硅纳米线热导率边缘效应的键弛豫理论研究

发布时间：2018-08-06 09:44

【摘要】：随着世界能源危机以及环境污染的日益严重,对新型热电材料的探索受到了人们的关注与重视,使得热电材料已经成为纳米材料科学和凝聚态物理学研究的前沿和热点课题之一。作为一种新型的热电材料,硅纳米线结构已经成为科学家们关注的目标。与相应的体材料相比,硅纳米线表现出了一些奇特的物理和化学性质。例如:纳米线体系边缘部分原子具有的高配位缺陷和异常能态,将影响体系的力、热、光和电子学等性能。在影响硅纳米线热电性质的参数当中,热导率是一个极其重要的物理参量。对此,科学家们在降低硅纳米线热导率中取得了相当多的进展,但是,也存在不少没有解决的问题,比如:纳米线表面粗糙度的定义、界面调制等等。因此,在本论文中,基于原子键弛豫理论和连续介质力学理论,建立了尺度和表/界面参数依赖的硅纳米线热导率模型。在此基础上,系统阐述了边缘效应(包括不同表面粗糙度、形貌、生长取向以及界面调制等)对硅纳米线热导率影响的物理机制,取得的主要进展如下:(1)定义了表征纳米线表面粗糙度的因子,并且系统地研究了不同的表面粗糙度、尺寸、形貌(圆形、六边形、四边形和三角形)以及生长取向([111]、[110]、[100])对硅纳米线热导率的影响的物理机制。结果表明:第一,在一定条件下,与圆形、六边形和四边形相比,三角形的硅纳米线的热导率最小。第二,在一定的尺寸下,生长取向为[110]的四边形纳米线与其他生长取向([111]、[100])相比具有最高的热导率。第三,硅纳米线热导率可以通过设计边缘结构,比如:体积、表面小晶面的形状等来控制。我们的理论结果与实验和模拟的结果一致,给硅纳米线热导率的可控调制提供了一种理论指导。(2)基于原子键弛豫理论和连续介质力学理论,探索了外延层对硅纳米线轴向热导率的调制机理。结果表明:由于应变和界面失配与表面弛豫引发的弹性应变能的改变,核壳纳米结构的结合能和热导率与裸线的硅纳米线的不相同。同时,也研究了核壳纳米结构的热导率与尺寸的关系,结果表明可以在界面中有效地调节热性能。这进一步表明了,该方法提供了一个基本的理论方法来解释在核壳结构中热导率的界面效应,并且在实验装置设备中起了指导性作用。
[Abstract]:With the world energy crisis and environmental pollution becoming more and more serious, people pay more attention to the exploration of new thermoelectric materials. Thermoelectric materials have become one of the frontier and hot topics in nanomaterial science and condensed matter physics. As a new thermoelectric material, the structure of silicon nanowires has become the focus of scientists. Compared with the corresponding bulk materials, the silicon nanowires exhibit some peculiar physical and chemical properties. For example, the high coordination defects and abnormal states of the atoms at the edge of nanowires will affect the mechanical, thermal, optical and electronic properties of the system. Among the parameters affecting the thermoelectric properties of silicon nanowires, thermal conductivity is an extremely important physical parameter. In this regard, scientists have made considerable progress in reducing the thermal conductivity of silicon nanowires, but there are still many unsolved problems, such as the definition of surface roughness of nanowires, interface modulation and so on. Therefore, based on the atomic bond relaxation theory and continuum mechanics theory, a thermal conductivity model of silicon nanowires based on scale and surface / interface parameters is established in this paper. On this basis, the physical mechanism of the effect of edge effect (including different surface roughness, morphology, growth orientation and interface modulation) on the thermal conductivity of silicon nanowires is systematically expounded. The main advances are as follows: (1) the factors that characterize the surface roughness of nanowires are defined, and different surface roughness, size, morphology (circular, hexagonal, hexagonal) are systematically studied. The physical mechanism of the effects of quadrilateral and triangular) and growth orientation ([111], [110], [100]) on the thermal conductivity of silicon nanowires. The results show that: first, under certain conditions, the thermal conductivity of triangular silicon nanowires is the least than that of circular, hexagonal and quadrilateral silicon nanowires. Secondly, the quadrilateral nanowires with a growth orientation of [110] have the highest thermal conductivity compared with other growth orientations ([111], [100]) at a certain size. Thirdly, the thermal conductivity of silicon nanowires can be controlled by designing edge structures, such as volume, shape of surface facets, etc. Our theoretical results are consistent with the experimental and simulation results, which provide a theoretical guide for the controllable modulation of thermal conductivity of silicon nanowires. (2) based on the atomic bond relaxation theory and continuum mechanics theory, The modulation mechanism of the epitaxial thermal conductivity of silicon nanowires was investigated. The results show that the binding energy and thermal conductivity of core-shell nanostructures are different from those of bare wire silicon nanowires due to the change of strain and interface mismatch and elastic strain energy induced by surface relaxation. The relationship between the thermal conductivity and the size of core-shell nanostructures is also studied. The results show that the thermal properties can be adjusted effectively in the interface. This further indicates that this method provides a basic theoretical method to explain the interfacial effect of thermal conductivity in core-shell structures and plays a guiding role in experimental equipment.
【学位授予单位】：湖南师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.2;TB383.1

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