二维材料的缺陷力学性质

发布时间：2017-12-28 07:13

本文关键词：二维材料的缺陷力学性质　出处：《清华大学》2016年博士论文　论文类型：学位论文

【摘要】：2004年二维石墨烯晶体材料的发现,使得二维材料迅速成为了科学研究和产业应用的持续热点。受益于近年来实验制备和表征技术的快速发展,新型的二维材料层出不穷,据相关预测其总数可以达到500余种。时至今日,已初步形成了一个新兴的材料门类。由于二维材料自身独特的低维结构特征,它们大多各自具有优异的力学、热学、电学、磁学和光学等物理性能,被认为有潜力在能源环境、电子信息、航空航天、生物医药等领域引起革命性的突破。本文使用理论分析和计算机模拟相结合的方式对以石墨烯中拓扑缺陷为代表的单原子层厚的二维材料的缺陷力学性质进行了系统的研究,重点考察缺陷在二维材料中引起的拓扑效应和几何效应。按照本文的行文顺序,研究内容可组织归纳为以下四个方面:(1)二维材料缺陷的拓扑效应。通过基本缺陷结构和应力场的组合叠加,标定了石墨烯中常见缺陷的应力场分布。在此基础上,建立了5|7位错和5|8|5位错偶极子的应力堆积模型,在多晶石墨烯的脆性断裂行为中发现了赝(逆)Hall-Petch效应,即拉伸强度反相关(正相关)于晶粒尺寸,裂纹一般在晶界接合处萌生,可沿晶或穿晶扩展;(2)二维材料缺陷的几何效应。几何效应来源于缺陷产生的内建畸变应力场诱导二维材料产生的局部几何结构屈曲。首先分析了石墨烯薄膜承压下的变形行为和尺度效应。以此为基础,指出了在纳米压痕实验中一直被忽视的几何效应对二维材料强度和刚度测量值的影响,为微纳尺度下精确表征超薄材料的力学性能提供了理论指导;(3)缺陷在曲面上的力学性质。以碳纳米管张开形成石墨烯条带的过程为研究对象,借助于断裂力学Griffith理论,从能量的角度出发,考察了缺陷在曲面上诱导断裂的力学特性,分析了氧和氢化学刻蚀缺陷对不同管径和手性的碳纳米管张开机制的影响;(4)二维材料的力学相关应用举例。基于前述对二维材料力学性能的研究,结合人类社会自身的实际需求,探索了三个关于二维材料的未来应用方向。为二维材料未来的应用推广做出了初步的尝试。
[Abstract]:The discovery of the two dimensional graphene crystals in 2004 makes two dimensional materials rapidly becoming a hot spot in scientific research and industrial applications. Because of the rapid development of the experimental preparation and characterization technology in recent years, the new type of two-dimensional materials emerge in endlessly. According to the related prediction, the total number can reach more than 500. Today, a new type of material has been formed. Due to the low dimensional structure characteristics of two-dimensional materials unique, most of them have excellent mechanical, thermal, electrical, magnetic and optical properties, is considered to have the potential to cause a revolutionary breakthrough in energy and environment, electronic information, aerospace, biomedical and other fields. Mechanical properties of the defects of theoretical analysis and computer simulation method of combining the two-dimensional graphene materials with topological defects are represented by a single atomic layer thickness were studied, focusing on the topological effect and geometric effect caused by defects in two-dimensional materials in. According to the order of this article, the research content can be organized into four aspects: (1) the topological effect of two-dimensional material defects. The distribution of the stress field of the common defects in graphene is calibrated by the combination of the basic defect structure and the combination of the stress field. On this basis, established the 5|7 5|8|5 dislocation and dislocation dipole stress accumulation model, pseudo found in brittle fracture behavior of polycrystalline graphene in Hall-Petch (inverse) effect, such as tensile strength and anti correlation (positive correlation) on grain size, cracks in the grain boundary junction can be adorable, intergranular or wear crystal growth; (2) the geometric effect of two-dimensional material defects. The geometric effect derives from the built - in distortion stress field induced by the defect, which induces the local geometric buckling of a two-dimensional material. First, the deformation behavior and scale effect of graphene film under pressure are analyzed. Based on this, the influence of geometric effects on the strength and stiffness measurement of two-dimensional materials is pointed out, which provides theoretical guidance for accurately characterizing the mechanical properties of ultra-thin materials at micro and nano scale. (3) the mechanical properties of defects on surfaces. To open the forming process of carbon nanotube graphene strip as the research object, based on the Griffith theory of fracture mechanics, from the view of energy, investigated the mechanical properties of defects on the surface induced fracture, analyses of oxygen and hydrogen chemical etching defect opening mechanism effect on different diameter and chiral carbon nanotubes; (4) for example, mechanical application of two-dimensional materials. Based on the previous research on the mechanical properties of two dimensional materials and the actual needs of human society, three future applications of two dimensional materials are explored. A preliminary attempt was made for the future application and popularization of two dimensional materials.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O341

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