基于分子动力学模拟的硅纳米线谐振特性研究

发布时间：2018-01-06 16:01

本文关键词：基于分子动力学模拟的硅纳米线谐振特性研究　出处：《东南大学》2015年硕士论文　论文类型：学位论文

【摘要】：由于半导体工艺技术的快速发展,工艺线宽从微米量级到纳米量级逐渐缩小,使得纳机电系统的应用更加广阔,但是在研究方法、制造工艺、实验设备等方面也面临很多问题。当材料的尺度进入纳米量级,尺寸效应、表面效应、量子效应对材料性能的影响会更加明显,这些甚至成为纳米材料发展的瓶颈。如何准确的去描述纳米材料的物理特性成为了设计、制造、优化纳米器件的关键。硅纳米线作为一维硅纳米材料的典型代表,除具有半导体所具有的特殊性质,还显示出不同于体硅材料的场发射、热导率及可见光致发光等物理性质,在纳米电子器件、光电子器件以及新能源等方面具有巨大的潜在应用价值,因此硅纳米线可能成为未来纳机电系统构建的核心单元。近年来硅纳米线的制备工艺有很大发展,人们可以制造出各个方向、各个截面的硅纳米线,并且通过实验手段探索到了硅纳米线的一些性质,但是在现有的理论基础上还无法解释或者表征一些物理特性,其中有一个就是硅纳米线的本征谐振频率。近年来,由于硅纳米线在谐振器、振荡器等器件上有广泛的运用,使得对硅纳米线谐振频率的研究成为热点。随着尺寸的缩小,纳米线的频率从几个兆的频率到几百兆的频率,最后到现在上GHz的频率,不禁让人感到疑惑硅纳米线的谐振频率到底是什么量级,有什么规律可循呢?本文基于分子动力学的模拟,采用material studio软件系统地研究了硅纳米线的谐振特性。本文总共研究了111、110、112三个方向的硅纳米线的谐振频率,分别考虑硅纳米线的晶向、尺寸(长度、边长、厚度)、表面结构(截面形状,表面重构)对其谐振频率的影响。结果发现在纳米尺度下,由于表面积与体积之比(SVR)的增大,表面的原子与体内的原子所处的环境不同,因此材料的性质发生变化,导致了纳米梁的谐振频率不完全遵守Euler-Bernoulli梁的理论。111、110、112三个方向的硅纳米线的谐振频率近似与其长度的二次方成反比,但是与其截面的边长没有明显关系,然而边长的增大必然会导致厚度的增加,因而其谐振频率会产生轻微的漂移。111方向的三种截面的硅纳米线,由于其表面积与体积之比(SVR)不相同,表面效应的影响也不一样,因此其谐振频率也不一样。同样,不同晶向的硅纳米线其表面结构不一样,则表面效应的影响也不一样,因此谐振频率有差异。通过仿真发现,硅纳米线的表面重构对其谐振频率有着重大的影响。本论文提出的AFM探针模型,利用分子间的范德瓦尔斯力使硅纳米梁发生振动,这些建模工作对以后的理论研究工作具有一定的借鉴价值,在一定程度上为进一步研究纳米线的各种性质提供了新的思路。
[Abstract]:Due to the rapid development of semiconductor process technology, the process linewidth from micron to nano-scale gradually shrinks, which makes the application of nano-electromechanical system more extensive, but in the research methods, manufacturing technology. When the scale of the material enters the nanometer order, the size effect, the surface effect, the quantum effect will be more obvious to the material performance. These even become the bottleneck of the development of nanomaterials. How to accurately describe the physical properties of nanomaterials has become the design and manufacture. As a typical representative of one-dimensional silicon nanomaterials, silicon nanowires not only have the special properties of semiconductors, but also show different field emission from bulk silicon materials. Thermal conductivity and visible photoluminescence have great potential applications in nanoelectronic devices, optoelectronic devices and new energy sources. Therefore, silicon nanowires may become the core unit of nanoelectromechanical system construction in the future. In recent years, the preparation process of silicon nanowires has been greatly developed, people can produce silicon nanowires in all directions and sections. Some properties of silicon nanowires have been explored by means of experiments, but some physical properties can not be explained or characterized on the basis of existing theories. One of them is the intrinsic resonance frequency of silicon nanowires. In recent years, silicon nanowires have been widely used in resonators, oscillators and other devices. As the size of the nanowires shrinks, the frequency of nanowires ranges from several megabytes to hundreds of megabytes, and finally to the current frequency of GHz. People can not help wondering what is the order of magnitude of the resonant frequency of silicon nanowires, and what rules can be followed? Based on the simulation of molecular dynamics, the resonant characteristics of silicon nanowires are systematically studied by material studio software. A total of 111,110 has been studied in this paper. The resonant frequencies of the silicon nanowires in three directions are taken into account in the crystal direction, size (length, side length, thickness) and surface structure (section shape) of the silicon nanowires. The effect of surface reconstruction on the resonance frequency. It is found that the surface atoms and the atoms in the body are in different environments at nanometer scale due to the increase of the ratio of surface area to volume (SVR). Therefore, the properties of the materials change, which leads to the resonance frequency of the nanocrystalline beam does not fully comply with the Euler-Bernoulli beam theory. The resonant frequency of 112 silicon nanowires in three directions is approximately inversely proportional to the quadratic power of its length, but it has no obvious relationship with the side length of the section. However, the increase of the side length will inevitably lead to the increase of the thickness. As a result, the resonance frequency of silicon nanowires with three cross sections with slight drift of .111 direction will be slightly different, because the surface area to volume ratio (SVR) is different, the effect of surface effect is also different. Therefore, the resonant frequency is different. Similarly, the surface effect of silicon nanowires with different crystal directions is different, so the resonant frequency is different. The surface reconstruction of silicon nanowires has a great influence on the resonant frequency. In this paper, the AFM probe model is proposed, which uses the van der Waals force between molecules to make the silicon nanoscale beam vibrate. These modeling works have certain reference value to the later theoretical research work, and to some extent provide a new way of thinking for the further study of various properties of nanowires.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN304.12;TB383.1

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