支持表面等离子激元回音壁模式的石墨烯纳米腔的研究

发布时间：2018-01-13 07:16

  本文关键词：支持表面等离子激元回音壁模式的石墨烯纳米腔的研究　出处：《华侨大学》2016年硕士论文　论文类型：学位论文

  更多相关文章： 回音壁模式 表面等离子激元 石墨烯 可调谐 耦合

【摘要】：表面等离子体激元(Surface Plasmon Polaritons,SPPs)的高局域性,与回音壁模式(Whispering Gallery Mode,WGM)谐振腔的共振模式特性相结合可以构成具有高品质因子(Quality Factor,Q值)、小模式体积(Mode Volume,V_m)的表面等离子体激元回音壁模式谐振腔,这种谐振腔由于克服了传统介质WGM微腔所受的衍射极限的限制,可以将尺寸缩小到纳米量级。对于传统的贵金属材料来说,例如金和银,一旦其结构固定,SPPs的性质便难以调节,并且在传统金属界面上传播的SPPs损耗较大,因此基于金属的SPPs装置的优良特性受到了限制。石墨烯作为单碳原子层的二维(2 dimension,2-D)材料,当电导率虚部为正值时,石墨烯能够支持横磁(Transverse Magnetic,TM)模式的SPPs。并且石墨烯的高限制性、低损耗、易于调节等特性已经在理论上和实验上得到了证实。通过改变化学掺杂或者改变施加于石墨烯上的静电场可以改变石墨烯化学势,进而改变石墨烯电导率,从而调制其支持的SPPs的性质。本论文利用了石墨烯的局域可调谐性,在一片石墨烯上构造等离子体激元回音壁模式谐振腔,模拟计算其模式特性随腔体的几何参数和石墨烯的材料参数的变化,并分析探讨其物理机制。本文利用有限元方法数值模拟计算了石墨烯等边三角形纳米腔,分析了纳米腔的模式特性与腔尺寸R_1、频率、石墨烯动量豫驰时间t和石墨烯化学势μ_c之间的关系。研究结果表明,在近红外波段,当其他参数保持不变时,腔Q值随R_1的变化不显著,而频率、τ以及μ_c的变化对腔Q值的影响较大。当真空波长大约在1.415μm时,该腔可支持Q值约为147.93的一种高阶回音壁模式,对应的模式体积可达10~(-7)(λ_0/2n)~3量级,purcell因子能达到108量级。其次对连接有顶级输出波导的石墨烯等边三角形纳米腔进行模拟数值计算,分析了该结构的模式特性和输出特性随结构的几何尺寸以及石墨烯材料参数的变化。研究结果表明,当μ_(c1)和μ_(c2)分别设定为0.9eV和0.59eV时,R_1为30nm且输出波导宽度为5nm的该种集成等离子体器件中purcell因子可达107量级,输出系数达到20.2%。在本文中除了探讨石墨烯等边三角形纳米腔以外,我们利用同样的方法对石墨烯纳米盘的耦合进行数值分析,对于基于石墨烯纳米盘的双原子等离子体分子,主要分析其两盘间距g以及两盘大小差异对模式耦合的影响。研究结果表明,随着g的减小该结构中存在简并模式分裂的现象,并且存在基模TM_(8,1)和高阶模TM_(5,2)耦合的情况;两盘大小差异的变化也对该等离子体分子的模式耦合产生影响。对于基于石墨烯纳米盘的三原子等离子体分子,主要研究对称性退化(由等边三角形结构逐渐变化成为线性链结构)对于模式耦合特性的影响。研究结果表明,随着结构的变化,模式电场E_z的分布,及其对应的频率与Q值也逐渐发生相应的变化,当a=135时其中一种耦合模式的Q值可达105量级。
[Abstract]:Surface Plasmon Polaritons (SPPs). And the echo wall pattern is the whispering Gallery Mode. The combination of the resonance mode characteristics of the WGM resonator can form a high quality factor (Q value) and a small mode volume mode (Volume). The surface plasmon resonator echo mode resonator cavity, which overcomes the diffraction limit of the traditional dielectric WGM microcavity. For traditional precious metal materials such as gold and silver it is difficult to adjust the properties of SPPs once their structure is fixed. And the SPPs loss propagating on the traditional metal interface is larger. Therefore, the excellent properties of metal-based SPPs devices are limited. Graphene, as a two-dimensional dimentision2-D) material of mono-carbon atomic layer, has a positive conductivity when the imaginary part of conductivity is positive. Graphene can support the SPPsof Transverse Magneticum (TM) mode, and the graphene has high limit and low loss. The easy-to-adjust properties have been proved theoretically and experimentally. By changing the chemical doping or changing the electrostatic field applied to graphene, the chemical potential of graphene can be changed and the conductivity of graphene can be changed. Therefore, the properties of the supported SPPs are modulated. In this paper, the plasmon echo wall mode resonator is constructed on a graphene piece by using the local tunability of graphene. The variation of the mode characteristics with the geometric parameters of the cavity and the material parameters of graphene is simulated, and its physical mechanism is analyzed and discussed. In this paper, the equilateral triangular nano-cavities of graphene are numerically simulated by the finite element method. The relationship between the mode characteristics of the nanocavity and the cavity size, frequency, graphene momentum relaxation time t and graphene chemical potential 渭 c was analyzed. When the other parameters remain unchanged, the Q value of the cavity does not change significantly with the R _ S _ 1, while the changes of the frequency, 蟿 and 渭 _ C have a great effect on the Q value of the cavity, when the vacuum wavelength is about 1.415 渭 m. The cavity can support a high-order echo wall model with Q value of 147.93, and the corresponding volume of the model can reach 10 ~ 10 ~ 7 ~ (-1) (位 _ 0 / 2 ~ (2) n ~ (-1)). The purcell factor can reach the order of 10 8. Secondly, the graphene equilateral triangular nanocavity with top output waveguide is simulated. The mode and output characteristics of the structure are analyzed with the geometric size of the structure and the parameters of graphene materials. When 渭 s / c _ (1) and 渭 _ s _ s _ 2) were set to 0.9eV and 0.59eV, respectively. The purcell factor of the integrated plasma device with 30 nm R1 and 5 nm output waveguide can reach 107 orders of magnitude. The output coefficient is 20.20.In this paper, we use the same method to analyze the coupling of graphene nanodisk in addition to the discussion of graphene equilateral triangular nano-cavity. For diatomic plasma molecules based on graphene nanodisk, the effects of the distance between two disks g and the size difference of the two disks on the mode coupling are analyzed. With the decrease of g, there is a degenerate mode splitting in the structure, and there is a coupling of the base mode TMSP 8 / 1) and the higher order mode TMSP 5 / 2). The variation of the size of the two disks also affects the mode coupling of the plasma molecule, for the triatomic plasma molecule based on the graphene nanodisk. The effect of symmetry degradation (from equilateral triangular structure to linear chain structure) on the mode coupling properties is studied. The results show that the distribution of mode electric field E _ z varies with the structure. The corresponding frequency and Q value change gradually, when a = 135, the Q value of one of the coupling modes can reach 105 orders of magnitude.
【学位授予单位】：华侨大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O539;O613.71
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本文编号：1417978