低温低维纳米结构中声子热输运性质及非线性热现象的研究

发布时间：2018-06-20 14:07

本文选题：关键字 + 非对称纳米线　；参考：《太原理工大学》2015年硕士论文

【摘要】：随着纳米技术的迅速发展，许多微器件的尺度逐年小型化。当器件的特征尺寸达到纳米量级时，无论声子是以何种方式进行热输运，其热导率已经不再是材料的本质属性，而是依赖于结构和器件的具体形状、尺寸和边界。所以，研究几何形状、结构参数等对纳米尺度量子结构中的声子弹道热输运和非线性热现象的影响非常重要。然而，在低维纳米结构中，，传统的热输运理论已经不再适用，体系的声子模及其热输运性质完全由量子力学原理所支配，从量子力学原理出发对系统的声子模及其热输运性质进行研究，是设计和发展新型纳米器件的重要基础。本文分别对低温低维下非对称纳米线的量子化热导及非对称弹道四终端纳米结构中的热整流进行了研究。首先，本文研究了低温下非对称Z型纳米线中弹道声子热导的性质。其中，简单介绍了Z型纳米线的模型结构。然后，推导出其透射系数公式，接着讨论了透射系数以及热导的特性。最后发现在温度趋于零的极限下，研究结果与之前T型纳米线的研究结果相似，即能够在反对称纳米线中观察到普适量子化热导值（2k2B3h），但在其他非对称纳米线中观察不到。由此可知，纳米线左、右引线的横向尺寸比率a1a2决定了是否能够观察到弹道声子热导的普适量子值2k2B3h。而且，只有当a1a21时，才能测得普适值。其次，本文对非对称弹道四终端纳米结构中的热整流性质进行了理论研究。文章中，展示了非对称弹道四终端电介质纳米结构中的热整流行为，声子输运的非线性特性，同时分析了热整流的原因。最后，研究得到了非对称弹道四终端电介质纳米结构中产生热整流的两个必要条件：1）能量输入端与能量输出端之间存在不等的横向声子模密度；2）除了具有连接热库的输入端和输出端以外，还需有连接其它热库的终端。而且，只有这两个条件共同作用才能产生热整流，其中的任何一个都不能单独导致弹道系统的热整流行为。
[Abstract]:With the rapid development of nanotechnology, many microdevices are miniaturized year by year. When the characteristic size of the device reaches nanometer-scale, no matter how the phonon is transported, its thermal conductivity is no longer the essential property of the material, but depends on the structure and the specific shape, size and boundary of the device. Therefore, it is very important to study the effects of geometry and structural parameters on the thermal transport of acoustic bullet channels and nonlinear thermal phenomena in nanoscale quantum structures. However, in low-dimensional nanostructures, the traditional thermal transport theory is no longer applicable, and the phonon modes and their thermal transport properties of the system are completely controlled by the quantum mechanics principle. Based on the principle of quantum mechanics, the phonon modes and their thermal transport properties of the system are studied, which is an important basis for the design and development of new nanodevices. In this paper, the quantized thermal conductivity of asymmetric nanowires at low temperature and low dimension and the thermal rectification in four terminal nanostructures with asymmetric trajectory are studied. Firstly, the thermal conductivity of ballistic phonons in asymmetric Z-type nanowires at low temperature is studied. The model structure of Z-type nanowires is briefly introduced. Then, the transmission coefficient formula is derived, and the transmission coefficient and thermal conductivity are discussed. At the limit of temperature approaching zero, the results of the study are similar to those of the previous T type nanowires, that is, the universal quantized thermal conductance of 2k2B3hs can be observed in antisymmetric nanowires, but not in other asymmetric nanowires. It can be seen that the transverse size ratio of the left and right leads of nanowires a1a2 determines whether the universal quantum value of thermal conductivity of ballistic phonons can be observed at 2k2B3h. Moreover, only when a1a21 is measured can the universal value be obtained. Secondly, the thermal rectifying properties of four-terminal nanostructures with asymmetric trajectory are studied theoretically in this paper. In this paper, the behavior of thermal rectification and the nonlinear characteristics of phonon transport in asymmetric ballistic four-terminal dielectric nanostructures are demonstrated, and the causes of thermal rectification are analyzed. Finally, two necessary conditions for thermal rectification in asymmetric ballistic four-terminal dielectric nanostructures are obtained: 1) there are different transverse phonon mode densities between the energy input and the energy output. 2) in addition to the input and output terminals connected to the heat storage, there must also be terminals connected to other hot banks. Moreover, only these two conditions can produce thermal rectification, neither of them can lead to the thermal rectifying behavior of ballistic system alone.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1

【共引文献】