摘 要

红外光谱通过探测各种分子和化合物的基团振动，能够有效表征分子振动和转动指纹，在材料分析中发挥着越来越重要的作用。但是，由于红外光的波长（微米级）比典型分子尺寸（纳米级）大三个数量级，因此红外光与分子之间的相互作用十分微弱，导致红外光谱检测分子的灵敏度很低，难以获得微量纳米材料的红外光谱。而近年来纳米材料和技术的快速发展，对传统红外光谱的检测灵敏度提出了更高的要求。石墨烯等离激元具有可电学调控、低本征衰减、宽光谱响应范围、电磁场的高度局域化等特点，在红外探测领域的应用前景广泛。但是，由于石墨烯独特的几何结构，石墨烯的光、电性质极易受周边介电环境的影响，导致石墨烯等离激元增强纳米材料红外吸收的效果受到影响。因此，研究介电环境对石墨烯等离激元的影响对提高红外光谱探测分子灵敏度有重要意义。

本毕业设计基于有限元法，利用软件COMSOL Multiphysics对石墨烯等离激元进行模拟仿真，得到有效激发的石墨烯等离激元仿真模型。在模拟环境中，通过改变悬空石墨烯的条带宽度W和费米能级E_f，发现随石墨烯条带宽度的减小，石墨烯等离激元的共振峰蓝移且强度减小；随费米能级的增加，石墨烯等离激元的共振峰蓝移且强度增加。通过分析得到石墨烯等离激元共振频率ω_pl∝q^0.48374和ω_pl∝Ef^0.5159，验证了石墨烯表面等离激元的色散关系；通过增加双层石墨烯的宽度，发现石墨烯等离激元共振峰蓝移且强度增加，为石墨烯等离激元的调控提供了更多的可能；分别给石墨烯加上无声子的CaF₂基底和有声子的SiO₂基底，探究基底声子对石墨烯等离激元的影响，发现SiO₂基底的石墨烯等离激元消光光谱存在三个共振峰而CaF₂基底的石墨烯等离激元消光光谱只有一个共振峰，分析得知这是由于SiO₂的两支声子与石墨烯等离激元发生耦合所导致的共振峰劈裂；在此基础上，进一步探究了石墨烯等离激元增强探测h-BN单层分子的红外振动模式，同时得到h-BN的面外和面内振动模式；探究石墨烯等离激元增强探测SO₂气体分子的性能。

关键词：石墨烯等离激元、仿真模拟、色散关系、声子耦合、增强探测

Abstract

Infrared spectroscopy has played an increasingly important role in material analysis through probing the atomic vibration of various molecules and compounds which can effectively characterize molecular vibration and rotational fingerprints. However, the sensitivity of IR light for the detection of molecules is extremely low since the wavelength of infrared light (micrometer) is about three orders of magnitude larger than the typical molecular size (nanoscale), the interaction is very weak. As a result, it is difficult to detect trace chemicals. In particular, the rapid development of nanomaterials and technologies has put forward higher requirements for the sensitivity of traditional infrared spectroscopy. Graphene plasmons have broad prospects of application in the field of infrared detection due to its’ characteristics of electrical tunable, low intrinsic attenuation, wide spectral response range and high localization of electromagnetic fields. However, the optical and electrical properties of graphene are highly susceptible to the surrounding dielectric environment due to the unique geometry structure of graphene. Leading to the alternative of the enhancement effect of graphene plasmon enhanced infrared absorption of nano-materials. Therefore, studying the influence of graphene plasmons in the dielectric environment is important for improving the detection sensitivity of infrared spectroscopy.

Based on the finite element method, the graduation project use software COMSOL Multiphysics to study graphene plasmon. In the simulated environment, by changing the nano-ribbon width W and the Fermi level Ef of the suspended graphene, it is found that as the width of the graphene ribbon decreases, the resonance peak of the plasmon blue shift and the intensity decreases. While as the Fermi level increases, the resonance peak of the plasmon blue shift and the intensity increases. The surface plasmon resonance frequencies ω_pl∝q^0.48374 and ω_pl∝Ef^0.5159 are obtained through analysis, and the dispersion relationship of graphene plasmon is verified. In addition, by increasing the width of the bilayer graphene, it is found that the graphene plasmon resonance peak blue shift and the intensity increases which provides more possibilities for the tunability of graphene plasmons. Moreover, in order to verify the influence of the substrate phonon on the graphene plasmon, the addition of CaF₂ (phonon-free) and SiO₂ (phonon-containing) substrate to graphene has done in the simulated environment. It is found that there are three resonance peaks in the extinction spectrum of the SiO₂ substrate while only one exists of the CaF₂ substrate. This is due to the coupling of graphene plasmon with two phonons of SiO₂. Furthermore, this work probe the vibration mode of h-BN monolayer molecules enhanced by graphene plasmon which can simultaneously obtain the out-of-plane and in-plane modes of h-BN. And also explore the performance of graphene plasmon enhanced detection of SO₂.
Key Words：graphene plasmon，simulation，dispersion relation，phonon coupling，enhanced detection

目 录

摘 要 I

Abstract II

第1章 绪论 1

1.1 引言 1

1.2 石墨烯材料的概述 2

1.2.1 石墨烯的结构和性质 2

1.2.2 石墨烯的制备方法 3

1.3 表面等离激元 4

1.3.1 表面等离激元的发展 4

1.3.2 表面等离激元电磁学理论 4

1.4 石墨烯表面等离激元 5

1.4.1 石墨烯表面等离激元的性质 5

1.4.2 石墨烯表面等离激元的激发 6

1.5 等离激元增强表面红外吸收研究进展 7

1.6 本论文的研究目的和意义 8

第2章 石墨烯等离激元的仿真模拟 10

2.1 COMSOL Multiphysics模拟软件简介 10

2.2 石墨烯等离激元仿真模型建立 10

第3章 石墨烯等离激元性能研究及增强探测h-BN、SO₂分子性能 13

3.1 石墨烯等离激元的色散关系 13

3.1.1 不同条带宽度对石墨烯等离激元的调控 13

3.1.2 不同费米能级对石墨烯等离激元的调控 14

3.2 双层石墨烯宽度对等离激元的调控 16

3.3 基底声子对石墨烯等离激元的影响 16

3.4 石墨烯等离激元分子指纹探测 18

3.4.1 石墨烯等离激元增强h-BN红外振动模式 18

3.4.2 石墨烯等离激元增强探测SO₂气体分子 20

第4章 结论与展望 22

4.1 结论 22

4.2 展望 23

参考文献 24

致 谢 27

第1章 绪论

1.1 引言

随着人们对生活环境健康的重视，环境中有害气体和固体颗粒的监测受到越来越多的关注。在众多检测方法中，红外光谱分析由于具有快速无损的优点而成为优选的检测手段。但是，由于红外光的波长（微米级）比典型分子尺寸（纳米级）大三个数量级，因此红外光与分子之间的相互作用十分微弱，导致红外光谱检测分子的灵敏度很低，严重限制了其基于微量检测的应用。而环境监测力度的加大，对传统红外光谱的检测灵敏度提出了更高的要求。