至关重要的缺陷动力学缺少关注。新兴的二硫化钼、磷烯等二维材料因化学成分和晶格结构的差距使得缺陷的形态更丰富，但相关问题更复杂。申请人拟发展描述二维材料缺陷的物理力学方法，针对石墨烯类材料中点缺陷、位错等的动力学和功能性开展理论和辅助性实验研究。本项目通过考虑缺陷结构的长程作用，立足于不同类缺陷之间的耦合，研究该耦合作用下缺陷的结构成核、演化、扩散和融合，探索纳尺度下新的位错滑移机制并深化对材料塑性变形的认识；进一步通过外加应变、化学势等参数调控缺陷的平衡浓度，以控制缺陷的动力学和材料的塑性。研究拓扑缺陷对二维材料力学和电子性质的影响，建立基于缺陷的结构-功能关系，为设计新型纳米器件提供理论和技术储备。

项目组采用连续介质力学、分子力学与量子力学等方法理论，并发展了用于研究低维材料缺陷的建模方法，系统开展了石墨烯、二维黑磷、金属硫化物等低维纳米结构的缺陷结构组装、动力学及其功能性的研究，还深入探索了基于低维功能材料与水作用的固-液耦合能量转换效应等。研究发现了由硼烯孪晶界自组装形成的硼烯超晶格并被实验证实，预测了基于二维硫化物半导体中的位错具有优异的单光子发射性能和应变可调的光子频率，预测具有二维螺旋结构的单层螺旋冰并完美解释了先前的实验，设计了一系列由螺旋位错构成的三维碳结构。发展了基于蒙特卡洛算法的二维材料曲面生长模拟方法，发现曲面导致的晶格应力决定着生长过程中石墨烯缺陷的形态及结构演化；发现二维硫化钼的晶界具有独特的双位错核构成单元，并引起独特的结构多态性和丰富的功能性；合作提出了通过功能材料与水相互作用将雨滴、水波动和水蒸发等形式的能量转化为有用电能的“水伏效应”，为从地球自然水循环中以零的碳排放捕获能量提供了可能。为深化水伏机理的认识，围绕石墨烯与水的界面建立了基于传统双电层和石墨烯镜像电荷层的“三电层”模型，使得石墨烯的滴水发电电压可稳定达到亚伏量级。利用高通量计算发现了一大类高度稳定，结构和性质极为丰富的二维金属氢化物。上述研究加深了对低维材料结构缺陷行为和固-液耦合能量转换机理的认识，并为相关器件的研发奠定了理论基础。研究成果发表论文34篇，其中第一/通讯作者论文26篇，申请发明专利4项，授权2项，培养博士生4名。