应力作用下石墨烯能带结构研究

发布时间：2018-03-01 13:26

本文关键词： 石墨烯应力密度泛函理论第一性原理紧束缚方法　出处：《山东大学》2015年硕士论文　论文类型：学位论文

【摘要】：石墨烯作为一种二维材料,具有很高的机械强度,非常高的电导率和热传导性以及其它很多非常好的特性,使得其在很多的应用方面都具有很大的潜力。自从2004年石墨烯发现以来,很多理论和实验方面的科学家对这种材料展开了研究。然而,对于理想的石墨烯,这种由碳原子构成的二维蜂窝状晶格结构,是一种零带隙的半导体材料,这限制了其在场效应管等电子器件方面的应用。为了解决这一问题,人们一直在探索调控石墨烯能带的方法,其中包括通过构建石墨烯纳米带和量子点以及通过构建对称性破缺的双层石墨烯的方法。此外,通过应力修正,理论上可以对石墨烯引入一个可以调控的带隙,并能够在实验上观测到。石墨烯的能带调控对于解决其在纳米电子器件应用中所面临的重大障碍提供了可行的方案。本论文从密度泛函理论出发,对石墨烯引入局部应力并通过构建褶皱形石墨烯结构研究了三种不同类型的内部应力对于石墨烯能带结构的影响,并通过紧束缚方法对计算结果进行了解释,主要的研究内容和研究结果如下：(1)对晶格内单个原子进行移动。密度泛函理论计算结果表明对于采取的两种不同的移动方向,在石墨烯狄拉克点处均产生一个大小为几十meV的带隙,且带隙的大小随着原子偏离初始位置的程度逐渐变化。对于所选取的两种移动方向的对比情况来看,其最终产生的带隙大小与结构的对称性有很大关系。通过紧束缚方法计算结果表明,这种带隙的产生主要归因于结构改变引起的π电子轨道作用能的改变。(2)改变单个六元环大小。通过改变所选取晶胞内单个六元环形状,并没有使石墨烯产生带隙,结合紧束缚计算,表明这种结果的产生是由于在结构改变之后,其仍然保持很高的对称性,即使对π电子的作用能进行拟合,最终得到的石墨烯能带仍然是零带隙的。(3)构建褶皱。本文选取两种不同方向对石墨烯构建褶皱,DFT计算结果表明最终带隙与所选取的褶皱的方向没有太大关系：为了研究褶皱程度以及褶皱周期对于石墨烯能带结构的影响,我们构建了不同程度和周期的褶皱,结果表明其对于石墨烯能带结构具有较大影响。
[Abstract]:Graphene, as a two-dimensional material, has very high mechanical strength, very high conductivity and heat conductivity, and many other very good properties. It has great potential in many applications. Since the discovery of graphene in 2004, many theoretical and experimental scientists have studied the material. However, for the ideal graphene, This two-dimensional honeycomb lattice of carbon atoms is a zero-band gap semiconductor material, which limits the applications of electronic devices such as field effect tubes. People have been exploring ways to regulate graphene bands, including through the construction of graphene nanobelts and quantum dots, and by building symmetrically broken bilayers of graphene. It is theoretically possible to introduce an adjustable band gap into graphene. It can be observed experimentally that the energy band regulation of graphene provides a feasible scheme for solving the major obstacles to the application of graphene in nanoscale electronic devices. In this paper, we proceed from density functional theory (DFT). The influence of three different types of internal stresses on the graphene band structure was studied by introducing local stress into graphene and by constructing the folded graphene structure. The calculation results were explained by the tight-binding method. The main research contents and results are as follows: 1) the single atom in the lattice is moved. A band gap of tens of meV is produced at the graphene Dirac point, and the band gap changes gradually with the degree of atomic deviation from the initial position. The size of the band gap is related to the symmetry of the structure. The results of the tight-binding method show that, The generation of this band gap is mainly attributed to the change of 蟺 electron orbital interaction energy caused by structural change. (2) changing the size of a single six-member ring. By changing the shape of a single six-member ring in the selected unit cell, no band gap is produced for graphene. Combined with the tight-binding calculation, it is shown that this result is due to the high symmetry after the structural change, even if the action of 蟺 electrons can be fitted. The final graphene energy band is still a zero-band gap. The DFT calculation results show that the final band gap is not related to the selected fold direction: the following two directions are selected: the final band gap is not related to the selected fold direction: in this paper, two different directions are selected to construct the graphene fold. The DFT results show that the final band gap is not related to the selected fold direction. The effects of folding degree and folding period on graphene band structure are studied. We have constructed the folds of different degrees and periods, and the results show that they have great influence on the graphene band structure.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.11

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