基于原子尺度模拟的纳米晶超晶格相关可调控力学行为机理研究

Nanocrystal superlattices are highly ordered metamaterials composed of ligand-capped nanocrystals, and they possess wide application prospect in electronic and photoelectronic devices. Such kind of superstructures have ordered arrays analogous to standard atomic crystals, but the interaction between nanocrystals is much more complex compared with those interatomic potentials. Recent experiments show that nanocrystal superlattices exhibit some unusual mechanics phenomena. It is found that the elastic modulus and multiply twining of nanocrystal superlattices both depend sensitively on the nanocrystal type, size, shape and ligand length, and thus are adequately adjustable. However, the basic physical mechanism of these mechanical tunabilities of nanocrystal superlattice is still unclear, which grievously obstructs its design and application. From a microscopic point of view, this project performs atomistic simulations of two types of typical nanocrystal superlattices (metallic Au and semiconducting PbS) to understand these phenomena. Firstly, the influence of the nanocrystal type, size, shape and ligand length on the interaction between nanocrystals is investigated to support the subsequent research; Then the adjusting mechanisms of the elastic modulus and multiply twinning of nanocrystal superlattices are analyzed based on the interaction between nanocrystals and an energetic method; The project will also explore the tunability of the tensile behavior and the structural defects such as vacancy, stacking fault and dislocation of nanocrystal superlattices and its physical mechanisms. The results are helpful to uncover the physical nature of the amazing mechanics phenomena, and provide theoretical guidance for device application of nanocrystal superlattices.

纳米晶超晶格是一种由配体分子修饰纳米晶颗粒有序堆积而成的超材料，在电子和光电等领域具有广泛的应用前景。此类超结构与原子晶体的有序阵列相似，但晶粒之间的相互作用较为复杂。近期实验表明纳米晶超晶格表现出一些奇妙的力学现象，其弹性模量和多重孪晶化敏感地依赖于晶粒类型、尺寸、形状或配体长度，具有高度的可调控性，然而其基本物理机制尚不清楚，限制了该材料的设计和应用。本项目以两种典型纳米晶超晶格(贵金属金和半导体硫化铅)为研究对象，从微观尺度的研究思路出发，拟通过原子尺度模拟方法首先研究晶粒类型、尺寸、形状和配体长度对纳米晶相互作用的影响；其次基于纳米晶相互作用规律和能量学方法阐明纳米晶超晶格弹性模量和多重孪晶化的调控机理；该研究将进一步探索纳米晶超晶格的拉伸力学行为及空位、层错、位错等缺陷的可调控性及其机理。所得结果有助于揭示纳米晶超晶格奇妙力学现象的物理本质，为该材料的器件应用提供理论依据。

纳米晶超晶格是一种由配体分子修饰纳米晶颗粒有序堆积而成的超材料，在电子和光电等领域具有广泛的应用前景。此类超结构与原子晶体的有序阵列相似，但晶粒之间的相互作用较为复杂。近期实验表明纳米晶超晶格表现出一些奇妙的力学现象，其弹性模量和多重孪晶化敏感地依赖于晶粒类型、尺寸、形状或配体长度，具有高度的可调控性，然而其基本物理机制尚不清楚，限制了该材料的设计和应用。本项目采用原子尺度分子动力学模拟和理论建模相结合的方法，系统研究了配体修饰纳米晶颗粒的相互作用规律以及纳米晶超晶格的复杂力学响应行为。本项目的主要成果包括：1. 揭示了几何非对称球形纳米晶的相互作用规律，并构建了同时考虑材料属性和物理机制的经验势函数；2. 计算证实了非球形纳米晶相互作用具有明显的各向异性特征，发现了晶粒面对面排列时相互作用最强，探明了非球形纳米晶相互作用从各向异性向各向同性转变的配体分子调控机理；3. 解释了偏应力诱导下纳米晶超晶格形成有序纳米线阵列的微观机理，提出了有序纳米线阵列形成的应力发生条件；4. 揭示了温度对纳米晶超晶格结构稳定性及晶粒间距等关键结构力学性能参数的影响规律，为高温工况下纳米晶超晶格基微纳器件的结构设计提供了理论指导。综合上述结果，本研究为探讨纳米晶超晶格可调控弹性性能的机制奠定了坚实的工作基础，同时对于认识纳米晶超晶格复杂力学响应行为提供了重要的启示性线索。